In recent years, with the scale and standardization of Stichopus japonicus mariculture, artificial reefs are increasingly used in S. japonicus farming to promote the development of the S. japonicus aquaculture industry. To provide shelter and improve the habitat environment for S. japonicus, three types of artificial reefs (box-shaped reef, triangular-shaped reef, and trapezoidal-shaped reef) were designed according to the ecological habitats of S. japonicus and the marine environment of Haizhou Bay (China) in the present study. After comprehensively comparing the three reef structures, we found that the trapezoidal-shaped reef has good permeability, a larger attachment area, and excellent anti-slip and anti-overturning properties. Further, the flow field characteristics surrounding a trapezoidal-shaped reef at different angles and flow velocities are investigated by three-dimensional numerical simulations. Then, the impact of the placement distance on the flow field surrounding the artificial reef combination was investigated. At the head-on angle θ = 0°, the upwelling volume increases as the flow velocity increases and then decreases, and the back eddy volume remains relatively constant. At the longitudinal spacing D = 4 L, the large slow-flow area surrounding the reef under this condition is more suitable for the S. japonicus habitat. In this study, the trapezoidal-shaped reef design is suitable and beneficial for S. japonicus aquaculture. Moreover, this study will contribute theoretical references to the design and arrangement of artificial reefs in coastal areas.

This research focuses on the application of the optical flow method for target identification and tracking of largemouth bass in underwater environments. The optical flow field, representing pixel movement on a two-dimensional plane, is utilized to analyze grayscale variations in image sequences. The study employs the basic variational optical flow model and introduces the Horn-Schunck (HS) algorithm to address challenges such as the aperture problem. Additionally, the paper explores camera selection and calibration, emphasizing the importance of accurate calibration parameters for binocular vision systems. A domestication experiment is designed for California black bass, incorporating sound stimuli and optical flow-based motion tracking. The study concludes with an evaluation of fish domestication effects using motion trajectory and speed analysis.