Bio-Research, 6(1): 328 – 338 328

Parasites and their Freshwater Fish Host

Iyaji, F. O. and Eyo, J. E. Department of Zoology, University of Nigeria, Nsukka, Enugu State, Nigeria

Corresponding author: Eyo, J. E. Department of Zoology, University of Nigeria, Nsukka, Enugu State, Nigeria. Email: [email protected] Phone: +234(0)8026212686

Abstract

This study reviews the effects of parasites of fresh water fish hosts. Like other living organisms, fish harbour parasites either external or internal which cause a host of pathological debilities in them. The parasites live in close obligate association and derive benefits such as nutrition at the host’s expense, usually without killing the host. They utililize energy otherwise available for the hosts growth, sustenance, development, establishment and reproduction and as such may harm their hosts in a number of ways and affect fish production. The common parasites of fishes include the unicellular microparasites (viruses, bacteria, fungi and protozoans). The protozoans i.e. microsporidians and mixozoans are considered in this review. The multicellular macroparasites mainly comprised of the helminthes and are also highlighted. The effects of parasites on their fish hosts maybe exacerbated by different pollutants including heavy metals and hydrocarbons, organic enrichment of sediments by domestic sewage and others such as parasite life cycles and fish population size.

Keywords: Parasites, Helminths, Protozoans, Microparasites, Macroparasites, Debilities, Freshwater fish

Introduction the flagellates have direct life cycles and affect especially the pond reared fish populations. Several studies have revealed rich parasitic fauna Microsporidians are obligate intracellular parasites in freshwater fishes (Onyia, 1970; Kennedy et al., that require host tissues for reproduction (FAO, 1986; Ugwuzor, 1987; Onwuliri and Mgbemena, 1996). Fish hosts acquire the parasites by ingesting 1987; FAO, 1996; Kadlec et al., 2003) ranging from infective spores from infected fish or food (Klinger ectoparasites (Fryer, 1968, 1970; Sakiti et al., 1999; and Floyd, 2002). Infected cells usually enlarge Oniye et al., 2004) to endoparasites (Basu et al., (xenomas) to accommodate the proliferating 1993; Umoren et al., 1998; Auta et al., 1999) which parasite. According to Canning and Lom (1986) and affect fish health, growth and survival. In the survey Lom and Dykova (1992) the parasites undergo of freshwater parasites, the economic important merogonous and sporogonous development within parasitic groups include the microparasites; the xenomas, culminating in the spore production. protozoans - microsporideans and myxozoans while The spores are thick walled and contain a the macroparasites group is comprised of helminths characteristic coiled polar filament and one such as and the diagenes trematodes (Pleistophoridida) or two nuclei (Nosematidida) (flukes), cestodes (tapeworms), nematodes (Weiser, 1989). Replication within spores (roundworms) and Acanthocephala (thorny headed (schizogony) causes enlargement of host cells worms) The parasites are represented (Hypatrophy) and the infected fish may develop mainly by the (Marcogliese, 2002), while small tumor like masses in various tissues (Klinger the parasites are the . and Floyd, 2002). Hypertrophic infected cells which may Materials and Methods reach macroscopic sizes often yielding characteristic gross pathological signs; multiple A comprehensive literature search was made from whitish nodules in tissues or in case of bladder, a the Internet and serial materials of Nnamdi Azikiwe significant thickening of the walls (FAO, 1996). The Library, University of Nigeria, Nsukka. Various effect of microsporidian infection on fish hosts is journal articles, proceedings of learned societies of variable. Some fish hosts seem to survive even in fisheries and parasitology, World Health the presence of huge xenomata pressing on organs Organization and Food and Agricultural while in others microsporidians have morbid effect Organization documents and textbooks were (Putz and McLaughlin, 1970; Morrison and consulted vis-à-vis of the parasites and their Sprague, 1981). Intranuclear infection of freshwater fish host. The data collected were haemopoietic cells is often associated with acute synthesized into tables. anaemia (Elston et al., 1987). Myxozoan parasites affect many fish Results and Discussion families and are common in Cichilidae, Cyprinidae and Mugilidae (FAO, 1996). In Africa, more than Protozoa: Protozoan parasites are commonly 135 of myxozoans are known to infect encountered in fish (Klinger and Floyd, 2002). The freshwater, brackish water and marine fishes main groups include the ciliates, flagellates, (Kostroingue et al., 2001). Sakiti et al., (1999) microsporidians and myxozoans (Table 1). These observed and described 17 species, prominent can build up to very high numbers when fish are among which were the following parasitic protozoan crowded, causing weight loss, debilitation and genera: Henmeguya, Myxobolus, Myxobilatus and mortality (Klinger and Floyd, 2002). The ciliates and Parahenmeguya. Prevalence of infection can be

