Acute toxic effect of phenol on zebrafish Branchydanio rerio.

Groups of ten zebrafish were exposed to 21, 24, 28, 32, 37 and 42 ppm phenol concentrations at 24°C. Each test was repeated three times. From the estimated LC50s of each test the toxicity curve was made from which the 96 h-LC50 was estimated to be approximately 24.9 ppm. The fish swam wildly, dashing up and down almost immediately after placement in the test aquaria and all of them lost their equilibrium within a few minutes and most of them died within a few hours. Histological changes of the gill, liver, kidney and intestine were studied. A) Gill: in mild damage, the epithelial layer was swollen whereas in severe cases this layer was stripped away. B) Liver: sinusoids became enlarged and contained numerous blood cells, vacuolated and atrophic areas were visible. C) Kidney: extravasation, necrosis of the nephron and decreasing affinity toward H-E staining were observed. D) Intestine:slight damage of mucosa occurred after short term exposure, though this layer was partially or totally missing after longer exposure. Deformities in the shape and size of the blood cells were distinctive and many blood cells were at the stages of hemolysis.