Respiration of the bathypelagic fish Cyclothone acclinidens

The respiration of 3 adult females of Cyclothone acclinidens was measured in situ. These numerically dominant fish of the meso- and bathypelagic zones were individually captured off southern California at a depth of 1300 m using a multiple-chambered slurp-gun respirometer operated from the submersible Alvin. Continuous oxygen consumption measurements of each fish were made at the capture depth for about 28 h, spanning an interval from late morning to the following mid-afternoon. Nocturnal rates of respiration of these fish were 3 to 5 times higher than diurnal rates, suggesting a daily thythm in this non-migratory midwater species. Environmental factors such as tides, light, and food could serve to synchronize the observed respiration fluctuation.