Bio-Research Published June 2008 ISSN 1596-7409 Iyaji and Eyo 329

Table 1: Protozoan parasites and their effects on freshwater fish host Protozoan Protozoan Fish species Site of infection Symptoms Source Group Species infected Ciliates Ichthyophthirius Clarotis, Schilbe, Intestine, Gills Skin and gill Klinger and Chilodonella Clarias, Bagrus, Skin, Fins irritation Floyd, Tehrahymena Auchinoglanus displayed by (2002) Trichodina Synodontis, flashing, Ambiphyra Heterobranchus rubbing, rapid Apiosoma breathing, Epistylis white spot, Capriniana excessive mucus secretion in gill, and enlarged eye

Flagellates Hexamita, Angelfish, Intestine, Mucus secretion Klinger Ichthyobodo, Channel catfish, gills, and Piscinoodinum, skin, fins and Floyd, Cryptobia stomach (2002)

Microsporideans Plestophora, Tilapia. Cysts in lymphs Hypertrophy Paperna Enterocytozoans Haplochromis Epithelia cells, of tissues, (1973); FAO Sarotherodon swim thickening of (1996), Eels bladder, kidney walls, Sakiti Rainbow trout, gills, tumour-like and Bouix , Clarias viscera, masses of (1987); Gold fish kidney tissues. Loma and Dykova (1992)

Myxozoans Myxozoma, Salmon, Cysts in Hypertrophy FAO (1996); Sphaerospora Mullets, Lates muscles, of cells, Klinger and Mitraspora Channel catfish, connective turmor- like Floyd Thelohanellus, Channa tissue, epithelia masses of (2002); Hennegya Heterotis niloticus, lining of bladder, tissues Dzulinsky et Myxobolus Clarias kidney al. (1999) Distichodus tubules and gut Haplochromis lining high (Table 1) (Dzulinsky et al., 1999, Marcogliese melanotheron and Synodontis gambiensis and Cone, 2001) and the number of species respectively (Sakiti et al., 1999). Sakiti et al. (1999) infected in a host population can be very significant further stated that the weakening of arches (Cone and Anderson, 1977; Li and Dresser, 1985; subsequently ends at their breaking thus disturbing Salim and Dresser, 2000). Myxozoan parasites as the respiratory function of the gills, while the fusion such, have the potential to form species rich of secondary lamellae considerably reduces the infracommunities and component communities that breathing surface and prevents adequate gaseous might equal or surpass those formed by other exchange in the fish. Coelozoic myxozoans of the groups of fish parasites (Marcogliese and Cone, urinary and cavities are small and produce few 2001). They cause both histozoic (in tissue) and spores (FAO, 1996). Premature plasmodium are coelozoic (internal cavities e.g. gall and urinary attached by pseudopodia to the epithelial lining of bladders) infections (FAO, 1996). Signs of histozoic the bladder (Paperna et al., 1987). According to infections are whitish cysts with a milky substance Lom and Arthur (1989) diagnosis to species level is containing microscopic spores (Current and Janovy, based mainly on measurements of fresh unfixed 1976). In African fish, histozoic myxosporideans spores, their polar capsules dimensions as well as occur as skin infections with cysts formed in the the length of the extruded polar filaments. Several dermis under the scales extending to the surface of myxozoan infections in cultured fish have been the head, face, and lips or on the fins. (Myxobolus reported to be pathogenic, causing skeletal sp. have been reported in Cyprinids, Siluroids, deformities, locomotory disturbances, emaciation Characids and juvenile Cichlids. Henneguya and sunken eyes in brain infections (Dykova et al., laterocapsulata has been reported in the gill 1986) anaemia, haemorrhagic dropsy and mortality filaments of Clarias lazera. Other Henneguya sp in heavy cardiac infection (Bauer et al., 1991) and were found in both Cyprinids and Siluroids while circulatory dysfunctions in infections at the base of Thelohanellus sp. has been reported in Cyprinids the gill lamellae (Kovac-Geyer and Molner, 1983). (Paperna, 1973; Abolarin, 1974; Fomena et al., Paperna and Thurston (1968) found that body 1985; 1994; Landsberg, 1986). Visible or suspected deformities or curvatures in Barbus lineatus and pathogenic effects of gill infections are different cichlids were caused by large myxobolus cysts. according to the type of gill engraft and may result They also discovered that ovarian infection in in liquefaction of cartilage of gill arches due to female cichlids from Lake George enlarged the Myxobolus dosoni, M. sarotherodoni and M. ovary while displacing the entire ovarian tissue, oueensis, in Tilapia zilli, Sarotherodon evidently causing castration. Cone et al. (2005)

