Effects of Substituting Fish Meal with Two Types of Soybean Meal on Growth, Enzyme Activities, and Intestinal Morphology in Juvenile Rhynchocypris lagowskii

This study evaluated the effects of substituting fish meal with common soybean meal (SBM) or extruded soybean meal (ESBM) on growth, digestion, some nonspecific immune markers, and intestinal morphology in juvenile minnow Rhynchocypris lagowskii. In trial 1, five experimental diets were formulated with SBM replacing 0% (fish meal control; SBM0), 12.5% (SBM12.5), 25.0% (SBM25), 37.5% (SBM37.5), and 50.0% (SBM50) of the fish meal. Rhynchocypris lagowskii (6.81 +/- 0.19 g) were randomly stocked in 100-L cylindrical plastic tanks and fed to satiation thrice daily for 56 d. After the feeding trial, there was no significant differences in weight gain ratio (WGR), specific growth rate (SGR), feed efficiency ratio (FER) and protein efficiency ratio (PER), feed conversion ratio (FCR), and feed intake (FI) of the SBM0, SBM12.5, and SBM25 groups. But compared with the control group, WGR, SGR, and FI of the SBM37.5 and SBM50 groups were significantly decreased, FER and PER of the SBM50 group were significantly decreased, and FCR of the SBM50 group was significantly increased. Providing the SBM37.5 and SBM50 diets can significantly reduce the muscle protein content and protease activity of the hepatopancreas and intestine. Aspartate aminotransferase, alanine aminotransferase, lysozyme, and superoxide dismutase activities in the hepatopancreas decreased with increasing dietary SBM levels. Providing the SBM25, SBM37.5, and SBM50 diets caused atrophy, swelling, and rupture of the intestinal mucosal fold and separation of epithelial mucosa from the lamina propria. In trial 2, five experimental diets were formulated with ESBM replacing 0% (fish meal control; ESBM0), 12.5% (ESBM12.5), 25.0% (ESBM25), 37.5% (ESBM37.5), and 50.0% (ESBM50) of the fish meal. Rhynchocypris lagowskii (6.87 +/- 0.02 g) were randomly stocked in 100-L cylindrical plastic tanks and fed to satiation thrice daily for 56 d. After the feeding trial, WGR, FI, SGR, FER, PER, and muscle crude protein content of the ESBM50 group were significantly decreased compared with the control group, and FCR of the ESBM50 group was significantly increased. Meanwhile, the hepatopancreas and intestinal protease activities and the hepatopancreas superoxide dismutase, lysozyme, aspartate aminotransferase, and alanine aminotransferase activities decreased with increasing dietary ESBM levels, and the ESBM50 group was significantly different than the control group. Providing the ESBM37.5 and ESBM50 diets caused atrophy and rupture of intestinal mucosal fold and separation of epithelial mucosa from the lamina propria. These results indicated that SBM could replace 12.5% of fish meal in juvenile R. lagowskii diets, while ESBM could replace 25% of fish meal.

Automated summary

The study indicated that soybean meal could partially replace fish meal in juvenile R. lagowskii diets, with an optimal replacement ratio. However, high levels of soybean meal substitution had negative effects on the growth and digestion of juvenile R. lagowskii.