All fish were anaesthetized with 0.01% 2-phenoxyethanol
(Kanto Chemicals, Japan) before sampling and biometric parameters (total length and body weight) of each fish were measured.
The gonads were collected and fixed overnight in Bouin’s solution
at room temperature, then dehydrated in a series of ethanol concentrations, cleared in benzene, and embedded in paraffin. Seven
micrometer cross-sections were prepared. Hematoxylin and Eosin
(H&E) staining method was used and all slides were examined by