Two new species of Myxozoa from the brain of the green knife fish Eigemannia virescens are described: Myxobolus inaequus sp. n. has an unusually large spore body and extremely unequal polar capsules, and Henneguya theca sp. n. has an attenuated spore encased in a sheath not previously described in other Myxozoa. Only spores of the two species were observed, and infections caused no obvious pathological changes in the brain

Kent, Michael L.

Hoffman, Glenn L.

English

Livres de raison et correspondances de sculpteurs au XVIIIe siècle   Accueil des participants Allocution de bienvenue. Présentation du projet Arquimesa. Nicolas Marty, Professeur, Doyen de la faculté de lettres Julien Lugand, Maître de conférences, Université Perpignan-Via Domitia « Le livre de raison de Jean Ferrère : le quotidien d'un sculpteur bigourdan (1754-1779) ». Laure Decomble, Université Toulouse-le Mirail « Correspondances académiques. Le sculpteur Jean-Michel Verdiguier et l'Acadé..

Nicolas Marty

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1984 
Two New Species of Myxozoa, Myxobolus inaequus sp. n. and 
Henneguya theca sp. n. from the Brain of a South American Knife 
Fish, Eigemannia virescens (V.) 
Michael L. Kent 
University of California 
Glenn L. Hoffman 
U.S. Fish and Wildlife Service 
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Kent, Michael L. and Hoffman, Glenn L., "Two New Species of Myxozoa, Myxobolus inaequus sp. n. and 
Henneguya theca sp. n. from the Brain of a South American Knife Fish, Eigemannia virescens (V.)" (1984). 
US Fish & Wildlife Publications. 139. 
https://digitalcommons.unl.edu/usfwspubs/139 
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91 
J.Protozool .• 31(1).1984. pp. 91-94 
© 1984 by the Society of Protozoologists 
Two New Species of Myxozoa, Myxobolus inaequus sp. n. and 
H enneguya theca sp. n. from the Brain of 
a South American Knife Fish, Eigemannia virescens (V.) 
MICHAEL L. KENT' and GLENN L. HOFFMAN 
Office of Animal Resources, University of California, La Jolla, California 92093 and 
Fish Farming Experimental Station, u.s. Fish and Wildlife Service, Stuttgart, Arkansas 72160 
ABSTRACT. Two new species of Myxozoa from the brain of the green knife fish Eigemannia virescens are described: Myxobolus 
inaequus sp. n. has an unusually large spore body and extremely unequal polar capsules, and Henneguya theca sp. n. has an a.ttenu~ted 
spore encased in a sheath not previously described in other Myxozoa. Only spores of the two species were observed, and mfectlOns 
caused no obvious pathological changes in the brain. 
NUMEROUS descriptions of myxosporidans from fishes of the USA, Europe, and Asia have been reported but little 
is known of them from South American fresh waters. Species 
have been described from Brazilian freshwater fishes (3-7, 9, 
15, 16, 19) but none have been reported from the green knife 
fish Eigemannia virescens (Y.), of the family Sternopygidae. 
This common aquarium fish is used for neurophysiological re-
search at Scripps Institution of Oceanography, University of 
California, San Diego, California. Reported here are the de-
scriptions of Myxobolus inaequus sp. n. and Henneguya theca 
sp. n. from the brain of Eigemannia virescens held at Scripps 
Institution of Oceanography. 
'Present address: Department of Medicine, School of Veterinary 
Medicine, University of California-Davis, Davis, California 95616. 
MATERIALS AND METHODS 
From September 1981 to October 1982, 27 green knife fish, 
Eigemannia virescens, imported from Brazil between 1980 and 
1982 and maintained at Scripps Institution of Oceanography, 
were examined. Fish were received alive, sacrificed, and wet 
mounts of brain and visceral organs were prepared as described 
by Minchew (14) or preserved in 10% (v/v) buffered formalin. 
