Abstract

The blue-eyed plecostomus, Panaque suttoni, is a very popular and expensive fish in the tropical fish keeping hobby. This fish is native to the rivers of Colombia and Venezuela and is imported into the United States in relatively large numbers.

Microscopic examination of the kidney, liver and peripheral blood has revealed the presence of trypanosomes in several individuals of this species. Trypanosomes are commonly reported in fishes, however, very few papers involving Amazon basin fishes appear in the scientific literature. The invertebrate vector for these parasites is most likely a leech (leeches have been observed on this species of plecostomus). The clinical significance of the trypanosome infection in this species is not yet determined, as both healthy and moribund plecostomus have been found to harbor the parasites. Current investigations into the relationship between trypanosomes and P. suttoni are concentrated on: determination of the parasite complete life cycle and taxonomy, determination of the clinical importance of this infection, and identification of a safe and effective chemotherapeutic treatment for this parasitic infection.

Discussion

The blue-eyed plecostomus is a very popular fish among dedicated aquarists. The retail value of a healthy adult specimen is between thirty and fifty US dollars. These fish are native to South America and are captured and shipped to tropical fish importers in the United States, Europe and Asia. An adult of this species will measure up to 28 centimeters in length and may weigh up to 500 grams(1). These fish are not currently being raised in the commercial aquaculture industry.

Blue-eyed plecostomus consistently experience high mortality during the three week period following transcontinental shipping. Packing and shipping is stressful on fishes. Fishes shipped by air from South America to the United States experience crowding, poor water quality and temperature extremes. It is likely that these conditions stress the blue-eyed plecostomus to the point of immune compromise. Fish which become moribund nearly always die and do not respond to conventional broad spectrum antimicrobial and antiparasitic therapy. Current research is focusing on the clinical significance of these infections.

In January of 1992 a necropsy of a blue-eyed plecostomus revealed the presence of live trypanosomes in liver and kidney whole mount squash preparations. Subsequent examinations showed trypanosomes in the peripheral blood of other wild caught blue-eyed plecostomus. Random sampling of clinically healthy and moribund fish revealed the presence of live trypanosomes in seven of nine animals examined. Trypanosomes have been reported to occur naturally in many species of freshwater fishes(2,3). one study confirmed that certain species of freshwater fishes can be experimentally infected with trypanosomes (4). The work on the blue-eyed plecostomus is the first known report of a trypanosome infection in a species of fish belonging to the family Loricaridae. Blood was drawn by cardiac puncture. Whole blood samples were spun down with a centrifuge and the buffy coat was collected. Glass slide smears were made with this sample and stained with Giemsa. Tissues from necropsied animals were preserved in 10% neutrally buffered formalin. These tissues were prepared for histopathological examination and slides were stained with hematoxylin/eosin and Giemsa.

There have been several reports in the literature which have linked clinical disease and pathology with trypanosome infections in bony fishes(5,6,7,8,9). Statistically significant anemia and hemoglobinemia have been reported in goldfish, Carassius auratus,(9) and in the catfish, Heteropneustes fossilis, (6) with trypanosomiasis. Anorexia was produced in goldfish which were experimentally infected with Trypanosoma danilewskyi(8). Trypanoplasma salmositica is a flagellated protozoal parasite closely related to trypanosomes. Rainbow trout experimentally infected with T. salmositica developed hemoglobinemia, microcytic anemia, abdominal distension and exophthalmia(11). The actual mechanism for anemia in the presence of trypanosomiasis probably relates to the formation of antigen-antibody complexes forming on the surface of red blood cells and subsequent hemolysis(12). A similar mechanism is believed to be involved in cases of trypanoplasmosis(11).

Some bony fishes appear to have the ability to develop immunity to trypanosomes. Goldfish which were infected in the laboratory and survived for 190 days were completely resistant to re-infection(10). This study also proved that goldfish inoculated with very high numbers of parasites had a poor chance of survival.

At this time we are in the process of evaluating light level histopathological sections. Splenitis is common in infected fish and the spleen, kidney and liver appear to contain life stages of trypanosomes. When more fish become available, tissues will be fixed and prepared for transmission electron microscopy in order to confirm the extravascular presence of the parasites.

Future work will focus on determining the species of the parasite as well as the invertebrate vector. A controlled experiment is also planned in order to determine whether or not the observed trypanosomiasis is clinically important. If the parasites are indeed causing disease then an attempt will be made at developing a chemotherapeutic treatment protocol.

Acknowledgments

The authors thank David O'Beirne of Greenway Farms, Inc. for supplying the study animals and Dr. Ed Noga for helpful advice.

References

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