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In aquaculture, real-time and rapid detection of dead fish is important for early risk warning and improving aquaculture efficiency. However, the complex actual environment and uncontrollable fish movement have brought great challenges to the detection of dead fish. Therefore, this paper proposes a high-precision and lightweight dead fish-detection transformer (DF-DETR) based on machine vision and original RT-DETR (real-time detection transformer). The specific implementation is as follows: Firstly, the backbone of the original RT-DETR was replaced by the RepNCSPELAN module which extracts multi-scale features. This not only improves the model’s ability to detect targets of different sizes but also reduces the amount of model parameters. Secondly, the AIFI in the RT-DETR was improved to CascadedGroupAttention (CGA). By changing the original feature fusion method, different levels of features are grouped and attention mechanism is added, so as to capture more target features. Finally, the CCFM_CSP module was constructed to fuse important features using parallel dilated convolution with different expansion rates, which improves the detection accuracy. The experimental results show that the mAP@.5 of the proposed dead fish detection model DF-DETR can reach 96.6%, and the parameter amount is reduced by 27% compared with the original RT-DETR. In summary, the proposed DF-DETR model realizes real-time and high-precision dead fish detection, which can provide effective technical support for the development of intelligent inspection robots. [ABSTRACT FROM AUTHOR]

To address the low sewage collection performance in circular aquaculture tanks, this paper systematically investigates the influence of jet pipe flow rate Q, the deployment distance ratio d/r (where d represents the distance between the midpoint of the axis and the nearest tank wall, and r is the radius of the circular aquaculture tank), the deployment angle θ, and the structure of the jet pipe on the dynamic characteristics of sewage collection. In the field study, a high-definition camera was used to record the distribution of sewage, the distribution of the flow field in the aquaculture tank was measured by the Acoustic Doppler Velocimetry, and the distance between the sewage and the center of the tank was quantified. Furthermore, the sewage collection performance of the aquaculture tank was evaluated by comparing the maximum distance between the sewage and the center of the tank under different working conditions. The results indicated that the formation of an effective horizontal circulation in the circular aquaculture tank is the primary condition for sewage accumulation to the center of the tank, while different flow rate Q of the jet pipe, the deployment distance ratio d/r, the deployment angle θ, and the structure of the jet pipe all can affect the sewage collection effect in the tank. In the horizontal single-pipe single-hole jet pipe structure mode, the best sewage collection result was obtained at the deployment angle θ of 0°, the deployment distance ratio of 1/4, and the deployment flow rate Q of 7 L/s; when the deployment flow rate Q was less than 7 L/s, the sewage accumulated near the tank wall, and the sewage particle dispersion was relatively high. In the vertical single-pipe porous jet pipe structure mode, better sewage collection performance was achieved when the deployment flow rate Q was adjusted to 7 ~ 9 L/s, the deployment angle θ was set to 45°, and the deployment distance ratio d/r was set to 1/4. The sewage collection performance of the aquaculture tank under the vertical single-pipe porous jet pipe deployment mode was obviously better than that of the horizontal single-pipe single-hole jet pipe mode. These results can directly and effectively guide the inlet design of such aquaculture tanks to reduce the flow rate and energy consumption and improve sewage collection performance. [ABSTRACT FROM AUTHOR]

The liver metabolomics and related biochemical indices of large yellow croaker were investigated during packaging and oxygenation transport. The large yellow croaker was packed into bags and transported at a constant temperature of 20 ℃. Serum and liver samples were collected after 0, 6, 12, 18, and 24 h of transportation for subsequent analysis. The results showed that transport time had a significant effect on serum creatinine (CR) and glutamine transaminase (AST) levels, suggesting that the kidney and liver tissues of large yellow croaker were affected. Transport stress impacted the antioxidant capacity of large yellow croaker liver, indicated by increased activities of catalase (CAT), malondialdehyde (MDA), and alkaline phosphatase (AKP), which altered immune capacity. In the liver metabolome, we identified five metabolic pathways that were enriched based on differential metabolites and compared across different transport times. These pathways include biosynthesis, lipid, cofactor and vitamin, amino acid, and carbohydrate metabolism. These pathways may impact the morphology of liver cells, as well as the antioxidant and immune abilities of large yellow croaker. Additionally, the statistical analysis of the metabolites at each transportation time revealed that histidylarginine and 3-(4-hydroxyphenyl) pyruvate were consistently downregulated which serve as signature metabolites during live large yellow croaker transportation. [ABSTRACT FROM AUTHOR]