A review of the conservation status of seasonal Nothobranchius fishes (Teleostei: Cyprinodontiformes), a genus with a high level of threat, inhabiting ephemeral wetland habitats in Africa

Abstract

The small and colourful Nothobranchius fishes inhabit ephemeral habitats in freshwater wetlands of Africa and have extreme life‐history adaptations that allow their eggs to survive the periodic drying up of the seasonal natural habitats. They are subject to high levels of threat, with 72% of the 94 assessed species falling into one of the threatened Red List categories, as a consequence of habitat degradation of seasonal wetlands. There is, therefore, a need to conserve ephemeral waters for species that rely on the seasonality of habitats.
Extinction risk factors for all species of the genus were entirely reworked with IUCN Red List assessments, whereas first‐time assessments were established for species that had previously not been evaluated. These fishes complete their seasonal life cycle in ephemeral natural habitats and this makes them highly vulnerable, as such wetland habitats are often degraded owing to multiple interacting human‐induced stressors and threats, including cultivation of wetlands for agriculture, abstraction of water, expansion of urban areas and pollution load.
A fine‐scale classification scheme based on habitat type was used for each site to identify ecological characteristics and the pattern of threats. The classification scheme is based on a primary subdivision of natural habitats compared with those modified by human activities, with further subdivision within the two fundamental groupings. Out of the 478 analysed habitat site observations by the authors, 46% were affected by human activities.
Recommended conservation actions include: conducting surveys to better understand habitat trends and threats; establishing protected areas and effectively allocating resources to preserve wetland habitats; managing protection of the structural integrity of the habitats throughout the seasonal phases of wet and dry seasons; and raising awareness of the importance of healthy wetland systems and the value of the unique seasonal freshwater biodiversity.

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How to cite this article:
Nagy, B. & Watters, B.R. (2021). A review of the conservation status of seasonal Nothobranchius fishes
(Teleostei: Cyprinodontiformes), a genus with a high level of threat, inhabiting ephemeral wetland
habitats in Africa. Aquatic Conservation: Marine and Freshwater Ecosystems, 32(1), 199–216.
https://doi.org/10.1002/aqc.3741
A review of the conservation status of seasonal Nothobranchius fishes (Teleostei:
Cyprinodontiformes), a genus with a high level of threat, inhabiting ephemeral wetland
habitats in Africa
Béla Nagy¹ & Brian R. Watters²
¹Fontainebleau, France
²Nanaimo, British Columbia, Canada
Correspondence
Béla Nagy, 30, Rue du Mont Ussy, 77300
Fontainebleau, France.
Email: bela.nagy@neuf.fr
Abstract 1
1. The small and colourful Nothobranchius fishes inhabit ephemeral habitats in freshwater wetlands of 2
Africa and have extreme life-history adaptations that allow their eggs to survive the periodic drying up 3
of the seasonal natural habitats. They are subject to high levels of threat, with 72% of the 94 assessed 4
species falling into one of the threatened Red List categories, as a consequence of habitat degradation 5
of seasonal wetlands. There is, therefore, a need to conserve ephemeral waters for species that rely on 6
the seasonality of habitats. 7
2. Extinction risk factors for all species of the genus were entirely reworked with IUCN Red List 8
assessments, whereas first-time assessments were established for species that had previously not been 9
evaluated. These fishes complete their seasonal life cycle in ephemeral natural habitats and this makes 10
them highly vulnerable, as such wetland habitats are often degraded owing to multiple interacting 11
human-induced stressors and threats, including cultivation of wetlands for agriculture, abstraction of 12
water, expansion of urban areas and pollution load. 13
3. A fine-scale classification scheme based on habitat type was used for each site to identify ecological 14
characteristics and the pattern of threats. The classification scheme is based on a primary subdivision 15
of natural habitats compared with those modified by human activities, with further subdivision within 16
the two fundamental groupings. Out of the 478 analysed habitat site observations by the authors, 46% 17
were affected by human activities. 18
4. Recommended conservation actions include: conducting surveys to better understand habitat trends and 19
threats; establishing protected areas and effectively allocating resources to preserve wetland habitats; 20
managing protection of the structural integrity of the habitats throughout the seasonal phases of wet 21
and dry seasons; and raising awareness of the importance of healthy wetland systems and the value of 22
the unique seasonal freshwater biodiversity. 23
24

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KEYWORDS 25
conservation, distribution, ecology, extinction risk, habitat degradation, IUCN Red List, threats, wetlands 26
27
1 | INTRODUCTION 28
This article presents a comprehensive appraisal of the conservation status for the species of 29
Nothobranchius. Previously published International Union for Conservation of Nature (IUCN) Red List 30
assessments have been reworked and updated, and first-time assessments were established to cover all 31
remaining species of the genus. Our aim is to stimulate interest and create recognition for the genus 32
Nothobranchius, by identifying major threats to ephemeral freshwater resources and the need for 33
conservation measures, tailored to the protection of seasonal fishes. There is a need to diagnose threats 34
over the scale of the entire distribution of the genus (Nagy & Watters, 2020). At present, protected areas 35
(PAs) are not specifically targeted in their design to protect ephemeral freshwater biodiversity, thus 36
seasonal fishes with unique adaptations are being overlooked. Phases in the annual life cycle of these 37
small fishes underscore the vulnerabilities of the ecological processes, emphasizing that protection of 38
seasonal freshwater resources and wetland habitats in general is an urgent issue. 39
The loss of biodiversity on Earth has reached a point where urgent attention is needed for the 40
protection of wildlife. Above all, loss and degradation of natural habitat is the most widespread threat to 41
the biota in freshwater ecosystems, and three-quarters of inland wetlands have already been lost (Dudgeon 42
et al., 2006; Darwall et al., 2011; Davidson, 2014; Darwall et al., 2018). Water is widely regarded as the 43
most essential of natural resources, yet freshwater systems are directly threatened by transformation to 44
maximize human access to water and by other human impacts, often accompanied by impairment to 45
ecosystems and biodiversity (Vörösmarty et al., 2010; Arthington et al., 2016). Habitat degradation 46
imposes pertinent impact for the fauna that are adapted to the harsh conditions of seasonally arid aquatic 47
habitats (Nagy & Watters, 2020). 48
The present authors follow Junk et al. (2014) in that wetlands represent ecosystems at the interface 49
between aquatic and terrestrial environments. Ephemeral freshwater wetlands are home to specific plant 50
and animal communities adapted to the seasonality. The genus Nothobranchius currently comprises 95 51
valid species, occurring mainly in seasonal wetlands of river drainages in north-eastern, eastern and south-52
eastern Africa that are subject to seasonal rainfall (van der Merwe et al., 2020). They are recognized as 53
seasonal fishes, commonly also referred to as ‘annuals’, with all known species having an annual or semi-54
annual life cycle, a key adaptation to reproduce in the seasonally arid savannah biome characterized by 55
periodic drying out of their natural habitats (Vanderplank, 1940; Watters, 2009; Nagy, 2015). The 56
periodicity is determined by the rainfall pattern of the regions in which the habitats occur. Before the 57
habitats dry out, spawning takes place, and the eggs survive the dry season buried in the substrate mud. 58
When the ensuing rainy season arrives, the rivers overflow their banks, inundate the floodplains, and the 59
buried eggs hatch (Figure 1). 60
Nothobranchius species show marked sexual dimorphism and are highly dichromatic; the typically 61
robust and colourful males are in contrast to the slightly smaller and dull coloured females (Jubb, 1981; 62
Wildekamp, 2004). The distinctive colour pattern of the males provides important diagnostic characters 63
(Jubb, 1981; Nagy, 2018; Watters et al., 2019; Nagy et al., 2020). They are small fishes, most species 64
reaching 30–70 mm in standard length, with only a few species reaching 100 mm or more. The genus 65
includes Nothobranchius furzeri, the vertebrate species with the shortest lifespan recorded in captivity 66

