Abstract
The effects of soybean meal fermentation on the biliary bile status and intestinal and liver morphology of rainbow trout Oncorhynchus mykiss were investigated. A fish meal based diet (FM) and non-fish meal diets, composed mainly of fermented defatted soybean meal (FSBM), and of defatted soybean meal (SBM), fortified with and without essential amino acids (EAA) to simulate the EAA composition of FM diet, were prepared. Each diet was fed to five duplicate groups of rainbow trout (average body weight: 12 g) for 12 weeks. Weight gain and feed efficiency of fish fed FM diet were significantly higher than those of fish fed the non-fish meal diets. Total biliary bile acid content was lowest in fish fed SBM diets, intermediate in fish fed FSBM diets and highest in fish fed FM diet. Morphological changes occurred in the distal intestine and liver of fish fed SBM diets, although morphological features in some fish fed FSBM diets were similar to those of the FM diet. EAA supplementation to FSBM diet tended to improve the performances mentioned above. These results indicate that fermentation of soybean meal has certain effects on normalizing the biliary bile status and intestinal morphology of rainbow trout.
