The Importance of Water Quality in Siberian Sturgeon Farming: Nitrite Toxicity

Abstract

The maintenance of good water quality is of primary importance in aquaculture systems. Although nitrites usually occur in low concentrations, their presence in aquaculture systems at elevated levels is a potential problem due to its well-documented toxicity. Nitrites are not a problem in flow-through systems, but nitrite may become a serious problem in recirculating systems where water is reused. Nitrites are formed by nitrification, the process in which nitrifying bacteria oxidises ammonia into nitrite and then into nitrate. Nitrites in the ambient water can be actively taken up across the gill epithelium and get accumulated in the internal medium resulting in many physiological disturbances (oxidation of haemoglobin, ionic unbalance, liver damage, cardiovascular problems) that may result in the animal’s death. The median-lethal concentration of nitrite in juvenile (172 g) Siberian sturgeon after 72 h of exposure was 130 mg/L in water with high chloride content (130.5 mg/L). Levels of Cl⁻ in water are especially important in freshwater species to prevent/reduce nitrite toxicity, since nitrite is a competitive inhibitor of Cl⁻ uptake and vice versa. In any case, in aquaculture systems nitrites levels are recommended to be below than 1.0 mg NO₂/L. Siberian sturgeon exposed to toxic levels of nitrite showed several signs of behavioural distress characterised by an increase of ventilatory activity, erratic and torpid swimming, loss of equilibrium and overturning swimming. In this chapter, the effects of nitrite intoxication, as well as the recovery of animals exposed to an acute episode of nitrite intoxication are presented and discussed.