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(less than 12 weeks), and which has emerged as a model organism for biological and molecular studies of 67
ageing. 68
69
2 | RED LIST ASSESSMENTS 70
2.1 Evaluation process 71
Conservation challenges and opportunities commence by evaluation of the situation, followed by research, 72
monitoring and implementation of conservation actions. Recent progress towards updated IUCN global 73
assessments of the conservation status of all Nothobranchius species thus represents a first step of great 74
relevance. Overall, 94 of the 95 currently valid species of the genus were fully reassessed, mainly within 75
the frame of an assessment project on the genus, as well as part of IUCN regional assessment projects. 76
Updated information, especially results from field surveys over the course of the last 3 decades, were 77
adequate to allow informed assessments to be made. 78
The risk of extinction for each species was assessed according to the IUCN Red List Categories and 79
Criteria Version 3.1 (IUCN, 2012). A species assessed as Critically Endangered (CR) is considered to be 80
facing imminent risk of extinction in the wild, whereas a species assessed as Endangered (EN) or 81
Vulnerable (VU) is considered at very high or high risk of extinction in the wild, respectively. Those 82
species assessed as CR, EN or VU are termed ‘Threatened’. A species is evaluated as Near Threatened 83
(NT) if at present it does not fall into any of the threatened categories but is close to qualifying for that 84
status or is likely to in the future. A species is listed as Data Deficient (DD) if insufficient information is 85
available to determine conservation status. The editorial and reviewing process ensured that the IUCN Red 86
List categories and criteria were consistently applied between species and the regions within the entire 87
distribution range of the genus. In total, 46 species were reassessed from previous assessments and first-88
time assessments were carried out for an additional 48 taxa. 89
Conservation assessments and associated species maps for all species of Nothobranchius are available 90
on the IUCN Red List of Threatened Species™ (www.iucnredlist.org). 91
92
2.2 | Taxonomy and identification 93
Classification and species recognition support the identification of any developmental and experimental 94
work that needs to be done for conservation of each species. It also enables the development of species 95
recovery plans, habitat protection and restoration. In typical conservation processes, only those species 96
that are formally taxonomically described, with an assigned scientific name, are considered. It is possible, 97
therefore, that unidentified species might disappear, through silent extinction, before ever having been 98
studied or formally recognized. 99
The recent intensification in the use of molecular methods of characterization and increased field 100
surveys allowed the identification of lineages of separate phylogeographical patterns, which is certainly 101
very pronounced in this genus where the constituent species have limited dispersal capacity. Multiple lines 102
of evidence support a better species identification (Watters et al., 2019; Nagy et al., 2020). New taxa 103
continue to be identified at a significant rate, with 41 novelties described during the last decade 104
(representing 44% of the valid taxa), including nine species in 2019 and seven species in 2020. The 105
present authors have collectively contributed to the identification and taxonomic description of 35 species 106
of the genus. 107

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108
2.3 | Red List conservation assessments of Nothobranchius 109
The summary presented here contains the results of the complete assessment of the genus, based on global 110
Red List status (Table 1). Increased exploratory surveys and gradually improving accessibility will 111
continue to provide more information and enable better evaluation. 112
The Red List assessments indicate that Nothobranchius species are under high levels of threat. The 113
majority of the species, representing 72.3%, fall into one of the threatened categories. This includes three 114
species as CR, one of which is further assessed as CR (Possibly Extinct). These are species that have been 115
detected only once and not been found again since their original discovery in 1931, 1976 and 1997, 116
respectively, despite significant field efforts at the type localities and surrounding areas. Another 21 117
species are evaluated as EN and an additional 44 species are considered as VU, representing 22.3% and 118
46.8% of the species, respectively. These underscore how the African continent is affected by agricultural 119
and industrial development with associated aquatic habitat degradation. Eight species, representing 8.5%, 120
are NT. One species is listed as DD. There are only 17 species that are regarded as being of Least 121
Concern, meaning that these species have been evaluated against the criteria and do not qualify for 122
inclusion in any of the threatened categories. Usually, species that fall into this category are those that are 123
widespread and relatively abundant. 124
125
3 | DISTRIBUTION 126
3.1 | Field surveys 127
This study was based on a geographical and ecological dataset of Nothobranchius fishes compiled on the 128
basis of more than 50 field trips carried out by the authors in Africa. Fishing methods to monitor fish 129
populations included the use of hand scoop-nets and seine-nets (as described by van der Waal & Skelton, 130
1984), complemented by traditional active and passive fishing activities (Skelton, 2001). The field trips 131
covered 12 out of 16 countries where the species are known to occur, including Chad, Sudan, Uganda, 132
Kenya, Tanzania, Malawi, Zambia, Democratic Republic of Congo (DRC), Mozambique, Zimbabwe, 133
Namibia and South Africa. The authors' field observations include 76 species of the 95 presently known 134
valid species, as well as several additional putative species. The authors' dataset contains 726 records of 135
observations, as combinations of species and habitat sites. 136
Furthermore, the dataset has been enriched by field data recovered from about 1,500 museum 137
catalogue entries and specimen collection records. A combination of data derived from an extensive 138
literature survey, as well as from personal communication with colleagues, has resulted in the entire 139
dataset comprising approximately 3,000 observation records. Diversity and species richness patterns of the 140
different threat categories were determined by combining appropriate components of the dataset. Species 141
found in multiple countries or ecosystems, were assigned to each of those. Fine-scale classification of 142
habitat types for each species and the number of species per habitat type were recorded, based principally 143
on field observations, following the classification scheme proposed by Watters (2014). Water parameters 144
were determined by calibrated electronic handheld devices at each site. 145
146
3.2 | General distribution 147
A distribution map of Nothobranchius fishes is presented in Figure 2. At present, the confirmed 148
distribution range of Nothobranchius species includes north-eastern South Africa, the Zambezi Region 149

