The use of a soy product in juvenile yellowtail kingfish (Seriola lalandi) feeds at different water temperatures: 1. Solvent extracted soybean meal

Juvenile yellowtail kingfish (Seriola lalandi) were fed four iso-nitrogenous and iso-calorific (digestible basis) experimental diets containing 0, 10, 20 or 30% solvent extracted soybean meal (SESBM) for 34 days at optimal (22 °C) and suboptimal (18 °C) water temperatures to determine the effects of diet and water temperature on growth, feed efficiency, nutrient retention, apparent nutrient digestibility and digestive functions. The substitution of fish meal up to 20% SESBM did not significantly affect the growth of fish. No differences were detected in any of the other parameters measured between 0 and 10% inclusion. However, second-order polynomial regression demonstrated that increasing SESBM had a negative effect on growth performance, feed efficiency, nutrient retention and the apparent nutrient and energy digestibility of diets for yellowtail kingfish. Whole body moisture, crude lipid, ash and gross energy were affected by SESBM in the diet, except protein. The apparent nutrient and energy digestibilities all decreased linearly with increasing SESBM. Digestive enzyme activities in the pyloric caeca were not affected by diet, whereas activities in the foregut and hindgut varied with SESBM inclusion. Fish held at 18 °C had significantly reduced growth, feed efficiency and nutrient retention values. The whole body moisture increased at 18 °C, while the apparent nutrient and energy digestibilities and whole body protein and gross energy content were lower at 18 °C and there was no effect of temperature on whole body total fat or ash content. The impact of temperature on digestive enzyme activities depended on the section of the digestive tract. This study demonstrates that 10% inclusion of SESBM (21.7% fish meal substitution) can be used as a substitute for fish meal in diets for yellowtail kingfish.

► Substitution of fish meal with solvent extracted soybean meal leads to poor fish growth. ► Dietary solvent extracted soybean meal inclusion reduced growth and nutrient digestibilities. ► Abnormal histological gut morphology possibly compromised gut integrity. ► Digestive enzyme activities depend on diet, temperature and digestive tract section. ► 10% solvent extracted soybean meal is acceptable in diets for yellowtail kingfish.