Dietary lysine requirement of juvenile swimming crab, Portunus trituberculatus

An 8-week feeding trial was conducted to determine the optimal dietary lysine requirement for juvenile swimming crab reared in cement pools. Six iso-nitrogenous and iso-lipidic experimental diets (49.5% crude protein and 7.0% crude lipid) were formulated to contain graded levels of lysine, which were 1.58%, 1.89%, 2.15%, 2.41%, 2.67% and 2.90% of the dry matter, respectively. Each diet was randomly assigned to triplicate groups of 60 juvenile swimming crabs (approximately 7.86 +/- 0.16 g), which were stocked in rectangle plastics. The results indicated that weight gain (WG), specific growth rate (SGR), protein productive value (PPV), feed efficiency (FE) and protein efficiency ratio (PER) were significantly influenced by the dietary lysine levels (P < 0.05). WG and SGR significantly increased with the dietary lysine levels from 1.58% up to 2.41%, and decreased with higher levels. Survival was not significantly different among treatments (P > 0.05). There were no significant differences in the compositions of the whole body and muscle (moisture, crude protein, crude lipid and ash) (P > 0.05) except the crude protein content in the whole body; the crabs fed the diet containing 2.41% lysine had higher crude protein of the whole body than those fed the other diets. Amino acid composition of the muscles was not significantly affected by the dietary lysine levels (P > 0.05). Aspartate aminotransferase (AST) and aminotransferase (ALT) in hepatopancreas were significantly affected by dietary lysine levels (P < 0.05), while there were no significant differences in the serum (P > 0.05). The optimal dietary lysine requirement, estimated by the two slope broken-line model based on SGR against dietary lysine levels, was 2.41% of the dry matter (4.87% dietary protein) for juvenile swimming crabs. Considering the lysine leaching loss in sea water within 60 min (duration of feeding each time), the actual lysine requirement for swimming crab was estimated to be 2.17% of dry diet (4.38% of the dietary protein). Statement of relevance: The manuscript addresses lysine requirement of juvenile swimming crab. Although this study investigated a common nutritional research topic, it still had somehow research originality because such nutritional topic has not been studied in swimming crab yet. The results give some valuable data for this marine crab. What's more, the information obtained from the present study would be helpful in developing EAA balanced diets for this species. (C) 2015 Elsevier B.V. All rights reserved.