Digestible dietary protein and energy requirements of juvenile A sian horseshoe crabs, T achypleus tridentatus and C arcinoscorpius rotundicauda

A 84‐day feeding experiment of two juvenile horseshoe crab species, including nine formulated diets with three digestible protein ( DP ) levels (36%, 40% and 44%) and three digestible energy ( DE ) levels (14, 16 and 18 kJ g −1 ) versus the control, fed on frozen brine shrimp ( A rtemia salina ), was conducted. The results showed that the survival rate of T achypleus tridentatus ranged from 67% to 100%, while that of C arcinoscorpius rotundicauda varied from 44% to 100%. The results also indicated that the formulated diet containing 40% DP with 14 kJ g −1 DE was the best, in terms of growth and feed utilization, for the two juvenile horseshoe crab species. Final body weight ( FBW ), thermal‐unit growth coefficient ( TGC ), feed efficiency ( FE ), nitrogen retention efficiency ( NRE ) and energy retention efficiency ( ERE ) of T . tridentatus fed 40% DP and 14 kJ g −1 DE were significantly higher than that of T . tridentatus fed the control diet. However, for C . rotundicauda , only significantly higher FE , NRE and ERE were found in juveniles fed 40% DP and 14 kJ g −1 DE than the control diet. The present findings revealed that the optimum DP / DE ratio for the two species was 28 g protein MJ −1 .