Biochemical effects of stress

The stress response consists of an integrated pattern of adjustments to the physiology and behavior of a fish that promotes the best chance of survival in the face of a noxious or threatening situation. The response is characterized by a switch from an anabolic to a catabolic state, thereby providing the fish with the necessary resources to avoid or overcome the immediate threat, and has evolved as an adaptive response to short-term or acute stresses. If the fish is faced with a continuous, or chronic, stress from which there is no escape (e.g., sublethal pollution, and suboptimal aquaculture conditions), the adaptive value of the response is compromised. The fish may acclimate to the new environmental conditions, albeit at a reduced level of performance, or prolonged activation of the stress response may lead to damaging side effects (e.g., growth suppression, reproductive dysfunction, and immunosuppression) that can ultimately result in mortality. This chapter describes some of the major biochemical changes that occur in stressed fish, because of effects mediated either by stress hormones or because of specific responses to particular types of stress. Because of the diversity of such changes, the information presented is, of necessity, selective, but covers the major areas of respiration, metabolism and growth, osmoregulation, defense (including detoxification) and reproduction. The chapter describes the hormonal changes occurring in stressed fish and concludes by summarizing the biochemical parameters that can be employed as indicators of stress in fish.