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EFFECT OF PARASITIC ISOPODS IN COMMERCIAL MARINE FISHES

Samuthirapandian Ravichandran1*and Ganapathy Rameshkumar2

1Centre of Advanced Study in Marine Biology, Faculty of Marine Science,Annamalai University, Parangipettai-608 502, Tamil Nadu, India.2Unit of Toxicology, Department of Zoology, School of Life Sciences,Bharathiar University, Coimbatore 641 046, Tamil Nadu, India.*Email: sravicas@gmail.com

Received on: 10 October 2013, accepted on: 12 December 2013

Abstract: Crustacean ectoparasites on marine f ish are diverse. Isopods form an order in the crustaceans. Parasiticisopods are typically marine and usually inhabit the warmer seas. They are blood-feeding; several species settle inthe buccal cavity of f ish, others live in the gill chamber or on the body surface including the f ins. Isopods cancause morbidity and mortality in captive f ish populations. The damage of gill f ilaments thus was not only due tothe feeding but also by the pressure exerted by the dorsal side of the parasite. Erosion of gill lamellae, damage of gillrakers and pale gills were the severe gross lesions observed as a consequence of isopod infestation. Infested f ishexhibited histopathological anomalies such as tissue reactions, primarily associated with the formation of granu-lomas consisted of macrophages and epithelioid cells, which are occasionally surrounded by a thin rim of f ibro-blasts. A marked increase in the size of the parasite is associated with the development of marsupium full ofjuvenile parasite. The infestation usually pressure atrophy often accompanies the presence of larger parasites.They may lead to economic losses in commercial species of f ish.

Key words: Marine f ishes, Parasitic isopods, Infestation, Economic loss

INTRODUCTION

The majority of parasites extracts nutrients fromtheir hosts and thus, is expected to damage and/or exert an energetic def iciency in them. As aresult, host f itness is expected to decrease underparasitism. The majority of cymothoid isopodsare not histozoic. They are often abundantectoparasites attached to the skin, gills or insidethe buccal cavity. Single isopod can causedamage with their biting and sucking mouthparts. Heavy infestations of parasitic juvenilescan kill small f ish when they f irst attach (Noga,2000). These cymothoids have a variety ofpathogenic effects, causing direct damage notonly to skin, gills and tongue at the site ofattachment (Brusca, 1978; Adlard and Lester,1994), but also indirectly affect host condition,physiological performance and reproductiveoutput (Romestand, 1979; Ostlund-Nilsson et al.,2005). The effect of isopod parasites exhibitedconsiderable variation in host (Grutter et al.,2008; Rameshkumar and Ravichandran, 2013a).The studies of the effects of cymothoids mostlyconsider their effects on adult f ish, rather than

interactions between young isopods and youngf ish (Bunkley-Williams, 1984; Adlard and Lester,1995; Williams and Bunkley-Williams, 2000;Papapanagiotou and Trilles, 2001). The effectsof the cymothoid infection vary according to thecombination of the host-parasite status, withregard to the injurious effects on host species.These effects include: behavioral changes; tissuedamage; decrease in mean weight, size andgrowth; and in some cases, death (Trilles, 1979;Kabata, 1984). These isopods cause varyingdegrees of harm to their hosts, ranging fromminor tissue damage at the site of attachmentto differential rates of mortality (Adlard, 1989).All of these reports of isopod parasites pertainingto pathology effects of isopod parasites of hostcommercial f ishes are very scanty and no suchstudies have been made along Parangipettaicoastal environment. Though, that f ishes arecommercially important, they play an importantecological role and maintain balance inecosystem. Hence the present attempt was madeto understand the effect of isopod infestationon commercial f ishes.

Journal of Aquatic Biology and Fisheries Vol. 2/2014/ pp. 574 to 579

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MATERIALS AND METHODS

The host f ishes were collected directly fromthe trawlers landed at Parangipettai coast.Isopods were removed f rom the branchialcavities, buccal cavities and body surfaces ofthe f ish hosts and immediately placed into 70%ethanol. Mouthparts and appendages werecarefully dissected by using dissecting needlesand forceps. To study the effect of infestationon the host f ish data were analysed. Thefeeding status of the isopods was conf irmedby the presence/absence of a darkened and hostspecif icity of isopods was also examined. Theinf luence of infestation of respiratory surfacearea of the gill arch was studied. The averagegill raker count of f irst, second, third andfourth gill arches of infested and uninfestedf ishes were made. The data collected weretabulated and variation in the gill raker countas a function of infestation was recorded. Thedamaged f ish tissues were taken f rom theparasite attachment area of infested f ishes werecut out in fresh condition f ixed in 10% bufferedneutral formalin. T issues and gills wereconsidered for histopathological study.

