Appraisal of fish behaviour based on time series of fish positions issued by a 3D array of ultrasound transducers

We present a novel low-cost analysis platform and method for monitoring the behaviour of a fish population (starry sturgeons – Acipenser stellatus) – in an experimental tank using a 3-dimensional array of ultrasound transducers. The platform provides time series of fish positions, allowing for assessment of the dynamics of geometric centre (centroid) of fish population. We demonstrate that centroid evolution represents a sensitive indicator of fish behaviour under conditions varied from normal towards non-physiological limits, e.g. pH, dissolved oxygen concentration, feeding and light. Emphasis has been given to reversible effects i.e. after normalisation of water parameters undergoing “gentle” variations, the fish behaviour returns to the normal/physiological pattern. Fish behaviour was previously assessed by several techniques (e.g. electrical impedance, video monitoring, hydro-acoustics, etc.). To our knowledge, this is the first study that uses ultrasounds to continuously monitor the three-dimensional position of fish, having also the advantage of being independent on water turbidity or light level. We stress on the capabilities of the platform and related method to assess the occurrence of abnormal fish behaviour, revealed by the change over a predefined threshold exhibited by the dynamics of the fish population exposed to stimuli, and to automatically issue a warning alert (in case of e.g. non-optimum water quality), thus making it suitable for remote, cost effective monitoring of fish behaviour supporting an optimised aquaculturing.