Growth performance, antioxidant status and immune response in darkbarbel catfish Pelteobagrus vachelli fed different PUFA/vitamin E dietary levels and exposed to high or low ammonia

Triplicate groups of juvenile darkbarbel catfish (0.99 ± 0.01 g) were fed three levels of linseed oil (2, 4 and 6%) rich in polyunsaturated fatty acids (PUFAs) and three levels of vitamin E (50, 200 and 400 mg/kg diet) for 60 days under two ammonia concentrations (0.01 and 5.70 mg/L total ammonia nitrogen, TA-N). Growth performance, immune response and pathogen resistance of fish were higher in fish under low ammonia conditions. Under high ammonia, fish fed 400 mg/kg vitamin E showed higher growth performance and immune response. Blood status and immune responses were improved in fish fed 6% linseed oil. However, fish fed 2% linseed oil or 400 mg/kg vitamin E showed a lower level of malondialdehyde regardless of ammonia levels. After 14 days infection of Edwardsiella ictaluri, cumulative mortality was lowest when fish were exposed to high ammonia and fed on 4-6% linseed oil. Fish fed 6% linseed oil or 400 mg/kg vitamin E yielded a higher level of antibody titer regardless of ammonia addition. This study indicates that the harmful effects of ammonia on fish can be mitigated when fish are fed on 2% linseed oil and 400 mg/kg vitamin E.