MFR PAPER 1340
Comments on Trends in Researchon Parasitic Diseasesof Shellfish and Fish
Victor Sprague is with the Center forEnvironmental and EstuarineStudies, Chesapeake BiologicalLaboratory, University of Maryland,Solomons, MD 20688. This paper isContribution No. 797, Center for Environmental and Estuarine Studies ofthe University of Maryland, Solomons, MD 20688.
VICTOR SPRAGUE
This subject is arbitrarily limited inscope to the protozoa and in time to thepast decade. It deals very briefly withrecent developments in the biology andsystematics of some protozoan groupsthat are significant as pathogens. Moredetailed reviews have recently beenpublished by Couch (1978), Hazardand Oldacre (1976), Sindermann(1970), Sprague (1970a, b, 1971,(977), and Sprague and Couch (197 I).The symposium edited by Snieszko( (970) contains numerous articles pertinent to "fish health," the two bySprague being specifically cited aboveas being particularly relevant to thispresentation.
RECENT ADVANCES
Amoebae
In Crabs
Only one amoeba is believed to be aserious mortality factor in shellfish.This parasite, Paramoeba perniciosaSprague, Beckett, and Sawyer, 1969,was first reported and briefly describedin 1966 by Sprague and Beckett whofound it in the hemolymph of dead andmoribund crabs, CaLlinectes sapidus,in Chincoteague Bay, Maryland andVirginia. These authors did not recognize the parasite as an amoeba at thattime, but in a later note (Sprague andBeckett, 1968) assigned it to genusParamoeba Schaudinn, 1896.
The parasite occurs in thehemolymph of heavily infected crabs.Sometimes the body fluid of the hostbecame mil ky white due to the presence
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of enormous numbers of the parasites.As the number of parasites increases,the hemocytes decrease in number.Heavy infections may be accompaniedby lysis of the skeletal muscles.
Paramoeha perniciosa has been limited to the higher salinity waters. It hasbeen found most frequently in"peeler" crabs suffering heavy mortalities in holding tanks, but has beenfound also in "hard" crabs collected inenzootic areas. Lunz (1968) found itassociated with crab mortalities alongthe coast of South Carolina and Georgia. Sawyer (1968) gave preliminarydata on the epizootiology and hostparasite relations. Newman and Ward( 1973) reported a modest epizootic inChincoteague Bay. Sawyer (1968)found the parasite in the blood onlyduring mortalities, which occurredmainly in the spring. He postulated acryptic tissue phase in the parasite's lifecycle during other parts of the year.Very recently, Johnson (1977) discovered the' 'cryptic phase" in the connective tissues. She found that the parasiteis present in these tissues at all seasonsof the year and invades the circulatingblood in the vessels only when the disease is terminal. Johnson also transmitted the infection by inoculation,with fatal results to the inoculatedcrabs.
The evidence that this amoeba is avery significant mortality factor in Callinectes sapidus is overwhelming, iflargely circumstantial. The parasite hasnot been grown in pure culture, and itsnormal mode of transmission is unknown.
In Fish
Only very recently, amoebae havebecome generally recognized as important mortality factors in fish. Someamoebae pathogenic to man also occurin fish.
Disease conditions of epizooticproportions in rainbow trout on commercial trout farms of Italy and otherEuropean countries have been attributed by Ghittino et al. (1977) to anamoeba. Epizootics associated with thesame amoeba were reported by Ferguson and McC Adair (1977) in Scotlandand Ireland. It seems clear from thesereports that an amoeba (apparently notyet identified) is a very important factorin widespread mortalities of trout inEuropean fish farms.
Taylor ( 1977) isolated amoebae fromII species of fish in the southeasternstates. Among those isolated wasAcanthamoeba polyphaga whichTaylor regarded as the cause of a largekill, involving mainly blue tilapia, inFlorida. This study has special interestbecause A. polyphaga is pathogenic toman.
