CHANGES IN VERTICAL-DISTRIBUTION OF SEA BASS (DICENTRARCHUS-LABRAX L.) DURING A HYPOXIC EPISODE

The vertical distribution of free-swimming sea bass (Dicentrarchus lab rax I,.) was investigated in a 26 m(3) indoor tank by means of acousti c telemetry. During the experiment the bottom of the tank was made pro gressively hypoxic. In normoxic conditions, sea bass displayed a clear diurnal rhythm during which they occupied the surface at night and sw am deeper in the water column during the day. When a vertical oxygen g radient was established, this behaviour changed and sea bass reduced t he amplitude of their daily migration to avoid being exposed to the hy poxic bottom water layer.