Effect of salinity on fads2 and elovl gene expression and fatty acid profile of the euryhaline flatfish Paralichthys orbignyanus

Abstract

Paralichthys orbignyanus, a commercially important flatfish, presents in its natural environment, significant variations in salinity and fatty acid composition of its diet. In this work, we aimed to study the impact of salinity on the genetic expression of fads2 and elovl and its reflection in the muscle fatty acid profile of the fish. Since genetic resources for this species are absent, we performed hepatic transcriptome sequencing (mRNA-Seq) and conducted de novo assembly to obtain the novel transcripts of fads2 and elovl. The sequences obtained were used to analyze possible changes in the genetic expression of these enzymes in juvenile P. orbignyanus when cultured at four salinities (2, 10, 18 and 26 ppt) fed on a diet rich in 18:3n-3 and 18:2n-6 but poor in LC-PUFA. Results showed that salinity has a significant modulatory effect on fads2 gene expression, with an increase at 2 ppt salinity. Total lipid content in fish muscle decreased when moving away from the isosmotic point (10.9 ppt) suggesting higher energetic demands at 2, 18 and 26 ppt. This effect was also evident for specific fatty acids, such as 16:1n-7, 16:2n-3, 18:4n-3, 20:1n-9, 20:4n-3 and 20:5n-3. Interestingly, some fatty acids, particularly total MUFA, 18:2n-6 and 22:6n-3 presented a dichotomous profile between lower and higher salinities, suggesting the adaptation of P. orbignyanus to different environmental salinities. This study highlights the remarkable ability of P. orbignyanus to adapt to a wide range of salinities demonstrating the strong euryhalinity of this species. The observed salinity effects hold potential significance for its application in aquaculture.