Measurements of spores were made by using an oil immersion 
objective and a calibrated ocular micrometer, and drawings were 
made with the aid of a camera lucida. Lugol's iodine was used 
to demonstrate iodinophilous vacuoles in fresh material, and 
smears were stained in Gomori's trichrome (8). Formalin-fixed 
infected brains were embedded in paraffin and sectioned at 5 
j.Lm. The sections were stained with Mayer's hematoxylin and 
eosin, periodic acid Schiff (PAS), or Giemsa (8). 
Published in JOURNAL OF PROTOZOOLOGY 31:1 (February 1984), pp. 91-94.
92 J.PROTOZOOL. , VOL. 31 , NO.1 , FEBRUARY 1984 
'1 
Fig. 1. Spore of Myxobolus inaequus. Bar = 5 I'm. 
DESCRIPTIONS AND DISCUSSION 
Spores of Myxobolus inaequus sp. n. and Henneguya theca 
sp. n. were found in the brains in 24 (89%) ofthe 27 Eigemannia 
virescens examined. Spores of only M. inaequus sp. n. we/C 
present in nine samples (33%); spores of only H. theca sp. n 
were present in 12 samples (44%), and a mixed infection oc 
curred in three samples (II %). No myxosporidans were apparen\ 
in other organs. 
Myxobolus inaequus sp. n. 
(Figs. 1-3B) 
Host. Eigemannia virescens (V.) family: Sternopygidae. 
Locality. Northern South America, held at Scripps Institution 
of Oceanography. 
Habitat. Brain, spores occur in small nests, most commonly 
in medulla around ventricle IV above median longitudinal fas 
cicuius; occasional spores in cerebellum. 
Description. Trophozoites not found. Spore: pyriform, sheU 
valve smooth, sutural ridge in plane of polar capsules, sym-
metric without articulations or thickenings. Intercapsuiar pro-
cess small and rod-shaped. Polar capsules extremely unequal 
pyriform, elongated anteriorly. Sporoplasm encloses a small nil< 
deus and a glycogen vacuole, observed only in PAS-stained 
paraffin sections. 
Characteristics of spore (n = 30). Length 19.8 (15.6-22) /1m, 
width 8.6 (7.8-9.3) ~m, thickness 8.0 (7. 7-8.5) ~m. Polar cap-
sules (larger): length 11.8 (9.4-13) ~m, width 3.6 (3.1-3.9)/lm: 
(smaller): length 4.8 (3.9-5.5) ~m. Polar filament lengths (n =. 
4): larger, 191 ~m, smaller 22 ~m. 
Remarks. Spore characteristics of Myxobolus inaequus sp. n. 
agree with those described for the genus (10) but this specie! 
4 
Figs. 2-4. 2. Spore of M. inaequus with extruded polar filaments (Gomori's trichrome). x400. 3a, b. Section of Eigemannia virescens brain 
with "nests" of spores (arrows) of M. inaequus and Henneguya theca (Giemsa). 3a, x 100, 3b, x 400. H = H. theca spore and M = M. inaequus 
spore. 4. Free spore and empty sheath of H. theca (Lugol's iodine-stained wet-mount). x 1000. 
KENT & HOFFMAN-NEW MYXOZOA OF SOUTH AMERICAN KNIFE FISH 93 
5 
Fig. 5. Spore of Henneguya theca sp. n. Stippled area represents 
theath. Bar = 10 /Lm. 
differs from all others due to its large spore size, extremely 
unequal polar capsules, and site in the host. Myxobolus inaequus 
sp. n. is larger than all other Myxobolus spp., except M. gigas, 
M. magnasherus, and M. ovoidalis but differs from these in its 
pyriform shape and extremely unequal polar capsules. Certain 
Myxobolus spp. such as M. anioscapsularis, M. toyami, M. dis-
par and M. pseudodispar have unequal polar capsules (2), but 
the spores of all of these are considerably smaller than those of 
M. inaequus sp. n. and do not infect nervous tissue. As shown 
in Fig. 3, no obvious tissue reactions were observed to be as-
sociated with spore "nests." 
The genera Myxobolus and Myxosoma appear closely related 
and are separated by the presence of an iodinophilous vacuole 
in the former (17). This vacuole is sometimes difficult to dem-
onstrate (18) and may not be present in all spores (11). Therefore 
it has been suggested that the genus Myxosoma be abolished 
and its species be transferred to the genus Myxobolus (18). Though 
