Abstract
To investigate the cause of changes occurred in the liver morphology of rainbow trout Oncorhynchus mykiss, fed defatted soybean meal (SBM)-based non-fish meal diets, a casein-based semi-purified diet supplemented with cholestyramine (CH) and a soy protein concentrate-based diet supplemented with soya saponin and soya isoflavone (SPC+Sa+I) were fed to rainbow trout for 10 weeks. An unsupplemented casein-based diet (Cont), an unsupplemented SPC-based diet (SPC) and a SBM-based diet were also tested as references. Five of seven liver samples from fish fed a SBM-based diet showed severe morphological change (e.g., atrophy of hepatocytes). Only one of seven liver samples from fish fed diet SPC showed the severe morphological changes. However, five liver samples from this diet group showed normal features observed in fish fed diet Cont. Three of seven liver samples from fish fed diet CH and diet SPC+Sa+I showed the severe morphological changes, although three liver samples from these diet groups showed normal features. These results suggest that a combined effect of alcohol soluble substances such as soya saponin and an unidentified substance in SPC having bile acid binding ability like cholestyramine is probably responsible for the occurrence of atrophy of hepatocytes in rainbow trout fed SBM-based diets.
