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Although some fish species have been shown to be able to discriminate between two groups (shoals) of conspecifics differing in the number of members, most studies have not controlled for continuous variables that covary with number. Previously, using angelfish (Pterophyllum scalare) we started the systematic analysis of the potential influence of s...
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... type juvenile angelfish (Pterophyllum scalare) were obtained from local commercial suppliers (Fig. 1). Only juveniles of this sexually monomorphic species were studied so as to eliminate possible confounding effects arising from courtship or agonistic/ territorial interactions. The fish were housed in glass holding aquaria (length 6 width 6 depth: 60 cm630 cm640 cm) in groups of 20-22 when fish were of small and medium size, and in ...
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... In general, these experiments were unable to determine whether fish used numerical information or the other perceptual variables that covary with number; for example, the total activity of the shoals, the cumulative surface area occupied by fish, or the density of groups (Agrillo et al. 2007;Hager and Helfman 1991;Hoare et al. 2004). Indeed, studies that have attempted to experimentally control for non-numerical variables have frequently found teleosts' discrimination of shoal numerosity dropped to chance level when the cumulative surface area and activity level of two stimulus shoals were equated (Agrillo et al. 2008b;Gómez-Laplaza and Gerlai 2013;Pritchard et al. 2001). This prevents a direct comparison with birds and mammals, which instead are generally studied using paradigms of forced two-choice appetitive operant conditioning with artificial stimuli for which non-numerical variables can be easily controlled. ...
... We presented four different numerical ratios: 2 versus 3 (ratio 0.67), 3 versus 4 (ratio 0.75), 4 versus 5 (ratio 0.80), and 5 versus 6 (ratio 0.83). As other vertebrates, fish can discriminate two quantities of items using non-numerical cues that covary with number, such as the cumulative surface area of the items, the space occupied by the array or "convex hull" (measured drawing the smallest polygon enclosing all dots in an array) and the density of items (Gómez-Laplaza and Gerlai 2013;Lucon-Xiccato et al. 2015). We used 24 different pairs of stimuli for each ratio that were controlled for the three above-mentioned non-numerical variables. ...
Numerical discrimination is widespread in vertebrates, but this capacity varies enormously between the different species examined. The guppy (Poecilia reticulata), the only teleost examined following procedures that allow a comparison with the other vertebrates, outperforms amphibians, reptiles and many warm-blooded vertebrates, but it is unclear whether this is a feature shared with the other teleosts or represents a peculiarity of this species. We trained zebrafish (Danio rerio) to discriminate between numbers differing by one unit, varying task difficulty from 2 versus 3 to 5 versus 6 items. Non-numerical variables that covary with number, such as density or area, did not affect performance. Most fish reached learning criterion on all tasks up to 4 versus 5 discrimination with no sex difference in accuracy. Although no individual reached learning criterion in the 5 versus 6 task, performance was significant at the group level, suggesting that this may represent the discrimination threshold for zebrafish. Numerosity discrimination abilities of zebrafish compare to those of guppy, being higher than in some warm-blooded vertebrates, such as dogs, horses and domestic fowl, though lower than in parrots, corvids and primates. Learning rate was similar in a control group trained to discriminate between different-sized shapes, but zebrafish were slightly more accurate when discriminating areas than numbers and males were more accurate than females. At the end of the experiment, fish trained on numbers and controls trained on areas generalized to the reciprocal set of stimuli, indicating they had used a relational strategy to solve these tasks.
... Briefly, when conspecific shoals differing in numerical size (number of shoal members) were contrasted, angelfish chose the numerically larger one. Although this response has been generally robust, it has also been shown to depend upon a variety of factors, including non-numerical continuous variables (Gómez-Laplaza & Gerlai, 2012;Gómez-Laplaza & Gerlai, 2013a, 2013b. ...
... To directly address this question, we contrasted the video-recorded shoal with the live shoal in Experiment 5, and found the latter to be preferred to the former. The fact that angelfish showed equal choice between a live shoal of four conspecifics and a videotaped shoal of nine conspecifics (experiment 6) also supports the notion that angelfish prefer live to video-recorded shoals, because angelfish have been shown to exhibit strong preference for the shoal with larger number of members when the numerical ratio between the contrasted shoals is at least 2:1 (Gómez-Laplaza et al., 2017;Gómez-Laplaza & Gerlai, 2011a;Gómez-Laplaza & Gerlai, 2013b;Gómez-Laplaza & Gerlai, 2016a, 2016b. Other fish species too have been found to prefer live to video-recorded fish. ...
