Determination of MATC and LOEC of ZnSO4 in rainbow trout (Oncorhynchus mykiss) Emphasis by tissue lesion

The aim of  this study conducted in Gonbad Kavous aquaculture laboratory was to  determine MATC and LOEC of ZnSO4 in fish using tissue lesion examinations. To do this, rainbow trout (Oncorhynchus mykiss) juveniles (6.18±1.33 g) were exposed zinc sulphate over 96 hours (in December 2021). Zinc sulphate salt was used to examine toxicity of zinc. The lethal dose of zinc for Oncorhynchus mykiss was 21 mgL-1 over 96 hours. According to the linear regression and relationship between the percentage of mortality and different concentrations of zinc, the LC50 (median lethal dose) was obtained 11.54 mgL-1 for Oncorhynchus mykiss. However, acute toxicity of zinc sulphate showed that mortality was  directly proportional to the concentration of the zinc sulphate, whilst there was no mortality in the control treatment. No behavioral changes were observed in control treatment over the experiment. Microscopic studies showed that the common lesions of gill in fish exposed to zinc lethal concentration were hyperplasia, edema, hyperemia, hemorrhage and expansion of secondary lamellae. Therefore, the results and information obtained in this study can be applicable in ecological risk assessment studies.