- Article
Research on Underwater Fish Scale Loss Detection Method Based on Improved YOLOv8m and Transfer Learning
- Qiang Wang,
- Zhengyang Yu and
- Renxin Liu
- + 3 authors
Monitoring fish skin health is essential in aquaculture, where scale loss serves as a critical indicator of fish health and welfare. However, automatic detection of scale loss regions remains challenging due to factors such as uneven underwater illumination, water turbidity, and complex background conditions. To address this issue, we constructed a scale loss dataset comprising approximately 2750 images captured under both clear above-water and complex underwater conditions, featuring over 7200 annotated targets. Various image enhancement techniques were evaluated, and the Clarity method was selected for preprocessing underwater samples to enhance feature representation. Based on the YOLOv8m architecture, we replaced the original FPN + PAN structure with a weighted bidirectional feature pyramid network to improve multi-scale feature fusion. A convolutional block attention module was incorporated into the output layers to highlight scale loss features in both channel and spatial dimensions. Additionally, a two-stage transfer learning strategy was employed, involving pretraining the model on above water data and subsequently fine-tuning it on a limited set of underwater samples to mitigate the effects of domain shift. Experimental results demonstrate that the proposed method achieves a mAP50 of 96.81%, a 5.98 percentage point improvement over the baseline YOLOv8m, with Precision and Recall increased by 10.14% and 8.70%, respectively. This approach reduces false positives and false negatives, showing excellent detection accuracy and robustness in complex underwater environments, offering a practical and effective approach for early fish disease monitoring in aquaculture.
Fishes,
29 December 2025



