Li Xinyu, Han Tao, Zheng Shixuan, Wu Guoyao
Department of Animal Science, Texas A&M University, College Station, TX, USA.
Department of Aquaculture, Zhejiang Ocean University, Zhoushan, Zhejiang, China.
Adv Exp Med Biol. 2021;1285:169-198. doi: 10.1007/978-3-030-54462-1_9.
Crustaceans (e.g., shrimp and crabs) are a good source of protein-rich foods for human consumption. They are the second largest aquaculture species worldwide. Understanding the digestion of dietary protein, as well as the absorption, metabolism and functions of amino acids (AAs) and small peptides is essential to produce cost-effective and sustainable aquafeeds. Hepatopancreas (the midgut gland) is the main site for the digestion of dietary protein as well as the absorption of small peptides and AAs into the hemolymph. Besides serving as the building blocks of protein, AAs (particularly aspartate, glutamate, glutamine and alanine) are the primary metabolic fuels for the gut and extra-hepatopancreas tissues (e.g., kidneys and skeletal muscle) of crustaceans. In addition, AAs are precursors for the syntheses of glucose, lipids, HS, and low-molecular-weight molecules (e.g., nitric oxide, glutathione, polyamines, histamine, and hormones) with enormous biological importance, such as physical barrier, immunological and antioxidant defenses. Therefore, both nutritionally essential and nonessential AAs are needed in diets to improve the growth, development, molt rate, survival, and reproduction of crustaceans. There are technical difficulties and challenges in the use of crystalline AAs for research and practical production due to the loss of free AAs during feed processing, the leaching of in-feed free AAs to the surrounding water environment, and asynchronous absorption with peptide-bounded AAs. At present, much knowledge about AA metabolism and functions in crustaceans is based on studies of mammals and fish species. Basic research in this area is necessary to lay a solid foundation for improving the balances and bioavailability of AAs in the diets for optimum growth, health and wellbeing of crustaceans, while preventing and treating their metabolic diseases. This review highlights recent advances in AA nutrition and metabolism in aquatic crustacean species at their different life stages. The new knowledge is expected to guide the development of the next generation of their improved diets.
甲壳类动物（如虾和蟹）是供人类食用的富含蛋白质食物的良好来源。它们是全球第二大水产养殖品种。了解膳食蛋白质的消化以及氨基酸（AAs）和小肽的吸收、代谢和功能对于生产具有成本效益和可持续性的水产饲料至关重要。肝胰腺（中肠腺）是膳食蛋白质消化以及小肽和氨基酸吸收进入血淋巴的主要部位。除了作为蛋白质的组成部分外，氨基酸（特别是天冬氨酸、谷氨酸、谷氨酰胺和丙氨酸）是甲壳类动物肠道和肝胰腺外组织（如肾脏和骨骼肌）的主要代谢燃料。此外，氨基酸是葡萄糖、脂质、HS和具有巨大生物学重要性的低分子量分子（如一氧化氮、谷胱甘肽、多胺、组胺和激素）合成的前体，这些分子具有物理屏障、免疫和抗氧化防御等功能。因此，日粮中需要营养必需氨基酸和非必需氨基酸来提高甲壳类动物的生长、发育、蜕皮率、存活率和繁殖率。由于在饲料加工过程中游离氨基酸的损失、饲料中游离氨基酸向周围水环境的浸出以及与肽结合氨基酸的吸收不同步，在研究和实际生产中使用结晶氨基酸存在技术困难和挑战。目前，关于甲壳类动物氨基酸代谢和功能的许多知识是基于对哺乳动物和鱼类的研究。该领域的基础研究对于为改善日粮中氨基酸的平衡和生物利用率奠定坚实基础至关重要，以实现甲壳类动物的最佳生长、健康和福祉，同时预防和治疗它们的代谢疾病。本综述重点介绍了水生甲壳类动物在不同生命阶段氨基酸营养和代谢的最新进展。这些新知识有望指导下一代改良日粮的开发。
