Concentrations of ammonia, nitrite and nitrate in recirculatingseawater systems causing bay scallop, Argopecten irradians irradians,mortality

摘要

Good water quality is crucial to high survival and growth rates of bivalves held in closed or semi-closed rearing systems. As concentrations of nitrogenous waste increase in recirculating sea-water systems, they can become toxic to marine organisms. Juvenile bay scallops, Argopecten irradians irradians, (10-30mm), were exposed to experimentally-varied concentrations of ammonia, nitrite and nitrate for 72 hours to investigate thresholds of acute toxicity. Un-ionized ammonia is the toxic form of ammonia, and since ionization varies with pH scallops were exposed to ammonia concentrations at pH levels of 7.6, 8.0 and 8.4. Un-ionized ammonia concentrations greater than 0.60 mg L super(-1) resulted in 100% mortality, while a concentration of 0.45 mg L super(-1) resulted in 50% mortality. Nitrite was less toxic than un-ionized ammonia, requiring a concentration of 750 mg L super(-1) to result in 100% mortality. Nitrate was the least toxic to bay scallops with 100% morality occurring at 5000 mg L super(-1). These results indicate the importance of monitoring and maintaining low nitrogenous waste levels in semi-closed systems to ensure an environment suitable for high survival of bay scallops.