Sawyer et at. (1974) describedThecamoeba hoffmani from the gills offingerling rainbow trout, coho salmon,and chinook salmon. They concludedthat the species is essentially a freeliving form, although it seems to be acontributory factor in mortalities.
Microsporidia
In Bivalve Mollusks
Microsporidium sp. has been found,but not yet reported, by Brian Jones' inthe visceral mass of Ostrea lutaria inNew Zealand. This is the third species'known in bivalve mollusks. Thesespecies are not significant pathogens.
'Jones, B., Zoology Department. Victoria University, Wellington, N.Z.
Marine Fisheries Review
Figure 1.-Amesol1 pulvis (Perez, 1905), spores, in muscle of green crab.
In Crabs
Microsporidia are common pathogens of crabs and shrimp, mainly in theskeletal muscle. About a dozen speciesare now known in crabs, four of them inthe muscles of the blue crab, Cal/inectes sapidus Rathbun. Three of thelatter are rare, but one. Nosemamichaelis Sprague, 1970a, is common,widely distributed, and lethal to itshost; the impact on the host populationhas not been assessed. Nosemamichaelis, being readily obtainable ingreat quantity, has become a useful object for studies on cytology of the parasite (Sprague et aJ. 1968; Weidner,1970, 1976; Weidner and Trager,1973) and on intracellular parasitism(Trager, 1974). This species was recently made the type of a new genus,now beingAmeson michaelis (Sprague,1970) Sprague, 1977. One of the fourspecies known in Callinectes,The/ohania sp. Johnson, /972, is undescribed. The first two species of microsporidia reported in crabs, The/ohaniamaenadis Perez, 1904, and Nosema pu/vis Perez, 1905, both in the green crabCarcinus maenas (L.), were recentlyrediscovered, the first by Sprague andVivares independently and the secondby Vivares. Vivares (1975) has alreadypublished on the former, while Vivaresand Sprague (in press) have redescribed
October /978
the latter, now Ameson pu/vis (Perez,1905) Sprague, 1977 (Fig. I).
In Shrimp
Nosema ne/soni recently becameAmeson ne/soni (Sprague, 1950)Sprague, 1977. This species, originallyfound in the muscles of Penaeus aztents Ives, has now been identified insix species of penaeid shrimp.Thelohania macrocystis, in muscles ofPalaemonetes varians, recently became Chapmanium macrocystis (Gurley, 1893) Hazard and Oldacre, 1976.Thelohania penaei, in ovary Penaeussetiferus (L.), recently became Agmasoma penaei (Sprague, 1950) Hazardand Oldacre, 1976.
Quite recently, a relatively largenumber of new species have been discovered in shrimp. A new genus andnew species, Inodosporus spragueiOverstreet and Weidner, 1974, wasfound in Pa/ael11onetes pugio Holthiusand P. kadiakensis. P/eistophora lintoni Street and Sprague, 1974 was described in Pa/aemonetes pugio. Severalundescribed species were found in pandaJid shrimp sent to me from BritishColumbia by T. H. Butler. One ofthese, The/ohania sp. Vernick,Sprague. and Krause, 1977, in Panda/us jore/ani Rathbun, has been described by Johnston, Vernick, and
Sprague (in press) as a new species(Fig. 2). Pleistophora penaei Constransitch. 1970 was found in commercial shrimp. Pleistophora crangoniBreed and Olson, 1977 was found infour species of Crangon. Some undescribed species have been listed bySprague ( 1977).
In Fish
Microsporidia are very common infish; over 100 species of fish are nowknown to be parasitized. Some microsporidia are also known to be seriousmortality factors in fish. Delisle, 1972found massive mortalities of smelt, associated with this parasite, in certainCanadian lakes. G/ugea stephani(l-Iagenmuller, 1899) has been foundby different investigators to be an important mortality factor in youngflatfish of different species. Spragueand Vernick (1968) found thatIchthyosporidium giganteul11 (Thelohan, 1895), long treated as haplosporidium, is a microsporidium. This (ora very similar species) is not uncommon in .. spot," Leiostol11us xanthurusLacepede, in tributaries of the Chesapeake Bay. It produces a very largeabdominal swelling, usually in youngfish, that probably kills the host.
