Chronic toxicity of nitrate to Pacific white shrimp, Litopenaeus vannamei: Impacts on survival, growth, antennae length, and pathology

Chronic toxicity of nitrate (NO3−) has not been well documented in the culture of penaeid shrimp. To interpret this problem, lab-scale research was conducted in recirculating aquaculture systems (RAS) to determine the long-term impacts of nitrate on shrimp growth, survival, total mass of shrimp per system (shrimp biomass), antennae length, and tissue pathology. The first experiment, Trial (A), was performed over a six week period at 11 (ppt) salinity and consisted of a Control A (35 ppm nitrate-N), Treatment A1 (220 ppm nitrate-N), Treatment A2 (435 ppm nitrate-N), and Treatment A3 (910 ppm nitrate-N). No differences were observed between control A and treatment A1 in terms of shrimp survival, growth, shrimp biomass, and antennae length. Treatment A2 exhibited no significant differences compared to Control A in terms of survival and growth, but did exhibit significant negative impacts (P < 0.05) on shrimp biomass and antennae length. Lastly, treatment A3 significantly and negatively impacted (P < 0.05) survival, growth, total mass, and antennae length. Histopathology of shrimp from Trial A and all three groups of Treatments A1 through A3 demonstrated lesions in the hepatopancreas, and a few individuals from each of these three groups had gill abnormalities (e.g. fouling). A second experiment, Trial (B), was conducted over a five week period to evaluate the effects of elevated nitrate at various salinities. This trial consisted of Control B (9 ppt salinity, 18 ppm nitrate-N), Treatment B1 (9 ppt salinity, 440 ppm nitrate-N), Treatment B2 (2 ppt salinity, 440 ppm nitrate-N), and Treatment B3 (18 ppt salinity, 440 ppm nitrate-N). When compared to Control B, Treatments B1 through B3 exhibited significantly negative effects (P < 0.05) on shrimp survival, growth, and shrimp biomass, irrespective of salinity. Even though all treatment groups with 440 ppm nitrate-N exhibited negative responses to elevated nitrate, there was evidence (P < 0.05) that an increase in salinity significantly (P < 0.05) improved survival and shrimp biomass.