Influence of photoperiod on follicular development, morphometry, and oxidative stress in zebrafish (Danio rerio)

The photoperiod is a crucial factor in controlling the reproductive processes of teleost fish. This study aimed to evaluate the effects of different photoperiods on the follicular population percentage, morphometry, and oxidative stress in Danio rerio. Twenty-four female zebrafish were divided into two photoperiod groups: 12 h light/12 h dark (12 L:12D) and 14 h light/10 h dark (14 L:10D). Histological processing of the ovaries was conducted to determine the follicular population and the morphometry of both oocytes and follicles. Biochemical analyses were performed to assess oxidative stress markers, including nitric oxide (NO), thiobarbituric acid reactive substances (TBARS), hydrogen peroxide (H2O2), reactive oxygen species (ROS), superoxide dismutase (SOD), catalase (CAT), total proteins, acetylcholinesterase (AChE), and butyrylcholinesterase (BuChE). The photoperiod significantly influenced various follicular and oocyte structures, such as area, vitelline envelope thickness, and follicular cell thickness, although the overall follicular population did not differ between the groups. The 12 L:12D photoperiod notably affected biochemical indices, resulting in altered levels of NO, TBARS, H2O2, ROS, SOD, and CAT, along with decreased total protein concentration and increased AChE activity. Despite the heterogeneity of follicular structures observed in the ovaries of fish across both photoperiods, this study concludes that the 14 L:10D photoperiod enhances follicular maturation in Danio rerio and reduces oxidative stress during ovarian development. These findings underscore the importance of photoperiod manipulation in optimizing reproductive health and managing oxidative stress in aquaculture practices.