Haplosporidia
There has been much interest in haplosporidia during the past decade,mai nly because they are very destructi ve pathogens of oysters. This has ledto the discovery of a few new species,much better understanding of thegroup, and new ideas on classification.
In Biva/ve Mollusks
Perkins (1968, 1969) and Rosenfieldet aJ. (1969) have contributed much toour understanding of haplosporidia bymaking the first electron microscopestudies on some typical forms-thosefamiliar species in Crassostrea virginica (Gmel in).
Minchinia arl110ricana van Banning,1977, was found in the European flatoyster, Ostrea edulis. This is the onlyknown haplosporidian that has tails onits spores like those seen in the typespecies M. chitonis (Lankester, 1885).Sprague (1970c) suggested that presence or absence of these tails be used as
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Figure 2.-The/ohania sp. Vernick et al., 1976, various sporulation stages,in muscle of the shrimp Panda/us jordani. Bouin, section, Heidenhain;1,300 x.
the basis for distinguishing MinchiniaLabbe, 1896 from HaplosporidiumCaullery and Mesnil, 1899.
Two species of a previously unfamiliar kind have been found in associationwith oyster mortalities. They areMarteilia refringens Grizel et al., 1974(type species), in the European flat oyster Ostrea edulis L., and M. sydneyiPerkins and Wolf, 1976, in the Australian oyster, Crassostrea commercialis.Perkins (1976a) suggested that they arerelated to the haplosporidia, mainly because they have "haplosporosomes."
/n Decapods
"Minchinia sp." Marchand, 1974,was found in the mud crab, Rhithropanopeus harrisii, in France. Plasmodia of a haplosporidian were foundby Newman et al. (1976) in Callinectessapidus from Virginia and NorthCarolina.
Myxosporidia
New species are frequently added tothe long list of myxosporidian speciesin fish. Most are not noted forpathogenicity, but one highly pathogenic form, Myxosoma eerebralis(Hofer, 1903), has been the object ofmany recent studies. An interestingspecies recently described is Unieapsula pflug/elderi Schubert, Sprague,and Reinboth, 1975. It has spores withtwo rudimentary polar capsules, as wellas the fully formed one that is characteristic of the genus. Another species,interesting because it infects an important sport fish, is Henneguya sp.Meyers, Sawyer, and MacLean, 1977,in the heart of the bluefish, Pomatomussaltatrix (L.).
Protista Incertae Sedis
An unidentified parasite with vagueresemblance to the Coccidia was recently found by Peter Wolf (1977) inova of the blacklipped oyster, Crassostrea echinata, from Australia.Another unidentified protist was foundin the digestive epithelium of the pearloyster, Pinctada maxima, in Australia(Wolf and Sprague, 1978).
A parasite in spleen and liver of rainbow trout, causing epizootic disease inEngland, was recently sent to me by
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John Finlay 2 for identification. I noted aresemblance to intracellular stages ofHexamita but, being unable to makepositi ve identification, sent the sl ides toGlenn Hoffman. At first, Hoffman 3
suspected the parasite might be identical with the amoebae reported by Ghittino et al. (1977), but after further consideration, he doubted that it is anamoeba. The identity of the parasiteremains undetermined.
CLASSIFICAnON
Some minor changes in classification, particularly the transfer of somemicrosporidian species to new genera,have already been mentioned. One ofthe most spectacular of the minor developments in recent years was thefinding by Perkins (1976b) that theflagellated zoospore of Dermocystidium marinum Mackin, Owen, andCollier, 1950 has an apical complex.This led Perkins to conclude that theparasite, long regarded as a fungus, isrelated to the Coccidia.
