Preparing for the future offspring: European perch (Perca fluviatilis) biosynthesis of physiologically required fatty acids for the gonads happens already in the autumn

Long-chain polyunsaturated fatty acids (PUFA) are critical for reproduction and thermal adaptation. Year-round variability in the expression of fads2 (fatty acid desaturase 2) in the liver of European perch (Perca fluviatilis) in a boreal lake was tested in relation to individual variation in size, sex, and maturity, together with stable isotopes values as well as fatty acids (FA) content in different tissues and prey items. ARA and DHA primary production was restricted to the summer months, however, perch required larger amounts of these PUFA during winter, as their ARA and DHA muscle content was higher compared to summer. The expression of fads2 in perch liver increased during winter and was higher in mature females. Mature females stored DHA in their gonads already in late summer and autumn, long before the upcoming spring spawning period in May. Lower delta C-13(DHA) values in the gonads in September suggest that these females actively synthesized DHA as part of this reproductive investment. Lower delta C-13(ARA) values in the liver of all individuals during winter suggest that perch were synthesizing essential FA to help cope with over-wintering conditions. Perch seem able to modulate its biosynthesis of physiologically required PUFA in situations of stress (fasting or cold temperatures) or in situations of high energetic demand (gonadal development). Biosynthesis of physiologically required PUFA may be an important part of survival and reproduction in aquatic food webs with long cold periods.

Automated summary

Long-chain polyunsaturated fatty acids (PUFA) are critical for reproduction and thermal adaptation in fish. In a study on European perch in a boreal lake, the expression of the fatty acid desaturase 2 (fads2) gene in the liver was found to vary with individual size, sex, and maturity, as well as the stable isotopes values and fatty acids content in their diet. The production of ARA and DHA, two important PUFA, was limited to the summer months, but perch required more of these fatty acids during winter when their muscle content was higher. The expression of fads2 in perch liver increased during winter, particularly in mature females, who stored DHA in their gonads even before the spawning season in spring. These findings suggest that perch can regulate the biosynthesis of physiologically required PUFA in response to stress or high energetic demand.