DISEASES OF AQUATIC ORGANISMS Vol. 22: 67-76. Published May 4 1995 Dis aquat Org

REVIEW

Ultrastructural and developmental affinities of piscine

I. Paperna

Department of Animal Sciences, Faculty of Agriculture of Ule Hebrew University of Jerusalem, Rehovot 76-100, Israel

ABSTRACT: Piscine coccidia differ from terrestrial-host coccidia in having a soft, membranous oocyst wall. In contrast, however, to the structural and developmental conformity observed among the highly evolved and specialized monoxenous eimeriid coccidia of avian and mammalian hosts, piscine coccidia demonstrate extreme diversity in developmental sites, sporocyst morphology, macrogamont organiza- tion and oocyst wall formation. Sporozoites and some merozoites of several piscine coccidia contain refractile bodies, while those of others contain crystalline ones. Some are obligatorily heteroxenous, while in others transmission is mediated by paratenic hosts. Structural and developmental variability among piscine coccidia could imply a polyphyletic origin, but it could also be an evidence for a lower degree of evolutionary specialization. Many of the structural and developmental features found in piscine coccidia occur in other lower vertebrate and invertebrate-host coccidia, as well as in the heteroxenous cyst-formlng coccidia of higher vertebrates.

KEYWORDS: Coccidia . . Ultrastructure Development . Transmission . Diversity . Phylogeny

INTRODUCTION HOST-PARASITE RELATIONSHIPS

Piscine coccidia differ structurally and in the way Extraintestinal infection they develop in their hosts from homeothermic verte- brate coccidians. They have a soft, membranous Extraintestinal infections are not exceptional oocyst wall (Fig. 1) (Dykova & Lom 1981, Paperna & among piscine hosts, as they are among avian and Cross 1985) and their sporocysts lack true Stieda and mammalian ones (Overstreet 1981). Ultrastructural Substieda bodies (Paperna & Landsberg 1985, Davies data are now available from several extraintestinal 1990, Azevedo et al. 1993). Piscine coccidia demon- species: Calyptospora Eunduli (Hawluns et al. 1983a, strate extreme morphological and biological diversity, b, 1984), Goussia clupearum (Morrison & Hawkins and consequently have been divided into several 1984), infecting hepatocytes; sardinae infect- genera (Dykova & Lom 1981, Overstreet et al. 1984, ing testes (Morrison & Hawkins 1984); G. spraguei Davies & Ball 1993). The purpose of this review is to (Morrison & Poynton 1989) and an undescribed summarize and update our knowledge on the ultra- species (Lukes 1993) infecting the kidneys; G. cichli- structure and biology of piscine coccidia and to darum infecting the swimbladder epithelium (Pa- examine, in light of this new knowledge, our concept perna et al. 1986, Kim & Paperna 1993a) and G. gadi of the piscine coccidia's phylogenetic origin and infecting the swimbladder's loose connective tissue affiliations. (Morrison et al. 1993a, b).