Parasites and their freshwater fish host 330 found that the study of myxozoan parasites in fish Species of Macrogylodactylus has been was traditionally labour intensive rendering the reported in fish with potentials for aquaculture in compilation of community data difficult and rare. Africa: such as Clarias sp., Lates niloticus and Although the life histories of myxozoans in African Anabantidae (Paperna, 1979). In natural habitats, fish are unknown (FAO, 1996), it has been shown increase in infestation is inhibited due to physical from studies in other parts of the world (Wolf and (depth, currents, temperature) and chemical Markiw, 1984; El-Matboulina and Hoffman, 1989) (oxygen and salinity) factors (FAO, 1996). that transmission of myxozoan parasites of trout Studies on the seasonal occurrence of and other fishes involves tubicifid oligochaetes as monogenetic trematode parasites of fishes in the intermediate hosts. tropics, according to Obiekezie et al. (1987) generally abound. Chubb (1977) had earlier : The class trematoda comprises of identified temperature as the most important single monogeneans and the digeneans (Table 2). factor controlling the seasonal prevalence of Monogenean trematodes are also referred to as dactylogyrids and gyrodactylids. or flukes (Klinger and Floyd, 2002) and Digenean trematodes are numerous. Over commonly invade the gills, skin and fins of 50 species from 15 families have been listed (Khalil, freshwater and brackish water fish from most 1971), occurring in a variety of freshwater fish hosts families of Teleostei (Khalil, 1971; Paperna, 1979; in Africa. They have complex life histories involving Whittington et al. 2000). larval stages, which infect mostly juvenile fish, Monogeneans have direct life cycles (no bottom dwellers and shallow water habitats in inland intermediate hosts) and are host and size specific water bodies of Africa (Fahmy and Selim, 1959; (Klinger and Floyd, 2002) throughout their Williams and Chaytor, 1966; Van As and Basson, distribution range (FAO, 1996). According to 1984). FAO, (1996) stated that the life histories of Whittington et al. (2000) monogeneans can live on trematodes which infect African fish have so far not the epidermis, scales, fins, lipfolds, nares, been studied and their primary molluscan or branchiostegal membranes and gills of their hosts. intermediate hosts remain yet unknown. They are Their anterior end contains apical sensory however heteroxenous with multiple host life cycles structures, a mouth with or without accessory involving both bivalves and gastropod molluscs as suckers and special glands and clamps for the intermediate hosts (FAO, 1996). Fish can also be attachment and they are all haemaphrodite (FAO, the primary or intermediate host, depending on the 1996). digenean species and they can be found externally Monogeneans are subdivided into three or internally in any organ (Klinger and Floyd, 2002). major taxa: Dactylogyroidae, Caspaloidae and Shaw et al. (2005) reported several trematode Polyopisthacotylea (Noble and Noble, 1982; FAO, metacercariae infecting more than one tissue or 1996). Most monogeneans found in inland water organ in the fish hosts. Metacercariae maybe fish are of the family Dactylogyroidae while the distributed throughout the host with mean intensity other two families usually lager in size, are of several hundreds per fish. Only the extra predominantly marine fish parasites (FAO, 1996). intestinal species are however potentially harmful to Dactylogyroids are oviparous with one or two fish hosts (FAO, 1996). Species of Sanguinicola anterior-dorsal pairs of eyes, a posterior- ventral (the blood flukes) are reported to infect Synodontis opisthaptor and are mostly gill parasites of fish. schall and Auchinoglanus occidentalis in the Sudan Gyrodactylidae are viviparous with no eyespots, two (Table 2) (Khalil, 1969) Clarias lazera and pairs of anchor hooks and generally found on the Oreochromis sp. in Israel (Paperna, 1964). Adult skin and fins of fish (FAO, 1996). A few are Sanguinicola worms and trapped eggs can specialized endoparasites inhabiting the nasal physically obstruct the passage of blood causing cavities, stomach and urethra of freshwater fish thrombosis and subsequent necrosis (Hoffman et hosts (Table 2) (Du Plessis, 1948; Paperna, 1963b; al. 1985) while escape of miracidia through the gills Ergens, 1988). epithelium causes loss of blood and may lead to Fish appear to co-exist with their specific anaemia (Evans, 1974). According to Sandland and monogeneans in natural habitats as well as in Goater (2003), trematode metacercarie have been culture conditions even when infestations are shown to modify the morphology of fish hosts by intense (FAO, 1996). A few, especially the disrupting the heart (Coleman, 1993) the brain gyrodactylids are pathogenic to their fish hosts, (Hoffman and Hoyne, 1958) and the eye lens usually to younger fish and in intense culture (Larsen, 1965) (Table 2). The digenean Syphodera conditions (Chapman et al., 2000). ghanensis and the aspidogastrid, Aspidogaster vastator infection in the gills of fry according to africanus occurred occasionally in the intestines of Paperna (1963b, 1964), Chan and Wu (1984), Chrysichthyes nigrodigitatus from the Cross River Barker and Cone (2000) induces severe estuary Nigeria, where they cause general debilities hyperplasia of the gill filament epithelium, which (Table 2) (Obiekezie et al., 1987). In many systems, interferes with respiratory function at extreme the extent of the alteration in host traits is proliferation and seems to be the cause of death. dependent on the intensity of the infection and on Dactylogyrus extensus were found to be fatal to the specific tissues affected (Sandland and Goater, both young and fully-grown fish (Prost, 1963; Sarig, 2003). 1971). Obiekezie and Taege (1991) reported severe mortalities (up to 90%) of two weeks old Nematoda: Nematodes occur worldwide Clarias gariepinus fry in a hatchery in Nigeria due to particularly the species utilizing fish as intermediate severe infestation of Gyrodactylus groschefti. or transient hosts and can infect all organs of their

