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 alcoho l extracts (PAES) from soybean meal (PAES I) and soy protein isolate ( PAES II) on feed intake, growth and intestinal mucosa of chinook salmo n and rainbow trout. The PAES were prepared by an extraction process a iming at the isolation of soyasaponins. In the first study, a series o f diets were formulated to have one half of the protein coming from fi sh 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 P AES 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 suppl emented with Quillaja bark saponin at 0.15% (QBS15 diet) and 0.30% (QB S30 diet). Feeding the PAES I diet and the SBM diet resulted in comple te suppression of growth of chinook salmon due to a dramatic reduction of feed intake (P < 0.05), The PAES I diet significantly depressed th e growth of rainbow trout (P < 0.05). Feeding the QBS30 diet, but not the QBS15 diet, significantly depressed growth of chinook salmon and r ainbow trout (P < 0.05), Both the QBS15 and QBS30 diets caused signifi cant intestinal damage. The PAES I diet had only a minimal effect on t he intestinal mucosa of rainbow trout. The majority of the chinook sal mon 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 h igh fish meal diet was supplemented with 0.3% PAES II and fed to chino ok salmon and rainbow trout. The PAES II diet had a highly significant effect on feed intake and growth of chinook salmon. This tended to re duce growth of rainbow trout although not significantly. The effect on feed intake of chinook salmon was statistically significant on the th ird 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 a re responsible for the effect of these PAES. (C) 1998 Elsevier Science B.V.