O Inter-Research 1995 68 Dis aquat Org 22: 67-76. 1995

Except for members of the genus Calyptospora which developmental cycle the oocyst enters the gut epithelial are all intrahepatic and, thus far, all species from Amer- cell to sporulate (Fig. 5; Landsberg & Paperna 1986, ican fishes (Overstreet et al. 1984, Cheung et al. 1986, Paperna 1987). Cryptospondium sp. establishes a unique Bekesi & Molnar 1991, Azevedo et al. 1993), there is elaborate juncture (in the form of an attachment organ) no common structural pattern separating the extra- with the host cell cytoplasm (Fig. 6). This, as well as its intestinal species as a group from species found in the peculiar nonflagellated microgamont, justifies its ex- gut epithelial cells. Endogenous sporogony is common clusion from the eimeriid coccidia. sp. to all extraintestinal species, but it could be the in- is therefore not related, as was previously suggested evitable consequence of their location. It is also common (Levine 1984), to eimeriid epicytoplasmic coccidia. among intestinal species (Dykova & Lom 1981). In Gous- Among vertebrate hosts, epicytoplasmic eimeriid coc- sia cichlidarum and G. gadi sporozoites or trophozoites, cidia have only been found to date among (the free or within macrophages, reach the swimbladder via genus Acroeimeria; Paperna 1989, Paperna & Lands- the bloodstream, and in G. cichlidarum, via the rete berg 1989) and (Dykova & Lom 1981).Noteworthy is mirabilis into the lining epithelium (Kim & Paperna also the epicytoplasmic position of terrapine haemogre- 1993a, Morrison et al. 1993a). In G. subepithelialis, sex- garines in the epithelial cell of the leech gut (Siddall & udi bidyes spledci, ciuliily the iioriiial coiirse of i~fectiori, Zessei 1990).There is no phylogenctic :c!aticnship Sc from the gut epithelium into the lamina propria (Stein- tween reptilian and piscine epicytoplasmic species, hagen et al. 1990). In Eimeria vanasi, when intestinal in- each has features in common with those of the intra- fection declines, asexual stages may be found in the cytoplasmic coccidia of their respective host group macrophages of the lamina propria, where merozoites (Paperna 1989). There is, however, great ultrastructural are further divided by endodyogeny (author'spers. obs). variability among the piscine species studied to date During heavy infections of E. vanasi, merogonal stages (see Figs. 3, 9, 13 & 23). Dykova & Lom (1981) proposed were found in the intestinal serosa, the pancreas and the a new genus, Epieimeria, to contain the epicytoplasmic liver, in the latter organ macrogamonts become estab- piscine coccidia. Of all the epicytoplasmic species, how- lished too (Kim 1992). ever, only E, anguillae from eels (Molnar & Baska 1986) and E. isabellae from conger eels (Daoudi et al. 1985) seem to be congeneric. Sporocysts of Epieimeria spp. Epicytoplasmic infection have an apical aperture with a plug reminiscent of a (Lom & Dykova 1982). The remaining spe- Epicytoplasmic infections are established either cies are Eimeria S. 1,vanasi and species of Goussia, with through penetration beneath and then lifting of the bivalved sporocysts [ultrastructurally studied: G. zar- brush border of the host cell (Paperna 1991, Kim & nowskii (Jastrzebski & Komorowski 1990), G. cichli- Paperna 1992), or, alternatively, while becoming en- darum, G. spraguei (Morrison & Poynton 1989). G. pan- closed on the host cell surface by microvilli-derived nonica (Lukes 1992), G. trichogasten (Km & Paperna extensions (Lukes 1992). The parasitophorous vacuole 199313) and an unnamed species (Lukes 1993)l. Despite (PV) containing the growing parasites is covered by the having similar bivalved sporocysts, G. cichlidarum and host cell apical wall as it expands above the epithelium G. spragueiseem to differ ultrastructurally, as well as in (Fig. 2). The PV wall merges with the apical host cell the nature of their parasitophorous junction, from the wall (which usually loses its microvilli in the process) to rest. form a parasitophorous envelope (PE) (Fig. 3). The most Eimeria vanasi forms both epicytoplasmic and intra- notorious epicytoplasmic infection is that of the genus cytoplasmic endogenous generations, which include Crypfospondium. Cryptospondium sp. of Landsberg & both merogonous and gamogonous stages. Moreover, Paperna (1986) infecting cichlid fish differs from those ultrastructural studies reveal an active transition from found in higher vertebrates in that the villi are retained intracellular to epicytoplasmic positions in the host cell on the PE (Fig. 4)and, more important, at the end of its (Fig. 7) (Paperna 1990, 1991, hm & Paperna 1992).

