Effect of soybean meal, raffinose and stachyose on the growth, body composition, intestinal morphology and intestinal microflora of juvenile allogynogenetic silver crucian carp (Carassius auratus gibelio♀ x Cyprinus carpio♂)

The study was conducted to investigate the effects of soybean meal (SBM), raffinose and stachyose on juvenile crucian carp (Carassius auratus gibelio? x Cyprinus carpio?). The experimental diets consisted of one control diet based on fish meal (FM), one diet containing 300 g kg-1 SBM and four FM-based diets with the addition of either 6.7 g kg-1 raffinose (Raf), 33.9 g kg-1 stachyose (Sta), a combination of raffinose and stachyose (Raf-Sta) and finally a Raf-Sta diet supplemented with 2.5 g kg-1 saponins (Raf-Sta-Sap). After 3 weeks of feeding, the relative gut lengths of SBM-fed fish and the fish fed stachyose-containing diets were shorter than those of the FM-fed fish; further, more SBM-fed fish showed fissures on the tips of the intestinal folds. After 8 weeks of feeding, the growth of SBM-fed fish was significantly lower than that of FM-fed fish (P<0.05). The fish fed Raf-Sta-Sap had a low relative gut length (P<0.05). In comparison with the other fish, the SBM-fed fish had a higher number of large-sized homogeneous vacuoles in the cytoplasm of epithelial cells and shorter microvilli. No significant difference was observed in body composition or intestinal microflora. The results indicated that raffinose and stachyose played no or only minor roles in the development of soybean-induced growth reduction.