The effects of purified alcohol extracts from soy products on feed intake and growth of chinook salmon (Oncorhynchus tshawytscha) and rainbow trout (Oncorhynchus mykiss)

Two studies were conducted to determine the effects of purified alcohol extracts (PAES) from soybean meal (PAES I) and soy protein isolate (PAES II) on feed intake, growth and intestinal mucosa of chinook salmon and rainbow trout. The PAES were prepared by an extraction process aiming at the isolation of soyasaponins. In the first study, a series of diets were formulated to have one half of the protein coming from fish meal and the other half from soy products. They included a control diet containing 32% soy protein concentrate (SPC diet) and a diet with 44% soybean meal (SBM diet). The SPC diet was supplemented with the PAES I (PAES I diet) to produce a diet with a saponin level similar to that expected to be found in the SBM diet. The SPC diet was also supplemented with Quillaja bark saponin at 0.15% (QBS15 diet) and 0.30% (QBS30 diet). Feeding the PAES I diet and the SBM diet resulted in complete suppression of growth of chinook salmon due to a dramatic reduction of feed intake (P < 0.05), The PAES I diet significantly depressed the growth of rainbow trout (P < 0.05). Feeding the QBS30 diet, but not the QBS15 diet, significantly depressed growth of chinook salmon and rainbow trout (P < 0.05), Both the QBS15 and QBS30 diets caused significant intestinal damage. The PAES I diet had only a minimal effect on the intestinal mucosa of rainbow trout. The majority of the chinook salmon fed the PAES I diet had intestinal morphology representative of a fasting state which corresponded well with the observation that these fish stopped feeding early in the experiment, In the second study, a high fish meal diet was supplemented with 0.3% PAES II and fed to chinook salmon and rainbow trout. The PAES II diet had a highly significant effect on feed intake and growth of chinook salmon. This tended to reduce growth of rainbow trout although not significantly. The effect on feed intake of chinook salmon was statistically significant on the third day of feeding the PAES II diet. The two PAES diets used in these studies had potent feeding deterrent properties for chinook salmon and also affected growth of rainbow trout. We suggest that soyasaponins are responsible for the effect of these PAES. (C) 1998 Elsevier Science B.V.