Ultrasonic monitoring of early larval development of fish in tanks. Case study: Gilthead seabream (Sparus aurata)

Swimbladder inflation is a significant matter in intensive fish farming, since it is related to larval survival rate and the morphological quality of individuals. In this work, we propose a non-invasive acoustic technique using ultrasound to monitor the swimbladder development of gilthead seabream (Sparus aurata) in tanks. The fundamental hypothesis is that, due to the high acoustic contrast of gas, the swimbladder’s inflation process can be detected by measuring the larvae’s target strength during their early development. Backscatter numerical models using the finite element method, developed from biological measurement data, were applied to evaluate the feasibility of the proposed method. The acoustic measurements were obtained using an EK60 Simrad echosounder working at 200 kHz. The target strength values were evidenced with and without the presence of a developed swimbladder, showing a statistically significant relationship with the swimbladder’s standard length, area and the percentage of larvae with a swimbladder. The experiments were carried out in the Spanish Institute of Oceanography (IEO)’s marine aquaculture plant at Mazarrón (Murcia, Spain).