Methionine in fish health and nutrition: Potential mechanisms, affecting factors, and future perspectives

Amino acids do not only work in protein synthesis but also act as molecular signals regulating energy meta-bolism, and the immune and antioxidant systems in animals. As an essential amino acid, crystalline methionine is widely applied in fish feed, especially when fishmeal is replaced by other alternative protein sources. To sys-tematically understand the present knowledge of methionine application and utilization in fish, this paper reviewed studies conducted on farmed fish, encompassing methionine requirements of various fish species, the potential mechanisms of methionine in regulating growth, feed utilization, lipid and glucose metabolism, anti -oxidative and immune status, and its interactions with cysteine and taurine. This review concludes that the dietary methionine requirement of fish ranges from 0.49% to 2.5% of the diet (1.49% to 4.7% of dietary protein), and the requirement is influenced by species, life stage, methionine forms, and dietary cystine and taurine levels. The lipid and glucose metabolism responses to dietary methionine differ by species, and inconsistent results were reported. In addition, there is a need for further studies on the impact of methionine on intestinal microbiota, and lipid and glucose metabolism regulated by methionine, and methionine toxicity in different fish species. Furthermore, the current trend of high plant protein and lipid inclusion in fish feed necessitates a careful reevaluation of dietary methionine requirement of certain species.

Automated summary

Amino acids play important roles in protein synthesis and also function as molecular signals in animals, regulating energy metabolism, immune response, and antioxidant systems. This review focuses on the application and utilization of methionine in fish feed, including its effects on growth, feed utilization, lipid and glucose metabolism, immune status, and interaction with other amino acids. The review concludes that methionine requirement in fish varies depending on species, life stage, and dietary composition, and further research is needed to study its impact on intestinal microbiota and potential toxicity.