5
(Caprivi) of Namibia, Zambia, south-eastern DRC, south-eastern Zimbabwe, central and southern Malawi, 150
Mozambique, Tanzania, south-western and eastern Kenya, Uganda, southern Somalia, southwestern 151
Ethiopia, southern Sudan, South Sudan, southern Chad, and northern Cameroon (see the Red List 152
assessments for details). Within the extensive range of distribution, their occurrence is scattered owing to 153
the availability of habitats with a suitable soil substrate, climatic conditions and other ecological elements. 154
Pools suitable to host Nothobranchius species are limited mainly to ephemeral wetland habitats in 155
grassland and woodland savannah, typically within the floodplains of rivers. 156
Some species have a wide distribution and are known to have dispersed over the catchments of several 157
river drainages. The currently known largest extent of occurrence (EOO) of 429,000 km2 is for 158
Nothobranchius orthonotus, a species that is endemic to seasonal freshwater habitats in river drainages in 159
southern Malawi, south-eastern Zimbabwe, southern and central Mozambique, and north-eastern South 160
Africa. There is some genetic and phenotypic structure within the complex, and peripheral populations 161
might be recognized in the future as representing distinct species. The second largest EOO of 202,000 km2 162
is observed for Nothobranchius virgatus, endemic to seasonal freshwater habitats in the middle and upper 163
Nile drainages in southern Sudan, South Sudan and western Ethiopia. This species has a disjunct 164
distribution and genetic and phenotypic differentiation indicates that it might be a complex including more 165
than one species (van der Merwe et al., 2020). Better resolved species identification would fragment the 166
current range of the species and have influence on conservation status owing to more restricted 167
distribution ranges at the species level. Other extended ranges are observed for: Nothobranchius jubbi 168
(186,000 km2) from coastal Kenya and southern and south-eastern coastal Somalia; Nothobranchius 169
makondorum (156,000 km2) from south-eastern coastal Tanzania and north-eastern Mozambique; and 170
Nothobranchius robustus (134,000 km2) from southern and western Uganda, south-western Kenya, and 171
north-western Tanzania. These species are typically widespread and abundant in suitable freshwater 172
habitats. 173
However, the insular nature of seasonal freshwater habitats has led to the evolution of many species 174
with small, fragmented geographical ranges. Range‐restricted species are intrinsically at risk. Among the 175
most restricted species are those inhabiting islands: Nothobranchius insularis and Nothobranchius 176
korthausae, both from Mafia Island, with an estimated maximum EOO of 100 and 200 km2, respectively; 177
another insular species, Nothobranchius guentheri (Figure 3a) from Unguja Island of Zanzibar, previously 178
had a maximum estimated EOO of 200 km2 but the loss of at least three previously known sub-179
populations has restricted the present EOO to 66 km2. 180
Another example, from the mainland, is Nothobranchius interruptus that inhabits seasonal wetland 181
habitats within a limited distribution in a restricted area of the Mtomkuu system in coastal Kenya. The 182
main existing location, from where most of the observations have been made, is a large marsh of about 183
200 x 100 m, situated adjacent to Kikambala village about 15 m above sea level. There are a few 184
additional sites in the area, comprising smaller associated swamps around the village. However, the 185
presence of the species at a second, earlier reported, location a few kilometres further inland from 186
Kikambala could not be confirmed during recent surveys by the authors. 187
Further examples include some species restricted to the Mbezi Triangle (sensu Watters, 2009) in 188
coastal Tanzania, such as Nothobranchius albimarginatus, Nothobranchius luekei and Nothobranchius 189
rubripinnis. Their currently known EOO is 179, 238 and 291 km2, respectively, and their distributions will 190
remain restricted by geographical confinement and configuration of the drainage systems. According to 191

6
current knowledge, 55% of species have an observed EOO that is less than 1,000 km2, whereas the 192
maximum estimated EOO of 81% of the species is less than 20,000 km2, the threshold below which a 193
species potentially qualifies as being threatened according to the IUCN Red List categories and criteria. 194
The present distribution of the fish fauna reflects the complex geomorphological history of river 195
drainages (Skelton, 1994; van der Merwe et al., 2020). Cotterill et al. (2016) pointed out that spatio-196
temporal landscape-shaping events, when wetlands became linked or isolated, are congruent with the 197
biotic evolutionary patterns, such as the tempo and mode of speciation as represented in phylogenetic 198
signals of the seasonal killifishes, because of the limited dispersal ability of the seasonal killifishes. 199
Drainage separations confine the seasonal wetland habitats in the disconnected floodplains and endemics 200
emerge with limited distribution. 201
202
3.3 | Spatial patterns 203
A distribution map of Nothobranchius fishes (Figure 2), based on about 3,000 site records, is presented 204
also to show species richness patterns resulting from sympatric occurrences. The most important species 205
hotspot with up to eight sympatric species is found within the drainages of coastal rivers in eastern Africa. 206
Other areas where multiple species are concentrated occur in drainages of river systems within the Lake 207
Victoria basin. Sympatric occurrences and species richness are less pronounced at peripheral parts of the 208
distribution. 209
210
3.3.1 | Species richness by country 211
The number of species of the genus Nothobranchius by country in each Red List Category, and proportion 212
of threatened species, is given in Table 1. Two species are known from sites in the territories of three 213
countries, whereas 13 species are known from two countries. Most species (78) are each known to occur 214
only in a single country. In general, there is a high level of threat for Nothobranchius fishes throughout the 215
overall range of the genus, whereas there is a high concentration of species in threatened categories in 216
some countries. The latter phenomenon reflects a high degree of endemicity and restricted distribution, 217
such as species in south-eastern DRC, north-western Zambia and Namibia. The high number of threatened 218
species found in Tanzania, where speciation was especially active, has resulted in a ‘hotspot’ of 219
distribution for the genus with 44 endemic species, many of which have restricted distribution. 220
221
3.3.2 | Species richness by freshwater ecoregion 222
The number of species of the genus Nothobranchius per freshwater ecoregion in each Red List Category, 223
and the proportion of threatened species, are listed in Table 2. The classification of freshwater ecoregions 224
follows Abell et al. (2008), except for Lakes Chilwa and Chiuta which are classified according to Thieme 225
et al. (2005). Two species are known from sites in three ecoregions, whereas nine species are known from 226
two ecoregions. The majority of species (83, representing 87%) are known to be confined to one 227
ecoregion, implying that the boundaries of the ecoregions represent effective barriers to dispersal of these 228
seasonal fishes. The high number of threatened endemics in the Coastal East Africa ecoregion reflects 229
species flocks restricted to small river drainages along the coast. The high proportion of threatened species 230
in Bangweulu–Mweru and Upper Lualaba ecoregions represents the evolutionary legacy of landscape 231
evolution that has been invoked to explain relatively recent speciation of endemics (van der Merwe et al., 232

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2020). Threatened taxa in the Lake Victoria basin ecoregion reflects species in separated and isolated 233
small drainages around the lake (Nagy et al., 2020). 234
235
3.3.3 | Protected areas 236
The number of species of the genus Nothobranchius found in PAs in each Red List Category, and the 237
proportion of threatened species, are listed in Table 3. A relatively small part of the distribution of some 238
species occurs within PAs. Of the 94 species assessed, 25 are known to occur in PAs: 21 species in 239
national parks, two species from game reserves, one species in a conservancy and one species in a 240
management area. For 16 species, the number of observations from PAs represents less than 10% of the 241
observations of those species. One species is known from four different national parks, two species are 242
known from three PAs and a further two species are known from two PAs; however, overall, less than 5% 243
of total observations are known from PAs. Twenty species could be observed in only one PA. Only 16 % 244
of the species belonging to one of the threatened categories are known from PAs. None of the species 245
found in PAs are the focus at present of any targeted management actions. However, regulations in PAs 246
should prevent habitat destruction and this represents an incidental benefit to those species included in 247
PAs. 248
249
4 | LIFE HISTORY AND ECOLOGY 250
Nothobranchius fishes do not occur everywhere in Africa, nor are they present in every seasonal pool 251
within their known range; there are certain factors and special conditions that define the Nothobranchius 252
biotope (Watters, 2009; Nagy, 2015). Within the general distribution area, interrelated and interdependent 253
ecological factors of the ephemeral biotopes, essential for the life cycle of these seasonal fishes, determine 254
the suitability of the habitats. 255
256
4.1 | Life history traits 257
The biological life cycle (Figure 1), reproductive behaviour and egg development of Nothobranchius 258
species are perfectly adapted to the special conditions prevailing in the seasonal natural biotopes that they 259
inhabit. Identifying key points in the life history of organisms could prove to be a fruitful approach for 260
focusing often-limited management efforts (Reynolds, Dulvy & Roberts, 2002). 261
Nothobranchius species display the following traits: relatively small adult size; adaptation to unstable 262
climatic and environmental conditions; produce large numbers of eggs to ensure a potentially adequate 263
number of offspring; no parental care and protection of the offspring; and a low ability to compete, with 264
most offspring not reaching reproductive age. 265
Seasonal habitats host adult Nothobranchius fishes for a limited period only and, consequently, 266
conditions dictate that the fish grow rapidly and reach an early reproductive stage. The adult lifespan of 267
any particular Nothobranchius species will depend on regional rainfall patterns but under optimal 268
conditions most can be sexually mature in 3–4 weeks after hatching. The life expectancy of 269
Nothobranchius fishes is predicted by the specifically harsh conditions of the temporary natural habitats in 270
which they occur. As the season advances, the adult fish are eliminated from the biotope. Studies 271
conducted in Tanzania after the end of the rainy season showed a significant change in the presence of the 272
species in the habitats, when sites were visited 3 weeks apart (Nagy & Horváth Kis, 2010). 273