Video playback is a widely used technique for presentation of visual stimuli in animal behavior research. In the analysis of behavioral responses to social cues, presentation of video recordings of live conspecifics represents a consistently reproducible stimulus. However, video-recordings do not interact with the experimental subject, and thus this stimulus may be inferior in the social context. Here, we evaluated how angelfish ( Pterophyllum scalare ) respond to a video playback of conspecifics versus a live shoal of conspecifics. Using binary choice tests, subjects were presented different stimuli. Time spent close to one versus the other stimulus was considered an index of preference. We found angelfish to prefer a live shoal of conspecifics to an empty tank, and also the video playback of a shoal of conspecifics to a blank screen, although the level of preference in the latter was lower than in the former. These results indicate that video-playback of live conspecifics may be appropriate in angelfish, thus allowing manipulation of specific cues that angelfish may use in quantity discrimination. However, when we directly contrasted a live and a video recorded shoal, both having the same number of members, experimental fish preferred the live shoal. When the choice consisted of a live shoal of four conspecifics versus a video playback of a shoal of nine conspecifics no clear preference emerged. These results imply that video-playback has disadvantages in quantity discrimination studies with angelfish. Exploring procedural and/or technological parameters will verify the suitability of video-recording-based stimulus presentation for future use in angelfish.
... Stimuli were made with Adobe Illustrator CC 2019 and consisted of sets of black dots of differing numerosity on a white background: 3 vs. 12, 2 vs. 3, 3 vs. 4, 4 vs. 5, and 5 vs. 6. Like other vertebrates, guppies can discriminate two quantities of objects using non-numerical attributes of the stimuli, such as cumulative surface area, density, and convex hull (the convex polygon that circumscribes all items) [44,45]. To prevent fish from using this alternative strategy, we controlled the stimuli for all the above-mentioned non-numerical variables. ...
The growing use of teleosts in comparative cognition and in neurobiological research has prompted many researchers to develop automated conditioning devices for fish. These techniques can make research less expensive and fully comparable with research on warm-blooded species, in which automated devices have been used for more than a century. Tested with a recently developed automated device, guppies (Poecilia reticulata) easily performed 80 reinforced trials per session, exceeding 80% accuracy in color or shape discrimination tasks after only 3–4 training session, though they exhibit unexpectedly poor performance in numerical discrimination tasks. As several pieces of evidence indicate, guppies possess excellent numerical abilities. In the first part of this study, we benchmarked the automated training device with a standard manual training procedure by administering the same set of tasks, which consisted of numerical discriminations of increasing difficulty. All manually-trained guppies quickly learned the easiest discriminations and a substantial percentage learned the more difficult ones, such as 4 vs. 5 items. No fish trained with the automated conditioning device reached the learning criterion for even the easiest discriminations. In the second part of the study, we introduced a series of modifications to the conditioning chamber and to the procedure in an attempt to improve its efficiency. Increasing the decision time, inter-trial interval, or visibility of the stimuli did not produce an appreciable improvement. Reducing the cognitive load of the task by training subjects first to use the device with shape and color discriminations, significantly improved their numerical performance. Allowing the subjects to reside in the test chamber, which likely reduced the amount of attentional resources subtracted to task execution, also led to an improvement, although in no case did subjects match the performance of fish trained with the standard procedure. Our results highlight limitations in the capacity of small laboratory teleosts to cope with operant conditioning automation that was not observed in laboratory mammals and birds and that currently prevent an easy and straightforward comparison with other vertebrates.
... Hence, our results suggest that rock lizards might have the ability to discriminate between prey quantities. In this regard, we must remark that, in our design, we did not control for other quantity-related continuous cues such as area, volume, density, weight, movement, or contour length that could be used for quantitative judgments (Uller et al. 2003;Krusche et al. 2010;Abramson et al. 2011;Garland et al. 2012;Vonk and Beran 2012;Gómez-Laplaza and Gerlai 2013;Mehlis et al. 2015), neither for olfactory cues (Plotnik et al. 2019). These continuous variables usually covariate with quantity, but discrimination among them does not necessarily imply processment of numerical information (Agrillo and Bissaza 2014). ...