Figs. 1 to 7. Fig. 1. Sporulated oocyst of Goussia cichlidarum. Note transparent oocyst wall. SEM, x4500. Fig. Gamonts of G. cichlidarum in the swimbladder of . SEM, x8000. E-92 Epicytoplasmic macrogamont of Eimeria vanasi enclosed in a parasitophorous envelope, from intestine of 0, aurea X niloticus. H.host cell; W, W. type 1 (W) and 2 (W) wall- form~ngbodies; arrow: juncture zone. TEM, x9200 Cryptospon'dlum sp. of Landsberg & Paperna (1986), in stomach of 0. aureusx nilotjcus. SEM, X 17 000. Fig. C~ryptospondiuni-sp. in Landsberg & Paperna (1986),oocyst in stomach mucosa TEM, ~25000.FSg2$L Juncture zone (arrow) and attachment organ (A) of Cryptospondium sp. in Landsberg & Paperna (1986) (P); H: host ceU. TEM, ~72000.--Fig. 7. E. vanasi rnacrogamonts in transition from intracytoplasmic to epicytoplasrnic position. Arrows: emerging tips of the parasitophorous vacuole (PV); W, W: type 1 (W) and 2 (W) wall-forming bodies. TEM, x5100

Dis aquat Org 22: 67-76. 1995

Intranuclear infections places the tubular system funnels during certain de- velopmental phases (Paperna & Landsberg 1987, Pa- Several species of piscine coccidia (with both Eime- perna 1991). Invaginations of various sizes and num- na S. 1. and Goussia-type sporocysts) undergo their bers, usually containing an electron-dense core or entire endogenous development in the nucleus of the deposit, occur at the adjoining host cell cytoplasm/PV host cell (Daoudi et al. 1987, Davis & Ball 1993). In zone of epicytoplasmic species (Epieirneria spp., G. E. vanasi, intranuclear infections (Fig. 8) (with mero- zarnowskii) or epicytoplasmic stages (in E. vanas]) gonal stages and gamonts) occur concurrently with (Fig. 3). In the latter species, the PV membrane of ju- intracytoplasmic and epicytoplasmic stages. The con- venile parasites sends off numerous invaginations and specificity of these forms has not been definitely con- fibrillar bundles into the host cell cytoplasm, thus re- cluded (Paperna 1991). sembling an inverted brush border (Figs. 13 & 14). In spite of the similarities between funnels and the various types of invaginations, they need not neces- Endogenous sporulation sarily be homologous. An elaborate system of folds oc- curs in the PE of epicytoplasmic stages of E. vanasi iviusi cuccidid iedve i.i~iiin a sporii:ateb stage. Under {rig. 3) and of some undescrlbcc! mo:ir,c spccics certain circumstances, such as enhanced evacuation, (Boulard & Blanc 1985). oocysts of the same species may be defecated unsporu- lated. At the same time intestinal conditions do not inhibit sporulation of species normally defecated Endodyogeny unsporulated, where evacuation and release of oocysts is delayed (Molnar 1984, Paperna unpubl. obs). Endodyogeny, characteristic of asexual reproduction Sporulation in a number of coccidia (e.g. Goussia in cyst-forming coccidia [Toxoplasma, and carpelli) starts while the oocyst is still intracellular in Cystoisospora (syn. Levinea);Dubey (1977), Ferguson et the intestinal epithelium (Lom et al. 1991) and often al. (1980)], appears to be the common form of asexual only sporocysts emerge from such in sltu sporulated division in successive generations of piscine coccidian oocysts. merozoites (Fig. 15) prior to their differentiation into meronts (Paperna 1991, Kim & Paperna 1992, Morrison et al. 1993a). Endodyogeny also takes place in tropho- STRUCTURE AND DIFFERENTIATION zoites of Goussia cichlidarum before, or as soon as, they enter the swimbladder (Kim & Paperna 1993a).In Eime- The parasitophorous vacuole ria vanasi also merozoites enclosed wi.thin macrophages in the lamina propria undergo endodyogeny. Special structures, or organelles, found in the wall of the PV seem to be involved in metabolic exchange between the PV and the host cell cytoplasm. The en- Merogony tire contact zone between Goussia cichlidarum and the epithelia1 host cell llning the swimbladder is a Among all the ultrastructurally studied piscine coc- hemidesmosome (Figs. 9 & 10; Paperna et al. 1986). cidia to date, endomerogony, or rather endopolygeny, The elaborate tubular system which drains into nu- is the only demonstrated form of merogony in Epieime- merous funnels along the wall of the PV in intracyto- ria anguillae, Goussia aculeati, G. carpelli (Steinhagen plasmic merogonal stages and gamonts of Eimeria 1991a) and G. cichlidarum (Kim & Paperna 1993a). In vanasi (Fig. 11; Paperna & Landsberg 1987) has not G. iroquoina, ectomerogony occurs prior to subsequent yet been found in other piscine coccidia. Also unique generations of endornerogony (Paterson & Desser to E. vanasi is a multilayered PV (Fig 12) which dis- 1981a).

