Internal carbohydrates and lipids as reserved energy supply in the pubertal molt of Scylla paramamosain

Pubertal molt is critical for the reproductive process of mud crab Scylla paramamosain, during which female crabs molt and mate with males, and subsequently, ovarian development is initiated. Since fasting occurs during pubertal molt, the mechanism underlying how the internal energy reserves support crabs' survival is unclear. In this study, the hepatopancreas and ovaries were collected for metabolomics analyses. The results show 11 carbohydrate and 4 lipid metabolic pathways were remarkably modulated in hepatopancreas, suggesting carbohydrates and lipids may be the main energy reserves in hepatopancreas postmolt. Further analysis showed that the levels of glucose, glucose 6-phosphate, glucose 1-phosphate, and fructose 6-phosphate were increased, indicating glycolysis was upregulated for energy supply. Meanwhile, 65 lipids were significantly changed, including 16 glycerophospholipids and 33 fatty acids, suggesting lipids might be another main energy supplier in the hepatopancreas. In the ovary, 7 carbohydrate and 1 lipid metabolic pathways were obviously affected, and 12 carbohydrates and 23 lipids were also significantly changed postmolt. Differently from the changes in the hepatopancreas, the glucose level was significantly decreased in the ovary, whereas the levels of eight glycerophospholipids and four unsaturated fatty acids were increased in the ovary but decreased in the hepatopancreas, suggesting lipids might be major energy reserves for ovarian development, and they were possibly exported from hepatopancreas. Moreover, the obvious changes in seven fatty acyl carnitines in the ovary indicate they were consumed via beta-oxidation postmolt. Taken together, carbohydrates and fatty acyl carnitines were clearly the major energy reserves in pubertal molt. The hepatopancreas played a central role in the supply of energy reserves and nutrients. Numerous glycerophospholipids and unsaturated fatty acids may have accumulated in the ovary for the biosynthesis of egg yolk during ovarian development. This study suggests that proper increases in carbohydrate and lipid levels in crab feed ahead of pubertal molt may alleviate the effects of fasting and enhance successful reproduction.