RESPONSE OF RAINBOW-TROUT TO SOY LECITHIN, CHOLINE, AND AUTOCLAVED ISOLATED SOY PROTEIN

Fry of rainbow trout (Oncorhynchus mykiss) were fed, from first feeding (mean weight, 0.12 g), basal diets containing either a nonautoclaved (raw) sodium proteinate form of isolated soy protein (ISP) or the same ISP autoclaved at 0.56 kg/cm2 and 110-degrees-C for 30 min. In the three-way factorial, 16-week study, I measured the effects of autoclaving ISP on the growth, survival, and chemical composition of rainbow trout at three levels of soy lecithin (0, 4, and 8%) and two levels of choline (0 and 0.3%). Fish fed raw ISP grew no faster with or without choline than did those fed the basal diet, but those fed heated ISP with choline showed a quantitatively small but significant advantage in weight gain. Whereas fish fed 4% lecithin with raw ISP more than tripled weight gain compared with fish fed the basal diets, fish fed 4% lecithin with heated ISP grew seven times as fast as those fed no lecithin or choline. Rainbow trout fed choline and 4% lecithin with heated ISP (but not raw ISP) grew significantly faster than those fed heated ISP and 4% lecithin alone. The higher level (8%) of lecithin promoted no more growth than the 4% lecithin with either raw or heated ISP. Among rainbow trout fed heated ISP, 4 and 8% supplemental lecithin-either with or without choline-reduced mortality to the same level, but 8% lecithin was the only concentration that significantly reduced the mortality of fish fed raw ISP. The results of calorimetry and determination of nitrogen with larger (235-375 g) rainbow trout individually held in metabolism chambers indicated that autoclaved ISP enhanced the growth and survival responses of fish to lecithin by increasing digestible protein and energy and metabolizable energy. This higher amount of bioavailable energy and protein increased the deposition of body fat.