Effects of low salinities on growth, fatty acid composition, and transcriptome in Florida pompano (Trachinotus carolinus) at early developmental stages

The Florida pompano, Trachinotus carolinus, is a prime marine finfish candidate for commercial production in the United States (U.S.). Low salinity conditions (i.e., < 30 parts per thousand, ppt) can affect the early development of T. carolinus by increasing osmoregulatory stress. To address the knowledge gap regarding the impact of low salinity on Florida pompano health, we conducted an experiment to determine the optimal salinity for the culture of fingerlings. Larvae were reared in three salinities (10, 20, and 30 ppt) at local producers' farms and growth, fatty acid profiles, and transcriptome responses were quantified every three days after hatching (3, 6, 9, 12, 15, 18, and 24 days post hatch) and results were compared across salinities. Larvae reared at 10 ppt grew at a normal rate and the developmental stage had a greater impact than salinity on fatty acid composition and larval gene expression. Although there were few differentially expressed genes between salinities (n = 17), there was an upregulation of gene sets associated with ribosomes and oxidative phosphorylation and a downregulation of glycerophospholipid and carbon metabolism at lower salinities in comparison to higher salinities. In the early days of development, the fatty acids linoleic acid (LA), alpha linoleic acid (LNA), and 18:3 n-6 were proven to be important as potential energy fuels and precursors for long-chain polyunsaturated fatty acids (LC-PUFA) biosynthesis, which was supported by the whole transcriptomics analysis. The gene expression of fatty acid synthesis genes coincided with changes in the fatty acid levels suggesting the ability of Florida pompano larvae to biosynthesize LC-PUFAs from LA and LNA precursors. Overall, this study suggests that it is possible to raise Florida pompano larvae for 24 DPH under low salinity conditions as low as 10 ppt. However, it is important to run this study for a longer period to investigate the long-term effects of low salinity on larval health and development. Importantly, this research serves as a model study for future on-farm collaborations and helps build a bridge between scientists and farmers in aquaculture.