In April of 1990, a 1.8 kg walleye was found to contain hard cysts or nodules in the swimbladder and visceral fat. The nodules appeared to be formed around a worm-like mass. The nodules (10 ± 5 mm in diameter) were composed of five to seven layers of tightly packed granules, that were at least partially calcified and the layers were held together by a sticky matrix. The outer coat of the nodule was convoluted with many protuberances. This is a first report of such cysts from fish and they appear to be similar to nodules induced by worms (encysted nematodes) in the intestines of swine and ruminants

Mitchell, Andrew J.

Oates, David W.

English

DigitalCommons@University of Nebraska

University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Transactions of the Nebraska Academy of Sciences and Affiliated Societies Nebraska Academy of Sciences 2004 NODULAR MASSES IN THE SWIMBLADDER AND VISCERAL FAT OF THE WALLEYE, STIZOSTEDION VITREUM Andrew J. Mitchell USDA-ARS, dmitchell@spa.ars.usda.gov David W. Oates Nebraska Game and Parks Commission Follow this and additional works at: https://digitalcommons.unl.edu/tnas  Part of the Life Sciences Commons Mitchell, Andrew J. and Oates, David W., "NODULAR MASSES IN THE SWIMBLADDER AND VISCERAL FAT OF THE WALLEYE, STIZOSTEDION VITREUM" (2004). Transactions of the Nebraska Academy of Sciences and Affiliated Societies. 15. https://digitalcommons.unl.edu/tnas/15 This Article is brought to you for free and open access by the Nebraska Academy of Sciences at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Transactions of the Nebraska Academy of Sciences and Affiliated Societies by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. 2004. Transactions of the Nebraska Academy of Sciences 29: 25-27 NODULAR MASSES IN THE SWIMBLADDER AND VISCERAL FAT OF THE WALLEYE, STIZOSTEDION VITREUM Andrew J. Mitchell1 and David W. Oates2 1 Harry K. Dupree Stuttgart National Aquaculture Research Center Agricultural Research Service/United States Department Agriculture Stuttgart, Arkansas 72160 email: dmitchell@spa.ars.usda.gov 2Nebraska Game and Parks Commission 2200 North 33rd Street Lincoln, NE, 68503 ABSTRACT In April of 1990, a 1.8 kg walleye was found to contain hard cysts or nodules in the swimbladder and visceral fat. The nodules appeared to be formed around a worm-like mass. The nodules (10 ± 5 mm in diameter) were composed of five to seven layers of tightly packed granules, that were at least partially calcified and the layers were held together by a sticky matrix. The outer coat of the nodule was convoluted with many protuberances. This is a first report of such cysts from fish and they appear to be similar to nodules induced by worms (encysted nematodes) in the intestines of swine and ruminants. t t t This paper describes an unusual disease condition found in an adult walleye Stizostediori vitreum that was collected from the Merritt Reservoir in northwest-ern Nebraska. In April of 1990, a 1.8 kg walleye collected from Merritt Reservoir in northwestern Nebraska was fil-leted and found to contain hard, nodular, spherical masses from 5 to 15 mm (most were about 10 mm) in diameter attached to the inside of the swimbladder (Figs. lA, 1B, and 1C). These nodules or cysts had a raspberry-like appearance and several were slightly ovoid in shape. Similar but smoother nodules were also found throughout the visceral fat. Red immobile, worm-like masses (one mass from each nodule) were observed at the center of two nodules. Other nodules contained amorphous masses and a few had red blotches through-out the capsule (Figs. 2A and 2B). The nodules were composed of several layers (five to seven) of tightly packed granules held together in a sticky matrix. The layers could be peeled from one another - the inner-25 most layers were more easily separated than the more peripheral layers. The outermost layer or coat ap-peared to be thinner than the other layers. Material from the nodules reacted slowly with 10% hydrochloric acid (HCl) forming a few bubbles that suggested they were at least partially calcified. It is possible that the sticky matrix limited the HCI reaction. The two nodules with worm-like masses had inner layers surrounding and taking the shape of the mass (Fig. 2A). Successive layers tended to make the nod-ules more rounded and the outer layers contained nu-merous protuberances. Dr. Roger Herman of the Na-tional Fisheries Center, Fish Health Laboratory, Leetown, West Virginia, examined histological sections of another group of nodules from the same case and reported that they were granulomas surrounding dead worms. The internal structure of the worms was not clear but they appeared to be nematodes. These nodules, that appear to have formed around a degenerating parasite (possibly a nematode), are simi-lar to swine and ruminant nodular worm infections that are known to be caused by nematodes (Olsen 1974; Dunn 1978; Merck and Company Inc. 1998). In swine and ruminants, nematode larvae of the family Oesophagostominae become encapsulated in the course of an excessive inflammatory response by the host. The encapsulation then caseates and calcifies, enlarging into a nodule to diameters in excess of 10 mm. The nodules can cause a mechanical obstruction in the in-testine. Although none of the nodules from the walleye were found in the alimentary canal the similarity be-tween the nodules in this fish and in those of swine and ruminants is striking. 