Animals often face situations that require quantity discrimination for decision-making. Differentiating between more and less amounts might be adaptative in different contexts such as in social relationships, navigation, or foraging. However, feeding close to conspecifics might change foraging behavior decisions due to changes in predation risk perception and competition for resources. Here, we tested the quantity judgment abilities of foraging rock lizards (Iberolacerta cyreni) in a spontaneous choice test between 5 and 10 cricket prey. Lizards tested had been previously housed alone or in a group to examine how social experience affected foraging decisions. Our results showed that “grouped” lizards had greater foraging activity than “solitary” lizards. Furthermore, all lizards demonstrated some ability to discriminate between the two amounts of prey. These results reveal the capability of quantity judgments in rock lizards and also that foraging decisions may be modulated by the previous social experience.
Significance statement
The presence of food sources differing in quantity, together with the proximity of conspecifics, can strongly affect foraging decisions. Previous studies showed various levels of quantitative abilities on different taxa, but results with reptiles are scarce and inconsistent. On the other hand, previous research showed that grouping may have a notable effect on foraging behavior. Here, we demonstrate that male rock lizards can discriminate between two amounts of prey and that there is an effect of the previous social experience on foraging behavior, as lizards that had been housed alone showed less interactivity with food. These outcomes reveal the existence of quantitative abilities in lizards and the importance of the previous social experience in foraging decisions.
... Many fish speciesincluding rainbow trout (Höjesjö et al., 2015;Johnsson & Åkerman, 1998) are able to recognize live conspecifics individually using visual cues (Culumber, 2015;Griffiths & Magurran, 1999;Roux et al., 2016). However, when males and females of the peacock blenny (Salaria pavo) were presented with a live conspecific male or a video of the same individual, the video images failed to elicit appropriate behavioral responses (Goncalves, Oliveira, Korner, Poschadel, & Schlupp, 2000). In the case of anemonefishes (Johnston & Dixson, 2017) and Lake Malawi cichlid species (Knight & Turner, 1999), it was shown that a combination of visual and other senses stimuli (chemical cues) can be fundamental in conspecific recognition. ...
Cognitive abilities were studied in rainbow trout, the first continental fish production in Europe. Increasing public concern for the welfare of farmed-fish species highlighted the need for better knowledge of the cognitive status of fish. We trained and tested 15 rainbow trout with an operant conditioning device composed of self-feeders positioned in front of visual stimuli displayed on a screen. The device was coupled with a two-alternative forced-choice (2-AFC) paradigm to test whether rainbow trout can discriminate 2-D photographs of conspecifics (S+) from different visual stimuli (S-). The S- were applied in four stages, the last three stages representing increasing discrimination difficulty: (1) blue shapes; (2) black shape (star); (3) photograph of an object (among a pool of 60); (4) photograph of another fish species (among a pool of 60). Nine fish (out of 15) correctly managed to activate the conditioning device after 30–150 trials. The rainbow trout were able to discriminate images of conspecifics from an abstract shape (five individuals out of five) or objects (four out of five) but not from other fish species. Their ability to learn the category "fish shape" rather than distinguishing between conspecifics and heterospecifics is discussed. The successful visual discrimination task using this complex operant conditioning device is particularly remarkable and novel for this farmed-fish species, and could be exploited to develop cognitive enrichments in future farming systems. This device can also be added to the existing repertoire of testing devices suitable for investigating cognitive abilities in fish.
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... However, other studies have shown the importance of non-numerical variables, which usually covary with number, in this discrimination. Non-numerical cues such as contour length of the items (Clearfield and Mix 1999;Mix et al. 2002), surface area (Clearfield and Mix 2001;Hurewitz et al. 2006;Feigenson et al. 2002;Agrillo et al. 2008Agrillo et al. , 2009Tomonaga 2008;Pisa and Agrillo 2009;Vonk and Beran 2012;Gómez-Laplaza and Gerlai 2013a;Lucon-Xiccato et al. 2018;Xiong et al. 2018), movement (Agrillo et al. 2008;Krusche et al. 2010;Gómez-Laplaza and Gerlai 2012), and density (Allik and Tuulmets 1991;Durgin 1995;Emmerton 1998;Tomonaga 2008;Frommen et al. 2009;Gómez-Laplaza and Gerlai 2013b;Parrish et al. 2017) of items have all been shown to affect and occasionally 1 3 dominate decision making when choosing between numerically different sets of items. ...
