Acid Tolerance and Effects of Sublethal Acid Exposure on Iono-Regulation and Acid-Base Status in Two CrayfishProcambarus ClarkiandOrconectes Rusticus

Acid-toxicity tests were performed using two crayfish species, Procambarus clarki Girard and Orconectes rusticus Girard to determine the median lethal pH (LC5O) after 4 days exposure to acid. Four-day LC50 values of pH 2*5-2-8 were observed, indicating that these animals are more acid-tolerant than most fish species. Haemolymph acid-base variables and major ion concentrations were measured during 4 days exposure of P. clarki to sublethal acid H2SO4, pH 3-8) levels. A major haemolymph acidosis was observed. While minimal changes were seen in haemolymph [Cl−], [K+], and [Mg2+], haemolymph [Na+] decreased. Haemolymph [Ca2+] increased significantly during acid exposure, suggesting that dissolution of exoskeletal carbonate buffers was being employed as a compensatory mechanism for the acidosis; this process would be expected to contribute to exoskeletal rigidity problems in the long term.