Digestible dietary protein and energy requirements of juvenile Asian horseshoe crabs, Tachypleus tridentatus and Carcinoscorpius 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 (Artemia salina), was conducted. The results showed that the survival rate of Tachypleus tridentatus ranged from 67% to 100%, while that of Carcinoscorpius 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.