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Table 2: Trematode parasites and their effects on fresh water fish host Trematode Trematode Fish species Site of infection Symptoms Source Group Species infected Monogenean Paraguadriacanthus Most families of Skin, gills, fins, Hyperplasia of Paperna (1963); Enterogyrus, fish from fresh epidermis, gill epithelium Baker and Cone Acolpenteron water and lipfolds, nares, and (2000); Dactylogyrus extensus brackish water. branchiostegal interference Prost (1963); Gyrodactylus groschefti, membranes, with Sarig (1971); Macrogylodactylus stomach and respiratory Obiekezie and Taege urethra. function. (1991) FAO (1996)

Digenean Sanguinicola Syphodera Synodontis Tissues, Organs, Rupture of Agure-Macedo et al. Aspidogaster Auchinoglanus Blood passages, gills epithelium (2005); Clarias Heart, Brain and causing Khalil (1969) Oreochromis Eye lens. anemia, Paperna (1964); Chrysichthyes disruption of Hoffman et al.(1985), the heart, Sandland and Goater brain and eye (2003); lens and Obiekezie et al. general (1987) disabilities.

Table 3: Nematode parasites and their effects on fresh water fish host Nematode Nematode Fish species Site of Symptoms Source Group Species Infected Infection Oxyuroidea Oxyuris Distichodus Intestine Worms locked in the Khalil (1971) Enterobius Synodontis and abdomen or trapped Citherinus Stomach in tissue provoke Oreochromis severe inflammatory Barbus responses.

