Device and method for monitoring activity in fish

The invention relates to a device placed on the operculum to monitor the metabolic state and well-being of fish through joint, simultaneous measurements of breathing frequency and physical activity via a plurality of accelerations that are coplanar (x and y axes) and normal to the operculum (z axis). The substrate is flexible and is covered with an water-resistant coating, which contains an electronic circuit with an acceleration sensor (208), a control unit (202), a microcontroller (206) configured to execute at least one activity-monitoring routine, a memory (210) and a battery (204). Data are collected via an external unit (201) which can optionally process them in a complete or partial manner. This type of measurement can be processed jointly with another type of measurement, obtained from other sensors of environmental parameters