Effects of stress on fish reproduction, gamete quality, and progeny

Different taxa of fish have different tolerances to stress. This implies that for a particular stressor, severity may vary depending on the species to which it was applied. Species may differ in the nature of their physiological response and reproductive consequences to stressors. For example, disturbance or handling may affect the timing of reproduction-accelerating or delaying it as the case may be-in species such as rainbow trout (Oncorrhynchus mykiss); however, tilapia (Oreochromis niloticus) respond by acceleration or complete inhibition of reproduction, depending on the maturational stage when the stressor is experienced. Strategies for coping with stress affect reproductive fitness either in terms of gamete or progeny quality. The physiology associated with maturation and spawning appears tightly coupled with stress physiology. Environmental variables, particularly nutrition, are ultimately important in affecting gamete quality and reproductive timing. The physiological response to stressors is also quite polymorphic, within and between species. For trample, the circulating concentration of the primary stress response factor cortisol varies greatly among resting and among stressed rainbow trout stocks. Immunocapacity can be influenced by stress, reducing reproductive fitness of broodfish. We propose that maternal systems have been developed to buffer eggs from deleterious consequences of stressors, including regulation of transfer of substances of maternal origin to the egg and in mechanisms controlling the timing of reproduction. Effects of nutritional stressors are moderated by effects on timing of first maturity or subsequent reproductive events and/or by maintenance of quality of some eggs via atresia of others. Deleterious overload of eggs with substances such as cortisol is likely prevented by limiting entry of these compounds into the eggs. Barriers to vertical transmission of numerous pathogens seem to exist, while maternally derived immune protection is provided to assist with disease prevention of pathogenic organisms acquired from parents or by direct post-spawning infection. Timing of reproductive events including puberty, atresia, maturation and ovulation are influenced by other physiological variables responsive to stressors. Knowledge of how a stressor might affect the physiology of a species can help in development of management tactics that lessen the impact of a stressor or even in the development of therapeutants. Published by Elsevier Science B.V.