Effects of alcohol extract of defatted soybean meal on growth performance and digestive physiology of yellowtail Seriola quinqueradiata

The effects of alcohol extract of soybean meal on growth performance, digestibility, and pancreatic enzyme and bile acid status of yellowtail Seriola quinqueradiata were studied. Fish were fed one of the following for 8 weeks: a fish meal (FM) control diet (FMD), a defatted soybean meal diet (SBMD), an alcohol-extracted SBM diet (ExSBMD), an ExSBMD with alcohol-extract diet (ExSBM + ExtD), and an FMD with alcohol-extract diet (FM + ExtD). Growth performance was significantly inferior in fish fed with SBM, ExSBM + ExtD, and FM + ExtD compared to FMD- or ExSBMD-fed fish. Total bile acid levels, and trypsin and lipase activities in the anterior intestine were significantly lower in fish fed with SBM, ExSBM + ExtD, and FM + ExtD than in fish fed with ExSBMD and FMD, despite similar values in gallbladder or pyloric caeca. Cholecystokinin mRNA levels of the former diet-fed fish were significantly lower than those of FMD- or ExSBMD-fed fish. Lipid and protein digestibility of fish fed with SBMD, ExSBM + ExtD, and FM + ExtD was significantly reduced in comparison with that of fish fed with FMD or ExSBMD. These findings indicate that the alcohol extract of soybean meal inhibited the secretion of bile acids and pancreatic enzymes by a decrease of cholecystokinin stimulation. This inhibition seemed to be responsible for a low growth performance through impairment of the assimilation of lipid and protein.