抄録
n-3 Long-chain polyunsaturated fatty acids (n-3 LCPUFA) such as docosahexaenoic acid (DHA, 22:6n-3) and eicosapentaenoic acid (EPA, 20:5n-3) play crucial roles in the development and maintenance of health in vertebrates. Insufficient intake of n-3 LC-PUFA leads to a significant decrease in the survival rate of marine fish, especially at larval and juvenile stages. Most freshwater fish and salmonids require α-linolenic acid (ALA, 18:3n-3), which is found in vegetable oils, as an essential fatty acid but they do not require n-3 LCPUFA. On the other hand, carnivorous marine fish such as red sea bream and Japanese flounder require large amounts of n-3 LC-PUFA for their growth (approximately 1-3% of their dry diet).
Genomic analyses of many fish species and heterologous gene expression experiments have enabled identification of the desaturases and elongases involved in n-3 LC-PUFA biosynthesis in various fish species. These analyses show that almost all teleost fish have lost FADS1, the enzyme responsible for del ta-5 desaturase activity in vertebrates, and possess FADS2, which is responsible for delta-6 desaturase activity, as the sole desaturase to synthesize PUFA. Some teleost fish have acquired the ability to synthesize DHA through duplication and multifunctionalization of the FADS2 gene during evolution, which has enabled them to adapt to their nutritional environments. As marine environments are rich in microorganisms that can synthesize DHA and EPA, it is believed that marine teleost fish no longer possess the capacity for n-3 LC-PUFA biosynthesis due to their reliance on the environment for their supply of DHA.
The price of fishmeal, which serves as a significant source of n-3 LC-PUFA, has increased over time with the expansion of the sea aquaculture industry. Therefore, it is necessary to explore options for enhancing aquaculture technology, such as the development of alternative feeds and genome-editing technology, to achieve sustainable fisheries.