Many animal species share the ability to discriminate between sets with different quantity of food items. In fish, this ability has rarely been investigated, although findings have been obtained do indicate a preference, as in other animals, for sets with large over small quantities. The role played by food item size has also been found to be important in the discrimination. However, another potentially important non-numerical variable, food density, has not been investigated. In this study, we examined the influence of density (inter-item distance) in the decision-making process of food discrimination in angelfish (Pterophyllum scalare). In a binary choice task, we kept the number and size of food items constant, but contrasted a set containing food items spaced further apart (sparse set) to another set with food items spaced more closely (dense set). We conducted this analysis with sets in the small (3 vs 3 food items) and in the large number range (5 vs 5 food items) and also varied the specific spatial arrangements of the food items in the sets. Contrary to expectations, angelfish showed a preference for the sparse sets over the dense sets in the five vs five contrasts irrespective of the specific spatial arrangement, but exhibited no preference in case of the three vs three contrasts. Subsequently, we slightly lengthened the inter-item distance in the dense sets, and found preference for the dense over the sparse sets. Last, we further examined the potential effect of spatial configuration of the items in the sets, but found no effect of this latter factor. Overall, these results indicate that higher density of the contrasted food item sets significantly influences choice in angelfish, which prefer denser sets if a clear discriminability of each individual item within the sets is provided.
... No study has established whether fish can transfer numerical information from one sensory modality to another, a fact that prevents to understand whether the complexity of abstract numerical representation is similar or not in human and fish. Also, the investigation of continuous quantities used by fish is limited to a few species (Agrillo et al., , 2011Gómez-Laplaza and Gerlai, 2013;Miletto Petrazzini et al., 2018). In order to understand whether the cognitive mechanisms used by human and fish are similar, we need to enlarge the number of species under investigation. ...
In 1985, Macphail argued that there are no differences among the intellects of non-human vertebrates and that humans display unique cognitive skills because of language. Mathematical abilities represent one of the most sophisticated cognitive skills. While it is unquestionable that humans exhibit impressive mathematical skills associated with language, a large body of experimental evidence suggests that Macphail hypothesis must be refined in this field. In particular, the evidence that also small-brained organisms, such as fish, are capable of processing numerical information challenges the idea that humans display unique cognitive skills. Like humans, fish may take advantage of using continuous quantities (such as the area occupied by the objects) as proxy of number to select the larger/smaller group. Fish and humans also showed interesting similarities in the strategy adopted to learn a numerical rule. Collective intelligence in numerical estimation has been also observed in humans and guppies. However, numerical acuity in humans is considerably higher than that reported in any fish species investigated, suggesting that quantitative but not qualitative differences do exist between humans and fish. Lastly, while it is clear that contextual factors play an important role in the performance of numerical tasks, inter-species variability can be found also when different fish species were tested in comparable conditions, a fact that does not align with the null hypothesis of vertebrate intelligence. Taken together, we believe that the recent evidence of numerical abilities in fish call for a deeper reflection of Macphail’s hypothesis.
... In a social context, where angelfish had to discriminate between numerically different shoals (groups) of conspecifics, we have already obtained evidence demonstrating the importance of continuous variables, a finding also obtained with other fish species [34][35][36] . The variables we found to play roles were the level of activity, size, and the density of the presented stimulus fish [37][38][39] . ...
Comparative studies on quantity discrimination in animals are important for understanding potential evolutionary roots of numerical competence. A previous study with angelfish has shown that they discriminate numerically different sets of same-sized food items and prefer the larger set. However, variables that covary with number were not controlled and choice could have been influenced by variables such as size or density of the food items rather than numerical attributes. Here using a recently developed approach, we examined whether contour length of the food items affects choice in a spontaneous binary choice task. In Experiment 1, a contrast of 1 vs. 1 food item was presented, but the ratio between the size (diameter) of the food items was varied. In Experiment 2, numerically different food sets were equated in overall size by increasing the size (diameter) of the items in the numerically small sets. In both Experiments, subjects showed a preference for the larger sized food items with a discrimination limit. These results show that item size plays a prominent role in foraging decisions in angelfish. Experiment 3 placed numerical and size attributes of the sets in conflict by presenting one larger-sized food item in the numerically smaller set that also had smaller overall size (diameter) of food items. Angelfish showed no preference in any of the contrasts, suggesting that they could not make optimal foraging decisions when these attributes were in conflict. Maximization of energy return is central to optimal foraging. Accordingly, here item size was also found to be a key feature of the sets, although the numerical attributes of the sets also influenced the choice.
... The ability to estimate BSA has broad scale application in the fields of fish biology and aquaculture studies. Gomez-Laplaza and Gerlai (2013) measured BSA of individual freshwater angelfish (Pterophyllum scalare Schultze, 1824) among differing sized shoals to test capabilities of numerical discrimination. The number of taste buds per mm 2 of body areas (e.g. ...
