This study aimed to investigate the effects of different water velocities on the growth performance, blood physiology, and digestive capacity of coral trout (Plectropomus leopardus) in a Recirculating aquaculture system (RAS). One hundred and twenty healthy, uniformly sized coral trout (body mass (92.01 ± 8.04) g; body length (15.40 ± 0.65) cm) were randomly assigned to three flow velocity groups (1 bl/s, 2 bl/s, and 2.5 bl/s) and one control group (0 bl/s). The results show that the weight gain rate (WGR) and specific growth rate (SGR) of coral trout in the 2.5 bl/s water flow velocity group were significantly lower than those in the control group and 1 bl/s water flow velocity group (p < 0.05), while their feed coefficient (FC) values were significantly higher than those of the control group and 1 bl/s water flow velocity group (p < 0.05). The blood glucose (GLU) concentration of coral trout in the 2 bl/s water flow velocity group and the 2.5 bl/s water flow velocity group significantly decreased compared to those in the control group (p < 0.05), while the lactic acid (LD) concentration increased. As the cortisol (COR) concentration and lipase (LPS) enzyme activity of coral trout did not significantly change (p > 0.05), the α- AMS enzyme activity significantly decreased (p < 0.05). Under 2.5 bl/s water flow velocity, the intestinal structure of coral trout changed, and the number of goblet cells decreased. High-water flow velocities affect the physiological homeostasis and intestinal digestion of coral trout, resulting in a decrease in their growth performance, indicating that coral trout is more sensitive to high-water flow velocities. In actual RAS aquaculture, the flow rate should be controlled within 1 bl/s.

To maximize the utilization of ocean resources, shorten the return period of investment and directly supply energy to the fishing cage, this paper performs a preliminary study for a state-of-the-art concept integrating a floating offshore wind turbine with a fishing cage. An octagonal semisubmersible rigid fishing cage with a slack catenary mooring system is designed to match the NREL 5 MW offshore baseline wind turbine. Combined with the blade pitch controller, fully coupled aero-hydro-elastic-servo-mooring simulations are performed through FAST and AQWA to explore the dynamic performance of the integrated system. Free decay conditions, uniform wind with irregular and regular waves, and turbulent wind with irregular waves are tested. The results showed that the integrated system works normally at the operating conditions and exhibits different dynamic characteristics for various scenarios. Additionally, the study on the influence of mooring line length indicates that the increasing line length can significantly affect the cage surge motion and the maximum and mean values of the upwind line tension at fairlead. Specifically, the maximum surge motion with a 924-m-long line is 404.8% larger than that with an 880-m-long line. When the line length increases by 5%, the maximum and mean line tensions decrease by 45.7% and 47.7%, respectively, while when the line length increases by 10%, the maximum and mean line tension decrease by 52.9% and 54.2%, respectively. It should be noted that the main purpose of this work is to conduct a preliminary study on this integrated system, aiming to provide an idea for the conceptual design, modeling and simulation analysis of this integrated system.

This study innovatively proposes a pipeline-type pneumatic lift sediment removal device for cleaning pollutants at the bottom of fish breeding tanks and conducts hydrodynamic characteristic analysis on its core component, the pneumatic lift pipeline structure, which consists of a horizontal circular tube with multiple micro-orifices at the bottom and an upward-inclined circular tube. The pipeline has an inner diameter of 20 mm and a vertical length of 1.2 m, with the orifice at one end of the horizontal tube connected to the gas supply line. During operation, compressed gas enters the horizontal tube, generating negative liquid pressure that draws solid–liquid mixtures from the tank bottom into the pipeline, while buoyant forces propel the gas–liquid–solid mixture upward for discharge through the outlet. Under a constant gas flow rate, numerical simulations investigated efficiency variations through three operational scenarios: ① different pipeline orifice diameters, ② varying orifice quantities and spacings, and ③ adjustable pipeline bottom clearance heights. The results indicate that in scenario ①, an orifice diameter of 4 mm demonstrated optimal efficiency; in scenario ②, the eight-orifice configuration achieved peak efficiency; and scenario ③ showed that the proper adjustment of the bottom clearance height enhances pneumatic efficiency, with maximum efficiency observed at a clearance of 10 mm between sediment suction pipe and tank bottom.

In the fish grading process, traditional mechanical sorting devices tend to cause fish stacking, collisions, and increased stress responses, seriously affecting fish health and commercial value. This paper designs a power-free fish pre-sorting device based on a spiral chute structure, achieving automatic and gentle separation and output driven by the fish’s own weight and water flow; it constructs a multi-stage dynamic model of fish in the spiral chute to analyze the forces and motion patterns; and it introduces an innovative DEM-SPH coupled numerical simulation technology to accurately simulate the complex interactions between fish and water, thereby revealing the self-sorting mechanism of fish inside the device. By setting different conditions such as fish length and water layer thickness, the sorting effect and stability of the device are systematically verified. The results show that this spiral power-free sorting device can effectively achieve automatic spacing separation of fish, reducing collisions and stress responses; fish of 130 mm length have better sorting stability under a water layer thickness of 3–5 cm, and the minimum initial release spacing for effective operation of the device is determined to be 0.11 m.

The journal retracts the article titled “Design and Hydrodynamic Performance Analysis of Airlift Sediment Removal Equipment for Seedling Fish Tanks”

In response to the demand for precise feeding in high-density aquaculture, this study established a dynamic prediction model for fish feeding intensity by integrating vibration signal quantification and deep learning. Through multidimensional experiments (fish size: 50–300 g; stocking density: 20–60 fish/group; feeding speed: 1-3 g/s; feed particle size: 2#4#6#), we quantified the three-axis displacement signals of Micropterus salmoides during feeding. Results demonstrated significant effects of all parameters on water surface fluctuations ( p < 0.05). Vibration displacement exhibited linear relationships with fish size and density. The 300 g group showed 109.7% higher peak amplitude than the 50 g group, while the 60-fish density group exceeded the 20-fish group by 141.9%. Optimal palatability (4#) reduced fluctuation frequency by 42%. A predictive model for feeding vibration patterns was developed, incorporating fish size (S), density (D), feeding speed (V), feed particle size ( Φ ), real-time triaxial vibration sum, and time series (t) as inputs to predict the summed vibration displacement at t + 5 s, which serves as a quantitative proxy for feeding intensity. The Long Short-Term Memory (LSTM) model accurately captured fish feeding dynamics (RMSE = 69.43 μm, MAE = 48.00 μm, R ² = 0.883). In comparative analysis, the LSTM outperformed Gated Recurrent Unit (GRU) and Transformer models in forecasting accuracy. Deployed on an embedded system (Orange Pi AiPRO), closed-loop tests demonstrated superior performance: residual feed rates were ≤ 0.8% across all trials, outperforming optical flow (2.69% residuals) and graph neural network (6.58% residuals) methods. The space complexity of the vibration-LSTM approach was only 6.4–31.8% of GCN-based approaches, enabling cost-effective (<$200) real-time control.