Histopathological assessment of gonadal tissue in wild fishes

Histology offers a powerful tool in the study of reproductive health of fishes. It is routinely used for sex verification, identifying stage of development, documenting presence of intersex, tumors, parasites and other abnormalities and quantifying atresia. It can also be used for more subtle changes such as thickness of the vitelline envelope at various stages, yolk appearance, necrosis of sperm, and Sertoli cell proliferation. Gonadal histology, in conjunction with hormone and vitellogenin measurements, morphological and fecundity studies, can provide insights into the effects of various environmental stressors on reproductive health. However, much research, both field and laboratory, is needed to understand cause and effect for observed changes and to understand the meaning of many of the histological observations made in field studies, in terms of reproductive success of fish populations.