Camallanidae Procamallanus Clarias, Intestine Worms locked in the Boomker (1982); Spirocamma- Synodontis and abdomen or trapped Paperna and llanus and other stomach in tissue provoke Zwerner (1976) Paracamallanus Catfishes severe inflammatory Camallanus responses. Cucullanus

Philometridae Nilonema Gymnarchus Tissues or Granuloma Moravec Twastia Bagrus Inner cavities and fibrosis and Tarasc- Anguilicola Anguilla and swim- hewski (1988) bladder Anisakidae Amplicaecum Synodontis Larval forms Localized Mbahinzireki Contracaecum Clarias Encyst in tissue inflammation (1980) Porocaecum Heterobranchus tissues, and fibrosis free in encapsulation body cavities Dioctophymidae Eustrongyloides Synodontis Larval forms Localized Mbahinzireki Clarias Encyst in tissue inflammation (1980) Heterobranchus tissues, and fibrosis free in encapsulation body cavities Rhabdochonidae Rhaditis Synodontis Larval forms Localized Mbahinzireki Rhabdochona Clarias Encyst in tissue inflammation (1980) Spinitectus Heterobranchus tissues, and fibrosis free in encapsulation body cavities

hosts with heavier infections in predatory fishes (Citharinus, Distichodus) and omnivorous fish (Table 3) (Klinger and Floyd, 2002; FAO, 1996). (Synodontis, Oreochromis and Barbus) (Khalil, Khalil (1971) reported 40 species of adult 1971). Camallanidae, Cucullanidae, Philometridae nematodes, representatives of 9 families from fish and Anguillicolidae have copepods as their in Africa with majority occurring in the alimentary intermediate hosts (FAO, 1996). Within the system and a few in tissues or inner cavities (Table host, nematodes are often fastidious in their choice 3). Nematode worms are very distinctive in and will not develop in species of Cyclops, shape; with solid resistant cuticle, which enables Diaptomus or Cladocerans. them last longer than flatworms in post-mortem Host specificity of nematodes is variable in conditions (FAO, 1996). their definitive hosts. Among the Camallanidae, Oxyuroidae are monoxenous (single host) Procamallanus laevionchus has been reported from and occur in the intestines of detritus feeders fish hosts of six different families while

