Effect of isopod parasite, Cymothoa indica on gobiid fish, Oxyurichthys microlepis from Parangipettai coastal waters (South-east coast of India)

Abstract

The present study reported for the first time on the effect of isopod parasite, Cymothoa indica infestation on Oxyurichthys microlepis an ecologically important gobiid fish from Parangipettai coastal environment (South-east coast of India). The loss of weight in host fishes (male 20.47 and female 32.84%) were observed due to parasitism. The weight of uninfested female fish was found to be higher than that of infested one. The calus like thickening developed on the gill arch and gill filaments of host fish due to the persistent irritation caused by the appendages of the parasite. The reduction of gill surface area was observed due to the attachment of the parasites. The maximum reduction noticed in the first gill arch is mainly due to the heavy pressure exerted by the parasite. Details of gross lesions observed in the branchial chamber, buccal cavity and body surface was enumerated. Heavy infestations of parasitic juveniles have the potential to kill small fingerlings. The swimming capacity of the fish was also found to be affected.

Full text

Journal of Environmental Biology

April, 2007
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Effect of isopod parasite, Cymothoa indica on gobiid fish, Oxyurichthys microlepis from
Parangipettai coastal waters (South-east coast of India)
V. Ravi and M. Rajkumar*
1
Centre of Advanced Study in Marine Biology, Annamalai University, Parangipettai–608 502, India
(Received: Decemebr 25, 2004 ; Revised received: June 02, 2005 ; Accepted: July 05, 2005)
Abstract: The present study reported for the first time on the effect of isopod parasite, Cymothoa indica infestation on Oxyurichthys microlepis an
ecologically important gobiid fish from Parangipettai coastal environment (South-east coast of India). The loss of weight in host fishes (male 20.47
and female 32.84%) were observed due to parasitism. The weight of uninfested female fish was found to be higher than that of infested one. The
calus like thickening developed on the gill arch and gill filaments of host fish due to the persistent irritation caused by the appendages of the parasite.
The reduction of gill surface area was observed due to the attachment of the parasites. The maximum reduction noticed in the first gill arch is mainly
due to the heavy pressure exerted by the parasite. Details of gross lesions observed in the branchial chamber, buccal cavity and body surface was
enumerated. Heavy infestations of parasitic juveniles have the potential to kill small fingerlings. The swimming capacity of the fish was also found
to be affected.
Key words: Isopod fish parasite, Loss of weight, Gross lesions, Gill surface, Reduction
*Corresponding author: E-Mail: arunachalashivamdr@yahoo.com., Tel : 04144 243223, 243533, 243070, 243071, Fax: 04144 243 555
Introduction
Parasites play an important role in the biology of fishes
and can affect their behaviour, health and distribution (Rohde,
1993). Several facultative and obligatory parasitic members of
the order Isopoda are deleterious parasites on fishes, capable of
exhibiting tremendous destructive activity (Trilles, 1979; Maxwell,
1982). Most are cymothoids flabelliferans, a group of isopods
with a short free living planktonic phase. Cymothoids are
exclusively parasitic, and the presence of a few adults can cause
damage to hosts. They are protandric hermaphrodites, living on
the skin in the gill chambers or in the mouth of the host fish, the
position is thus highly specific (Baer, 1951; Trilles, 1969). Isopods
absorb their nourishment directly from the host’s body and depend
upon their hosts for feeding. Segal (1987), observed that the host
fish, Meniida beryllina died due to attack of isopod Nerocila
acuminata.
Studies pertaining to pathological effects of isopod
parasites on the physiology of host fishes are scanty and few
studies have been made along Parangipettai coastal environment.
Though, Oxyurichthys microlepis is not a commercial important
fish, it plays an important ecological role and maintains a balance
in ecosystem. Hence the present attempt was made to study the
effect of isopod infestation on host fish, with reference to reduction
of the respiratory surface area and loss of weight in the gobiid
fish O. microlepis.
