Comparative transcriptome analysis reveals factors involved in the influence of dietary astaxanthin on body colouration of Malabar Snapper (Lutjanus malabaricus)

The farming of several species in aquaculture often produces pale coloured fish due to a deficiency in dietary carotenoid sources compared to their wild caught counterparts, resulting in the loss of market value and consumer acceptance. Supplementation of feed with astaxanthin as a carotenoid source has since been found to enhance red colouration in several important fish species. In this study, comparative transcriptome analysis was performed on the skin from the main body (dorsolateral region) and caudal fin of Malabar snappers (Lutjanus malabaricus) fed with and without astaxanthin over a 32-day period to identify genes related to the trait. All clean reads were assembled into 205,940 unigenes with a N50 of 2079 bp. A total of 881 and 178 differentially expressed genes (DEGs) between Control Body (CB) vs Treatment Body (TB) and Control Fin (CF) vs Treatment Fin (TF) were identified respectively, where expression patterns suggested that pigment-related genes bco1, bco2l, pax7, slc7a11, hsp70, and stard5 are key genes involved in the enhancement of red colouration in Malabar snappers. Metabolic pathways related to pigmentation such as PI3k-Akt, MAPK, Wnt, cAMP, and Ras signaling are likely to play vital roles in the enhancement of red colouration in juvenile Malabar snappers. In addition, numerous immune-related genes were found to be differentially expressed for both CB vs TB and CF vs TF, suggesting the potential use of dietary astaxanthin as an immunostimulant. The present study provides a foundation to the understanding of the molecular mechanisms involved in carotenoid-induced colouration, and development of breeding and culture practices to produce farmed Malabar snappers with the desired consumer-favoured traits