  Successful aquaculture systems can reduce the pressure and help secure the
most diverse and productive Red Sea coral reef ecosystem to maintain a healthy
and functional ecosystem within a sustainable blue economy. Interestingly,
recirculating aquaculture systems are currently emerging in fish farm
production practices. On the other hand, monitoring and detecting fish
behaviors provide essential information on fish welfare and contribute to an
intelligent production in global aquaculture. This work proposes an efficient
approach to analyze the spatial distribution status and motion patterns of
juvenile clownfish \textit{(Amphiprion bicinctus)} maintained in aquaria at
three stocking densities (1, 5, and 10 individuals/aquarium). The estimated
displacement is crucial in assessing the dispersion and velocity to express the
clownfish's spatial distribution and movement behavior in a recirculating
aquaculture system. Indeed, we aim to compute the velocity, magnitude, and
turning angle using an optical flow method to assist aquaculturists in
efficiently monitoring and identifying fish behavior. We test the system design
on a database containing two days of video streams of juvenile clownfish
maintained in aquaria. The proposed displacement estimation reveals good
performance in measuring clownfish's motion and dispersion characteristics
leading to assessing the potential signs of stress behaviors. We demonstrate
the effectiveness of the proposed technique for quantifying variation in
clownfish activity levels between recordings taken in the morning and afternoon
at different stocking densities. It provides practical baseline support for
online predicting and monitoring feeding behavior in ornamental fish
aquaculture.