Figs. 8 to 16. Fig. 8. intranuclear Eimeria vanasi trophozoite. N: host-cell nucleus. TEM, X 14 800. Young Goussia cichli- darum macrogamont; arrows po~ntat PV- host cell junctures. TEM, x4900. Fig. 10. Enlarged view of the PV-host cell juncture. H: host cell. TEM, ~20000.Fig. 11, Tubuli (t) and funnels (f)connected to E. vanasi (E) PV wall; H: host cell. TEM, ~22800. Fig. 12. E. vanas1 PV wall (fine arrows) with residual funnel (f)doubled through addition from the endoplasmic reticulum (bold arrow): H: host cell. TEM, x25 000. Fig. 13. Epicytoplasmic E. vanasi trophozoites with its special~zedinvaginated PV juncture. TEM, ~10500.Fig, 14. Enlarged view of E. vanasi (E) PV juncture with lnvaginations (i)and fibrillar bundles (arrows); H: host cell. TEM, ~46200.Fig. 15. Two E. vanasi merozoites undergoing endodyogeny (arrows). TEM, ~7500.Fig. 16. Crystalline organelles in E. vanasi merozoite. TEM,x24000

72 Dis aquat Org 22: 67-76, 1995

Figs. 17 to 23. Fig. 17. Goussla cichlidarurn with pellicular projections (arrows). T~M,~15000. Fig. 18. Granular WF2-like organelles (W) in G. cichlidarum macrogamont. TEM,X 11 250. Fig. 19. Small WF1-like (W) and large WF2-like (W) organelles in intracytoplasmic macrogamont of Eirneria vanasi. EM,~22500. Fig. 20. Forming oocyst wall in G. cichlldarurn sporoblast. g: granular aggregates; L: laminae. TEM, ~27000.Fig. 21. Forming wall in E. vanasi epicytoplasmic oocyst. W: WF2-like organelles. TEM, X 15800. Fig. 22. Enlarged view of oocyst wall from Fig. 21, showing wall membrane (arrow) and overlaid lamellae layer (2 arrows). TEM, ~20000.Fig. 23. Goussia tnchopteri (young macrogamont) from intestine of a gourami T'chogaster pectoralis. TEM,x9500 Paperna: Affinities of piscine coccidia 73