Materials and Methods
The gobiid fish were collected from Vellar estuary (Lat.
11
o
29’N, Long. 79
o
46’E) (Parangipettai coast, Fig. 1) and the
fishes were examined thoroughly for the presence of isopod
parasites. The gobiid fish, Oxyurichthys microlepis can be
identified by its 5 large brown blotches on sides first one below
D
1
(first dorsal fin) in middle, 2 to 4 in D
2
(2
nd
dorsal fin) region
while the fifth one on the caudal base and a small dark brown
spots in the upper half of the caudal fin body elongate,
compressed ventral fins unified and oblong while caudal fin
pointed about twice head. The total length of the fish was ranged
from 59 to 125 mm. It is a common species occurring throughout
the year. The site of attachment, orientation of parasites on the
host and the number of parasites in each location was recorded.
To study the effect of infestation on the gobiid fish O.
microlepis, the length (mm) and weight (g) data were analysed.
The fishes were categorized as infested and uninfested and the
average length and weight were determined. The loss of weight
and percentage loss of weight of male and female fishes was
determined. Respiratory surface area of gill arch was measured
to find out the influence of parasites on the gill surface area. The
gill arches of uninfested and infested fishes were carefully
dissected out and blotted to remove the moisture. Then the total
surface area of gill arch of both infested and uninfested fish was
compared and the difference in area was considered as the
reduction of respiratory area due to infestation.
Results and Discussion
Effect on weight of host fish: The effect of Cymothoa indica
infestation on the weight of O. microlepis is presented in Table 1,
2 and Fig. 3, 4). It is evident from the results that the infestation
affected the weight was 8.4 g when compared to that of parasitised
Journal of Environmental Biology April 2007, 28(2) 251-256 (2007)
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Journal of Environmental Biology
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April, 2007
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V. Ravi and M. Rajkumar
fish. Further the weight loss was more pronounced in female
(32.8% in O. microlepis) than in males (20.4% in O. microlepis).
Effect on length and weight relationship: The effects on length
and weight relationship of O. microlepis due to infestation of C.
indica in both male and female fishes were compared and the
results are as follows :
(i) Length and weight relationship in male fish -
The rate of growth is almost similar in uninfested and
infested fishes. It can be inferred that the rate of growth by
weight and average size was not affected much due to
infestation.
(ii) Length and weight relationship in female fish -
The rate of increased growth by weight in uninfested female
fish was found to be higher than that of the infested. It can
be inferred that the weight gain is more in uninfested fish
than in the infested fish.
Table - 1: Effect of Cymothoa indica in relation to the body weight (g) of
Oxyurichthys microlepis
Nature Mean Reduction Percentage
of body of reduction
infestation weight weight of weight
Uninfected 8.71 2.47 8.47
Infected 6.17 1.26
–
Table - 2: Percentage weight (g) variation in male and female of
Oxyurichthys microlepis
Mean weight Sex of host Uninfected Infected
Male 6.59 5.47
Female 9.10 6.85
Loss of weight Male – 1.12
Female – 2.25
Percentage loss Male – 20.47
of weight Female – 32.84
Effects on respiratory surface area: Variations in the respiratory
surface area of O. microlepis were due to the infestation of C.
indica. Maximum reduction in respiratory surface area was noticed
in the first gill arch and a minimum in the third gill arch. Thus
considerable variation in the respiratory area was observed due
to the attachment of the parasite (Fig. 2).
Gross lesions: The gross lesions observed in the branchial
chamber, buccal cavity and body surface are reported.
