THE STRESS RESPONSE OF THE BRASSY CHUB, A LOCAL REEF FISH AND CANDIDATE FOR SUSTAINABLE AQUACULTURE

Abstract

The brassy chub, Kyphosus vaigiensis, is a reef herbivore that has been shown to growrapidly in captivity, though no information is available on how they respond to maintenance- related stress, a major component of captive fish welfare. Generally, in fish, the stress response has been shown to disrupt hydromineral balance and activate endocrine systems including the hypothalamus-pituitary-interrenal (HPI) axis, which are characteristic responses of the alarm phase. During the resistance phase of the stress response, typical changes involve energy metabolism affecting glucose availability and antioxidant enzyme activity. In this study, I characterized the effects of acute handling stress on the physiological responses of brassy chub over a 24-hour (h) time course, by measuring endpoints associated with both the alarm and resistance phases of the stress response. These included plasma and mucus cortisol, plasma glucose and osmolality, and hepatic activity of the antioxidant enzymes superoxide dismutase (SOD) and glutathione peroxidase (GPX), and hepatic lipid peroxidation. The results indicated that plasma and mucus cortisol levels were transiently increased in stressed fish by 1 h, suggesting activation of the HPI axis. Moreover, plasma glucose increased by 1, 12, and 24 h while plasma osmolality increased at 1 and 6 h and decreased at 12 and 24 h. SOD activity decreased in the stressed treatment at 6 and 12 h and returned to control levels by 24 h. GPX activity and lipid peroxidation were unaffected by the handling stressor throughout the 24 h period. In addition to validating the use of mucus as a minimally invasive technique to detect HPI axis activation, this study provides fundamental insight on the effects of a maintenance- related stressor on osmoregulatory function, energy mobilization, and the antioxidant defense system. Understanding these responses provides critical insights needed to inform management practices for the welfare and production of the brassy chub.