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Nothobranchius species disappear from the biotopes as a result of a shrinking of the habitat at the end of 274
the wet season, which also results in a loss of natural protection from predators that become an increasing 275
threat at this stage of their life cycle. These factors determine a constrained life expectancy, which, under 276
natural conditions, is restricted to a few weeks or, at most, only a few months. 277
278
4.2 | Habitat use 279
Males typically show territorial behaviour and protect suitable spawning sites, such as areas with a thick 280
mud base or an embayment protected by vegetation. The largest, most dominant males are often found in 281
those parts of the biotope where the eggs have the best protection in a deep layer of mud and the fish are 282
relatively well protected from predators. When the water recedes at the end of the rainy season, 283
Nothobranchius fishes tend to maintain their preferred position in a progressively restricting habitat. 284
Although that part of the habitat may soon dry out, resulting in the death of the adult fish, it does provide 285
the best substrate with a high content of the swelling clays that are essential for the survival of the eggs 286
deposited therein (e.g. illustrated in Figures 10 and 13 in Watters, 2014). 287
At many locations, several Nothobranchius species co-exist in the same habitat (Watters, 2009; 288
Reichard, 2015). This is especially common in the coastal region of Tanzania (Figure 2). Usually, each 289
species would occupy a different niche of the biotope (Nagy, 2015). 290
Specific habitat preference may also be shown by different species that occur in the same general area 291
but not usually in the same body of water (i.e. sympatric but not syntopic). For example, in Uganda, N. 292
robustus tends to favour relatively cool habitats at the edge of slow-flowing temporary streams or the 293
marginal zones of papyrus swamps, whereas Nothobranchius ugandensis in the same general area inhabits 294
the standing water of more isolated ephemeral pools. The authors found the two species to be syntopic in 295
only two pools compared with 61 sites where only one of these two species was present (Nagy & Watters, 296
2018b). 297
298
4.3 | Habitat characterization 299
A classification scheme of habitat types based on physical characteristics and setting, and the 300
identification of factors involved in habitat formation or modification, may be of importance when 301
assessing the conservation status of certain species (Watters, 2014). The principal benefits derived from 302
the development of a classification scheme for Nothobranchius habitats include the identification and 303
orderliness of diagnostic characteristics, and a better understanding of the factors involved in the 304
distribution of certain species and their habitat preferences. Moreover, the association of threats by habitat 305
type can aid in the assessment of conservation status and the formulation of conservation strategies 306
(Watters, 2014). A better understanding of ecological factors will help bridge the gap to conservation 307
biology (Strayer & Dudgeon, 2010). Temporary waters are diverse and are typically subdivided into those 308
of natural origin and those resulting from human activities (Williams, 2005). 309
Typical Nothobranchius habitats – those resulting from primarily natural formative processes – 310
comprise a variety of ephemeral natural biotopes on floodplains, e.g. isolated residual pools, seasonal 311
streams, seasonal marshes associated with river systems and marginal (ephemeral) zones of relatively 312
large bodies of water such as extensive marshes. In very general terms, a common natural habitat is a 313

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seasonal pond with turbid water, a marginal growth of grasses, sedges or reeds, and Nymphaea sp. in the 314
more open parts of the pond. 315
Another category of Nothobranchius habitat types are those in which human intervention has played a 316
role in their formation or in the modification of a natural habitat. Examples of these include rice fields or 317
other fields created by agricultural practices; roadside drainage ditches, often associated with culverts, 318
resulting from road construction activities; and water holes excavated for human water consumption or as 319
drinking reservoirs for livestock, near villages. 320
321
4.4 | Habitat types 322
A summary of habitat types for Nothobranchius fishes is presented in Table 4. The classification scheme 323
(after Watters, 2014) is based on a primary subdivision of natural habitats versus those created or modified 324
by human activities. Within these two fundamental groupings, further subdivision is based primarily on 325
physical characteristics, drainage system associations, geomorphological setting and the processes 326
involved in their formation including, for some types, the human activities that influenced them. Habitats 327
at any particular site are often formed and modified by multiple processes, the most fundamental of which 328
is here categorized as primary, whereas lower levels of formative processes are referred to as secondary, 329
tertiary and quaternary. Such categorization is based on the authors' assessment, made from the study of 330
field characteristics, of the relative importance of each formative element in defining the overall 331
characteristics of a habitat site. 332
A total of 478 observations, where the presence of Nothobranchius species were recorded, were 333
included in the classification. Seventy-nine per cent of the habitats were found to be formed primarily by 334
natural processes, resulting mainly in shallow seasonal pools occupying localized depressions on 335
floodplains (28%), isolated remnant pools and marshy areas in seasonal stream systems (18%) and flooded 336
areas adjacent to streams (16%). More than half of the habitat sites (55%) were found to be affected by 337
human activities. The most important human impact is represented by activities associated with road 338
construction, such as ditches at culverts and ditches alongside roads, as well as habitats associated with 339
agricultural activities, such as rice fields. A certain degree of sampling bias is present in the data of the 340
authors toward habitats modified by human intervention because sites situated close to roads are 341
frequently investigated, as a matter of expediency; these would reflect the influence of road-building 342
activities. 343
The dimensions of the temporary water bodies inhabited by Nothobranchius fishes are generally quite 344
small but can vary greatly, ranging from puddles formed in animal hoof prints to extensive, but shallow, 345
seasonal marshes. 346
347
4.5 | Habitat characteristics 348
4.5.1 | Substrate 349
The nature of the substrate in any Nothobranchius habitat, in particular its mineralogical make-up, is of 350
fundamental significance in determining the viability of the habitat (Watters, 2009). Nothobranchius fish 351
habitats are invariably associated in some way or another with floodplains (both recent and ancient), 352
which are underlain by alluvial deposits comprising black, grey or (much less commonly) brown soils. 353