'Finlay, J., Fish Diseases Laboratory, Ministryof Agriculture, Fisheries and Food, The Nothe,Weymouth, Dorset. England DT4 8UB.3 Hoffman, G. A., Fish Farming Experimental Sta·tion. U.S. Fish and Wildlife Service, SIUllgart,AR 72160. Pers. commun.
Drastic changes are taking place inthe classification of the highercategories of protozoa, since recent advances in knowledge indicate that theold phylum Protozoa is an artificial assemblage of several phyla. A . 'Committee on Classification and Nomenclature" of the Society of Protozoologists,headed by N. D. Levine, is making arevision. Microsporidia, haplosporidia, myxosporidia, and someother groups will probably becomedistinct phyla, as ciliates have alreadydone. Classification of microsporidiaprobably will be based on that ofSprague (1977). Classification of haplosporidia will probably include amajor new taxon to include Marteilia.Myxosporidia are now considered bymany protozoologists to be metazoawith coelenterate affinities, but theywill probably remain for awhile in thesystem of the protista.
This is a convenient occasion to takespecific action upon my previous(Sprague, 1970c) suggestion and transfer from genus Minchinia Labbe, 1896to Hap/osporidium Caullery and Mesnil, 1899 species which, like the typespecies H. sea/opli Caullery and Mesnil, 1899, have spores without tails.Accord ingly, Minchinia louisianaSprague, 1963b becomes Haplo-
Marine Fisheries Review
sporidium louisiana (Sprague. 1963b)comb. n. and M. nelsoni Haskin.Stauber. and Mackin 1966 becomes H.nelsoni (Haskin et al.. 1966) comb. n.Other species which Sprague (1963a:265-266) transferred (for reasons laterfound to be invalid) from Haplosporidium to Minchinia are now returned to Haplosporidium.
LITERATURE CITED
Breed, G. 1'1., and R. E. Olson. 1977. Biology ofthe microsporidan parasite Pleislophora erangoni n. sp. in three species of crangonid sandshrimps. J. lnvertebr. PathoI. 30:387-405.
Constransitch, M. J. 1970. Description, pathology, and incidence of Pleislophora penaei n.sp. (Microsporidia: Nosematidae), a parasiteof commercial shrimp. M.S. Thesis, Northwestern State Univ., Natchitoches, La.• 35 p.
Couch, J. A. 1978. Diseases, parasites, and toxicresponses of commercial penaeid shrimps ofthe Gulf of Mexico and South Atlantic coasts ofNorth America. Fish. Bull., U.S. 76: 1-44.
Delisle, C. E. 1972. Variations mensuelles deGlugea herlll'igi (Sporozoa: Microsporida)chez differents tissus et organes de I'eperlanadulte dulcicole et consequences de celie infection sur une mortalite massive annuelle de cepoisson. Can. J. Zool. 50:1589-1600.
Ferguson, H. w. ,and B. McC Adair. 1977. Protozoa associated with proliferative kidney disease in rainbow trout (Salmo gairdneri). Vet.Rec. /00:/58-159.
Ghittino, P., S. Andruello, and E. Vigliani.1977. L'amebiasi della trota iridea d'allevamento. Riv. Ital. Piscic. Ittiopat. 12:7489.
Grizel. H., M. Comps, J. R. Bonami, F. Cousserans, J. L. Duthoit. and M. A.le Pennec. 1974.Recherche sur I'agent de la maladie de laglande digestive de Ostrea edulis Linne. Sci.Peche 240:7-30.
Haskin, H. H.. L. A. Stauber, and J. A. Mackin.1966. Minchinia nelsoni n. sp. (Haplosporida,Haplosporidiidae): causative agent of the Delaware Bay oyster epizootic. Science (Wash.,D.C.) 153:1414-1416.
Hazard. E.I., and S. W. Oldacre. 1976. Revisionof Microsporida (Protozoa) close toThelohania. with descriptions of one new family, eight new genera, and thirteen newspecies. U.S. Dep. Agric., Agric. Res. Serv.,Tech. Bull. 15.\0. 104 p.