Refractile and crystalline organelles found in G. zarnowskii, however, have been proposed as the source of material deposited between the mem- Sporozoites, and some merozoite stages of piscine branes of the forming oocyst wall. Morrison & Hawkins coccidia, possess either a refractile body, characteristic (1984) report the presence of WF2-llke organelles, of all eimeriid coccidia (Hammond et al. 1970, Chobotar located within endoplasmic reticulum (ER) cisternae, & Scholtyseck 1982), or a crystalline body, character- in both G. clupearum and Eimeria sardinae. Similar istic of Cystoisospora, Sarcocystis, some invertebrate granules within ER cisternae are found in G. tri- coccidia and all haemosporidia (Trefiak & Desser 1973, chopteri (Kim & Paperna 1993b; see Fig. 23). WF2-like Chobotar & Scholtyseck 1982). Refractile bodies were organelles located in ER cisternae, occurring in the found in Eimeria sardinae and Coussia clupearum macrogamonts of G. cjchlidarum (Paperna et al. 1986), (Morrison & Hawkins 1984), G. carpelli and G. sub- seem to contribute their granular contents to the con- epithelialis (Lom et al. 1991, Steinhagen 1991b), and solidating oocyst wall (Fig. 18) (Paperna & Landsberg Calyptospora funduli (Hawkins et al. 1983a). Crys- 1985). So far, among piscine coccidia, only E. vanasi talline bodies were found in G. cichlidarum (Paperna & macrogamonts contain organelles which are struc- Landsberg 1985), G. spraguei (Morrison & Poynton turally reminiscent of the WF1 and WF2 in higher ver- 1989; also with refractile bodies?), merozoites of G. tebrate coccidia (Figs. 3, 7 & 19). WF1-like organelles gadi (Moriison et al. 1993a) and of E. vanasi (Fig. 16; seem to contribute material during the early stages of Kim & Paperna 1992). wall formation, while WF2-like organelles persist until later stages of wall formation, with their ultimate fate remaining unknown (Kim & Paperna 1992). Pellicular projections in merozoites

Pellicular projections occur in merozoites of Goussia Wall formation cichlidarum (Kim 1992; Fig. 17).They are unknown in other coccidians, but occur in intraerythrocytic stages In Goussia iroquoina, Eimeria laureleus, G. carpel11 of haemogregarines (Desser & Weller 1973, I. Paperna and G. spraguei, 1 or more membranes, formed after & Y. Boulard unpubl.) in and reptiles. macrogamete fertilization, together with the closely applied PV, make up the oocyst wall: a thin membra- nous or laminated envelope which degenerates when Wall-forming bodies the sporocysts mature (Desser & Li 1984, Paterson & Desser 1984, Lom et al. 1991). The dense bodies do not Macrogamonts of all terrestrial vertebrate-host seem to participate in the process and may be found eimeriid coccidia with hard-walled oocysts contain beneath the wall of the sporulating oocyst (Davies 1990). wall-forming organelles (WF1 and WF2), which pro- Detached oocysts often remain embedded in the residue vide the material for the outer and inner oocyst walls of their host cell. In the intrahepatocytic Calyptospora (Scholtyseck et al. 1971, Chobotar & Scholtyseck 1982). funduli the oocyst wall is particularly thin, 2-layered, One might expect piscine coccidia, which do not form with a finely deposited inner layer (Hawkins et al. 1984). hard oocyst walls, to be without wall-forming bodies. In G. zarnowskii wall formation, 3 additional distinct Indeed, Epieimeria anguillae and E. isabellae lack any membranes are formed above the triple-layered zygote organelles resembling wall-forming bodies. The iden- wall and a finely granulated material is deposited tification of wall-forming bodies in Calyptospora between the second and third membranes, possibly from funduli (Hawkins et al. 1983b) should be reexamined. the wall-forming-like bodies (Jastrzebski & Komorowski In Goussia iroquoina (Paterson & Desser 1981b), Eime- 1990). In G. cichlidarum the outer cytoplasmic layer of ria laureleus, G. aculeati, G. carpel11 and G. pannonica the zygote becomes the oocyst wall. Granular material, macrogamonts contain electron-dense bodies which apparently of WF2 origin, aggregates in the peripheral are involved in neither oocyst nor sporocyst wall- cytoplasm which subsequently consolidates into a lami- formation (Desser & Li 1984, Paterson & Desser 1984, nated layer (Fig. 20). However this layer eventually dis- Jastrzebski 1989, Lom et al. 1991, Lukes 1992). The integrates, becoming the fragile membrane, seen in the same applies to the large globular osmiophilic gran- other piscine coccidia, when sporocysts are formed ules seen in G. spraguei (Morrison & Poynton 1989) (Paperna & Cross 1985, Paperna & Landsberg 1985). In and the peripherically arranged dense inclusions of E. vanasi, an outer multilamellated layer is formed, G. subepithelialis (Steinhagen et al. 1990). It has which, together with a deposited substance, consoli- been suggested that these organelles, which persist dates into a wall with an outer and inner layer, re- throughout sporulation, become sporozoite refractile miniscent of higher vertebrate coccidia oocyst walls bodies (Paterson & Desser 1984). Similar dense bodies (Figs. 21 & 22) (Kim & Paperna 1992). Dis aquat Org 22: 67-76, 1995