10
These are either vertisols or show many of the characteristics of that soil order. By contrast, 354
Nothobranchius habitats are absent from areas underlain by red soils, of the order oxisols, that make up a 355
high proportion of the soil cover in Africa. The critical difference between a vertisol type of soil and an 356
oxisol, in the context of Nothobranchius habitat viability, is that the dominant clay minerals in the former 357
are of the swelling variety (e.g. smectite group, mainly montmorillonite) whereas in the red oxisols, non-358
swelling clays (e.g. kaolinite group) dominate the fine fraction. Also, vertisols are typically alkaline soils, 359
whereas oxisols are generally acidic. 360
During seasonal flooding events, as water moves across the floodplain it will wash fine clay from the 361
alluvium and allow it to be deposited in local depressions, ditches etc., as the water movement slows. In 362
this way, not only will these depressions develop a relatively thick layer of swelling clays, thereby 363
creating conditions suitable for supporting a population of Nothobranchius over the long term, but there 364
will be a resultant relatively impermeable layer on the bottom of the seasonal pool, inhibiting infiltration 365
and ensuring that water will stand in the pool far longer than it will on the surrounding, better drained, part 366
of the floodplain. In this way, the lifespan of the Nothobranchius fishes is optimized and they will have a 367
reasonable time to grow and spawn. 368
Swelling clay minerals of the smectite group have the capacity to absorb and adsorb water molecules, 369
between the layers of their crystal structures, and onto the grain surfaces, respectively. As the dry season 370
progresses, once the intergranular moisture of the substrate is lost, the absorbed and adsorbed water will 371
be lost only very slowly while maintaining an optimally moist micro-climate suitable to ensure viability of 372
the Nothobranchius eggs encased therein. The progressive loss of moisture from the clay-rich substrate 373
also results in a shrinking of the medium with consequent cracking to a significant depth (Watters, 2009; 374
Watters et al., 2019). As many as three stages of diapause can interrupt the developing embryo within the 375
egg (Peters, 1963; Furness, Lee & Reznick, 2015; Pinceel et al., 2015) and when the ensuing seasonal 376
rains occur, most of the eggs will be ready to hatch and begin a new cycle. 377
By contrast, seasonal bodies of water underlain by red muds, which are typically rich in non-swelling 378
clays, do not have the capacity to lose moisture in such a slow and progressive manner, and, with the start 379
of the dry season, would quickly become profoundly dry and unable to provide conditions that would 380
maintain the viability of Nothobranchius eggs. 381
382
4.5.2 | Vegetation 383
The temporary nature of Nothobranchius habitats, and the generally high turbidity of the water, limits the 384
growth of submerged aquatic vegetation. Plants present in the temporary habitats need to be capable of 385
withstanding periods of desiccation. Many of the habitats have abundant marginal vegetation in the form 386
of grasses, sedges and reeds, and such growth may extend to varying extent into the inner parts of the 387
pool. Nothobranchius often occupy the pool margins among the vegetation. In addition, overhanging 388
marginal vegetation offers enhanced protection against aerial predation by birds, especially for those 389
species that prefer the upper water levels of the habitats (those of the subgenus Aphyobranchius). 390
Numerous visits to the type locality of Nothobranchius fuscotaeniatus (Figure 3b), a species with a niche 391
preference of dense vegetation, have shown that habitat transformation through elimination of vegetation 392
has resulted in the recent absence of the species from the site (Figures 4a and b). 393
394

11
4.5.3 | Water quality parameters 395
Small, shallow ephemeral water bodies are likely to experience greater fluctuations in water quality 396
parameters than do larger and deeper permanent waters. The animals that inhabit seasonal habitats, such as 397
Nothobranchius fishes, have adapted to such variable conditions and can tolerate and thrive in habitats of 398
greatly varying water quality, provided these properties do not reach extreme levels (e.g. lethally high 399
temperatures). 400
The temporary habitats in which Nothobranchius fishes live are typically highly turbid. The source of 401
turbidity is mainly suspended clay particles, a consequence of the typical fine muddy substrate of the 402
habitat. Turbidity would influence the water quality, as turbid water absorbs solar heat in the upper 5–6 403
cm of the water column (Williams, 1987) and will reduce the effect of solar heating on deeper levels. 404
Furthermore, turbidity may serve for better protection against predation, especially for the colourful 405
males. 406
Temporary pools usually have a large surface area to volume ratio. The water temperature fluctuates 407
with the degree of exposure to the sun and temperature records may, therefore, be somewhat influenced by 408
the time of the day when this parameter is measured. Reduced water volumes heat more quickly under the 409
strong sun of the dry season and, in some cases, the temperature of shallow waters during the latest phase 410
of the drying out process may reach lethal levels for some fish. Site records of the authors indicate that the 411
average water temperature of the habitats where Nothobranchius species were found is 26.8 °C, based on 412
468 observations. The water temperature in 92% of the habitats was determined to be in the range 22–32 413
°C. 414
When a seasonal habitat refills after the dry season the water will, initially, be relatively soft. However, 415
dissolution of salts from the substrate occurs very rapidly, raising the total dissolved solids (TDS) content 416
in a relatively short time. Based on measurements made by the authors, 90% of sites examined had a total 417
dissolved solids content of less than 300 ppm. Only 5% of the observations had higher than 440 ppm TDS, 418
including some exceptionally high values. Omitting the extreme values, the habitats of Nothobranchius 419
fishes show an average TDS content of 108 ppm, based on 441 observations. 420
The dark swelling clay-rich substrate of Nothobranchius habitats is alkaline in nature and represents a 421
significant pH buffer that generally maintains alkaline conditions in the water. However, water with an 422
acidic pH has been observed at some sites, in spite of the alkaline substrate. Usually, a large quantity of 423
decaying vegetation or animal dung in the water accounts for that phenomenon, when the buffering 424
capacity of the substrate becomes overwhelmed by such acidification processes. Based on the field records 425
of the authors, the average pH value of the water in Nothobranchius habitats is 7.4, as determined from 426
452 observations. 427
428
5 | MAJOR THREATS 429
Degradation and loss of natural habitat is the greatest threat to seasonal fishes in Africa. Temporary 430
freshwater habitats represent harsh milieu, so fishes living in those types of habitats are highly dependent 431
on conditions in their environment. Degradation of wetlands has serious consequences for the fishes and 432
many other organisms living in the same habitats. Most of the threats to wetlands and seasonal freshwater 433
habitats are introduced by human activity (Dudgeon et al., 2006; Reid, 2013; Arthington et al., 2016; this 434

12
study). Habitat sites situated close to urban areas in particular are vulnerable and, for a variety of reasons, 435
at increased risk for their long-term survival. For example, cultivation of wetlands for growing crops can 436
modify Nothobranchius habitats such that they become non-viable; other human activities can result in 437
pollution and degradation of water quality; and changes in drainage that invariably accompany 438
urbanization and agricultural development can destroy habitats. As a result of such stressors, which often 439
interact, freshwater aquatic habitats are recognized as under an increasing level of threat (Vörösmarty et 440
al., 2010). 441
The major threats to Nothobranchius fishes, organized according to the categories identified in a 442
classification scheme used by IUCN, are represented in Figure 5. The direct threats and sources of stress, 443
as well as pressure caused by human activities or processes, may have an impact on the survival of the 444
species. The first-level hierarchy of threat categories is used, and threats are presented in order of the 445
proportion of threats listed for Nothobranchius species based on IUCN Red List assessments. 446
447
5.1 | Patterns of threats 448
Threats within the category of Agriculture & aquaculture account for the highest level of threat and are 449
coded for 93% of the species, including mainly pressure caused by Annual & perennial non-timber crops, 450
such as Small-holder farming or Shifting agriculture, as well as Livestock farming & ranching, such as 451
Nomadic grazing and Smallholder grazing, ranching or farming. The second highest level of threat was 452
identified in the category of Natural system modifications and coded for 38% of the species. Threats are 453
mainly the result of Abstraction of surface water for either domestic or agricultural use, as well as 454
Abstraction of groundwater. Important pressure was identified for 37% of the species within the category 455
of Residential & commercial development, representing coding of Housing & urban areas. Another 456
important threat factor was coded in the category of Pollution, listed for 27% of the species, including 457
Agricultural & forestry effluents, such as Nutrient loads, Soil erosion and sedimentation, and Herbicides 458
& pesticides, as well as Domestic & urban waste water, such as Sewage, and Industrial effluents, such as 459
Seepage from mining. An increasingly important stress is linked to Climate change & severe weather, 460
with Droughts affecting 12% of the species. 461
462
5.1.1 | Agriculture expansion 463
The fact that Nothobranchius fishes inhabit small seasonal wetland habitats, usually within a restricted 464
distribution, makes them highly vulnerable because such habitats are frequently cultivated for agriculture 465
during both the dry and wet seasons (e.g. for rice cultivation), thereby rendering them unsuitable to 466
support the seasonal life cycle of the fishes. 467
Seasonal wetlands serve as valuable natural infrastructure for agriculture providing fertile soils and 468
plentiful water in wet seasons. Wetlands are a key element in food production, and a source of water and 469
grazing for livestock. It is recognized that agriculture is a critical activity for poor rural households, as 470
many family farming operations rely on the soils, water, plants and animals found in wetlands to provide 471
food security and improve their livelihoods. However, it is also an unfortunate fact that increased 472
agricultural production in such wetlands, often accompanied by drainage modification, is having a 473
significant negative impact on the associated ecosystems and biodiversity. 474