Johnson, C. A., III. 1972. A preliminary reporton diseases of North Carolina coastal crabswith emphasis on the blue crab, Cal/inectessapidus. ASB (Assoc. Southeast. BioI.) Bull.19:77.
Johnson, P. T. 1977. Paramoebiasis in the bluecrab. Cal/ineues sapidus. J. Invertebr. Pathol.29:308-320.
Johnston, L. B., S. H. Vernick, and V. Sprague.In press. Light and electron microscope studyof a new species of Thelohania (Microsporida)in the shrimp Pandalus jordani. J. Invertebr.PathoI.
Lunz, G. R. 1968. In Hearings before the Subcommittee on Fisheries and Wildlife Conserva-
October /978
tion of the Committee on Merchant Marine andFisheries-House of Represenlatives. Commer. Fish. Res. Legisl. H. R. 18008. Ser. No.90-29, p. 99-104. U.S. Gov. Print. Ofr ..Wash .. D.C.
Marchand. J. 1974. Presence de Minchiniu sp.(Haplosporida - Haplosporidiidae) chez Iexanthide Rhilhrop(//lOpeu.\· harrisii (Gould)fridenlalUS (Maitland) dan Ie canal de Caen ala mer. Rev. Trav. Insl. Peches Marit.38:209-213.
Meyers. T. R.• T. K. Sawyer. and S. A. MacLean. 1977. Hennegu)'u sp. (Cnidospora:Myxosporida) parasitic in the heart of thebluefish. PomalOmus salTatrix. J. Parasitol.63:890-896.
Newman. M. W., C. A. Johnson. III. and G. B.Pauley. 1976. A Minchinia-like haplosporidanparasitizing blue crabs. Callinecfes sapidus. J.lnvertebr. Pathol. 27:311-315.
____, and G. E. Ward. Jr. 1973. Anepizootic of blue crabs, Callineues sapidus,caused by Paramoeba perniciosa. J. Invertebr.PathoI. 22:329-334.
Overstreet, R. 1'1., and E. Weidner. 1974. Differentiation of microsporidian spore-tails inInodosporus spraguei gen. et sp. n. Z.Parasitenkd. 44: 169-186.
Perkins. F. O. 1968. Fine structure of the oysterpathogen Minchinia nelsoni (Haplosporida,Haplosporidiidae). J. Invertebr. Pathol.10:287-307.
1969. Electron microscope studiesof sporulation in the oyster pathogen, Minchinia COSIO/is (Sporozoa: Haplosporida). J.Parasitol. 55:897-920.
1976a. Ultrastructure of sporulationin the European flat oyster pathogen, Marteiliarefringens-taxonomic implications. 1. Protozool. 23:64-74.
1976b. Zoospores of the oysterpathogen. Dermocysridium marinum. I. Finestructure of the conoid and other sporozoanlike organelles. J. Parasitol. 62:959-974.
____, and P. H. Wolf. 1976. Fine structure of Marleilia sydneyi sp. n.-haplosporidan pathogen of Australian oysters. J.Parasitol. 62:528-538.
Rosenfield. A.• L. Buchanan, and G. B. Chapman. 1969. Comparison of the fine structure ofspores of three species of Minchinia (Haplosporida, Haplosporidiidae). J. Parasitol.55:921-941.
Sawyer. T. K. 1968. Preliminary study on theepizootiology and host-parasite relationship ofParamoeba sp. in the blue crab, Callineclessopielus. Proc. Natl. Shellfish. Assoc. 59:6064.
____,J. G. Hnath, andJ. F. Conrad. 1974.Thecamoeba hoJJmaIIi sp. n. (Amoebida:Thecamoebidae) from gills of fingerling salmonid fish. J. Parnsitol. 60:677-682.
Schubert, G .. V. Sprague. and R. Reinboth.1975. Observations on a new species of Ullicapsula (Myxosporida) in the fish Maenasmaris (L.) by conventional and electronmicroscopy. I.. Parasitenkd. 46:245-252.