Branchial chamber: Infested fishes had extremely pale gills
indicating severe anemia. Gill rakers were seriously lost, apical
edges damaged and gill lamellae heavily destroyed. Some
secondary gill lamellae were fused or thickened. Between the
gill lamellae calus-like thickenings were observed. Gill lamellae
Fig. 1: Map showing the study area
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Isopod parasite on gobiid fish
Table - 3: Infestation of Cymothoa indica on Oxyurichthys microlepis in relation to different months (July 2003 - June 2004)
Months No. of fishes No. of fishes infested No. of parasites collected
examined (% prevalence) (Mean intensity)
July 2003 51 20 (39.2) 27 (1.3)
August 54 15 (27.7) 20 (1.3)
September 53 18 (33.9) 26 (1.4)
October 68 16 (23.5) 29 (1.8)
November 32 12 (37.5) 16 (1.3)
December 28 9 (32.1) 17 (1.8)
January 2004 31 7 (22.5) 14 (2.0)
February 42 10 (23.8) 14 (1.4)
March 47 13 (27.6) 16 (1.2)
April 30 8 (26.6) 12 (1.5)
May 36 5 (13.8) 9 (1.8)
June 45 11 (24.4) 14 (1.2)
Total 517 144 (27.8) 214 (1.4)
Fig. 2: Photograph showing the Oxyurichthys microlepis in the Cymothoa indica
Table - 4: Infestation of Cymothoa indica on Oxyurichthys microlepis in relation to sex at different months
Male fishes Female fishes
Months No. of fishes No. of fishes No. of parasites No. of fishes No. of fishes No. of parasites
examined infested collected examined infested collected
(% prevalence) (Mean intensity) (% prevalence) (Mean intensity)
July 2003 39 13 (33.3) 17 (1.3) 12 7 (58.3) 10 (1.4)
August 31 9 (29.0) 12 (1.3) 23 6 (26.0) 8 (1.3)
September 28 10 (35.7) 14 (1.4) 25 8 (32.0) 12 (1.5)
October 48 9 (18.75) 13 (1.4) 20 7 (35.0) 16 (2.2)
November 21 7 (33.3) 10 (1.4) 11 5 (45.4) 6 (1.2)
December 17 5 (29.4) 10 (2.0) 11 4 (36.3) 7 (1.7)
January 2004 21 4 (19.0) 7 (1.7) 10 3 (30.0) 7 (2.3)
February 26 7 (26.9) 11 (1.5) 16 3 (18.1) 3 (1.0)
March 25 9 (36.0) 12 (1.3) 22 4 (18.1) 4 (1.0)
April 18 5 (27.7) 8 (1.6) 12 3 (25.0) 4 (1.3)
May 21 3 (14.2) 7 (2.3) 15 2 (13.3) 2 (1.0)
June 27 7 (25.9) 10 (1.6) 18 4 (22.2) 4 (1.0)
Total 322 88 (27.3) 131 (1.4) 195 56 (28.7) 83 (1.4)
253

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0
5
10
15
20
25
30
35
40
50-60 60-70 70-80 80-90 90-100 100-110 110-120
Length of
O. microlepis
Number of C. indica
Male isopods Female isopods
Fig. 4: The number of male and female Cymothoa indica in relation to length of Oxyurichthys microlepis
0
20
40
60
80
100
120
50-60 60-70 70-80 80-90 90-100 100-110 110-120
Length of
O.microlepis
% prevalence
% prevalence of male % prevalence of female
Fig. 3: The percentage prevalence in relation to size and sex of Oxyurichthys microlepis
of the first and second gill arches were found eroded towards
posterior position due to C. indica. Due to the lodging of parasites
at the gill clefts and the gill arches showed lesions with a wide
depression. The parasites further stimulated over secretion of
the mucus production.
Buccal cavity: Gross lesions observed in the buccal cavity of
infested fishes showed small pin-holes in the cartilage support
of the gill arches developed, through which dactyls of peropod of
isopod were penetrated, claws are dig into the host tissues. The
result is usually a localized destruction of the epidermis and
inflammatory response around the attachment area was noticed.
Body surface: Isopods make frequent shifts in position on the
host causing a serious wound. They often move about as they
feed. The activities also stimulate mucus secretion, epidermal
proliferation and dilation of dermal capillaries. Mucous cells
increase in number in the epidermis peripheral to the wound.