13
The impact of agricultural activity is illustrated in Figures 4c and d. Four species, Nothobranchius 475
lucius, N. luekei, N. rubripinnis (Figure 3c) and Nothobranchius ruudwildekampi were recorded in a 476
densely vegetated swamp in 2002. During subsequent visits, starting from the following year, none of the 477
Nothobranchius species were found in that habitat as a result of important ecological changes caused by 478
the development of a rice field progressively encroaching into the swamp. 479
480
5.1.2 | Abstraction of water and drainage changes 481
The seasonal life cycle of Nothobranchius fishes requires that the habitats contain water for a certain 482
period of the year. Furthermore, the natural dry period is also essential, to provide the appropriate 483
conditions for egg development. Unsustainable abstraction of surface water or groundwater for 484
agricultural or domestic use, or even changes to the surface drainage, is likely to modify the natural 485
seasonal water balance in either direction, which could severely affect the survival of the fishes and even 486
threaten the very existence of the wetlands. 487
When temporary habitats are converted to permanent pools by pumping water from a river into the 488
pond the seasonal nature of the habitat is changed and the dry component of the life cycle of the fishes is 489
eliminated. Under such conditions the inhabitant species will not survive. Examples of where this has been 490
done can be found in association with some seasonal habitats adjacent to the main course of the lower 491
Ruvu River near Kwaraza (Kwalaza) in east-central Tanzania. This is an area in which numerous 492
Nothobranchius species occur, including the type locations for Nothobranchius lourensi and 493
Nothobranchius janpapi. Other instances of the conversion of temporary habitats to permanent water 494
bodies have been observed in the northern part of the distribution of the genus including the Nilo-Sudanic 495
region, as well as north-eastern Kenya and coastal Somalia, regions that regularly experience extended 496
periods of drought. 497
As shown by Watters (2016), habitat degradation such as drainage modification and water withdrawal, 498
in association with road construction activities, can modify habitats in ways that often render them 499
unsuitable to support the seasonal life cycle of Nothobranchius fishes. Habitat modification during road 500
works (as shown in Figures 4e and f), resulted in the complete eradication of Nothobranchius from a 501
habitat in the Kilombero drainage in Tanzania, where four species had previously occurred syntopically. 502
This particular site is the type locality for two of those species, Nothobranchius geminus and 503
Nothobranchius kilomberoensis (Figures 3d and 3e, respectively). 504
Another type of natural system modification observed by the authors involves the conversion of 505
freshwater habitats of N. jubbi, in the near-shore coastal region of Kenya, into seawater ponds for salt 506
production (as shown in Figures 4g and h). 507
508
5.1.3 | Urbanization 509
Human settlement and urban development most commonly occur close to sources of water (Strayer & 510
Dudgeon, 2010; Kingsford, Basset & Jackson, 2016) and population growth may lead to the 511
transformation of wetland habitats into terrain for subsequent expansion of urban settlements. Land use 512
changes caused by the growth of urban areas may, therefore, have a significant impact on biodiversity 513
simply by eradicating suitable habitats, or it may lead to habitat fragmentation, resulting in genetic or 514

14
demographic isolation of species. In Africa, there is a clear spatial congruence between centres of rural 515
poverty and threatened freshwater species, particularly in East Africa (Darwall et al., 2011). 516
The known occurrence of some Nothobranchius species is restricted to areas very close to urban 517
developments. For example, most of the currently known observations of Nothobranchius brieni are from 518
marsh habitats situated directly within the confines of Bukama village in south-eastern DRC. Another case 519
concerns Nothobranchius derhami (Figure 3f), for which there are only a few known observations from 520
sites situated adjacent to, or within, urban development around Ahero village north-east of Lake Victoria 521
in south-western Kenya (Nagy & Watters, 2020). This renders those populations highly vulnerable, as the 522
marshes within and close to the village will probably disappear, owing to the increasing demands on land 523
resources, drainage modification and contamination. 524
Tweddle, van der Waal & Peel (2014) pointed to cases in the Zambezi Region of Namibia where 525
reduction in population size of Nothobranchius capriviensis (Figure 3g) could be observed based on the 526
current absence of the species from three previously known habitat sites, owing to habitat degradation 527
through an increased human population, as well as predation and competition by the artificial introduction 528
of other fish species. 529
530
5.1.4 | Pollution 531
The impact of pollution on freshwater communities in Africa is clearly apparent (Darwall et al., 2011). 532
Significant water pollution can occur when nutrients, or toxic substances, are released into fresh waters in 533
quantities in excess of those normally required, or that can be tolerated, by the ecosystem. These can 534
include sewage and other organic loads, and chemical and industrial effluent. The harmful effects of 535
indiscriminate pesticide application are little recognized in Africa and banned pesticides are still 536
commonly used in wetlands. The potential for the release of such substances is in direct proportion to the 537
increase in urban and industrial development and agricultural land use. Habitats within village confines or 538
close to human settlements are often used for washing clothes which constitutes another potential source 539
of pollution. Small freshwater habitats, such as temporary wetland pools, are particularly vulnerable 540
because of their generally small volumes and their slow- or non-flowing nature which severely limits their 541
capacity to dilute contaminants or mitigate other impacts (Dudgeon et al., 2006; Arthington et al., 2016). 542
For example, in the Katanga region of south-eastern DRC, mining for cobalt, copper, tin and uranium, the 543
construction of dams, the use of toxic plants for fishing, and overfishing, all constitute severe threats to the 544
existence of Nothobranchius fishes in this region. In the upper Lufira drainage, Katemo Manda et al. 545
(2010) found high to very high levels of pollution in the water, in plankton, and in gills and muscle tissue 546
of inhabitant fish. Nothobranchius polli (Figure 3h) is endemic to temporary pools and swamps associated 547
with this drainage in south-eastern DRC. Repeated visits by Nagy, with Prof. Chocha Manda, to three sites 548
in 2013 and 2016 have shown that most specimens of N. polli at all three sites were in poor health, with a 549
fungal layer on the fins and the head, and a high level of imminent mortality after capture. Mature males 550
were found dead in the habitat, which is an unusual phenomenon. 551
552
5.1.5 | Other threats 553
Climate change is becoming an important threat both to human populations and to biodiversity (Sayer, 554
Máiz-Tomé & Darwall, 2018). An increasingly important stress is linked to Climate change & severe 555

