Assessment of nitrite toxicity of varied ages of Atlantic sturgeon

Broodstock Atlantic sturgeon stress and mortality was observed at a relatively low nitrite concentration of 1-1.5 mg/L.  Clinical pathology results indicated methemoglobinemia, with the fraction of Hb as MetHb at 90% at the time of death.  Previous nitrite toxicity studies indicate lower sensitivities in other sturgeons.  The 96-hour LC₅₀ reported for shortnose sturgeon was 11.3 mg/L and 72-hour LC₅₀ was 130 mg/L for Siberian sturgeon.  However, differences in water chemistry make comparisons between studies difficult. Nitrite toxicity is negatively correlated with chloride concentration and positively correlated with temperature.  This study will examine acute and chronic affects of NO₂^- toxicity on Atlantic sturgeon fry and sub-adults, and the role of chloride in reducing NO₂^- toxicity. The 24- to 96-h LC₅₀ will be determined by exposing fry and sub-adult Atlantic sturgeon to a range of NO₂^- concentrations, and affects of these concentrations on gill histopathology and clinical pathology will be studied.  To study affects of chronic exposure and recovery, changes in plasma Hc, Hb, MetHb, NO₂^-, ions and glucose will be measured in sub-adult fish exposed to NO₂^-  at 0, 100 and 200 mg/L Cl^- for 2 weeks followed by a 2-week period in NO₂^- free water.