Sea lice (Lepeophtheirus and Caligus spp) are parasitic copepods that infect the external surfaces of fish hosts. Salmon lice (L. salmonis) outbreaks are commonly reported by operations in Canada, Norway, Scotland, Ireland, and the United States and are a primary concern in aquaculture because of their fish health and economic impacts. When farmed fish mortalities and treatments are accounted for, annual losses from sea louse infestations exceed $300,000,000 (Costello 2009). Farms experiencing sea lice infections risk on-site re-infection and transmission to wild populations and other farms that are hydrographically connected. In Maine, Atlantic salmon farms are located in the northeast, with major operations in Machiasport and Cobscook Bay. The primary aim of this study was to establish the infection dynamics of sea lice in Cobscook because it is positioned at the mouth of the Bay of Fundy, where outbreaks are increasingly common but are not well described in the available literature. Sentinel cages housed Atlantic salmon juveniles for a total of 7 days every month to monitor sea lice settlement at 4 sites within Cobscook Bay: Broad Cove, Comstock Cove, Prince Cove, and Pembroke Landing. The survey revealed a pre-season (early summer) and season (autumn) peak for sea lice prevalence (percent infected fish) and abundance (lice/fish). Spatial differences in prevalence and abundance were also detected for most months of the study and Pembroke Landing became a site of interest because the observed infection trends were unique relative to the remaining coves. Copepodid and chalimus stages were not detected in the late winter or early spring in 2014 because temperatures were not supportive of egg hatching, naupliar survival, or copepodid attachment. The source of the infections observed over the course of 18 months was unclear and farm counts from the time of the study were not made available for farm to sentinel comparisons. The relationship between environmental factors and total sea lice counts were investigated using generalized linear mixed effect models (GLMMs) with a negative binomial distribution and a log link function. A mathematical model estimating body surface area of Atlantic salmon juveniles was designed and then used to generate fish morphometric data for GLMM development. Data from individual sites were initially pooled to generate a general model for the entire bay, but the significance of Pembroke Landing as an individual site prompted a need to generate site-specific GLMMs. Temperature had a positive relationship on total sea lice count at all sites, which was expected because of its biological relevance in expediting sea louse development and growth. Current velocity had a negative relationship with sea lice at Prince Cove and Pembroke Landing, likely because average velocities were within a range that limits sea lice attachment. Results from the survey and the mathematical model were linked with previous work on sea lice infection dynamics to develop scenarios that describe potential sources of infection for Cobscook Bay. These data and scenarios will be used to inform future bio-physical models and assist in developing hypotheses that can be tested once models are validated and confirmed.
... The experimental fish was allowed to swim freely for 20 min, the total length of the experimental session, after which it was removed and returned to its home tank. The contrasted shoal ratios used were chosen based on findings from prior studies conducted with angelfish (Gómez-Laplaza and Gerlai , b, 2012Gerlai , 2013aGerlai , b, 2015Gerlai , 2016a. We chose ratios which angelfish were able to discriminate. ...
... This discrepancy may be the result of numerous substantial methodological differences between the two studies. The impact of experimental procedural or methodological factors in discrimination of groups of fish differing in number of members is clearly demonstrated by a recent study by Lucon-Xiccato et al. (2017) as well as by the series of papers published by Gómez-Laplaza and Gerlai (2012;2013a;2013b;2016a;2016b). For example, Potrich et al. (2015) studied numerical preference in the context of sexual behaviour, not shoaling. ...
Numerical abilities have been demonstrated in a variety of non-human vertebrates. However, underlying biological mechanisms have been difficult to study due to a paucity of experimental tools. Powerful genetic and neurobiological tools already exist for the zebrafish, but numerical abilities remain scarcely explored with this species. Here, we investigate the choice made by single experimental zebrafish between numerically different shoals of conspecifics presented concurrently on opposite sides of the experimental tank. We examined this choice using the AB strain and pet store zebrafish. We found zebrafish of both populations to generally prefer the numerically larger shoal to the smaller one. This preference was significant for contrasted ratios above or equalling 2:1 (i.e. 4 vs. 0, 4 vs. 1, 8 vs. 2, 6 vs. 2 and 6 vs. 3). Interestingly, zebrafish showed no significant preference when each of the two contrasted shoals had at least 4 members, e.g. in a contrast 8 versus 4. These results confirm that zebrafish possess the ability to distinguish larger numbers of items from smaller number of items, in a shoaling context, with a potential limit above 4. Our findings confirm the utility of the zebrafish for the exploration of both the behavioural and the biological mechanisms underlying numerical abilities in vertebrates.