15
weather, with Droughts affecting 12% of the species. Development projects such as road construction and 556
road improvement, and reservoir construction, can result in habitat degradation or the complete 557
elimination of a habitat (Tweddle, 2009; Figure 4). In such cases, drainage modification is perhaps the 558
most common negative factor but physical changes to the habitat structure (e.g. activities that remove or 559
cover the critical habitat substrate) are also important potential consequences. Transportation & service 560
corridors are coded for 12% of the species. 561
Exploration and development work for energy production, such as very significant natural gas 562
discoveries in Palma Bay directly offshore from the Afungi peninsula in north-eastern Mozambique, 563
where the restricted distribution of Nothobranchius hengstleri is known, might adversely affect the coastal 564
ecosystem (ERM, 2014). 565
566
5.2 | Habitats created by human activities 567
The habitat classification revealed that a significant proportion of currently known sites represent habitats 568
that were created or modified by human activities. This suggests that if the extent of human intervention is 569
limited, some species are able to tolerate certain changes to the ecological factors and may not be 570
significantly affected. 571
Several examples illustrate the progressively increasing threats imposed to modified habitats. The type 572
locality of N. ugandensis near Iganga in south-eastern Uganda was a temporary pool in an open area 573
surrounded by a small forest. However, during the last two decades, the forest has disappeared and crops 574
are being cultivated on both sides of the road at the site. Although the species was still present at the early 575
stages of the land transformation (based on observations during 1988, 1990 and 1999), it could not be 576
detected there during repeated visits since 2009. Other examples are illustrated in Figure 4. 577
Habitats created or modified by human activities mainly represent habitats that are only temporarily 578
suitable for the seasonal fishes and typically represent locations with progressively increasing threats. 579
According to the classifications of the authors, 55% of the habitats are either the result of human activities 580
or represent natural habitats that have been severely modified. Continuous pressure on the land resources 581
will progressively render those habitats unsuitable to provide the ecological conditions required by 582
seasonal fishes. 583
584
6 | RECOMMENDED RESEARCH AND CONSERVATION ACTIONS 585
Based on these results, we can set priorities for research and recommend conservation actions to allocate 586
resources effectively for the preservation of seasonal wetland habitats and the Nothobranchius species 587
under threat. In addition, as recognized in Collen et al. (2014), similar threats drive different freshwater 588
organisms into categories of higher risk, which suggests that there are potential short-cuts for conservation 589
organizations addressing those threats that could reap multiple benefits. 590
591
6.1 | Research 592
More focused surveys should be aimed at monitoring conditions across the range of distribution of the 593
genus over the long term by repeat visits to specific habitat sites. This would lead to a better understanding 594

16
of fish population trends and the impact of threats, allowing better assessment of conservation status. 595
Ultimately, this would result in a more informed recognition of threatened species, and also an improved 596
determination of appropriate measures for conservation. In addition, the use of environmental DNA is 597
rapidly emerging as a potentially valuable survey technique for freshwater organisms that are hard to 598
survey, such as seasonal fishes in ephemeral habitats. It offers substantial potential for a method 599
associated with highly repeatable and reliable results, as a rapid way to involve citizens in monitoring the 600
presence of species through simple water sampling. Targeted environmental DNA surveys can be used for 601
the assessment and conservation of threatened species (Thomsen & Willerslev, 2015; Mauvisseau et al., 602
2020). 603
604
6.2 | Protection 605
Although wetlands are now widely recognized as important and valuable ecosystems, they are still largely 606
unprotected and are still rapidly disappearing around the world (van der Valk, 2012; Gardner & Finlayson, 607
2018). There is clearly a need to establish PAs for resource and habitat preservation in the wetlands. 608
Pertinently, the implementation of site management should be ensured in designated PAs and other 609
resource land. There is a need for improved habitat protection at the key sites where the species are known 610
to occur and to ensure that freshwater biodiversity is considered in conservation planning. Protection of 611
seasonal freshwater wetlands will also preserve the entire biota inhabiting these habitats. PAs, such as 612
national parks, game reserves and other community conservation areas are at the core of efforts aimed at 613
conserving nature and the most effective way of in situ biodiversity conservation. However, most of the 614
Nothobranchius species either are not known from existing PAs or those areas represent only marginal 615
components of their distribution range. 616
Many of the Nothobranchius habitats are isolated and fragmented. However, their generally small and 617
isolated nature, being spatially confined, may well render them easier to monitor and practical 618
management activities can be more targeted, especially in PAs. 619
Ultimately, available information should be used to identify sites as Key Biodiversity Areas, to 620
effectively conserve habitats and ensure greater recognition for this genus with a high level of threat. Sites 621
should be assessed against all relevant criteria for which data are available, to identify those that 622
contribute significantly to the global persistence of biodiversity (Darwall & Vié, 2005; Holland, Darwall 623
& Smith, 2012; IUCN, 2016). 624
625
6.3 | Integral management 626
Seasonal wetland habitats represent environments where the conditions and habitat characteristics are 627
constantly changing, requiring the implementation of a combination of several management actions. To 628
ensure that Nothobranchius species are able to complete their seasonal life cycle, the structural integrity of 629
the habitats needs to be protected throughout both seasonal phases. During the wet phase, the habitat 630
should be protected to allow the fishes to grow and breed. The impact of agriculture on wetlands can be 631
reduced by increasing productivity on agricultural land outside wetlands: efficient irrigation technologies 632
would prevent extensive water abstraction and drought-tolerant crops could reduce irrigation needs. 633
Sustainable use of water in agriculture, including wastewater, can also reduce withdrawals from wetlands. 634

17
Pollution loads reaching wetlands should be reduced and practices that strongly perturb water quality, 635
such as mining, should be avoided or be managed in a way that appropriately maintains the natural water 636
balance and adequately treats any waste products. During the dry phase it is also essential to preserve the 637
natural environment. The structure of the habitat substrate should be preserved and not disturbed in any 638
way to ensure favourable conditions for the development of the eggs before the ensuing wet phase, for the 639
completion of the fishes' life cycle. 640
641
6.4 | Awareness 642
Nothobranchius fishes, because of the very special conditions in certain seasonal wetlands to which they 643
have become adapted, are perhaps at greater risk of extinction than most other freshwater fishes. Beyond a 644
very basic knowledge of fish biology, education efforts should include information about the unique life 645
cycle of seasonal fishes, as limited familiarity with this aspect exists locally. Owing to the fact that these 646
fishes seem to appear ‘out of nowhere’ in small wetland pools as soon as the seasonal rains return, local 647
people often refer to the legend that they ‘fall from the sky with rain’ (Watters, 2006; Nagy & Watters, 648
2018a), not realising the important links between the existence of these fishes and the wetland ecosystem. 649
Raising awareness of the importance of healthy wetlands and the value of their unique seasonal 650
biodiversity is an essential step towards their preservation. For example, from personal interaction with 651
local people, the authors can attest to the interest that is generated when they are informed that preserving 652
the habitat of Nothobranchius constitutes a direct human benefit: the diet of the fishes consists mainly of 653
mosquito larvae, thereby reducing the incidence of malaria. 654
Education should also be aimed at encouraging government and construction departments to conduct 655
environmental impact assessments when planning major projects such as road building with culvert 656
drainage modification, dam construction and mining activities, to ensure minimum disturbance to the 657
seasonal pools and wetlands. Similarly, awareness raised among local university researchers and game 658
warden staff about the threats associated with the modification of seasonal water bodies will enhance the 659
management of roads, particularly within PAs. 660
661
ACKNOWLEDGEMENTS 662
The authors wish to express their gratitude to: all the colleagues who accompanied them on various field 663
trips for their important contributions to the field work; Denis Tweddle for collaboration on two species 664
assessments; Lars Grimsby, Holger Hengstler, Kiril Kardashev, Andrei Nikiforov and Martin Reichard for 665
providing field data. The authors are grateful to Catherine Sayer for her valuable help and guidance with 666
the species assessment process and to Jos Snoeks for critical review of the assessments. 667
668
CONFLICT OF INTEREST 669
The authors declare that they have no known competing financial interests or personal relationships that 670
could have appeared to influence the work reported in this paper. 671
672
DATA AVAILABILITY STATEMENT 673

