Protective effect of cutaneous antibody produced by channel catfish, Ictalurus punctatus (Rafinesque), immune to Ichthyophthirius multifiliis Fouquet on cohabited non-immune catfish.

Fish which survive a sublethal ichthyophthiriasis acquire protective immunity against Ichthyophthirius multifiliis Fouquet (Ich). This study evaluated the protective effect of cutaneous antibody secreted by channel catfish, Ictalurus punctatus (Rafinesque), immune to Ich on cohabited non-immune catfish. Non-immune and immune fish controls were separately maintained and infected with theronts. The Ich infection was assessed by scoring 0, < 50, 50-100, and > 100 trophonts fish(-1) at 5 days post-infection. The results of infection showed that cohabited fish at the ratio of 15 non-immune to two immune fish had < 50 trophonts fish(-1). Eighty per cent of the cohabited fish at the ratio of 10 non-immune to two immune fish showed 0 or < 50 trophonts fish(-1). The 76% of control non-immune fish had more than 100 trophonts fish(-1). The control immune fish had 0 trophonts fish(-1). Anti-Ich antibody was detected using enzyme-linked immunosorbent assay in water samples taken from tanks containing immune fish after the water samples were concentrated 40-fold. The study suggests that immune fish cohabited with non-immune fish may protect non-immune fish against Ich infection.