Ship aquaculture platforms are expected to become a meaningful way to expand offshore farming. The growth performance and nutritional composition of the large yellow croaker reared in an offshore ship aquaculture system and nearshore traditional cage system was evaluated in this study. The results showed that the aquaculture ship could effectively avoid the harsh environment such as typhoons and red tides. The test large yellow croaker adapted to the ship culture system in a short time. No serious stress events occurred during the whole rearing process. During the culture experimental period, the fish fed normally, and disease was controlled. The aquaculture ship has good environment conditions during breeding with a water temperature of 21.5–28.5 °C, salinity 20.7–31.8‰, pH 7.6–8.4, dissolved oxygen 7.2–12.8 mg/L, ammonia nitrogen < 0.08 mg/L, and the number of bacteria and vibrio in water were 1.2 ∗ 10³–1.6 ∗ 10³ CFU/mL and 1.2 ∗ 10²–1.8 ∗ 10² CFU/mL, respectively. The survival, weight gain rate, and monthly weight gain of the large yellow croaker in the ship were 99.02%, 41.48%, and 67.52 g, respectively, which were significantly higher than those of cage culture. The crude protein content of the large yellow croaker raised in the ship was significantly higher than that in the cage group, and the crude fat content was significantly lower than that in the cage group. These results indicated that the growth performance and nutritional composition of the large yellow croaker reared in offshore ship were better than those of the fish in the cage. These findings enhanced our understanding of an offshore ship aquaculture model of large yellow croaker.

To explore the effect of density on large yellow croaker (Larimichthys crocea) under intensive aquaculture conditions and determine the appropriate culturing density, this study investigate the effects of different stocking densities on the nutritional composition, stress, and immune levels of large yellow croaker. Through a long-term aquaculture experiment, conducted under flow-through conditions of intensive aquaculture, three initial density groups were set: a low density group [LD], 4.92 kg/m³; a medium density group [MD], 7.56 kg/m³; and a high density group [HD], 10.08 kg/m³, for a 150-day rearing trial. Large yellow croaker were fed to satiation twice daily (6:00, 17:00). At the end of this trial, the final densities were 10.38 ± 0.50, 14.41 ± 1.06, and 18.71 ± 0.99 kg/m³ in the LD, MD, and HD groups, respectively. The results showed that the growth performances were adversely influenced by a high stocking density. Levels of cortisol in serum, superoxide dismutase (SOD) and catalase (CAT) in liver, Na⁺-K⁺ ATPase and Na⁺-K⁺ ATPase gene in gills, and heat shock protein (HSP70/90) genes and glutathione S-transferase (GST) genes in the liver significantly increased under HD treatment. Results of immune response analyses showed that there was a clear decrease in immunoglobulin M (IgM), complement component 4 (C4), and lysozyme (LZM) in serum, lysozyme (LZM) genes, tumor necrosis factor-alpha (TNF-α) genes and interleukin-1β (IL-1β) genes in the head kidney of large yellow croakers reared in the HD group. An obvious increase in free amino acids and fatty acids in the muscle of large yellow croakers reared in HD group was also observed. Overall, this study showed that the optimal final culturing density of large yellow croaker under flow-through systems should be between 14.41 kg/m³ and 18.71 kg/m³ to improve aquaculture efficiency and product quality.

Guoxin No. 1, one of the largest smart aquaculture vessels currently in operation, represents an important development in large-scale mobile aquaculture platforms. Continuous circulation of oxygen-rich seawater is essential for maintaining suitable culture conditions in intensive aquaculture vessels. However, the complex pipeline arrangements used for distributing seawater among multiple farming tanks can result in uneven flow allocation. In this study, three-dimensional CFD simulations were conducted to investigate the internal flow behaviors and flow distribution in a T-type pipeline system for an aquaculture vessel. Extending previous studies based on coplanar branch configurations, a non-coplanar skew branch pipe arranged in the xy-plane was investigated. Particular attention was given to the influence of the spatial offset between the branch pipe and the main pipeline axis on velocity distribution, pressure variation, and outlet flow rates. The results show that the spatial offset modifies the momentum transfer process at the junction and generates a swirling motion inside the main pipeline. Compared with the conventional inclined branch configuration, the offset branch shifts the high-velocity core away from the pipe center and reduces the imbalance between the two outlet flow rates. The pressure field is also redistributed due to the asymmetric momentum injection, indicating a trade-off between improved flow uniformity and local pressure variation. The present study demonstrates the potential of non-coplanar skew branch configurations as a passive approach for improving seawater distribution in large-scale aquaculture vessel pipeline systems.

Large-scale offshore aquaculture vessels provide an effective approach for expanding marine aquaculture; however, the complex flow characteristics induced by water circulation systems and vessel motion remain insufficiently understood. In this study, a numerical model based on the volume of fluid (VOF) method and the k-$\omega$ SST-DES turbulence model was developed to investigate the vortex flow characteristics. The developed numerical model accurately captured the vortex flow characteristics and free-surface fluctuations in the aquaculture tank, and the dominant coherent structures were identified using Q-criterion-based proper orthogonal decomposition (POD). The results show that the mean vortex structure is mainly concentrated around the central axis, while higher-order POD modes reveal vortex-core oscillation, deformation, and interactions with surrounding flow structures. Furthermore, the effects of roll excitation and its coupling with inlet jet flow were investigated. The results demonstrate that roll motion induces significant periodic fluctuations in the flow field, while the inlet jet flow maintains the stability of the central vortex structure and reduces velocity variations. These findings provide new insights into the hydrodynamic mechanisms governing vortex evolution under combined vessel motion and water circulation and offer a scientific basis for optimizing flow conditions in large-scale offshore aquaculture tanks.