Combined Toxic Effects Of Acute Ammonia Nitrogen Stress And Dissolved Oxygen Levels On Zebrafish (Danio Rerio)

With the increasing intensification of aquaculture,excessive ammonia nitrogen in water has become an urgent problem to be solved in the sustainable development of aquaculture.Further understanding of ammonia nitrogen and its physiological effects on fish in collaboration with other breeding environmental factors is the scientific basis for ammonia nitrogen regulation in the future,which is the core research objective of this paper.Ammonia nitrogen in water environment mainly exists in two forms:ionic ammonia?NH₄⁺?and non-ionic ammonia?NH₃?.Non-ionic ammonia is the main source of ammonia toxicity.Dissolved oxygen,temperature and other environmental factors will affect the toxicity of ammonia nitrogen by affecting the proportion of non-ionic ammonia.However,as the most important environmental factor of water,the combined effect of dissolved oxygen and ammonia nitrogen has not been known.Therefore,zebrafish,a model animal,was taken as the experimental object.Under the condition of water temperature of 24?and p H of 7.8,the combined effect of ammonia nitrogen and dissolved oxygen on the physiological phenotype of zebrafish and the potential toxicological mechanism were studied.The main contents and conclusions are as follows:1.Under normal dissolved oxygen conditions,the lethal concentration?LC50?of total ammonia nitrogen at 96 h for zebrafish was 75.00 mg/L,and the safe concentration was 7.5 mg/L.The mortality rate of zebrafish increased with the increase of ammonia nitrogen concentration and the extension of stress time.2.Acute ammonia nitrogen stress and dissolved oxygen level in water have a combined effect on zebrafish,and the increase of dissolved oxygen will aggravate the toxicity of acute ammonia nitrogen stress on zebrafish.3,In the case of higher dissolved oxygen,acute ammonia nitrogen stress caused more serious damage to the gill tissue of zebrafish,influence the gills of ion exchange equilibrium,the amount of ammonia entering the fish increases,so that blood ammonia concentration is higher,and increased mortality,compensatory increases,its metabolic detoxification index dramatically increase fish body inflammatory reaction and apoptosis.4.The combined effect of acute ammonia nitrogen stress and dissolved oxygen on the toxic effect of zebrafish was different between males and females.Male zebrafish were more sensitive to ammonia nitrogen toxicity aggravated by dissolved oxygen than female zebrafish..It is worth noting that this study unexpectedly found that the increased dissolved oxygen level could aggravate the physiological toxicity of ammonia nitrogen to male and female zebrafish,which is completely contrary to the conclusions reported in some previous studies.After repeated experiments,this study confirmed that,at least in zebrafish,increased dissolved oxygen levels did enhance the physiological toxicity of ammonia nitrogen.Due to time constraints,this study was unable to verify the results in other fish species.However,this study at least shows that the combined effect of dissolved oxygen and ammonia nitrogen on fish may vary greatly among different species,which deserves the attention of fish farmers.