Dietary DHA limitation did not affect swimming and metabolic performance, but reduced growth in wild European sea bass.

Abstract

Long-chain polyunsaturated fatty acids (LC PUFA), particularly docosahexaenoic acid (DHA), are essential for cell membrane structure and function, impacting overall fish performance. These molecules, produced primarily by phytoplankton, are transferred up the trophic chain; however, climate change is predicted to modify phytoplankton communities with a cascading effect on the global DHA production and thus availability for consumers such as fish. This study aimed to evaluate the effects of dietary DHA limitation on i) the fatty acid composition in fish tissues ii) somatic growth, swimming performance, and metabolic rates, and iii) the activation of biosynthetic pathways at the molecular level, by measuring gene expression involved in DHA synthesis. We conditioned wild-caught European sea bass (Dicentrarchus labrax) juveniles for five months on a DHA-depleted or control diet. Dietary DHA limitation led to selective retention or synthesis of DHA in fish tissues (liver, brain, and muscle), a reduced growth and an up-regulation of DHA biosynthetic pathways without compensating for DHA deficiency in tissues. Fish fed the low DHA diet may have up-regulated biosynthetic pathway which may be energetically costly, as high tissue DHA correlated with reduced growth. Alternatively, the lower tissue DHA levels in these fish might cause slower growth. However, metabolic rates and swimming performance were not affected by dietary treatment. Inter-individual variability was observed across all variables, highlighting underlying trade-offs when facing DHA limitation. This work provides insight into the physiological consequences of dietary DHA reduction due to global change and the mechanisms fish employ to mitigate its effects.