Evaluation of fish meal replacement by Clostridium autoethanogenum protein in diets for juvenile red swamp crayfish (Procambarus clarkii)

A study was conducted to investigate the potential use of Clostridium autoethanogenum protein (CAP) replacing fish meal (FM) in the diet of red swamp crayfish (Procambarus clarkia). Crayfish were fed with FM-based diet and diets with graded levels of CAP replacing FM at 25%, 50%, 75%, and 100%, respectively. Compared to the FM group, the growth performance and feed utilization of crayfish were not significantly influenced by CAP in-clusion. The best weight gain of crayfish was observed in the 25% CAP replacement group. The content of arginine, histidine, tyrosine, cysteine, and hydroxyproline of muscle increased at first and then decreased, showing a quadratic relationship with CAP level. The activity of serum aspartate aminotransferase (AST) linearly increased, while alanine aminotransferase (ALT) firstly decreased and then increased with the increase of CAP level. The activity of serum phenoloxidase, gene expression of cyclophilin A (cypa), hemocyanin A chain-like (hem-B), and hemocyanin B chain-like (hem-B) in hepatopancreas of crayfish were increased in the 25 and 50% CAP replacement group, but were decreased at 100% replacement level. Enteritis was not observed among all the diet groups. The average length of longitudinal ridges was linearly decreased with the increment of CAP level, although it was highest in the 25% CAP replacement group. The overall structure of intestinal microbial community was similar among different experiment conditions, but Shannon and Simpson diversity indexes were quadratically influenced by CAP inclusion. Tyzzerella, Sphingomonas, and Weissella were enriched in the intestine of crayfish fed CAP diets. In conclusion, CAP replacing FM at tested levels did not impact growth performance of crayfish. CAP replacing FM at 25% and 50% improved immune response and muscle amino acid composition but depressed immunity at 100% replacement level. CAP tend to compromise intestinal histology and hepatopan-creas health, change the alpha-diversity and genus composition of intestinal microbiota. It is recommended that CAP replacing 25% FM in a diet containing 10% fish meal could achieve the optimal growth performance, immune response, amino acid composition, and intestinal histology for 6 g crayfish.