Reducing the effects of chronic sub-lethal nitrite exposure
Though monitoring and adjusting water quality parameters in RAS is effective in preventing accumulation associated with acute toxicity, there is a knowledge gap concerning the long-term effects of chronic sublethal exposure of nitrite (NO2-) and related water parameters on Atlantic salmon physiological health and robustness.
NO2-, if accumulated in the fish, can disrupt multiple physiological functions, such as chloride depletion, since NO2- and Cl- compete for the same uptake pathway, and may also have a critical influence on the potassium (K+) balance in fish (Frank B Jensen, 2003). Studies have shown, that NO2- exposure causes a general K+ loss from skeletal muscle and red blood cells, causing significantly elevated extracellular [K+] concentration in fish, a condition known as hyperkalaemia
Results from a recently completed Fiskaaling study indicate that after long-term sub-lethal exposure, large post-smolt salmon experience extracellular hyperkalemia due to elevated plasma levels of NO2—N. This extracellular K+ concentration is unfavourable for heart and other excitable tissues by causing depolarisation that could potentially lead to heart failure and nerve malfunction. (Frank B Jensen, 2003).
The results from this study are being prepared for publication and further studies will be planned to address optimizing the addition of salt to RAS systems in order to reduce NO2- uptake, as well as other water quality optimizations.
In addition, this focus area will be investigated further through our partnership with the “DigiHeart” project funded by NordForsk in December 2020.
Contact: Heidi Mortensen