Effects of chronic sub‐lethal nitrite exposure at high water chloride concentration on Atlantic salmon (Salmo salar, Linnaeus 1758) parr

Summary

The present study examined the protective effects of water chloride (Cl−) towards nitrite toxicity in Atlantic salmon parr during 84‐day long nitrite exposure. Effects on growth, histology, blood indices and gene expression were studied at a fixed nominal Cl− concentration of 200 mg/L and at several water nitrite concentrations (0, 0.5, 2, 5 and 10 mg/L NO2−–N). The specific growth rate was significantly reduced during the first three weeks at a Cl:NO2−–N ratio of 21:1, suggesting the activation of coping mechanisms at the later stages of the experiment. No significant effect of nitrite on gill histology and mortality was found. Nitrite accumulated in plasma; however, a Cl:NO2−–N ratio of 104:1 or higher prevented nitrite entry. The concentration of NO2−–N in plasma was significantly reduced at the end of the study, supporting the hypothesis of coping mechanisms. Cystic fibrosis transmembrane conductance regulator (cftr)‐1 showed a significant up‐regulation at highest nitrite concentration on day 22, and in three of the highest exposure groups at the end of the experiment. Our findings suggest that a Cl:NO2−–N ratio above 104:1 should be maintained through episodes of nitrite accumulation in water during the production of Atlantic salmon parr.