Change in vertical distribution of sea bass (Dicentrarchus labrax L.) during a hypoxic episode

The vertical distribution of free-swimming sea bass (Dicentrarchus labrax L.) was investigated in a 26 m3 indoor tank by means of acoustic telemetry. During the experiment the bottom of the tank was made progressively hypoxic. In normoxic conditions, sea bass displayed a clear diurnal rhythm during which they occupied the surface at night and swam deeper in the water column during the day. When a vertical oxygen gradient was established, this behaviour changed and sea bass reduced the amplitude of their daily migration to avoid being exposed to the hypoxic bottom water layer.