Toxic Effects of Ammonia, Nitrite, and Nitrate to Decapod Crustaceans: A Review on Factors Influencing their Toxicity, Physiological Consequences, and Coping Mechanisms

Nitrogenous wastes including ammonia-N, nitrite-N, and nitrate-N are increasingly becoming a global issue in aquatic ecosystems due to escalating anthropogenic activities and are a ubiquitous concern in aquaculture. These pollutants are interrelated via the nitrification cycle, with the direct metabolic product ammonia-N generally being the most toxic with high species specificity. Furthermore, while environmental factors influencing nitrogenous waste toxicity are similar, the causative underlying mechanisms are often substantially different. In this review, we focus on decapod crustaceans due to their high commercial value and likelihood of encountering these pollutants in their benthic or near-benthic habitat. While a large body of publications exists in this area, to date a comprehensive literature review on relative toxicities of all three nitrogenous wastes, physiological consequences, and adaptive mechanisms of crustaceans is lacking. Understanding these processes will likely have implications for environmental/fisheries management and the aquaculture industry. Additionally, there are strong indications that theoretical “safe” values, traditionally used for predicting toxicity thresholds, substantially underestimate the impact of nitrogenous waste on the growth and physiological condition of crustaceans. These consequences will be emphasized along with various methods of uptake, elimination, and detoxification that ultimately explain differences in nitrogenous waste toxicity to decapod crustaceans.