Intensive aquaculture of finfish species is often associated with a variable concentration of nitrogenous compounds in water. These compounds are derived from ammonia excretion by fish after protein catabolism and posterior bacterial denitrification of ammonia into nitrite and nitrate in water. Since the accumulation of these compounds can be toxic for fish, aquaculture practices include the maintenance of low levels of ammonium and nitrite (the most toxic forms). However, due to the high cost of water renewal, long term biofiltering, sudden fluctuations in water quality, etc., fish are often exposed to low concentrations of nitrite for long periods of time. Until now, it has been assumed that exposures to low concentrations of nitrite that don’t elicit an obvious stress response in fish are acceptable for fish culture. However, our research showed that long-term and low concentration nitrite treatments had a dramatic effect on sensory organs like the nose, mucosal microbiomes, brain function, oxidative stress and embryo neural development in several finfish species. Conversely, no other known nitrate/nitrite acute physiological effects were detected at the sublethal concentration tested (methemoglobinemia, loss of appetite, behavior, etc.). Thus, although no immediate effects are shown under chronic nitrite treatments, it is clear that fish are faced with morphological and physiological changes that will threaten their health in the long-term. Our research also sugestted alternative approaches to palliate the nitrite effects in aquaculture farms.
Understanding the broad physiological effects of water-borne nitrite as a toxin at specific concentrations for each fish species has a broad biological significance with impacts on neurobiology, animal behavior and aquaculture.