TRANSMISSION dividing by endodyogeny inside migratory macro- phages in extraepithelial sites during chronic stage of There seem to be several options for the transmission infection with Eimeria vanasi, recalls a chronic form of of piscine coccidia: via oral contamination (predation Toxoplasma infection (Dubey 1977), and 'cystozoites' or necrophagia) and via intermediate hosts. The of haemogregarines (Kirmse 1979). Endodyogeny has intestinal species Goussia iroquoina, G. subepithelialis, only rarely been observed among higher vertebrate G. carpelli and Eimeria vanasi and the swimbladder monoxenous eimeriid coccidia (Danforth & Hammond species G. cichlidarum were transmitted by oral inocu- 1972). In addition to having crystalline rather than lation of sporulated oocysts or by allowing fish to feed refractile bodies, other shared features with haemo- on contaminated feces and swimbladders containing gregarines are the pellicular projections found also on sporulated oocysts (Marincek 1973, Paterson & Desser intraerythrocytic stages of haemogregarines (Desser & 1981a, Steinhagen & Korting 1988, Kim 1992, Kim & Weller 1973), and the epicytoplasmic position which Paperna 1993a). Necrophagia seems to be an impor- also characterizes the association between gamonts tant route of transmission not only for extraintestinal and the gut cells of the leech (Siddall & Desser 1990). but also for intestinal coccidia which sporulate endoge- The existence of similar characteristics, however, does noilsli; (hl~liiki1984). Steinhager, B K8r:ing (1998) not nCccssafi!y imph direct phy!2gcnctic re!ati=n- were able to transmit G. subepithelialis and G. carpelli ship between the cyst-forming and piscine coccidia. via paratenic hosts, namely tubificid oligochaetes. An alternative possibility could be to regard all of the Sporozoites excysted from ingested oocysts, invaded above-listed traits as ancestral characteristics of coc- and survived in the gut cells (Steinhagen 1991b). cidia which, according to Landau's (1982) postulation, Fournie & Overstreet (1983) demostrated that trans- were lost or replaced by new devices (such as the hard mission of Calyptospora funduli requires an obligatory 2-layered oocyst wall or the sporocyst Stieda and intermediate host, the grass shrimp Palaemonetes Substieda bodies) in the process of evolutionary spe- pupio. Heteroxenous transmission has been demon- cialization. The epicytoplasmic form of infection could strated in moray eel coccidia via mysidacid shrimp also be regarded as one of the coccidian features (Landau et al. 1975). eliminated during the evolution of mammalian and avian eimeriid coccidia. The crystalline body which occurs in invertebrate coccidia as well as in haemo- CONCLUDING REMARKS sporidia seems to be older than the refractile body characteristic of eimeriid coccidia. Other apparently The wide variability among piscine coccidia in struc- ancient organelles are the pellicular projections found ture, host-parasite relationships and biology indicates in some merozoites, and otherwise found only in haemo- a polyphyletic origin. The best example of this is the gregarines and the invagination of the PV, which in finding of both crystalline and refractile organelles in addition to Cystoisospora spp. were reported in exo- the sporozoites and merozoites of piscine coccidia. erythrocytic stages of tortoise metchni- Alternatively, or complementarily, this diversity may kovi (Sterling & de Giusti 1972). be an expression of a lower degree of evolutionary The absence of true wall-forming bodies sets apart specialization, as compared to the high structural and all piscine coccidians from those of reptilian, avian and developmental conformity among the very specialized mammalian hosts, including the cyst-forming ones avian and mammalian monoxenous eimeriid coccidia. (which display at least one of the two; Dubey 1977, The heteroxenous development demonstrated in some Dubey et al. 1989). A recent study of coccidia coccidia may serve as further proof of a lower level of (Paperna & Lainson 1995) demonstrates their similari- specialization, following Landau's (1982) postulation ties with piscine coccidia, e.g. the occurrence of dense that monoxenous coccidia originated from ancestral organelles rather than wall-forming types, and oocysts heteroxenous forms. Many of the structural features with soft, disaggregating walls which complete sporu- found among piscine coccldia also occur in the hetero- lation in the host tissue prior to evacuation. xenous cyst-forming coccidla Sarcocystis and Cystoiso- spora: fragile oocyst; valved sporocysts lacking Stieda LITERATURECITED bodies which rupture along sutural lines; crystalline bodies in sporozoites and merozoites instead of refrac- Azevedo C, Matos P, Matos E (1993) Morphological data tile ones; a PV wall which is either multilayered, or has of Calyptospora spinosa n. sp. (, Calypto- funnels or invaginations, endodyogeny as a stage in sporidae) parasite of Crenicichla lepidota Heckel, 1840 (Teleostei) from Amazon river. Eur J Protistol 29:171-175 merogonous development and endopolygeny as the Bekesi L, Molnar K (1991) Calyptospora tucunarensis n. sp. main form of merogony (Pelster 1973, Dubey 1977, (Apicomplexa: Sporozoea) from the liver of tucunare Ferguson et al. 1980). The occurrence of merozoites, Cichla ocellaris in Brazil. Syst Parasitol 18:127-132 Paperna: Affinities of plscine coccidia