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Spirocamallanus spiralis has only been reported In naturally occurring infections among fish in from species of Clarias and Synodontis, African aquatic habitats, damage to the host is Paracamallanus cyathopharynx only from species rarely evident (FAO, 1996) but pose a potential risk of Clarias and Camallanus kiradensis only from to native fish species such as Clarias sp and Barbus sp (FAO, 1996). Species of Capillaria, most Heterotis niloticus introduced to farming. Hanzelova Oxyurids and the Philometrids Nilonema gymnarchi et al. (2005) affirmed that adult cestodes usually and Thwatia bagri are very host specific (Khalil, cause little or no noticeable damage to their hosts 1969; 1971; Moravec, 1974). but chronic Eubothrium has been shown to Infections by Camallanids are abundant significantly reduce fitness of farmed fish. Wabuke- and heavy up to 20 or more particularly in the Bunoti (1980) reported some tissue response stomach of Clarias sp and in many other catfishes (inflammation) due to attachment of P. clarias to gut (Paperna, 1964; Khalil, 1969; Mashego and mucosa in infected C. mossambicus of lake Saayman, 1980; Boomker, 1982). None of these Victoria. He further observed that bothridal were reported to be pathogenic inspite of the firm penetration into the gall bladder mucosa caused attachment of their buccal capsule to the stomach pronounced nodules containing granulomatous and mucosa. fibrous tissues (Table 4). In aquarium reared Neotropical cichlids Larval cestodes of the pleurocercoids and and silurids, massive infections by Capillaria and cysticercoids are among the most damaging Capillostrongyloides caused emaciation and parasites of freshwater fish (Klinger and Floyd, mortalities as they attach and feed on the intestinal 2002). Infections by Ligula pleurocercoids in the mucosa (Moravec and Gut, 1982; Moravec et al., body cavity and encysted Cyclophyllidean 1987). Similar findings were reported by Moravec cysticercoids are widespread in African fish (Table and Rehulka (1987) on massive infection of 4) (Mashego, 1982; Van As and Basson, 1984). cosmocercoid nematodes Railetrema synodontis in Ligula infections are very common in Barbus sp, aquarium held Synodontis eupterus of African Cyprinid sp in Lake Victoria and rarely in Cichlid sp origin. Aged and dying worms, lodged in the of Israel, while Cyclophyllidean cysticercoids are abdomen or trapped in tissue provoked severe common and numerous in the mesenteries of inflammatory responses, geranuloma and fibrosis siluriforms, Clarias and Bagrus sp (FAO, 1996). (Paperna and Zwerner, 1974). Larval nematodes Ligula pleurocercoids from African fish are referred are potential parasites in all fresh and brackish to as L. intestinalis (Table 4) (Prudhoe and Hussey, water fish with heavier infections occurring in fish 1977; Mashego, 1982). These larval tapeworms occupying higher positions in the food chain (FAO, have their definitive hosts as piscivorous birds such 1996). Larval nematodes reported in fish are of the as gulls and cormorants. Anisakidae (Heterocheiliadae) and include the The infected species of Barbus by Ligula genera: Amplicaecum, Contracaecum and pleurocercoids in southern Africa were observed Porocaecum. Dioctophymidae includes the genus with considerable distention of their abdomen and Eustrongylids and Rhabdochonidae includes the diffuse haemorrhages in the abdominal wall in some genera Rhabdochona and Spinitectus (FAO, 1996). fish (Table 4) (FAO, 1996). Infection with Ligula These larval nematodes occur either encysted in pleurocercoids according to Sweeting (1977) leads the tissues or free in the body cavities, most often in to interruption of the reproductive functions but this the abdominal or pericardial cavity (FAO, 1996; has not been confirmed. Ibiwoye et al., 2004) Acanthocephala: Acanthocephalan worms are Cestoda: Tapeworms are widespread in all major present in representatives of diverse African fish water systems of Africa and demonstrate a high families (Table 5) (Golvan, 1965; Khalil 1971). degree of host specificity (FAO, 1996). There are They are easily recognized by their two main forms; the monozoic forms notably evaginable proboscis crowned with several rows of Caryophyllaeidae and the amphilinid represented by recurved hooks (FAO, 1996). The number and the segmented Pseudophyllideans and arrangement of the hooks on the proboscis are the Proteocephalideans (Khalil, 1971; Van As and main criteria for differentiation of species; although Basson, 1984). Siluriform fish are the most common a wider range of anatomical details are considered hosts for both monozoic and segmented cestodes for determination of higher taxa (Kabata, 1985). (Table 4) (FAO, 1996). Acanthocephalans lack alimentary canal and are All cestodes occur in the digestive tracts, heteroxenous, adult worms are gut parasites (FAO, except the amphilinid Nesolecithus africanus, which 1996). Eggs laid in the intestinal lumen are occurs in the coelomatic cavity of its fish host, the evacuated via the feaces and ingested by the first mormyrid Gymnachus niloticus (Donges and intermediate hosts such as the amphipods, isopods, Harder, 1966) and Polyonchobothrium clarias in the copepods or ostracods (FAO, 1996) where they gall bladder of Clarias mossambicus (Wabuke- hatch to first stage larvae, the acanthella or Bunoti, 1980). The Asian tapeworm, acanthor. George and Nadakal (1973) and Schmidt Bothriocephalus acheilognothii affects fish of the (1985) reported the development to adult stage of families Cyprinidae, Poecillidae, Cichlidae and some species when their larvae in the intermediate Centrachidae (Table 4) (FAO, 1996). Infections are hosts are ingested by the definitive vertebrate widespread in farmed fish as well as in a variety of hosts, which may be fish, amphibians or reptiles. wild fish in Europe and Asia (Bauer and Hoffman, Pathogenic effects of acanthocephalans 1976). are due to attachment of the adult parasite in the digestive tract and also to the encapsulation of

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Table 4: Cestode parasites and their effects on fresh water fish host Cestode Cestode Fish species Site of Symptoms Source Taxa Species Infected Infection Caryophallaeidae Caryophylleus Siluriform fishes Digestive tract of Obstruction Khalil (1971); (Unsegmented) Khawia hosts of intestines Van As and Ligula Nodules in Basson (1984) the gall bladder

Pseudophyllidae Proteocephalus Alestes, Tissue Sweeting (segmented) Bothriocephallus Barbus, Digestive tract of inflammation and (1977); Nesolecithus Mormyrids, hosts. atrophy around Mitchel and Tilapia Coelomatic cavity site of bothria Hoffman Siluriform fishes penetration (1980); Woodland (1937)