Sindermann. C. J. 1970. Principal diseases ofmarine fish and shellfish. Academic Press,Lond., .169 p.
Snieszko. S. F. (editor). 1970. A symposium ondiseases of fishes and shellfishes. Am. Fish.Soc. Spec. Publ. 5.526 p.
Sprague. V. 196.1a. Rcvision of genus Huplosporidium and rc:storation of genus Millchi"ia(Haplosporidia. Haplosporidiidae). 1. Protozool. 10:263-266
____. 196.1b. Millchilli" louisialla n. sp.(Haplosporidia. Haplosporidiidac). a parasiteof Pallopeus herbslii. J. Protozool. 10:267274.
____. /970a. Some protozoan parasitesand hyperparasites in marine decapod Crustacea. In S. F. Snkszko (editOr). A symposiumon diseases of fishes and shellfishes. p. 4164.10. Am. Fish. Soc. Spec. Publ. 5.
1970b. Some protozoan parasitcsand hyperparasites in marine bivalve molluscs.In S. F. Snieszko (editor). A symp<lsiulll ondiseases of fishes and shell Ii shes. p. 511-526.Am. Fish. Soc. Spec. Publ. 5.
1970c. Recent problems oftaxonomy and morphol<lgy of Haplosporidia.(Abstr. 602) J. Parasitol. 56(4, Sec. II. Part1):327-328.
____. 197 I. Diseases of oysters. Annu.Rev. Microbiol. 25:21 1-230.
1977. Systematics of the Microsporidia. III L. A. Bulla. Jr. and T. C. Cheng(editors), Comparative pathobiology. Vol. 2.510 p.
____. and R. L. Becken. 1966. A diseaseof blue crabs (Callillecles sapidus) in Maryland and Virginia. J. Invertebr. Pat hoI.8:287-289.
____.and .1968. ThenalUreofthe etiological agent of' 'gray crab" disease. J.Invertebr. PathoI. II :503.
____, and T. K. Sawyer.1969. A new species of Paramoeba(Amoebida, Paramoebidae) parasitic in thecrab Callinectes supid/ls. J. Invertebr. PathoI.14:167-174.
- , and J. Couch. 1971. An annotatedlist of protozoan parasites. hyperparasites. andcommensals of decapod Crustacea. J. Protozool. 18:526-537.
____, and S. H. Vernick. 1968. Observations on the spores of Pleistophora gigallfea(Thelohan. 1895) Swellengrebel. 1911. a microsporidan parasite of th-e fish Crenilabrusmelops. J. Protozool. 15:662-665.
____, , and B. J. Lloyd. Jr.1968. The fine structure of Nosema sp.Sprague, 1965 (Microsporida. Nosematidae)with particular reference to stages insporogony. J. Invertebr. PathoI. 12: 105· I 17.
Street, D. A., and V. Sprague. 1974. A newspecies of Pleislophora (Microsporida: Pleistophoridae) parasitic in the shrimp PalaemolIeles pugio. J. Invertebr. Pathol. 23: 153-156.
Taylor, P. W. 1977. Isolation and experimentalinfection of free-living amebae in freshwaterfishes. J. ParasilOl. 63:232-237.
Trager, W. 1974. Some aspects of intracellularparasitism. Science (Wash., D.C.) 183:269273.
Van Banning, P. 1977. Minehinia annoricanasp. nov. (Haplosporida), a parasite of theEuropean flat oyster. OSlrea "dulis. J. Inverlebr. Pathol. 30: 199-206.
Vernick, S. H., V. Sprague, and D. Krause.1977. Some ultrastructural and functional aspects of the Gnlgi apparatus of Thelollllnia sp.(Microsporida) in the shrimp PW/llalllsjordaniRathbun. J. Protozool. 24:':>4-99.