26 A. J . Mitchell and D. W. Oates Figure 1. Five to 15 mm raspberry-like nodules found in the swimbladder and visceral fat of walleye (arrows point at nodules). A. View of nodules in swimbladder and on visceral fat. B. Nodules in the swimbladder. C. Close-up showing the numerous protuberances on the outer coat of nodules in the swimbladder. There are at least 14 nematodes species reported from walleye (Hoffman 1999). One of these 14, Cystidicola lepisostei, we cannot find reported in other walleye literature however, it is interesting that other Cystidicola do parasitize the swimbladders of salmo-nids and some are known to be associated with swim bladder lesions. These lesions are described as raised ulcers (1-8 or 1-20 mm in diameter) sometimes encircled by hyperemic mucosa and occasionally with hard, ochre-colored material covering a central crater (Lankester and Smith 1980; Black 1984). The cause of these lesions, although associated with the nematodes, is listed as unknown. These lesion differ from what we observed and more importantly Cystidicola spp. para-sitize fish that are physostomous not physoclistous (wall-eye are physoclistous). Another nematode of the swimbladder, Anguilla crass us (an eel swimbladder nematode), is found in European zander Stizostedion luciopera, a sister fish, but, instead of the formation of large hard nodules, an acute inflammatory response, fibrosis, and rupture of the swimbladder is reported (Haenen and van Blanning 1990; Moravec 1994). The cause of the nodules that we report is also unknown, but if a worm-like parasite is involved nema-todes are the most likely candidates. However, repre-Nodular masses in walleye 27 development will be necessary. Also, histopathological section of the nodules might have produced evidence important in determining origin but no suitable samples are currently available. No additional cases have shown up since 1990. Personal contacts made with those who deal with walleye diseases have yielded no similar find-ings published or unpublished. ACKNOWLEDGEMENTS The authors wish to acknowledge Roger Herman of the National Fisheries Center in Leetown, West Vir-ginia for the histopathological analysis of the worms and Andrew Goodwin, Jerry Ludwig, Joe Marcino, and James Miller for review of early drafts of the manu-A script. Figure 2. A. Original drawing from the 1990 diagnostic case of the cross-section of a walleye nodule showing a single non-living worm-like mass (WL) surrounded by several layers. B. Cross cut section of a nodule showing some of the layers of tightly packed granules and a centrally located amorphous mass. sentatives from the trematoda, cestoda, and acantho-cephala are also known to be encased in cysts in fish tissues (Hoffman 1999) so it is possible that one of these could have initiated the nodule formation. In order to determine the cause of the nodules, fresh samples offish with nodules in different stages of LITERATURE CITED Black, G. A. 1984. Swimbladder lesions in lake trout (Salvelinus namaycush) associated with mature Cystidicola stigmatura (nematoda). Journal of Para-sitology 70: 441-443. Dunn, A. M. 1978. Veterinary Helminthology, 2nd edition. London, William Heinemann Medical Books Limited: 323 pp. Haenen, O. L. M., and P. Van Banning. 1990. Detec-tion of larvae of Anguillicola crassus (an eel swimbladder nematode) in freshwater fish species Aquaculture. 87: 103-109. Hoffman, G. L. 1999. Parasites of North American Freshwater Fishes. New York, Comstock Publish-ing Associates, Cornell University Press: 539 pp. Lankester, M. W., and J. D. Smith. 1980. Host specific-ity and distribution of the swim-bladder nema-todes, Cystidicola farionis Fischer, 1798 and C. cristivomeri White, 1941 (Habronematoidea), in salmonid fishes of Ontario. Canadian Journal of Zoology 58: 1298-1305. Merck and Company Inc. 1998. The Merck Veterinary Manual, 8th edition. Philadelphia, Pennsylvania, National Publishing, Inc.: 2305 pp. Moravec, F. 1994. Parasitic Nematodes of Freshwater Fishes of Europe. Praha, Academia: 473 pp. Olsen, O. W. 1974. Animal Parasites and Their Life Cycles and Ecology, 3rd edition. Baltimore, Univer-sity Park Press: 562 pp. 

