EFFECTS OF SUDDEN CHANGES IN SALINITY ON ENDOGENOUS RHYTHMS OF THE SPOTTED SEA BASS LATEOLABRAX SP

The endogenous rhythm of oxygen consumption in juvenile spotted sea ba ss (Lateolabrax sp.) was measured to test the effects of sudden change s in salinity on the metabolic activity. Mean oxygen consumption rates of this euryhaline fish decreased by 13.5 to 16.0% and 25.3 to 36.4% when they were transferred from 31.5 to 15 parts per thousand seawater and to fresh water (0 parts per thousand), respectively. The maximum rate of oxygen consumption was observed between 18:00 and 19:00 hrs lo cal time, 1 to 2 h before sunset, even though they were kept in consta nt darkness. The peaks of oxygen consumption occurred in 23.2- and 23. 3-h intervals, which correspond with a circadian rhythm, as revealed b y maximum entropy spectral analysis. A markedly weakened rhythm in oxy gen consumption occurred from 8 to 10 d after onset of the experiments . This study indicates that spotted sea bass can withstand sudden drop s in salinity from 31.5 parts per thousand, to fresh water, and yet ma intain a regular though somewhat dampened endogenous rhythm of oxygen consumption.