THE CHANGE OF RESTING METABOLISM WITH THE RAPID LOWERING OF WATER TEMPERATURE ON CULTURED RED-SEA BREAM AND THE EFFECT OF HABITAT WATER TEMPERATURE ON THE CHANGE

The change of resting metabolism (RM) with rapid lowering of water tem perature was studied in cultured red sea bream Pagrus major acclimatiz ed at 25 and 15-degrees-C. The RM decreased with rapid lowering of wat er temperature from the habitat temperature to the range 10-9-degrees- C in the 15-degrees-C group (the group acclimatized to 15-degrees-C) a nd to the range 15-13-degrees-C in the 25-degrees-C group (the group a cclimatized to 25-degrees-C). However, after RM reached the minimum le vel as the water temperature was lowered, the metabolism of both group s increased contrary to expectation. The inflection temperature of the 15-degrees-C group was lower than that of the 25-degrees-C group. How ever, the minimum level of RM showed no significant difference between the two groups. The temperature dependence of RM in the 15-degrees-C group was significantly larger than that in the 25-degrees-C group wit hin the range from the habitat temperature to the inflection temperatu re. On the other hand, the reaction temperature dependence of Mf Mg2+- ATPase activity in the 15-degrees-C group was larger than that in the 25-degrees-C group within the same range of RM. This result of the rea ction temperature dependence of Mf Mg2+-ATPase activity coincided with that of RM. We consider that the increase of metabolism in low temper ature water might be caused by the increasing Ca2+ concentration aroun d myofibrils.