Effects of substituting dietary fish meal with soybean meal isolate on growth performance, digestive enzyme activity, and intestinal morphology of spotted seabass (<em>Lateolabrax maculatus</em>)

Abstract

Soy protein isolate (SPI) is a promising plant protein source to replace fish meal (FM) in aquatic feeds. This study investigated the growth performance, digestive enzyme activity, and intestinal morphology of spotted seabass (Lateolabrax maculatus) fed diets with FM partially substituted by SPI. Three iso-nitrogenous and iso-lipidic diets were formulated to replace 0, 25, and 50% of FM with SPI, being abbreviated as FM, SPI25, and SPI50, respectively. Each diet was allocated to triplicates of fish for 8 weeks. The results indicated that the weight gain was gradually reduced with increasing dietary SPI levels, as did intestinal trypsin and lipase activities. However, these traits were not significantly decreased until 50% of FM was substituted by SPI. Furthermore, feed intake and lipid digestibility significantly decreased with dietary SPI inclusion. Moreover, replacing 50% of dietary FM with SPI significantly reduced the intestinal villus height and perimeter ratio, whereas these traits did not markedly differ between FM and SPI25 groups. In conclusion, this study indicated that up to 25% of dietary FM could be substituted with SPI without significantly affecting the growth, digestive enzyme activity, or intestinal morphology in spotted seabass.