Physiological responses, desaturase activity, and fatty acid composition in milkfish (Chanos chanos) under cold acclimation

Physiological responses of milkfish (Chanos chanos) under cold shock and acclimation were investigated. The experimental milkfish, a warm-water teleost, were initially acclimated at 25 degreesC and then transferred directly to 15 degreesC stress responses of this species were monitored for 1 week. Parameters monitored included plasma glucose, lactate, and lipids, as well as stearoyl-CoA desaturase activity and fatty acid compositions of hepatic membranes. All parameters showed significant changes in the process of cold acclimation. A hyperglycemic response indicated by a notable and steady increase in plasma glucose levels from 85 mg dl(-1) to the highest level of 458.2 mg dl(-1) in 24 h was followed by a rapid decline thereafter. The elevation in plasma glucose content under cold shock resulted from gluconeogenesis and glycogenolysis, indicated by correlated changes in plasma glucose with fructose-1,6-biphosphatase and phosphorylase a activities. Plasma lactate concentrations remarkably increased from 47 mg dl(-1) on day 0 to 149.6 and 120.4 mg dl(-1) on days 1 and 2, respectively, and then rapidly declined to the same level as the control thereafter. In contrast, plasma lipids increased gradually from 44.8 mg dl(-1) to 191 mg dl(-1) over the 5-day acclimation period, followed by a declining trend from day 6 on. Furthermore, changes in monounsaturated fatty acids were highly correlated with those of stearoyl-CoA desaturase activities in hepatic microsomes of milkfish during cold acclimation. Results indicate that in milkfish subjected to cold stress, plasma hyperglycemic and hyperlactemic responses can be used as acute stress indicators, and plasma lipids can be used as a chronic stress indicator. (C) 2003 Elsevier Science B.V. All rights reserved.