Due to increased mucus secretion, there are signs of inflammation
in the dermis beneath the wound. The digestive secretion
apparently causes significant damage to the host’s tissues.
O. microlepis is commonly distributed and occurring
throughout the year in the Vellar estuary. They do not form
economic importance of fisheries but it is consumed by local poor
people; and is rarely displayed in local fish markets. It is used as
fish bait to catch seabass, Lates calcarifer. However, Al-
Abdersalaam (1995) pointed out that gobiid fishes play a very
important ecological role, which provides a critical and necessary
balance in the ecosystem.
Infestation causes serious problems to host animals either
directly or indirectly affecting the physiological status of host. Loss
of weight has been probably the most common effects on
crustacean infestation. The present study also revealed that there
was significant weight loss in the infested gobiid fish, O. microlepis
thereby showing the fact that infestation causes weight loss in
fishes.
V. Ravi and M. Rajkumar
Length of O. microlepis
Length of O. microlepis
Number of C. indica
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Journal of Environmental Biology
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Kabata (1984), expressed that the general effects as loss
of weight can be attributed to more than one cause and the most
obvious one could be the loss of food reserve drawn from the
various depots and other tissues to help in coping with the ranges
of infestation. Low weight of infested fish might result from failure
to grow normally. However, the present study on the length and
weight relationship proved that the infestation alter the growth of
the fish. It shows that the increase in length of fish is not in
accordance with the increase in weight of fish due to infestation.
Trilles (1979), found that several species of European cymothoids
were capable of slowing down the growth in their hosts, although
they did not affect weight-size ratios of the fish. However, Maxwell
(1982) reported that the significant difference in the length and
weight relationship of infested and uninfested fishes of Jack
Mackeral, Trachurus decliuis as infested by Cerotothea impricatus.
The present study showed significant reduction of
respiratory surface area due to infestation of cymothoids in the
branchial chamber was noticed. The dorsal surface of the parasite
was always in close contact with the first gill arch, causing more
atrophy of the first gill filament. The pressure exerted towards
second to fourth gill arches were comparatively lesser than the
first gill arch and the damage was also less.
Kroger and Guthrie (1972) stated that male, Olencira
praegustor damaged the gill of juvenile Atlantic Menhaden,
Brevoorita tyrannus. Stephenson (1976) studied that the gill
damage was owing to buccal parasites. Bowmen (1960), found
that the gill filaments of Hawaiian Moray eel, Gymnothorax
eurostus were missing in the anterior or posterior most region of
gill arches owing to the attach of Lirneca puhi. Overstreet (1978)
reported that the similar males and juveniles of isopod, Olencira
praegustator parasitic on Gulf Menhaden cause change on the
gill filaments through feeding.
In the present observation the parasites C. indica mostly
attach with buccal region and the branchial chamber of the (host
fish) first gill arch. C. indica first described from Bangkok, Thailand
has been recorded by Chilton (1924) from Chilka lake where it is
stated to infest the mouth of Gobius giuris, causing deformation
of the host’s tongue. Subsequently, Panikkar and Aiyar (1937)
recorded C. indica on Etroplus maculatus, E. suratensis and
Glossogobius giuris from the Adyar estuary. Evangeline (1963)
reported the occurrence of this parasite, in the Adyar fish farm,
from a variety of host’s, viz., E. suratensis, Tilapia mossambica,
Macrones gulio, Gobius giuris, Polynemus tetradactylus,
Pomadasys hasta and Sphyraena obtusata. It is thus evident
that C. indica exhibits a wide geographic and host distribution.
Jayadev Babu and Sanjeevaraj (1984) noticed the infestation in
several regions like the chin, nape and pectoral fin base and the
buccal cavity. But, Ravichandran et al. (1999) found that the
dorsal surface of the parasite facing the first gill arch where the
parasites were attached in Joryma brachysoma. The damage
of gill filaments thus was not only due to feeding but also by the
pressure exerted by the dorsal side of the parasite.
