Effects of alanine supplementation on the growth, biochemical composition and appetite of ivory shell (Babylonia areolata)

Abstract

Alanine has been shown to significantly promote feeding behavior in aquatic animals, particularly fish. Our preliminary experiment showed that dietary supplementation with alanine notably enhanced the appetite of ivory shells; therefore, we inferred that alanine could be used as feed attractant in artificial diets of ivory shells. This study conducted an 8-week feeding trial to investigate the effects of various levels of alanine supplementation (0.0% as the control group, 2.0, 2.5, 3.0, 3.5, and 4.0%) on the growth performance, body biochemical composition, and appetite in juvenile ivory shell. The results indicated that alanine supplementation significantly improved the specific growth rates (SGRs) and total feed intake (TFI) of the ivory shells, with statistically significant differences observed (P < 0.05). As the alanine supplementation increased, SGRs rose markedly, peaking in the group fed a 3.5% alanine-supplemented diet (2.56%/day). At this supplementation level, TFI reached 7.31 g, and the feed conversion ratio (FCR) decreased to its lowest value of 1.32. Alanine supplementation did not alter intestinal pepsin activity but significantly increased pepsin activity in the hepatopancreas of groups supplemented with 2.5–4.0% alanine. Additionally, alanine supplementation led to a marked elevation in lipase activities in both the intestines and hepatopancreas. Specifically, significantly higher lipase activities were observed in the intestines of groups supplemented with 2.5–3.5% alanine and in the hepatopancreas of groups supplemented with 2.0–3.5% alanine. Alanine supplementation also affected the expression of four appetite-related genes in the hepatopancreas, in which Orexin and NPY showed an initial increase followed by a decrease, while Leptin and Cholecystokinin exhibited a downward trend followed by an increase as alanine supplementation levels increased. The ivory shells fed alanine-supplemented diets showed a significant increase in the crude protein and glycogen content in their muscles compared to the control group, and the content of seven amino acids in the muscles of the groups supplemented with 3.0–3.5% alanine also increased significantly (P < 0.05). The lipid content did not differ significantly between the control group and the alanine-supplemented diet groups, with the exception of the 4.0% group. In contrast, the profile of PUFA in the alanine-supplemented diet groups showed a significant decrease compared to the control group (P < 0.05). In conclusion, appropriate alanine supplementation levels (3.0–3.5%) have beneficial effects on the cultivation of ivory shells.