Physiological and avoidance responses of juvenile mud crab Scylla serrata to mercury

Abstract

The physiological and avoidance responses of juvenile mud crab Scylla serrata to mercury was evaluated by determining mortality using a renewal-type acute toxicity test and assessing crabs’ ability to avoid toxic concentrations. The 96-h LC₅₀ of mercury to juvenile mud crab was computed to be 0.04 mg L^-1. When transferred to clean waters, crabs that survived exposure to concentrations lower than 0.04 mg L^-1 had better chances of surviving than those that were exposed to higher mercury concentrations. Avoidance of juvenile mud crabs to mercury was determined using a fluvarium, which provided the crabs a choice between untreated and Hg-treated waters. Results showed that juvenile crabs were not able to avoid waters that contain 0.1 mg L^-1 mercury, a concentration that was more than twice the 96-h LC₅₀ value. Juveniles previously pre-exposed in 1/50th of the 96-h LC₅₀ value had a higher avoidance threshold and were not able to avoid waters with 1 mg L^-1 mercury. Results suggest that juvenile mud crab is unable to avoid waters containing lethal levels of mercury and this may have potential impacts on crab biomass, distribution, growth, and development.