The development of a non-lethal diagnostic tool for the diagnosis of Ichthyophonus hoferi  

Ichthyophonus hoferi has been diagnosed at the Two Oceans Aquarium. Ichthyophonus is a mesomycetozoan parasite that multiplies in blood rich organs in the fish host causing a wide range of clinical signs relating to organ dysfunction. Ichthyophonus can be diagnosed from microscopic examination of tissue squash prep, culture or PCR. In the literature only lethal methods of diagnosis are described. The development of a non-lethal diagnostic tool for disease monitoring is vital for collections where sacrifice of specimens is not possible. Liver biopsies were obtained from (n=30) White Stumpnose (Rhabdosargus globiceps) comparing two surgical methods, coeliotomy (n=15) and coelioscopy, (n=15), ten fish used in a control group. Biopsy material for each fish was divided into three pieces for squash preparation examination, PCR and culture. All fish were monitored for43 days post-surgery and blood samples drawn at two week intervals. After 43 days fish were euthanized for full examination of the liver, kidney, spleen and heart allowing correct assignment to one of two groups; Ichthyophonus infected fish and non-infected fish. PCR and culture of liver tissue was also performed. Preliminary results show a 64% sensitivity of the wet mount biopsy and a 38% sensitivity of biopsy in culture with a100% specificity for both. Wet mount and culture of the biopsy showed a sensitivity of 81%. Final post mortem on all organs showed 25 fish to be positive for Ichthyophonus. 5 fish were negative for Ichthyophonus in all diagnoses. Coelioscopy was less invasive and caused fewer organ adhesions than coeliotomy.