RESULTS

C. boscii was found to occur only in Carangoidesmalabaricus, the site of infection in the buccalcavity of the parasite on a diagrammaticrepresentation of the individual f ish species. Fig.1 shows that mass of C. boscii invaded the buccalcavity of C. malabaricus. The site of attachmentof the parasite, indicative of mucus and bloodfeeding were found at the time of observation.The parasites were normally seen protrudingthrough the mouth opening of the host. Thestudies have found that parasitic infection mayreduced or interfere with the ability of the host.Gross lesions observed in the buccal cavity ofinfested f ish showed small pin-holes in thetongue region, through which dactyls ofpereopod’s penetrating claws dig into the hosttissues.

Table 1. Cymothoid isopods collected from commercial f ishes

Fig. 1. Infected mass of Catoessa boscii attachedCarangoides malabaricus

Joryma hilsae were found in the branchial regionof Stolephorus commersonii. Infested f ishes, gillrakers were seriously lost, apical edges damagedand gill lamellae heavily destroyed. Gill lamellaeof the f irst and second gill arches were erodeddue to isopods. A wide depression was founddue to the lodging of parasites at the gill debts

During the present study three species includingthree genera (Catoessa, Joryma and Nerocila)of isopods belonging to the family Cymothoidaeinfesting three species of commercial f ishesalong the Parangipettai coast were studied(Table 1). Catoessa were collected from thebuccal cavity and Joryma was noted on the gillregions and another one Nerocila species werefound to penetrate on the body surface of thehosts. Many cymothoids occur in the buccalcavity of the host f ish and their position is thushighly specif ic (Table 1).

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and the gill arches showed torsion. Nature ofdamage, observed in the gill remained the same,but the degree of damage varies, as the closelyopposed gill arch observed a higher damage.Terminal and middle regions of the gill lamellaebulged and the growth was stunted. Secondarygill lamellae uneven clubbed and showed fusion.Middle portion of some of the gill lamellaeexpanded to have some space or gap. Bifurcationwas noticed at the tip of lamellae and thecartilaginous support of the gill arch was twisted.The damage of gill f ilaments thus was not onlydue to the feeding but also by the pressureexerted by the dorsal side of the parasite. Erosionof gill lamellae, damage of gill rakers and palegills were the severe gross lesions observed as aconsequence of isopod infestation (Fig. 2).

modif ied to hold the body surface and tearingthe body muscles of host f ish strongly. Isopodsmake frequent shifts in position on the hostcausing a series of wounds. The parasites oftenmove about as they feed. These activities alsostimulate mucus production, stimulateepidermal proliferation and dilation of dermalcapillaries.

Fig. 2. Joryma hilsae attached in the gill regionof Stolephorus commersonii

Species belonging to the genus Nerocila aregenerally found as external parasites on f ishes.N. phaeopleura invading on the body surface ofDussumieria acuta. They were found attachedto the host by hook-like projections mandiblesand f irst maxillae and f irst two thoracic legs (Fig.3). In all cases of the attached position, the bodywas directed towards the anterior end of thef ish. The hooks of the pereopods penetrate intothe skin and anchor the isopod to the f ish host.At the mouth part or pereopod site ofattachment, the skin (epidermis and dermis) areeroded and exposed to the underlying tissue(Fig. 4). All these appendages are highly

Fig. 3. Nerocila phaeopleura using hook-like legspenetrated in the skin of Dussumieria acuta

Fig. 4. Demaged at the skin caused by biting ofN. phaeopleura

Infested f ish exhibited histopathologicalanomalies such as tissue reactions, primarilyassociated with the formation of granulomasconsisted of macrophages and epithelioid cells,which are occasionally surrounded by a thin rimof f ibroblasts (Fig. 5). The tissue damage to hostby cymothoids was often impressive, but thisdamage was caused by crypting (a necroticeroding reaction of host tissues pressed againstthe parasite) or deformation (host growing againstthe parasite). Cymothoid piercing sucking mouthparts seemed more suited to body fluid.

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DISCUSSION

The f indings of the present study also supportswith earlier works. Jayadev Babu and SanjeevaRaj (1984) noticed infestation in several regionslike the chin, nape and pectoral f in base andthe buccal cavity. The damage of gill f ilamentsthus was not only due to feeding but also by thepressure exerted by the dorsal side of theparasite. The f indings of the presentinvestigation indicate that infestation causesserious problem to host animals either directlyor indirectly affecting the physiological statusof host. Parasites can infect larval, juvenile oradult marine f ishes; however, the effects ofparasites on the growth and condition of f ishlarvae have seldom been investigated (Palacios-Fuentes et al., 2012). The site of attachment ofC. boscii in C. malabaricus the brushlike padson the roof of the buccal cavity renders muchprotection to the parasite. The threat of beingwashed into oesophagus with the incomingwater current, which parasites of the buccalcavity have overcome by resorting to f irmattachment to the host tissue. C. boscii, althoughcomparatively primitive in being a buccal parasiteand being highly host specif ic is also highlyspecialised to a mode of life upon a pelagic, fastswimming host. This position is determined bythe needs of the parasite and the limitationsexerted by the morphology and habits of thehost. However, our data indicate that infectionby C. boscii had little effect on the mass ofC. malabaricus stomach contents.

