A feeding experiment was undertaken for 84 days to investigate the growth performance and the feed utilization of two horseshoe crab species from partial replacement of fish meal (FM) with blood meal (BM), meat and bone meal (MBM), and poultry by-product meal (PBM) in their diet. Triplicate groups of Tachypleus tridentatus or Carcinoscorpius rotundicauda were fed nine isonitrogenous (digestible protein 40%) and isoenergetic (digestible energy 14 MJ kg^-1) diet treatments. For both species, the growth performance, that is, final individual body weight and thermal-unit growth coefficient (TGC), and feed utilization, that is, including feeding rate (FR) and feeding efficiency ratio, of the juveniles fed with PBM and MBM at 2:1 ratio were higher than those of juveniles fed with diets containing PBM and MBM at 1:1 ratio at the same FM replacement level. Final individual body weight, TGC, and FR of the two species fed with the 100% FM replacement diets were significantly lower than in other diet treatments. The optimal replacement levels ofFMby the combination of PBM, MBM, andBMwere 50% and 75% in the protein of T. tridentatus and C. rotundicauda, respectively. Based on literature data, FM replacement reduced feed costs by 15%–25% in aquaculture practices.