Responses of growth and hemolymph quality in juvenile Chinese horseshoe crab Tachypleus tridentatus (Xiphosura) to sublethal tributyltin and cadmium

Responses of growth endpoints and hemolymph constituents in juvenile Chinese horseshoe crab Tachypleus tridentatus under treatments of 0.01 and 0.1 mg/l tributyltin (TBT) and 0.1 and 1 mg/l cadmium (Cd) were examined in a 12-week experiment. A significant decline in final body weight, final prosomal width, percentage of individuals molted and mean molting time was detected under TBT exposures. While morphological abnormalities of the juveniles between TBT treatments and the control were statistically indistinguishable, significantly higher occurrences of carapace erosion and appendage loss were noted under 0.1 and 1 mg/l Cd exposures. Various hemolymph quality indicators, including hemolymph plasma protein level, amebocyte viability and percentage of granular-spherical state of amebocytes of the juveniles exposed to TBT or Cd were significantly lower than the control. Such a decrease in hemolymph quality suggested deleterious effects of metal contaminant-induced stressors on the health status of the juveniles even at low exposure levels (i.e., 0.01 mg/l TBT and 0.1 mg/l Cd). Changes of hemolymph parameters in juvenile horseshoe crabs were more sensitive than growth performance as well as morphological abnormalities in response to metal stressors, and can be used as an indicator to reflect habitat conditions and contaminant levels.