Abstract
A 90-day feeding trial was conducted to evaluate the effects of Clostridium autoethanogenum protein (CAP) replacing dietary fishmeal on growth, feed utilization, intestinal health and muscle quality of large yellow croaker (Initial body weight: 189.9 ± 1.11 g). The control diet (CAP0) contains 62% fishmeal, which was replaced with CAP at 15% (CAP15), 30% (CAP30), 45% (CAP45), 60% (CAP60), 75% (CAP75) and 100% (CAP100), respectively. Results showed that the weight gain rate, protein efficiency ratio, feed intake, condition factor and intestinal villus height of fish significantly decreased when the replacement level of dietary fishmeal by CAP exceeded 30%, while feed conversion ratio increased significantly in the CAP60, CAP75 and CAP100 treatments (P < 0.05). Increasing replacement levels of dietary fishmeal by CAP linearly decreased the activities of intestinal digestive and absorptive enzymes (P < 0.05). In addition, the mRNA expression level of intestinal peptide transporter 1 and nuclear factor κB genes was up-regulated with increasing dietary CAP level, while the intestinal peptide transporter 2, occludin-like and interleukin 10 genes was down-regulated (P < 0.05). The muscle amino acid compositions and skin color were not significantly affected by dietary CAP supplementation. Compared with those in the CAP0 group, fish in the CAP75 and CAP100 group showed a significantly lower muscle firmness, water holding capacity and myofiber diameter, and a higher myofiber density (P < 0.05). The mRNA expression of myogenic differentiation, myogenin, myogenic factor 5 and paired box 7 genes was significantly up-regulated, while the expression of myostatin gene was significantly down-regulated in the muscle of fish in the CAP75 and CAP100 group (P < 0.05). In conclusion, CAP can replace up to 30% of dietary fishmeal protein for large yellow croaker without negative effects on the growth, feed utilization, intestinal health and muscle quality.
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