Fish Oocyte Ageing and its Effect on Egg Quality

In fish, delayed spawning in nature, delayed egg collection in capture and delayed fertilization after egg stripping can lead to oocyte ageing and over-ripening. Oocyte ageing is reported as one of the most important factors affecting the egg quality. During over-ripening, morphological, physiological, biochemical, histological, cellular, and molecular changes occur inside the eggs and ovarian fluid. These alterations can negatively affect the egg fertilization capacity and successive developmental stages. The time period during which eggs remain viable after ovulation or stripping has been reported from a few minutes to a few weeks depending on the fish species and the storage temperature. Although several biomarkers that characterize the over-ripening phenomenon have been defined, the reliability of these parameters in the field of aquaculture is controversial. For future researches, inhibition of oocyte ageing by antioxidants could be a valuable research topic. In the present article, the morphological, physiological, biochemical, histological, cellular, and molecular changes that occur during oocyte over-ripening under in vivo conditions and during in vitro storage are reviewed and possible reasons for the decrease in viability of eggs are presented. Species-specific changes in the egg viability and larval development are also considered.