Group Effect on Oxygen Consumption of the Red Sea Bream Pagrus major from Postlarval to Young Stages

マダイの酸素消費量が群形成によって影響されるかを明らかにするため、着底前の後期仔魚(全長7.3-10.6mm)、それに着底後の稚魚(27.1-37.6mm)と若魚(52.0-65.8mm)を対象として、室内実験を行った。酸素消費量の測定は、各発育段階の魚を単独と2-16個体の群に分離して呼吸室に収容し、17±0.6℃・明状態(4500lx)で行った。後期仔魚期では、個体数が増加しても酸素消費量に変化がみられなかった。稚魚期では負の群効果がみられ、単独と8個体群の間での酸素消費量の平均増加率は1.8倍(1.51→2.71μg/hr/mg dry weight)を示した。若魚期では、単独と8個体群の間で酸素消費量に有意な差がみられたが(1.22→1.99μg/hr/mg dry weight)、これは個体当たりの生活空間が著しく減少したためと考えられる。このような酸素消費量の変化はいずれも、各発育段階のマダイ自身の行動様式と良く対応していた。

Group effect on the respiration of red sea bream Pagrus major is examined at 17°C under a light condition (4500 lx). Postlarvae, juveniles and youngs were separately accomodated in respiration chamber (100-1000 ml) solitarily or in a group of 2-16 fish. In the postlarvae (7.3-10.6 mm in total length), oxygen consumption hardly changed with the number of fish. The juveniles (27.1-37.6 mm) revealed a negative group effect, which was indicated by an increase of oxygen consumption in a group of more than 4 fish. There was a significantly 1.8-fold difference between solitariness (1.51 g O2/hr/mg dry weight) and grouped 8 fish (2.71 g O2/hr/mg dry weight). In the young (52.0-65.8 mm), a higher amount of respiration was observed in grouped 8 fish. This was presumably influenced by a remarkable decrease in living space per fish. These group effects on the respiration of red sea bream well coincided with its behavioral change, e.g., group formation, which occurred apparently at the settlement from pelagic to benthic lives.