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Acoustics as non-invasive technique to monitor swimbladder inflation and larval growth in seabream (Sparus aurata)
July 21, 2022 By Ruby Gonzalez
“It should be remarked that this tool can be applied even under working conditions and therefore it does not interfere in the usual rearing process,” said A. Ladino et al in the research article, “Ultrasonic monitoring of early larval development of fish in tanks. Case study: Gilthead seabream (Sparus aurata).” It was published on Aquacultural Engineering.
Gilthead seabream possess gas-filled swimbladders, which a high acoustic contrast. “This gas has a high acoustic contrast, which means the swimbladder acts as a great reflector of acoustic energy. Hence, when there is a swimbladder present, it is responsible for 90 to 95 percent of the total backscattered acoustic energy from the fish,” the authors cited.
Swimbladder inflation is a significant matter in intensive fish farming, since it is related to larval survival rate and the morphological quality of individuals.
The experiments were carried out in the Spanish Institute of Oceanography’s marine aquaculture plant at Mazarrón.
“The numerical estimation of target strength (TS) has been proven as a useful tool for predicting and interpreting acoustic backscattering of larvae even in the early stages of larval development,” the authors said. TS, they explained, is defined as the ratio between backscatterred and incident acoustics intensifies when the target is insonified.
Monitoring on early larval growth, swimbladder area and inflation rate were conducted at three days post-hatch until end of experiment at 16 days post-hatch.
The general trend based on acoustics TS measurements showed that it is almost constant during the first post-hatching days, with low TS value recorded. They pinned this to the scattering of residual bubbles, larval food and larvae without on inflated swimbladder.
Acoustic detection starts at the onset of swimbladder inflation. “From this moment, the inflation rate and swimbladder area on one hand and the early larval growth on the other can be monitored by measuring and processing the TS automatically, providing a non-invasive technique to monitor swimbladder inflation and larval growth,” they said.
One of the causes of increase in larval mortality rate in the aquaculture industry is traced to non-activation of the swimbladder in the early stages of development. It compromises growth rate because of more energy exerted to maintain the swimming position in the water column, considering that swimbladder enable buoyancy control.
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