NODULAR MASSES IN THE SWIMBLADDER AND VISCERAL FAT OF THE WALLEYE, \u3ci\u3eSTIZOSTEDION VITREUM\u3c/i\u3e

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University of Nebraska - Lincoln 
DigitalCommons@University of Nebraska - Lincoln 
Transactions of the Nebraska Academy of 
Sciences and Affiliated Societies Nebraska Academy of Sciences 
2004 
NODULAR MASSES IN THE SWIMBLADDER AND VISCERAL FAT 
OF THE WALLEYE, STIZOSTEDION VITREUM 
Andrew J. Mitchell 
USDA-ARS, dmitchell@spa.ars.usda.gov 
David W. Oates 
Nebraska Game and Parks Commission 
Follow this and additional works at: https://digitalcommons.unl.edu/tnas 
 Part of the Life Sciences Commons 
Mitchell, Andrew J. and Oates, David W., "NODULAR MASSES IN THE SWIMBLADDER AND VISCERAL FAT 
OF THE WALLEYE, STIZOSTEDION VITREUM" (2004). Transactions of the Nebraska Academy of Sciences 
and Affiliated Societies. 15. 
https://digitalcommons.unl.edu/tnas/15 
This Article is brought to you for free and open access by the Nebraska Academy of Sciences at 
DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Transactions of the 
Nebraska Academy of Sciences and Affiliated Societies by an authorized administrator of 
DigitalCommons@University of Nebraska - Lincoln. 
2004. Transactions of the Nebraska Academy of Sciences 29: 25-27 
NODULAR MASSES IN THE SWIMBLADDER AND VISCERAL FAT 
OF THE WALLEYE, STIZOSTEDION VITREUM 
Andrew J. Mitchell1 and David W. Oates2 
1 Harry K. Dupree Stuttgart National Aquaculture Research Center 
Agricultural Research Service/United States Department Agriculture 
Stuttgart, Arkansas 72160 
email: dmitchell@spa.ars.usda.gov 
2Nebraska Game and Parks Commission 
2200 North 33rd Street 
Lincoln, NE, 68503 
ABSTRACT 
In April of 1990, a 1.8 kg walleye was found to contain 
hard cysts or nodules in the swimbladder and visceral fat. 
The nodules appeared to be formed around a worm-like mass. 
The nodules (10 ± 5 mm in diameter) were composed of five to 
seven layers of tightly packed granules, that were at least 
partially calcified and the layers were held together by a 
sticky matrix. The outer coat of the nodule was convoluted 
with many protuberances. This is a first report of such cysts 
from fish and they appear to be similar to nodules induced by 
worms (encysted nematodes) in the intestines of swine and 
ruminants. 
t t t 
This paper describes an unusual disease condition 
found in an adult walleye Stizostediori vitreum that 
was collected from the Merritt Reservoir in northwest-
ern Nebraska. 
In April of 1990, a 1.8 kg walleye collected from 
Merritt Reservoir in northwestern Nebraska was fil-
leted and found to contain hard, nodular, spherical 
masses from 5 to 15 mm (most were about 10 mm) in 
diameter attached to the inside of the swimbladder 
(Figs. lA, 1B, and 1C). These nodules or cysts had a 
raspberry-like appearance and several were slightly 
ovoid in shape. Similar but smoother nodules were also 
found throughout the visceral fat. Red immobile, worm-
like masses (one mass from each nodule) were observed 
at the center of two nodules. Other nodules contained 
amorphous masses and a few had red blotches through-
out the capsule (Figs. 2A and 2B). The nodules were 
composed of several layers (five to seven) of tightly 
packed granules held together in a sticky matrix. The 
layers could be peeled from one another - the inner-
25 
most layers were more easily separated than the more 
peripheral layers. The outermost layer or coat ap-
peared to be thinner than the other layers. Material 
from the nodules reacted slowly with 10% hydrochloric 
acid (HCl) forming a few bubbles that suggested they 
were at least partially calcified. It is possible that the 
sticky matrix limited the HCI reaction. 
The two nodules with worm-like masses had inner 
layers surrounding and taking the shape of the mass 
(Fig. 2A). Successive layers tended to make the nod-
ules more rounded and the outer layers contained nu-
merous protuberances. Dr. Roger Herman of the Na-
tional Fisheries Center, Fish Health Laboratory, 
Leetown, West Virginia, examined histological sections 
of another group of nodules from the same case and 
reported that they were granulomas surrounding dead 
worms. The internal structure of the worms was not 
clear but they appeared to be nematodes. 
These nodules, that appear to have formed around 
a degenerating parasite (possibly a nematode), are simi-
lar to swine and ruminant nodular worm infections 
that are known to be caused by nematodes (Olsen 1974; 
Dunn 1978; Merck and Company Inc. 1998). In swine 
and ruminants, nematode larvae of the family 
Oesophagostominae become encapsulated in the course 
of an excessive inflammatory response by the host. The 
encapsulation then caseates and calcifies, enlarging 