Isopods inhabiting the branchial chamber inflictdamage to gills through attachment and feedingand that the extent of damage is directly

proportional to the size of the parasite andduration of settlement. Erosion of gill lamellae,damage of gill rakers and pale gills were thesevere gross lesions observed as a consequenceof isopod infestation. Pale gills of infested f ishesindicated anemia, which may be due to loss ofblood the obstruction of branchial circulationby the attachment of parasite and of thehomophagous nature of the branchialcymothoids (Romestand, 1979). Meyers (1978)recorded damage done to two specimens ofbluef ish (neither age or size given), stating thatthe crustacean caused an erosion of the gillf ilaments, and that their bulk caused theopercula of the f ish to flare. While it is possiblethat as the parasite grows there is an increase inthe amount of mechanical damage done to thegill, we found no visible evidence of this damagein our young-of the-year bluef ish sampled(Matthew Landau et al., 1995). There was noobvious bleeding, loss of gill f ilaments, ordiscoloration; this f inding agrees with thedescription of hosts of Elthusa neocyttus, asimilar isopod gill parasite (Stephenson, 1987).But in the present study damage of gill f ilamentsthus was not only due to the feeding but also bythe pressure exerted by the dorsal side of theparasite. Erosion of gill lamellae, damage of gillrakers and pale gills were the severe gross lesionsobserved as a consequence of isopod infestation.The damage of gill f ilaments thus was not onlydue to the feeding but also by the pressureexerted by the dorsal side of the parasite. Thegross size and shape of parasites can act asphysical irritants, which may be responsible forthe observed damages of the branchial tissues.The reduction in the surface area was thus dueto several factors such as the mode ofattachment, movement, size and duration ofstay of the parasites. Kabata (1985) observeddestruction of host tissues as a result of thepressure exerted by the parasite’s body. Longerstay of parasite within the gill chamber may alsoprevail and obstruct the normal growth of thegill arches. This may be the reason for the torsionof gill arch and fusion of gill lamellae.

Generally, most pelagic f ish within a populationare not infected by isopod parasites. In this case,more than 50% of the commercial f ish sampledwere infected by the cymothoid isopod.Furthermore, infected f ish were found to be

Fig. 5. Infected tissue of Dussumieria acuta

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lighter than uninfected f ish, indicating theeffect of infection on the host. All known speciesof Nerocila, as adults, reside on the surface oftheir hosts (Brusca, 1981). In this study, N.phaeopleura was most frequently found on thebody surface area. The position of attachmentarea might depend on the host’s bodymovement. Fish swim using undulatorymovements of their body and/or their paired andunpaired f ins. In undulatory swimming, abackward-travelling wave is generated by thesequential activation of the segmental myotomesfrom head to tail (Altringham and Ellerby, 1999).The cause of attachment at this position may bedue to easier attachment at this site by theparasite or due to easier shedding of the parasitefrom other areas by the host.

Histopathological studies reviewed the damagecaused by the cymothoid isopod on the infectedf ish host. The pathological effects of cymothoidisopods on their hosts cluster at two extremes.Some associations are quite severe and can evencause host death (Adlard, and Lester, 1994].Infested f ish exhibited histopathologicalanomalies such as tissue reaction, primarilyassociated with the formation of granulomasconsisted of macrophages and epitheleoid cells,which are occasionally surrounded by a thin rimof f ibroblasts (Radhakrishnan and Nair, 1981).The damage caused to the tissues and theirsubsequent exposure could have caused thedeath of f ish, thus causing the f ish populationto decline (Printrakoon and Purivirojkul, 2011).Healthy tissue were absent at the pereopodattachment sites. Infested tissues appear to bedeteriorated and are irregular in structure. Theeffects may be due to the stress excreted by theparasite to the underlying tissues (Rameshkumarand Ravichandran, 2013b). However, in thisstudy, tissue damage to host by cymothoids wasoften impressive, but this damage was causedby crypting or deformation. The infestationusually pressure atrophy often accompanies thepresence of larger parasites. They may lead toeconomic losses in commercial species of f ish.

ACKNOWLEDGEMENTS

Author (G. Rameshkumar) is thankful to UGC,New Delhi for the grant of Dr. D.S. Kothari Post-Doctoral Fellowship No.F.4-2/2006 (BSR)/13-1011/

2013 (BSR) and Head of the Department forproviding facilities and encouragement.

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