Effects of water temperature changes on the endogenous and exogenous rhythms of oxygen consumption in glass eels Anguilla japonica

Abstract

The oxygen consumption rate (OCR) of glass eels Anguilla japonica was measured to determine the effects of water temperature changes on their endogenous and exogenous rhythms. Glass eels were exposed to different water-temperature patterns during simulated 12, 14 and 24 h cycles. The OCR of wild glass eels, freshly collected from estuaries, exhibited a clear endogenous circatidal rhythm while kept in constant darkness at 15 ± 0.1°C. However, if the temperature was varied, the glass eels OCR coincided with the gradually increasing water temperature (Δt = 1°C per 12 or 24 h) in the experimental chamber. This minor variation in water temperature (Δt = 1°C per 12 or 24 h) was significant enough to affect the rhythmicity of the glass eels' OCR. When the glass eels were exposed to a cyclic increase or decrease in water temperature (1°C per 14 h), the OCR peaks displayed a clear rhythmicity at 14 h intervals. The results indicate that the glass eels' OCR is controlled not only by an endogenous circatidal rhythm, but also by exogenous rhythms related to small environmental changes, such as water temperature changes of as little as 1°C. The possible mechanisms underlying these temperature responses are discussed and the implications of the findings for the eco-physiology and metabolic activity rhythms of glass eels are highlighted.