AbstractBleeding of horseshoe crabs (Limulus polyphemus) for the biomedical industry can have both sublethal and lethal impacts. Bleeding induces a significant drop in the concentration of hemolymph hemocyanin, as well as decreased levels of activity. Furthermore, horseshoe crabs with low hemocyanin prior to being bled have been found to be more likely to die after the procedure. The goal of this project was to determine whether feeding horseshoe crabs after bleeding them could enhance the recovery of their hemocyanin levels and, in doing so, improve their physiological status. The feeds tested in separate experiments included (1) natural forage items, blue mussels (Mytilus edulis) or softshell clams (Mya arenaria); (2) a formulated diet containing green crabs (Carcinus maenas) and Limulus hemolymph; and (3) a modified commercially available shrimp (Litopenaeus vannamei) broodstock aquafeed. Horseshoe crabs (n = 63) were bled and then either fed or not fed, and their hemolymph hemocyanin concentrations were measured before they were bled and for the following 6-14 days. An additional 25 horseshoe crabs were treated in the same manner but not bled. In three experiments, horseshoe crabs that were fed consistently showed significantly higher hemolymph hemocyanin concentrations compared to those that were not fed. These data suggest that relatively simple modifications of the industrial bleeding procedure, such as feeding horseshoe crabs after bleeding them, may improve their physiological status prior to release.