Abstract
Continuous record of ambient water temperature and depth was obtained for a free-ranging red sea
bream using a data logger in the natural sea for over 150 days. The fish (FL 43.0cm, BW 1.5kg) was
releasedon 1 December, 1997 at a point in Wakasa Bay (35° 35' N, 135° 29' E) and recovered on 5
May, 1998 at a pointwhere was 15km far from the releasing point(35° 44' N, 135° 26' E). Temperature
recordwasdividedintothree typicalpatternsin accordance withseasonal environmental change;decreasing
temperature period from early to mid winter, low and constant temperature period from mid February to
early April, and increasing temperature period from early to mid spring, respectively. Swimmingactivity
increased with rising water temperature in the increasing temperature period. The critical temperature for
activity to beginwas 12° C. This value wasequal to the lowerlimit of optimum temperature of red sea
breams whichwas determined by respiratory trials. Risingup to 12° Cambientwatertemperature seems
to switch the behaviour of red sea bream in the natural sea.
