Hemolymph quality as indicator of health status in juvenile Chinese horseshoe crab Tachypleus tridentatus (Xiphosura) under laboratory culture

The growth performance and hemolymph quality of juvenile Chinese horseshoe crabs under four diet treatments: brine shrimp Artemia salina, short-neck clam Ruditapes philippinarum, sandworm Marphysa sanguinea and mixed clam and sandworm were evaluated in a 12-week experiment. The growth responses in terms of final body weight, specific growth rates and percentage of individuals molted under the clam diet were significantly higher than those fed with brine shrimp and sandworm, whereas the mixed clam and sandworm diet was not statistically different from the other three treatments. While the hemolymph properties among these diets were similar, significant declines in hemocyanin concentration, percentage of oxyhemocyanin, and ratio of granular-spherical to granular-flattened states of amebocytes were noted at the end of the study. Such a decrease in hemolymph quality indicated deleterious effects due to prolonged culture on the health status of the juveniles, which might be attributed to captivity-related issues, such as deficiencies of essential diet compositions, movement constraints and absence of tidal rhythms. This was further supported from the finding that the hemolymph quality of the experimental juveniles was significantly poor compared to that of the juveniles collected from the field. Changes of hemolymph constituents could thus be a useful indicator to reflect the health status of juvenile horseshoe crabs under laboratory culture.