Effects of insecticide Thiodan®on the morphology and quantification of ovarian follicles in lambarisAstyanax bimaculatus(Linnaeus, 1758) in different treatments

Thiodan® is an insecticide which can cause morphological changes in fish tissues, dependent on the concentration. To investigate possible morphological changes, this study evaluated the number and diameter of ovarian follicles in lambaris Astyanax bimaculatus exposed to Thiodan® for 96 h in different treatments at three sub-lethal concentrations: 1.15, 2.3 and 5.6 μg L−1 and a control group without Thiodan®. Females exposed to Thiodan® were divided into four treatments: (i) without acclimation and without food, (ii) without acclimation and with food, (iii) with acclimation for 10 days and without food; (iv) with acclimation for 10 days and with food. In this study, it was noted that the action of Thiodan® at sub-lethal concentrations in a static system did not affect the morphology of follicular development. However, the treatments with acclimation showed lower numbers of primary and secondary follicles when compared to fish from treatments without acclimation. For the groups exposed to Thiodan®, a greater number of atretic follicles were observed compared to the control groups. The follicular diameter of secondary follicles in fish exposed to Thiodan® in the treatment with acclimation and with food was highest in the control group (P < 0.05). Furthermore, the mean gonadosomatic (GSI) and hepatosomatic (HSI) indices of treatments with acclimation were lower than those for treatments without acclimation. These data suggest that the fish may be being affected by the pesticide to which the fish were submitted, and may cause impairment to the follicular development.