the vacuole was not evident in wet mounts of Myxobolus in-
aequus stained in Lugol's iodine, this species is placed in this 
genus because a PAS-postive vacuole, corresponding to the io-
dinophilous vacuole, was clearly evident in stained sections. 
Henneguya theca sp. n. 
(Figs. 3A-5) 
Host. Eigemannia virescens (V.) family: Sternopygidae. 
Locality. Northern South America, held at Scripps Institution 
of Oceanography. 
Habitat. Brain, spores occur in small nests most commonly 
in medulla around ventricle IV above median longitudinal fas-
ciculus; occasional spores in cerebellum. 
Description. Trophozoites not found. Spore attenuated, an-
terior convex, spherical in front view, valves smooth without a 
clear sutural ridge, tapering to two pointed tails. Polar capsules 
slightly unequal, attenuated anteriorly. Sporoplasm encloses two 
small nuclei and an iodinophilous vacuole. Individual spores 
encased in a tight-fitting sheath that conforms to the shape of 
the spore as shown in Fig. 5. Anterior of sheath compressed 
laterally; anterior appears convex when viewed dorsally and 
truncate when viewed in the plane of the polar capsules. Spores 
emerge from the anterior of sheath when pressure is applied in 
wet-mount preparations. 
Characteristics of the spore (n = 30). Spore free from sheath 
including tails; length 48.0 (40.6-52.6) /-Lm, width 3.5 (3.0-4.1) 
jim. Polar capsules (larger): length 11.1 (9.8-12.5) /-Lm, width 
1.4 (1.0-1.6) /-Lm; (smaller): length 10.4 (8.7-11.7) /-Lm, width 
1.4 (1.0-1.6) /-Lm. Tail length 23.2 (20.3-24.2) /-Lm. Sheath only: 
length 50.8 (43.7-55.4) /-Lm, width 5.78 (5.5-6.6) /-Lm. Polar 
filaments (n = 20, Giemsa-stained), 19.9 (17.1-23.4) /-Lm. 
Remarks. Henneguya theca sp. n. is placed in this genus on 
spore characteristics as described by Kudo (1966) but differs 
from all other species in that genus in having a sheath that 
conforms closely to the shape of the spore and in its unique host 
and site in the host. No Henneguya spp. have been described 
from nervous tissues; the spore is considerably more attenuated 
and is larger than others in this genus from South American 
freshwater fish (9). As in Myxobolus inaequus sp. n., no obvious 
tissue reaction was observed associated with "nests" of spores 
in the brain. 
The sheath structure that surrounds spores of Henneguya 
theca sp. n. has not been described in Myxozoa. Unlike spores 
of many myxosporidans, which are encased in a loose, amor-
phous, gelatinous envelope that is not visible in bright field or 
phase contrast examinations (13), the sheath described here 
conforms closely to the spore shape and is clearly visible in wet-
mount preparations. 
Pathology. The pathology associated with brain infections by 
these species was similar to that described by Bond (1) for Myxo-
bolus subtectalis in that even in heavy infections little host re-
sponse was observed, which is typical of myxosporidan infec-
tions (12). The infections were also similar to those caused by 
Myxobolus kisutchi from salmon brains (21), in which no cysts 
or vegetative stages were found in the brain. The "nests" of the 
spores that we describe are probably comparable to the cysts of 
M. kisutchi described by Wyatt (20). Though spores were not 
specifically associated with blood vessels in the knife fish, the 
immature stages may be carried to the brain from other organs 
via the circulatory system. 
All knife fish examined had been in captivity in the USA for 
at least one week and some had been maintained for over a year 
before examination. Therefore the possibility that the fish were 
infected in the USA exists; however, in a subsequent study 12 
green knife fish hatched and raised in captivity were found to 
