The Effect of Paraquat on Hepatic EROD Activity, Liver, and Gonadal Histology in Males and Females of Nile Tilapia, Oreochromis niloticus, Exposed at Different Temperatures

The activity of fish monooxygenases has been used as a monitoring tool to evaluate contamination by cytochrome P450 inducing agents. In this study ethoxyresorufin O-deethylase (EROD) activity was analyzed in males and females of Nile tilapia exposed to a low concentration of paraquat (PQ) at 17°C and 27°C. PQ-treated fish showed a high hepato-somatic index, except females acclimated at 17°C. No differences were found for the gonado-somatic index (GSI) between males. However, PQ-treated females showed high GSI values (6.46 ± 1.75) when compared with the control group (2.30 ± 0.26) maintained at 27°C. Males and females exposed to PQ showed higher microsomal protein values than the control group (9.46 ± 0.22 vs. 6.20 ± 0.18 at 17°C; 9.51 ± 0.35 vs. 4.70 ± 0.19 mg of protein at 27°C, in PQ-treated and control groups, respectively). The EROD activity was high in females exposed to PQ when compared with the control group at 17° and 27°C. The liver histology showed that PQ also caused some hepatic alterations of parenchyma, like vacuolization, necrosis, and an increase of macrophages aggregates and eosinophilic granular cells. Females exposed to PQ showed a greater increase of late-vitellogenic (22.2 ± 3.2) and mature (12.1 ± 2.0) percentage of oocytes than the control group (9.9 ± 3.0 and 8.0 ± 4.3, respectively), and a lower percentage of primary oocytes (8.0 ± 3.3) at 27°C. In short, this work has advanced new knowledge on the influence of gender in biotransformation activity and the reproductive activity of Nile tilapia exposed to a low concentration of paraquat, and demonstrated that their effects could be observed at different temperatures.