The gross size and shape of parasites can ac t as physical
irritants, which may be responsible for the observed damages of
the branchial tissues noticed in the present study. The reduction
in the surface area was thus due to several factors such as mode
of attachment, movement, size and duration of stay of the
parasites.
Pale gills, damaged gill rakers and erosion of gill
lamellae are the severe gross lesions observed as a
consequence of isopod infestation. Pale gills of infested fishes
indicate anemia, which may be due to the loss of blood and
the construction of branchial circulation by the attachment of
parasite and of the haemophageous nature of the branchial
cymothoids (Romestand and Trilles, 1977; Romestand, 1979).
The calus like thickening observed on the gill arch and gill
filaments may be due to the constant irritation caused by the
body and appendages of the parasite. Erosion and thickening
are the two unique morphological changes noticed owing to
the infestation. These changes are mainly due to the heavy
pressure exerted by the parasite and also by their feeding
nature. Kabata (1985) observed destruction of host tissues
as a result of the pressure exerted by the parasite body, when
present in the gill cavity. Longer stay of parasite within the gill
chamber may also prevent and obstruct the normal growth of
the gill arches. This may be the reason for the erosion of gill
arch and fusion of gill lamellae. More mucus secreted in the
infested gills may be due to the reaction to irritation created by
the parasite. Romestand and Trilles (1977) observed that the
secretion of mucus on the ligament surface as a reactive
response of the host against infestation. Due to the attachment
of peropods host tissues were compressed and eroded at the
attachment sites, which were surrounded by an inflamed
peripheral welt of peropods.
Lesions associated with reproduction of parasite to the
host are related to the direct activity of the parasites. A marked
increase in the size of the parasite may be seen with the
development of marsupium full of juvenile isopods. This can
significantly increase the pressure atrophy caused by the
presence of the parasites. These reproduction related activity in
the host increases the chance that the parasite will serve as a
vector for microbial parasites such as hematozoans (Smith, 1975).
Uninfested fishes were more so active than the infested, and
were quite still or swim feebly than the infested fishes, resulting
to low rate of activity. Assessment of the general effects of
parasites on the condition of their hosts is beset with numerous
difficulties. The main difficulty in garging the extent of damage
inflicted on the fish lies the normal condition of the fish. Some
reports suggested that the effects of parasitization might become
apparent after a latent period of fairly long duration (Reichenbach
Klinke et al., 1968). The parasitic infections also result in the
abnormal behaviour of the host. The parasitic infections change
the blood picture and also the parasitic condition of many species
leads to the secondary infections by bacteria and fungi. Some
reports (Venkataraman and Sreenivasan, 1952, 1954) indicated
Isopod parasite on gobiid fish 255

Journal of Environmental Biology
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that the environmental factors may influence the bacterial flora
of the skin and gills.
In general, parasitic infection of fishes mainly depends
upon host factors such as age, size, sex, maturity, stage,
behaviour, feeding and breeding, lifecycle, physico-chemical and
particularly environment factors. The negative impact of parasites
on host’s growth and survival has been demonstrated for several
parasite-host systems, both in aquaculture and in natural
populations (Sindermann, 1987). However, host parasite
relationships are generally very complex and difficult to clarify.
With the exception of cases of mass mortalities caused by
outbreaks of parasites, assessment of the effects of parasite
infection in natural fish populations is particularly difficult because
of the presence of predators or scavengers which rapidly remove
moribund or dead fish.
It appears that C. indica occurs in a limited range of teleost
fishes and that it takes shelter in the host mainly for the purpose
of breeding (Misra and Nandi, 1986). In the present study, the
gobiid fish, O. microlepis parasitised by the isopod, C. indica
showed loss of weight, loss of fat content, changes in the water
content of various tissues and reduction in respiratory surface
area of the host fish.
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V. Ravi and M. Rajkumar256