18
Data supporting the findings of this study are available for all species in the conservation assessments and 674
associated species distribution maps online at IUCN Red List of Threatened (www.iucnredlist.org). 675
Additional data to support the findings of this study are available from the corresponding author upon 676
reasonable request. 677
ORCID 678
Béla Nagy https://orcid.org/0000-0003-4718-0822 679
680
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23
TABLES
TABLE 1 Number of species of the genus Nothobranchius per country in each IUCN Red List category, and proportion of threatened species.
Note that 15 species are known from more than one country. Important values are in bold
Country Threatened Categories Species
CR EN VU NT LC DD Total
% Threatened
%
Tanzania 2 8 24 5 8 47 42.0 34 72.3
DR Congo 3 5 8 7.1 8 100
Kenya 3 5 3 11 9.8 8 72.7
Zambia 4 3 1 8 7.1 7 87.5
Mozambique 1 4 1 5 11 9.8 5 45.4
Uganda 1 2 2 5 4.5 3 60.0
Somalia 2 2 4 3.6 2 50.0
Sudan 1 1 1 1 1 5 4.5 2 50.0
Namibia 1 1 0.9 1 100
Ethiopia 1 1 2 1.8 1 50.0
Malawi 1 1 1 3 2.7 1 33.3
South Africa 1 2 3 2.7 1 33.3
Zimbabwe 2 2 1.8
Chad 1 1 0.9
South Sudan 1 1 0.9
Total 3 21 44 8 17 1 94 68
% 3.2 22.3 46.8 8.5 18.1 1.1 72.3

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TABLE 2 Number of species of the genus Nothobranchius per freshwater ecoregion in each IUCN Red List Category, and proportion of
threatened species. Important values are in bold
Ecoregion Threatened
Categories Species
CR EN VU NT LC DD Total % Threatened
%
Coastal East Africa 2 7 11 5 5 30 27.8 20 66.7
Bangweulu–Mweru 4 5 9 8.3 9 100
Lake Victoria basin 4 4 3 11 10.2 8 72.7
Tana, Athi and coastal drainages 2 4 2 8 7.4 6 75.0
Southern Eastern Rift 5 2 7 6.5 5 71.4
Upper Lualaba 2 2 4 3.7 4 100
Upper Nile 1 3 1 2 1 8 7.4 4 57.1
Shebelle–Juba 3 2 5 4.6 3 60.0
Lake Tanganyika 2 2 1.9 2 100
Pangani 2 2 1.9 2 100
Lake Rukwa 1 1 0.9 1 100
Malagarasi–Moyowosi 2 3 5 4.6 2 40.0
Upper Zambezi floodplains 1 1 2 1.9 1 50.0
Lake Chilwa and Chiuta 1 1 0.9 1 100
Middle Zambezi–Luangwa 1 1 0.9 1 100
Zambezian Lowveld 1 1 4 6 5.6 1 16.7
Lower Zambezi 1 2 3 2.8
Lake Chad 1 1 0.9
Lake Malawi 1 1 0.9
Kafue 1 1 0.9

25
TABLE 3 Number and proportion of species of the genus Nothobranchius known from protected areas (PA) in each IUCN Red List Category.
Importantly low values are in bold
Species Threatened Categories
Total Total
Threatened
CR EN VU NT LC DD
Known in PA 2 9 4 10 25 11
Not known from PA 3 19 35 4 7 1 69 57
% in PA 0 9.5 20.5 50.0 58.8 0 26.6 16.2
TABLE 4 Number of observed habitats by type for Nothobranchius fishes. The classification scheme is based on a fundamental division of natural
habitats versus those created or modified by human activities, and further subdivision based on physical characteristics, drainage system
associations, geomorphological setting and the processes involved in their formation. Habitats at any site are often formed and modified by
multiple processes, the most fundamental of which is primary, whereas lower levels of formative processes, in order of importance in defining the
overall characteristics of a habitat, are referred to as secondary, tertiary, and quaternary
Habitat type Primary Secondary
Tertiary Quaternary
Total
Category 1: Habitats formed by natural processes 378 113 8 499
1.1 Isolated pools on floodplains 132 34 1 167
1.2 Flooded areas adjacent to streams 76 23 1 100
1.3 Marshes associated with stream systems 53 27 1 81
1.4 Isolated pools in seasonal drainage systems
1.4.1 Seasonal streams 85 29 4 118
1.4.2 Ancient drainage channels 3 3
1.5 Papyrus marshes
1.5.1 Marginal zones of papyrus marshes 8 1 9
1.5.2 Small streams feeding papyrus marshes 7 7
1.6 Habitats associated with topographical highs
1.6.1 Relict habitats on top of topographical highs 1 1
1.6.2 Habitats on the flanks of topographical highs 2 2
1.7 Habitats in small shallow valleys 11 11
Category 2: Habitats formed or modified by human activities
100 166 34 8 308

26
2.1 Habitats resulting from road construction 267
2.1.1 Ditches and eroded depressions at culverts 58 87 11 1 157
2.1.2 Ditches alongside (parallel to) roads 26 34 8 1 69
2.1.3 Flooded areas and small marshes with ditches 1 6 2 2 11
2.1.4 Flooded areas and small marshes near roads 5 23 2 30
2.2 Habitats associated with agricultural activities
2.2.1 Rice fields 4 11 6 4 25
2.2.2 Other agricultural associations 1 2 3 6
2.3 Other water bodies associated with human habitation 5 2 1 8
2.4 Borrow pits and quarries 1 1 2

27
FIGURES
FIGURE 1 Diagrammatic representation of the annual life cycle of Nothobranchius fishes. Phases in the
seasonal life cycle underscore the vulnerabilities of ecological factors that need to be preserved in order to
maintain the integrity of the habitats throughout both wet and dry seasons. All inset photographs by B.R.
Watters except the spawning photograph by A. Terceira

28
FIGURE 2 Distribution map and species richness of Nothobranchius fishes, based on dataset of the
authors

29
FIGURE 3 Photographs of selected wild-caught male specimens of Nothobranchius species mentioned
herein; with IUCN Red List categories in parentheses: (a) N. guentheri (EN), Zanzibar, eastern Tanzania;
(b) N. fuscotaeniatus (CR), Rufiji River drainage, eastern Tanzania; (c) N. rubripinnis (EN), Luhule and
Mbezi river systems, eastern Tanzania; (d) N. geminus (VU), Kilombero River system, eastern Tanzania;
(e) N. kilomberoensis (VU), Kilombero River system, eastern Tanzania; (f) N. derhami (EN), Nyando
River system, south-western Kenya; (g) N. capriviensis (EN), Zambezi Province, north-eastern Namibia;
(h) N. polli (EN), Lufira River system, south-eastern DR Congo. Photographs by B.R. Watters (a, b, c, d,
e, g) and B. Nagy (f, h)

30
FIGURE 4 Examples of habitat degradation and impact of threats: (a) site in the Rufiji drainage in
Tanzania, as photographed in 1997, with four inhabitant species of Nothobranchius, and type locality of
N. fuscotaeniatus (CR), a species with a specific niche including dense vegetation; (b) same site as ‘a’
photographed in 2017, when N. fuscotaeniatus was absent from the habitat during multiple subsequent
visits, due to the lack of dense vegetation; (c) site in the Luhule River system in eastern Tanzania, as
photographed on June 2, 2002, with four inhabitant species of Nothobranchius; (d) same site as ‘c’ in
2003, when Nothobranchius species were absent, as a result of development of a rice field progressively
encroaching into the marsh habitat; (e) site in the Kilombero drainage in Tanzania, as photographed on
June 7, 1995, with four inhabitant species of Nothobranchius - type locality for two of them; (f) same site
as ‘e’ on June 10, 2000, with all previously inhabitant Nothobranchius species eliminated from the site
due to drainage modification; (g) site in coastal south-eastern Kenya, as photographed 9 June, 2008, with
N. jubbi inhabiting the biotope; (h) same site as ‘g’ in 2010, the species eliminated as a result of the
habitat being converted into seawater ponds for salt production. Photographs by B.R. Watters (a, c, d, e, f)
and B. Nagy (b, g, h)

31
FIGURE 5 Ranking of major threat types for Nothobranchius species, based on IUCN Red List
assessments