This study was aimed to evaluate the effects of dietary supplementation of Bacillus cereus as probiotics on growth, fillet quality, serum biochemical parameters and intestinal histology of Pengze crucian carp (Carassius auratus var. Pengze). Fish were fed basic diet (Control group) and three diets such as CD7, CD9 and CD11 supplemented with B. cereus at dose of 10⁷, 10⁹ and 10¹¹ CFU/kg for 70 days. The results showed that supplementation of 10⁹ CFU/kg B. cereus significantly improved the growth performance compared to that in the Control group. The textures of muscle were improved by dietary supplementation of probiotics, and the hardness, gumminess, chewiness and the resilience of fish fillet increased with increasing dose of B. cereus. Total cholesterol including high‐density lipoprotein and low‐density lipoprotein level in serum decreased correspondingly with increasing level of probiotics whereas, acid phosphatase and catalase activities increased in serum. B. cereus supplementation enhanced the immunity and antioxidant capacity via an increase in acid phosphatase, alkaline phosphatase, glutathione peroxidase, reduce glutathione, and catalase, accompanied by a significant reduction in malondialdehyde. Higher intestinal fold height was observed in CD9 group than other groups. The lowest enterocyte height was exhibited in the Control group, HE values increased with increasing dose of probiotics. Moreover, dietary inclusion of B. cereus significantly affected the digestive enzymes activities in terms of higher lipase and trypase activities. In conclusion, dietary supplementation of B. cereus could promote the growth, elevate the immunity and antioxidant status of carp, and importantly improve the texture of fish fillet.

Goal of this research is to explore the effects of graded dietary levels of hydrolysed feather meal (HFM) protein as an alternative of fishmeal protein on Pengze crucian carp (Carassius auratus var. Pengze). Five isonitrogenous (35% crude protein) diets were formulated as Control diet and four other diets F15, F30, F45 and F60 wherein 15%, 30%, 45% and 60% fishmeal protein replaced by HFM protein fed for 70 days. The results showed that fish growth was unaffected up to 45% fishmeal protein replacement. Dietary HFM protein could reduce the crude protein composition of body and further affect fillet quality through a significant increase in springiness, gumminess, chewiness and/or resilience. Activity of digestive enzymes (amylase, lipase and tryptase) increased as the fishmeal protein replacement increased, whereas a higher replacement level had negative impacts on absorptive capacity of intestine by decreasing its absorptive area, following by a reduction in concentration of lactate dehydrogenase, total cholesterol, high‐density lipoprotein, low‐density lipoprotein and ammonia in serum. Although intestinal antioxidant parameters were elevated by dietary HFM protein, the content of malondialdehyde in intestine was also positively associated with the protein replacement level. Overall, our results indicate that up to 45% of fishmeal protein could be replaced by HFM protein in diet without significant impact on the growth of Pengze crucian carp, whereas the crude protein content of whole body, fillet quality and oxidative status would significantly be affected when the replacement level of fishmeal protein reaches 30% together with a negative effect on the intestinal histology.