Effect of gamma irradiation on inactivation of Ichthyophthirius multifiliis trophonts and its efficacy on host response in experimentally immunized rainbow trout (Oncorhynchus mykiss)

The present study was conducted to investigate the effects of gamma irradiation on Ichthyophthirius multifiliis trophonts and to determine the effects of exposure on inactivated parasites in rainbow trout. In the first trial, fish were treated with irradiated Ichthyophthirius multifiliis trophonts for 21 days. Results showed that irradiation at doses of 150 Gy and higher was required to inactivate Ichthyophthirius multifiliis trophonts. The LD50 value obtained was 52.2 Gy. In the second trial, the effects of irradiated Ichthyophthirius multifiliis trophonts on physiological and biochemical components of blood and mucus, as well as skin morphology, were studied for 30 days. Results showed that total protein levels increased in fish exposed to 100 and 150 Gy irradiated trophonts. Fish exposed to 150 Gy treated parasites showed significant increases in serum lysozyme activity. Serum alkaline phosphatase levels were significantly lower in the treatment groups. In the skins of fish exposed to 100 and 150 Gy irradiated trophonts, a higher percentage of goblet cells was observed. Mucus protease and esterase levels were also higher in the treatment groups compared to the control group on days 20 and 30. This suggests that rainbow trout appear to benefit from treatment with gamma-irradiated Ichthyophthirius multifiliis trophonts, especially at 150 Gy.