Melatonin concentrations in relation to oxidative status and oocyte dynamics in the ovary during different reproductive phases of an annual cycle in carp Catla catla

The present study on carp Catla catla is the first attempt to search for a relationship between the concentrations of melatonin, oxidative status, and oocyte dynamics in the ovary of any fish. We measured the levels of melatonin, different antioxidative agents, and the marker of intracellular stress along with the profiles of different developmental stages of oocyte in the ovary of adult carp during four distinct phases in an annual reproductive cycle. Ovarian melatonin titers displayed significant seasonal variations with a peak during spawning and nadir during post-spawning, and thereby underlined its proximity to the course of ovarian development. A significant positive correlation was found between the ovarian levels of melatonin and the activity of superoxide dismutase (SOD), catalase (CAT), and glutathione transferase (GST), although each of them showed a negative correlation with the level of malondialdehyde (MDA)-a faithful indicator of intracellular stress. However, ovarian melatonin titers did not exhibit any correlation with the levels of reduced glutathione (GSH) and the activity of glutathione peroxidase (GPx). Collectively, our findings suggest that melatonin measured in carp ovary may be associated with an enhanced activity/level of selective antioxidative agents for reduction in oxidative stress to augment ovarian functions during the spawning.