Influence of dietary calcium to phosphorus ratio on growth, minerals bioaccumulation and energy metabolism in juvenile swimming crab (Portunus trituberculatus)

An 8-weeks feeding trial was conducted to investigate the effects of dietary calcium/phosphorus ratios on the growth performance, minerals bioaccumulation, and energy metabolism in juvenile swimming crab (Portunus trituberculatus). Five semi-purified experimental diets were formulated to contain different ratios of calcium to phosphorus (1.00∶2.00, 1.00∶1.50, 1.00∶1.00, 1.00∶0.75 and 1.00∶0.50, respectively). A total of 150 swimming crab juveniles initial weight (12.82 ± 0.37) g were randomly allocated into five groups with three replicates, each and consisted of 30 crabs. The results indicated that crabs fed the diets with calcium to phosphorus ratios of 1.00∶1.00 and 1.00∶0.75 had significantly higher specific growth rate (SGR) and feed efficiency (FE) than those fed the other diets. The highest activity of GOT in hemolymph was observed at crabs fed the diet with calcium to phosphorus ratio of 1.00∶0.50, and AKP and GPT exhibited an increasing trend with the increase of dietary calcium to phosphorus ratios. Moreover, the content of phosphorus in tissues significantly increased with dietary calcium to phosphorus ratios decreasing from 1.00∶0.50 to 1.00∶2.00. Furthermore, the highest ATP content in hepatopancreas was observed in crab fed the diets calcium/phosphorus ratios of 1.00∶1.50 and 1.00∶1.00. The activities of enzymes such as hexokinase (HK) and succinate dehydrogenase (SDH) related to energy metabolism were significantly higher in hepatopancreas of crabs fed the diet with calcium to phosphorus ratio of 1.00∶1.00. Crabs fed the diet containing calcium to phosphorus ratio 1.00∶1.00 also showed significantly higher expression of genes involved in electron transport chain complex, such as nd1, sdhc, cytb and cox Ⅱ than those fed the other diets. The genes related to mitochondrial energetic metabolisms, such as atpase6, sirt3, and nrf1 were significantly up-regulated in crabs fed the diet with calcium and phosphorus ratio of 1.00∶0.75. Overall, based on broken-line and quadratic regression analysis between PWG against dietary calcium to phosphorus ratios, the optimal dietary calcium to phosphorus ratio was estimated to be 1.06-1.26, and this range could be recommended to maintain optimal phosphorus bioaccumulation and promote energy production for juvenile swimming crab.