Table 5: Acanthocephala parasites and their effects on the fresh water fish host Acanthocephala Acanthocephala Fish species Site of Symptoms Source Taxa species Infected infection Acanthocephala Acanthocephalus Tilapia Guts of hosts Granuloma Khalil (1969, Paragorgorhynchus Barbus where they attach and fibrosis 1971); Termisentic Heterotis niloticus to the walls by inflammation, Paperna and Neoechinorhynchus Citherinus proboscis Peritonitis, Zwerner (1976) Synodontis Obstruction and perforation of the digestive tube. larval stages in the tissues where the extent of and other Ergasilus sp have caused problems damage is proportional to the depth of penetration among captive freshwater fishes (including eels) in of the proboscis (FAO, 1996; Oniye et al., 2004). Europe (Grabda, 1991; Tuuha et al., 1992) and Damages become extreme with extensive North America (Kabata, 1981; Hogans, 1989). In granulloma and subsequent fibrosis when the African fishes, heavy infestations of Ergasilus sp worms proboscis is anchored in the muscle layer or cause severe haemorrhaging and gill inflammation entirely perforates the intestinal wall (Paperna and that are associated with attachment and feeding of Zwerner, 1974; McDonough and Gleason, 1981; the parasite (Paperna, 1975). Chronic infections Kabata, 1985), which may vary in different host fish cause blockage of lamellar blood vessels and (Taraschewski, 1988). Dovellou (1992a, b) excessive production of gill mucus (Paperna and observed a single attached specimen of Zwerner 1974) leading to both respiratory and Acanthogyrus tilapia in juvenile cichlids (Table 5) osmoregulatory failure (Hogans, 1989; Barker and (<60mm) obstructed the digestive tube in farmed Cone, 2000). Secondary infections of the fungus fish apparently with no clinical implications. In sp have also been reported with Africa, information on infection among fish is very Ergasilus sp infections (Table 6) (Reichenbach- limited and none of the conditions described above Klinke and Landolt, 1973) has been reported (Table 5). Lernaea sp also known as anchor worms Host specificity of acanthocephalans is are common parasites of freshwater fishes (Klinger variable as they infect several fish families (Khalil, and Floyd, 2002). The copepod attaches to the fish 1971; Troncy and Vassillides, 1973; Troncy, 1974; hosts, mates and the male dies while the zygote 1977; Batra, 1984; Dovellou, 1992a, b; and Oniye et then penetrates under the skin of the fish and al. 2004) differentiates into an adult. The copepod develops holdfasts that penetrate deeply into the hosts Copepoda: Parasitic are increasingly (Kabata, 1979; 1988). The genitoabdominal trunk becoming serious problems in both cultured and and egg strings of ovigerous pennellids protrude wild fish populations (Klinger and Floyd, 2002). from their fish host musculature as in Pennella sp They are ectoparasites, which attach to gills, body (Hogans et al., 1985; Hogans, 1989) or gill regions and fins of the fish hosts. Klinger and Floyd (2002) as in Lernaeocera sp and Haemobaphes sp listed three main genera that are of economic infestations (Table 6) (Kabata, 1958, 1967). The importance: Ergasilus, Lernaea and Argulus. last two genera are haematophagus and their Ergasilus species are widely distributed. holdfasts often penetrate into the heart of fish hosts Twenty-one species have been described from (Goater and Jepps, 2002) causing serious debilities. different hosts in Brazil (Table 6) (Motta et al., 1995; Heavy infections often lead to secondary bacterial Thatcher, 1998; Engers et al., 2000). Ergasilus sp or fungal infections (Klinger and Floyd, 2002). are often incidental findings on wild or pond raised Argulus or fish louse, a Brachiurid, is a fish and probably causes little problems in small large parasite that attaches to the external surface numbers but their feeding activities in heavy of the host and can be easily identified with unaided infestation can be debilitating. Ergasilus sieboldi eye (Klinger and Floyd, 2002).