Boulard Y, Blanc I (1985) Presence d'une coccidie sous- Jastrzebski M (1989) Ultrastructural study on the develop- epitheliale dans I'intestin de Labrus berggylta. 24eme ment of Goussia aculeati, a coccidium parasitizing the colloque g.p.1.f.. La Rochelle, 16-19 May 1985. Society of three spined stickleback Gasterosteus aculeatus. Dis Protozoologists Abstracts, No 36 aquat Org 6:45-53 Cheung PJ. Nigrelli RF, Ruggieri GD (1986) Calyptospora Jastrzebski M, Komorowski Z (1990) Light and electron serrasalrni sp. nov. (Coccidia: Calyptosporidae) from the microscopic studies on Goussia zarnowskii (Jastrzebski, liver of the black piranha, Serrasalrnus niger Schom- 1982): an intestinal coccidium parasitizing the three burgh. J Aquaricult Aquat Sci 4:54-57 spined stickleback, Gastrosteus aculeatus (L.). J Fish Dis Chobotar B, Scholtyseck E (1982) Ultrastructure. In: Long PL 13:l-12 (ed) The biology of the coccidia. Edward Arnold, London, Kim SH (1992) Developmental biology of tilapia coccidia: p 101-165 Eimeria vanasi in the intestine and Goussia cichlidarum Danforth HD, Hammond DM (1972) Stages of merogony in in the swimbladder. MSc thesis, Faculty of Agriculture of multinucleate merozoites of Eimeria magna Perard. 1925. the Hebrew University of Jerusalem J Protozool 19:454-457 Kim SH, Paperna 1 (1992) Fine structure of epicytoplasmic Daoudi F, Marques A, Bouix G (1985) Ultrastructure d'Epie- stages of Eimerja S. 1. vanasi from the gut of cichlid fish. imeria isabellae Lorn et Dykova, 1982, coccidie epicellu- Dis aquat Org 12:191-197 laire parasite intestinal du poisson teleosteen Conger Kim SH, Paperna I (1993a) Development and fine structure of conger Llnne, 1758. 24eme Colloque g.p.l.f., La Rochelle, intracytoplasmic and epicytoplasmic meronts, merozoltes 16-19 May 1985. 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Responsible Subject Editor: W. Korting, Hannover, Germany Manuscript first received: July 18, 1994 Revised version accepted: December 20, 1994