Low-temperature induced changes in hepatic aerobic metabolism in fresh water- and seawater-acclimated milkfish, Chanos chanos

• Main Authors: Zong-Zheng Liu, 劉宗政
• Other Authors: 李宗翰
• Format: Others
• Language: zh-TW
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/92348912240816269178

碩士 === 國立中興大學 === 生命科學系所 === 104 === Milkfish (Chanos chanos) is a euryhaline fish intolerant to hypothermal environments. Previous studies indicated that seawater (SW)-acclimated milkfish was more tolerable to hypothermal challenge than fresh water (FW)-acclimated individuals. The liver of fish provided sufficient energy which was required through aerobic and anaerobic metabolic pathways. In this study, we focused on the hypothermal (18ºC) effects on aerobic metabolism pathway to maintain energy homeostasis. The ventilation frequency of both SW- and FW-acclimated milkfish were down-regulated under hypothermal challenge. On the other hand, the oxygen consumption in the hypothermal environment was down-regulated in SW-acclimated milkfish, but not changed in the FW-acclimated groups. The citrate synthase (CS) and cytochrome c oxidase (COX) are important enzymes in TCA cycle and electron transfer chain (ETC) of aerobic metabolism, respectively. Moreover, cytochrome c oxidase subunit 4 (COX4) is an important subunit in the COX complex which is able to regulate COX activity. Hence we focused on COX4 mRNA and protein expression of COX in the liver. Upon hypothermal challenge, hepatic CS activity of FW-acclimated milkfish was up-regulated. COX4 mRNA and protein expression were up-regulated, while COX activity was down-regulated in the FW/18ºC group. SW-acclimated milkfish upon hypothermal challenge, however, CS mRNA and protein expression were down-regulated, while CS activity was increased. COX4 protein abundance and activity revealed the same pattern in FW and SW-acclimated milkfish. Taken together, the whole body aerobic metabolism would decrease with hypothermal challenge which was speculated by the results of ventilation frequency and oxygen consumption. However, COX4 mRNA and protein expression were up-regulated and compensatory to ETC capacity. CS activity increased for compensation to drive the up-regulation of TCA cycle capacity, which enhanced production of energy and amino acids to synthesis protein and lipids to resistant cold stress. Hepatic TCA cycle and ETC capacity may lead to different abilities of hypothermal tolerance between SW- or FW-acclimated milkfish.