Effect of environmental stressors on fish health - Possible action of controlled stress as a eustress in fish

Abstract

Fish are exposed to various local and global environmental stressors （or stimuli）, such as pollutants, chemicals, acute and chronic changes in temperature, and the subsequent increased chances of succumbing to infectious diseases are concerned. The exposure of organisms to stressors may result in a series of biochemical and physiological changes. At the living state, these changes are mediated by the neuroendocrine system. There is also a cellular stress response, which includes the induction of stress proteins, a family of heat shock proteins, following exposure to stressful situations. These stress responses in organisms can affect their general health. We observed the decrease in the redox state in response to heat shock or high doses of dietary antibiotics, oxytetracycline （OTC）, in coho salmon（Oncorhynchus kisutch）. The results indicate that both heat shock and the high doses of dietary OTC induce oxidative stress, which would enhance oxidation in fish. In addition to physical and chemical stress trials, we found that mild physiological stress by handling can affect the expression of growth-related genes in fish. In general, the word " stress " has a negative connotation and is likely to be considered undesirable. However, the effects of stress differ depending on the intensity of the stimulus, the condition of the recipient, etc. It is considered that there are two types of stress: eustress （positive or desirable stress） and distress （negative or undesirable stress）. Accordingly, eustress provided by environmental stresses under control in aquaculture, are useful to accomplish the maintenance and improvement of farmed fish health as well as fish welfare.