Transcriptome analysis provides insights into the high ability to synthesize fatty acids in "yellow oil" mud crab...

Yellow oil mud crab (YOC) is a new variant of mud crab (Scylla paramamosain), which was attracted much attention in recent years due to its high level of nutrition. However, the nutritive values and the physiological changes in YOC have not been clearly understood. In this study, we aimed to identify the nutrient compositions (including total carotenoid content (TCC), total lipid content (TLC), total antioxidant capacity (TAC), and fatty acids) and differences in genes related to the biosynthesis of fatty acids using transcriptome analysis in YOC in comparison with those of normal mud crabs. As a result, observations on the morphological characteristics showed that the YOC exhibits a difference in the color of the muscle, gills (orange-yellow), and hemolymph (yellow) compared with the normal female crabs (NFC) (blue or nattier blue). The TCC and TLC (84.96 ± 9.65 μg/g in muscle and 1.39 ± 0.10 μg/mL in hemolymph) or TAC (1.52 ± 0.17 mM in hemolymph) of YOC were higher than that of NFC and normal male crab (NMC). YOC had lower saturated fatty acids, but higher unsaturated fatty acids, as well as the ratio of n-3/n-6 of fatty acids in muscle and hemolymph, compared with those of NFC and NMC. Furthermore, the transcriptome profile revealed that the unigenes in YOC were enriched in the synthesis of n-3 fatty acids. Furthermore, more unigenes related to 'Biosynthesis of unsaturated fatty acids' were identified in muscle and hemocytes, while fewer were in the gonads of YOC. Additionally, the positive (in muscle and hemocytes) and a negative correlation (in gonads) between expressions of unigenes and contents of TLC, TCC, and UFA were found, indicating a better synthesis ability of fatty acids in the muscle and hemocytes of YOC. Overall, compared to NFC and NMC, YOC has higher nutrients and is a better food nutrient source for humans.