be free of myxosporidans, indicating that the fish become in-
fected in their native waters. 
Further studies of myxosporidans from the brain of Eige-
mannia virescens are warranted. The identification and descrip-
tion of vegetative stages remain to be done, as well as electron 
microscopy of spores of Henneguya theca sp. n. to elucidate the 
structure of the sheath that surrounds them. 
LITERATURE CITED 
1. Bond, F. F. 1938. Cnidosporidia from Fundulus heteroclitus L. 
Trans. Am. Microscop. Soc., 57: 107-122. 
2. Bykhovskaya-Pavalovskaya, I. E., et a!. 1962 (1964). Key to the 
parasites of freshwater fish of the USSR (Opredelitel') Parazitov Pres-
novoknyh Ryb SSSR, Zoological Institute Moskova-Leningrad) 1964 
(Eng. trans!.) TT64-11040, US Department of Commerce, Off. Tech-
nical Service, Springfield, Virginia. 
3. Da Cunha, A. M. & Da Fonseca, O. 1918. Estudos sobre Mix-
osporideos de peixes do Brasile. Ann. VIII Congr. Bras. Med. (Rio de 
J.),1: 691-695. 
4. Dunkerly, J. S. 1915. Agarella gracilis, a new genus and species 
of myxosporidan parasitic in Lepidosiren paradoxa. Proc. R. Phys. Soc. 
Edinb., 19: 213-219. 
5. Guimaraes, J. R. A. 1931. Myxsporideos da ichtiofauna brasi-
leira. Tese de Doutoramento, Faculdade de Medicina de Sao Paulo. 
University of Sao Paulo. 
6. --- 1934. Henneguya santae sp. n. Urn novo mixosporideo 
parasito de Tetragnopterus sp. Rev. Ind. Anim., 2: 110-113. 
7. Gurley, R. R. 1894. The Myxsporidia, or Psorosperms of Fishes, 
and the Epidemics produced by Them. US Comm. ofFish and Fisheries. 
Report for 1892: 65-304. 
8. Humason, G. L. 1979. Animal Tissue Techniques. W. H. Free-
man, San Francisco. 
9. Jakowska, S. & Nigrelli, R. F. 1953. The pathology of myxo-
sporidiosis in the electrical eel, Electrophorus electricus (Linnaeus), caused 
94 J. PROTOZOOL., VOL. 31, NO. I, FEBRUARY 1984 
by Henneguya visceralis and H. electrica spp. nov. Zoologica (NY), 38: 
183-191. 
10. Kudo, R. R. 1966. Protozoology. Charles C Thomas Publ., 
Springfield, Illinois. 
II. Lorn, J. 1969a. On a new taxonomic character in Myxosporidia 
as demonstrated in descriptions of two new species of Myxobolus. Folia 
Parasito/. (Prague), 16: 97-103. 
12. --- 1969b. Cold-blooded immunity to protozoa, in Jackson, 
J. A, ed., Immunity to Parasitic Animals, Appleton-Century-Crofts, 
New York, I: 247-266. 
13. Lorn, J. & Vavra, J. 1963. Mucous envelope of spores of the 
subphylum Cnidospora (Doflein, 1901). Vestn. Cesk. Spol. Zool., 27: 
4-6. 
14. Minchew, C. D. 1977. Five new species of Henneguya (Pro-
tozoa; Myxosporida) from ictalurid fishes. J. Prototoo/., 24: 213-220. 
15. Nemeczek, A. 1926. Beitrage zur Kenntnis der Myxospori-
dienfauna Brasiliens. Arch. Protistenkd., 54: 137-150. 
16. Pinto, C. 1928. Myxosporideos e outros protozoarios intesti-
J. Protozool., 31(1), 1984, pp. 94-98 
© 1984 by the Society of Protozoologists 
naes de peixes observados na America do SuI. Arch. Inst. Bioi., Sao 
Paulo, 1: 101-136. 
17, Podlipaev, S. A & Schulman, S. S. 1978. The nature of the 
iodinophilous vacuole in myxsporidia. Acta Protozoo/., 17: 109-124. 
18. Walliker, D. 1968. The nature of the iodinophilous vacuole of 
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Received 4 III 82; accepted 8 VI 83 


Two New Species of Myxozoa, \u3ci\u3eMyxobolus inaequus\u3c/i\u3e sp. n. and \u3ci\u3eHenneguya theca\u3c/i\u3e sp. n. from the Brain of a South American Knife Fish, \u3ci\u3eEigemannia virescens\u3c/i\u3e (V.)

https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1138&amp;context=usfwspubs

Two New Species of Myxozoa, \u3ci\u3eMyxobolus inaequus\u3c/i\u3e sp. n. and \u3ci\u3eHenneguya theca\u3c/i\u3e sp. n. from the Brain of a South American Knife Fish, \u3ci\u3eEigemannia virescens\u3c/i\u3e (V.)

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