Parasites and their freshwater fish host 334

Table 6: Copepod parasites and their effects on the fresh water fish host Copepod Copepod Fish species Site of Symptom Source taxa species Infected infection Ergasillis Ergasilus Fresh water fish Gills Gill inflammation, Grabda (1991); Species(in haemorrhaging, Tuuha et al captivity) excessive mucus, (1992); blockage of blood vessels Hogans (1989); leading to respiratory and Barker and Cone osmoregulatory failure. (2000) Lernaea Pennella, Freshwater Fish Skin, Anaemia Goater and Jepps Lernaeocera, muscles, and general (2002); Haemobaphes. heart. disabilities. Klinger and Floyd (2002) Argulus Argulus Fresh and Skin, Skin necrosis, Bowen and Putz brackish water gills haemorrhages (1966) fish general disabilities

Table 7: Hirundinea parasites and their effects on fresh water fish host Hirundinea Hirundinea Fish species Site of Symptom Source Taxa Species infected infection Glossiphoniidae Batrachobdelloides Bagrus, Around the Wounds, Oothuizen (1989); Protopterus, mouth, Inflammation, Paperna and Zwerner Clarias and external, haemorhage (1974); Synodontis internal. based on Roubal (1986); species Palate, hyperplexia Khalifa (1985); corners erosion of Kabata (1985); of the jaw and the mucus Volonterio et al, (2004) skin membrane Piscicoliidae Phyllobdella, Mormyrids Around the Wounds, Oothuizen (1989); Myzobdella Chichlids mouth, Inflammation, Paperna and Zwerner Mugilids external, haemorhage (1974); internal. based on Roubal (1986); Palate, hyperplexia Khalifa (1985); corners erosion of Kabata (1985); of the jaw and the mucus Volonterio et al, (2004) skin membrane

They have compound eyes, lateral carapace-like individuals habouring over 100 leeches. Among head lobes fused to the sides of the first thoracic fresh water fish hosts, piscicolid species attached to somite, an opening for genital products and a different sites generally produce serious damages proximal overhang of some of the thoracic at the sites of infection (Table 7) (Roubal, 1986; expodites (Noble and Noble, 1982). Both males and Sawyer, 1986). females are parasitic and require blood meals. They Volonterio et al. (2004) observed the are skin and gill parasites of both fresh and brackish effects of the Myzobdella urguayensis water fish hosts, where they cause serious skin infesting the gill filaments of Hoplias alabaricus necrosis, haemorrhages and other debilities (Bowen (Characiformes, Erythrinidae) and Rhamdia quelen and Putz, 1966; Noble and Noble, 1982). (Siluriformes, Pimelodidae), haemorrhage with clot formation and fibrin deposition at the attachment Hirudinea: Leeches are freshwater ectoparasites of sites. They equally observed inflammed gill a wide range of fish genera including Clariidae, filaments exhibiting oedema and infiltration of Synodontidae, Mormyridae, Cichlidae and mononuclear leukocytes. Damages to skin Mugilidae (Oothoizen, 1989). Leeches feeding on comprised of bite wounds, haemorrhages, erosion fish are of the genus Rhynchobdellae and belong of mucus membranes, the epidermis and basal either to the family Glossiphoniidae or the hyperplasia (Table 7) (FAO, 1996; Volonterio et al., Piscolidae (Table 7) (Mann, 1962). 2004). Apart from the mechanical injuries and Glossiphoniids have a depressed body pathological effects leeches have on fish hosts; they with no distinct anterior or posterior regions but have also been discovered to be vectors of taper at the anterior end with a sucker and eyes. haemoprotozoans (FAO, 1996). For example Piscicolids have cylindrical body divided into district Piscicola geometrea was shown to transmit viral anterior and posterior regions with head sucker disease to carp (Ahne, 1985). Bleeding wounds marked off from the body (Mann, 1962). may also become contaminated by opportunistic Heavy leech infections have variable bacteria and fungi (Table 7) (Kabata, 1985). effects on fish hosts (FAO, 1996). In Lake Victoria 19% of all studied Bagrus docmac harboured Conclusion: The effects of parasites on fish hosts leeches at the external perimeters of the mouth in the wild may be difficult to isolate and quantify. region with a mean of 26 per infected fish. However, studies of fish in captivity or under culture According to FAO (1996) pathological changes conditions have provided much information about were restricted to bite signs and mild tissue the effects of parasites on fish survival. From the changes even in the most heavily infected review, it is evident that parasites can act as severe

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