Changes induced by atrazine in Clarias gariepinus provide insight into alterations in ovarian histoarchitecture and direct effects on oogenesis.

Clarias gariepinus juveniles were exposed to environmentally relevant concentrations of 0 (control), 2.5, 25, 250 and 500 μg L−1 atrazine in a quality-controlled 28-day laboratory procedure. Findings revealed a significant decrease in the levels of follicle-stimulating hormone, luteinizing hormone and prolactin relative to control (p < 0.05). Atrazine reduced the levels of testosterone while increasing the concentration of progesterone. Histologically, the control and treatments presented three stages of oocyte maturation: the chromatin nucleolar oocyte stage, early perinucleolar oocyte stage and the vitellogenic oocyte stage. However, in the ovaries of the treatment group with the lowest treatment concentration (2.5 μg L−1), atretic oocytes with broken membranes invaded many of the dead ova and empty spaces. In other treatments (25, 250 and 500 μg L−1), interfollicular spaces, vacuolation in oocyte formation, and dissolution of oocyte walls were observed. Disruption of the yolk vesicle and clumping of the cytoplasm in maturing oocytes was observed only at the highest atrazine concentration (500 μg L−1). Gross alterations in ovarian histoarchitecture and reproductive hormone levels observed in this study showed interference with oogenesis which may result in reduced egg viability and fecundity in fish with ecological implications in water bodies exposed to atrazine even at reduced concentrations. [ABSTRACT FROM AUTHOR]