The Effect Of Fluoride On The Osmotic Regulation Of The Gill In Zebrafish (Danio Rerio)

The experiment was designed to investigate the toxicity mechanism of fluoride to aquatic organisms and provide theoretical basis for the evaluation of fluoride as environmental pollutants by studying the effects of waterborne fluoride exposure on osmotic regulation of zebrafish gills. Adult zebrafish were randomly divided into 4 groups and exposed to 0 mg/L of fluoride in the control group and 20 mg/L,40 mg/L,80 mg/L of fluoride in the test groups for 60 days. Each group had 1 replicate. After exposure for 30 days and 60 days, the body length and body weight of zebrafish were measured. Gills were rinsed in physiological saline (0.85% NaCl) and immediately fixed in 4% Bouin's solution for histopathological examination. ATPase activities and genes expression of gill tissue were determined. The test results were as follows:1. The effects of fluoride on body length and body weight in zebrafishAfter exposure for 30 days and 60 days, the body length and body weight were significantly decreased with the increase of fluoride concentration compared with the control group, but the changes in the same concentration group was not significant at different time.2. The effects of fluoride on histological sections of gillsAfter 30 days and 60 days of fluoride exposure, there were obvious pathological changes in the gill tissues of zebrafish, such as gill filament edema, gill lamella of cell swelling, shedding, and base adhesive. Severe injury was found in 80 mg/L fluoride group that the gills were filled with mucus and part of the gill lamella was full of inclusion which looked like a pan.3. The effects of fluoride on enzyme activityAfter 30 days and 60 days of fluoride exposure, the activities of Ca2+-ATPase and Na+-K+-ATPase in gill tissue were decreased with the increase of fluoride concentration, The enzyme activity was significantly decreased in 40 and 80 mg/L of fluoride groups. And with the increase of exposure time, enzyme activity also showed a decreasing trend in the same fluoride group.4. The effects of fluoride on genes expressionAfter exposure for 30 days, the expressions of AQP3, NKA and NHE genes showed a tendency to decrease first and then increase. The expressions of AQP3 gene in 40 mg/L group and 80 mg/L group were significantly higher than those in control group. NKA gene expression in 40 mg/L was significantly lower than the control group. NHE gene expression was significantly higher in 80 mg/L group than that in control group. The expression of CFTR gene was first increased and then decreased and the expression in 40 mg/L group was significantly higher than that in the control group. After 60 days of fluoride exposure, CFTR and NHE genes were found to show a decreasing trend, and there was a significant difference between 40 mg/L group and 80 mg/L group. The expressions of AQP3 and NKA genes showed a tendency to decrease first and then increase, while the expression of AQP gene in 80 mg/L group was significantly higher than that in control group. NKA gene levels in 40 and 80 mg/L groups were significantly higher than the control group.The results showed that fluoride could affect the structure and function of osmotic regulation in gills of zebrafish by disturbing the activities of enzymes and genes expressions in zebrafish, and the effects were aggravated with the increase of fluoride concentration. It is revealed that fluoride has a toxic effect on the osmotic adjustment of fish gills.