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MFR Paper 1340 From Marine Fisheries Review. Vol. 40, No. 10. October1978. Copies of this paper, in limited numbers, are available from 0822, UserServices Branch. Environmental Science Information Center, NOAA, Rockville.MO 20852 Copies of Marine Fisheries Review are available from the Superintendent of Documents, U.S. Government Printing Office, Washington, DC20402 for $1. 10 each.
Susceptibility Studies of VariousSalmonids to Whirling Disease:Histological Staining and SporeConcentration Procedures
Vivares, C. P. 1975. Elude comparative faile enmicroscopies photonique et electronique de troisespeces de microspiridies appartenant au genreThelohallia Henneguy. 1892, parasites de crustaces decapodes marins. Ann. Sci. Nal. Zool.BioI. Anim. Ser. 12,17:141-178.
____, and V. Sprague. In press. The finestructure of Amesoll pu/vis (Perez. 1905) (Microspora, Microsporida) and its implication regarding classification and chromosome cycle.J. Invenebr. PathoI.
Weidner, E. 1970. Ultrastructural study of microsporidian developmenl. J. Nosema sp.Sprague. 1965 in Callillectessl1pidus Rathbun.Z. lellforsch. Mikrosk. Anal. 104:33-54.
MFR PAPER 1341
JOSEPH O'GRODNICK
Since 1968, research on the transmission, life history, and control ofwhirling disease in trout has been conducted by the Pennsylvania Fish Commission. Whirling disease is caused bya myxosporidian parasite, Myxosomacerebralis, which invades and destroyscartilage of susceptible salmonidspecies. The parasite was introducedinto the United States from Europe andhas been established as a persistenthatchery disease in several areas.
Affected fish exhibit rapid, tail chasing behavior from the disintegration ofthe cartilaginous support skeleton of theorgans of equilibrium. Also, severecrippling may result from destruction of
Joseph O'Grodnick is with the Benner Spring Fish Research Station,Pennsylvania Fish Commission, Bellefonte, PA 16823.
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1976. Interaction of microsporidiawilh host cells. Proc. 1st Inl. Colloq. Invertebr. Pathol. and IXth Annu. Meel. Soc. Inver·lebr. Palhol., p. 82-84.
____, and W. Trager. 1973. Adenosinetriphosphate in the extracellular sun'ival of anintracellular parasite (Nosema michaelis, Mi·crosporidial. J. Cell BioI. 57:586-591.
the spinal skeleton if fish are exposed asfry. "Blacktail," which is caused bypressure on the nerves that control thecaudal pigment cells, may be seen insome fish.
In this research, two methods wereused to monitor the development of thewhirling disease parasite in varioussalmonid species: I) examination ofhistological sections, and 2) quantitative estimates of spores determined bythe use of the plankton centrifuge procedure (Fig. I). (This method involveshomogenization of head skeletons,screening out tissue shreds, andconcentrating with a continuous plankton centrifuge.
The life cycle of Myxosoma cerebralis was monitored in rainbow trout(highly susceptible species) and browntrout (highly resistant species) by theexamination of histological sections.Tissues were prepared from infected
Wolf, P. H. 1977. An unidentified protistan parasite in the ova of th~ bla~klipp~d oyster. Craswstr('u e('hil/uw. fmm n()rth~rn Australia. J.In\'ert~br. Pat hoI. 29:244-246.
_____. and V. Sprague. 1978. An uniden·tilicd protistan parasite of th~ p~arl oyster,Pillcwda maxima. in tropical Australia. J. Invertebr. PathoI. 31 :262-263.
Figure I.-The plankton centrifuge. Thecentrifuge removes water through the centrifugal force created by the revolvingdrum. The excess water is carried awaythrough a rubber tube situated below thedrum. Solid particles are deposited on thewall of the revolving drum.
fi sh at gi ven intervals, averaging 3 daysfrom initial exposure to the development of spores at 120 days. The following staining methods were used in thestudy: I) Hematoxylin and Eosin, 2)Mallory Heidenhain (CassonModification), 3) Wright's stain, and 4)Ziehl-Neelson (acid fast staining forspores) .
Marine Fisheries Review