into a nodule to diameters in excess of 10 mm. The 
nodules can cause a mechanical obstruction in the in-
testine. Although none of the nodules from the walleye 
were found in the alimentary canal the similarity be-
tween the nodules in this fish and in those of swine and 
ruminants is striking. 
26 A. J . Mitchell and D. W. Oates 
Figure 1. Five to 15 mm raspberry-like nodules found in the swimbladder and visceral fat of walleye (arrows point at nodules). 
A. View of nodules in swimbladder and on visceral fat. B. Nodules in the swimbladder. C. Close-up showing the numerous 
protuberances on the outer coat of nodules in the swimbladder. 
There are at least 14 nematodes species reported 
from walleye (Hoffman 1999). One of these 14, 
Cystidicola lepisostei, we cannot find reported in other 
walleye literature however, it is interesting that other 
Cystidicola do parasitize the swimbladders of salmo-
nids and some are known to be associated with 
swim bladder lesions. These lesions are described as 
raised ulcers (1-8 or 1-20 mm in diameter) sometimes 
encircled by hyperemic mucosa and occasionally with 
hard, ochre-colored material covering a central crater 
(Lankester and Smith 1980; Black 1984). The cause of 
these lesions, although associated with the nematodes, 
is listed as unknown. These lesion differ from what we 
observed and more importantly Cystidicola spp. para-
sitize fish that are physostomous not physoclistous (wall-
eye are physoclistous). Another nematode of the 
swimbladder, Anguilla crass us (an eel swimbladder 
nematode), is found in European zander Stizostedion 
luciopera, a sister fish, but, instead of the formation of 
large hard nodules, an acute inflammatory response, 
fibrosis, and rupture of the swimbladder is reported 
(Haenen and van Blanning 1990; Moravec 1994). 
The cause of the nodules that we report is also 
unknown, but if a worm-like parasite is involved nema-
todes are the most likely candidates. However, repre-
Nodular masses in walleye 27 
development will be necessary. Also, histopathological 
section of the nodules might have produced evidence 
important in determining origin but no suitable samples 
are currently available. No additional cases have shown 
up since 1990. Personal contacts made with those who 
deal with walleye diseases have yielded no similar find-
ings published or unpublished. 
ACKNOWLEDGEMENTS 
The authors wish to acknowledge Roger Herman of 
the National Fisheries Center in Leetown, West Vir-
ginia for the histopathological analysis of the worms 
and Andrew Goodwin, Jerry Ludwig, Joe Marcino, and 
James Miller for review of early drafts of the manu-
A script. 
Figure 2. A. Original drawing from the 1990 diagnostic case 
of the cross-section of a walleye nodule showing a single non-
living worm-like mass (WL) surrounded by several layers. B. 
Cross cut section of a nodule showing some of the layers of 
tightly packed granules and a centrally located amorphous 
mass. 
sentatives from the trematoda, cestoda, and acantho-
cephala are also known to be encased in cysts in fish 
tissues (Hoffman 1999) so it is possible that one of 
these could have initiated the nodule formation. 
In order to determine the cause of the nodules, 
fresh samples offish with nodules in different stages of 
LITERATURE CITED 
Black, G. A. 1984. Swimbladder lesions in lake trout 
(Salvelinus namaycush) associated with mature 
Cystidicola stigmatura (nematoda). Journal of Para-
sitology 70: 441-443. 
Dunn, A. M. 1978. Veterinary Helminthology, 2nd 
edition. London, William Heinemann Medical Books 
Limited: 323 pp. 
Haenen, O. L. M., and P. Van Banning. 1990. Detec-
tion of larvae of Anguillicola crassus (an eel 
swimbladder nematode) in freshwater fish species 
Aquaculture. 87: 103-109. 
Hoffman, G. L. 1999. Parasites of North American 
Freshwater Fishes. New York, Comstock Publish-
ing Associates, Cornell University Press: 539 pp. 
Lankester, M. W., and J. D. Smith. 1980. Host specific-
ity and distribution of the swim-bladder nema-
todes, Cystidicola farionis Fischer, 1798 and C. 
cristivomeri White, 1941 (Habronematoidea), in 
salmonid fishes of Ontario. Canadian Journal of 
Zoology 58: 1298-1305. 
Merck and Company Inc. 1998. The Merck Veterinary 
Manual, 8th edition. Philadelphia, Pennsylvania, 
National Publishing, Inc.: 2305 pp. 
Moravec, F. 1994. Parasitic Nematodes of Freshwater 
Fishes of Europe. Praha, Academia: 473 pp. 
Olsen, O. W. 1974. Animal Parasites and Their Life 
Cycles and Ecology, 3rd edition. Baltimore, Univer-
sity Park Press: 562 pp. 


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NODULAR MASSES IN THE SWIMBLADDER AND VISCERAL FAT OF THE WALLEYE, \u3ci\u3eSTIZOSTEDION VITREUM\u3c/i\u3e

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