Replacement of dietary fish meal with Clostridium autoethanogenum protein on growth performance, digestion, mTOR pathways and muscle quality of abalone Haliotis discus hannai

The present study was conducted to evaluate the replacement of dietary fish meal (FM) with Clostridium autoethanogenum protein (CAP) on abalone Haliotis discus hannai. Five isonitrogenous and isolipidic experimental diets with graded levels of FM replaced by CAP (0, 25, 50, 75 and 100%, respectively) were fed to abalone (initial weight: 21.83 +/- 0.25 g) for 110 days. The five diets were named as CAP0, CAP25, CAP50, CAP75 and CAP100, respectively. The results showed that total replacement of dietary FM by CAP did not significantly affect the growth of abalone compared with the control. The highest weight gain rate was observed in the CAP25 group. Compared to the CAP0 group, the CAP25 group also had significantly higher total essential amino acids content in muscle and trypsin activity in digestive gland. The expressions of mammalian target of rapamycin, phosphatidylinositol 3-kinase and threonine kinase/protein B were significantly upregulated, and the expression of AMP-activated protein kinase alpha 2 was significantly downregulated in the muscle of abalone in the CAP25 and CAP50 groups. The crude protein content, hardness, hydroxyproline content, pH value, pyridinium crosslink content, activities of lysyl hydroxylase and prolyl 4-hydroxylase in muscle were significantly elevated in the CAP25 and CAP50 groups. Considering the growth performance, digestion, mTOR pathways and muscle quality, 25% replacement of dietary FM by CAP (4.1% of dietary CAP inclusion level) was recommended for abalone.