Abstract
A case report of an outbreak of coccidiosis in juvenile aquarium-reared three spot gouramis (Trichogaster trichopterus) is presented. The experimental infection through two serial passages is described. In the spontaneous infection, mortality exceeded 50 per cent in both untreated and treated fish. Adult gouramis and other aquarium species in the infected tank were unaffected. Treatments with terramycin, chloramphenicol and Nifurpirinol had no affect on the course of the disease. The unique features of the disease included the discharge of fully sporulated oocysts from the infected fish, the concentration of oocysts by aquaria filters, and the distinctive life cycle and lesions.
Notes
Occurrence: Coccidiosis is a common disease in blue gouramis, however, only fry get clinical disease and die.
Pathogenesis
This case report deals with the entero epithelial type of coccidiosis which tends to be localized in parts of the gut. Other forms of coccidia can affect other systems such as the air bladder or liver. In this case, mostly the foregut was involved.
The normal fish intestine is coiled and thin walled, with a folded rather than villous mucosa. The coccidia attach superficially to the mucosa and destroy it by lysis. There are no significant pathological changes in fish which are infected after becoming adults.
Diagnosis
Remove the gastrointestinal tract and fix it. Too much autolysis occurs if the entire fish is fixed. Histology reveals macro and microgametes adhered to the mucosa. Merozoites are evident between mucosal folds in the gut lumen but adhered to the mucosa. Schizonts can also be seen. Eimeria oocysts which are sporulated and infective can be found in the gut. These thin walled green hued oocysts containing four sporocysts are discharged into the water.
Conclusion
Coccidiosis will likely be an important disease in future aquaculture. It certainly is present in aquarium cyprinids. It is possible that the adults are carriers which allow infection of the susceptible young.