International Journal of Marine Science, 2025, Vol.15, No.1, 28-34 http://www.aquapublisher.com/index.php/ijms 29 2 Deficiencies of Traditional Morphological Methods 2.1 It is difficult to accurately distinguish between similar species In Hainan Island and the South China Sea region, people usually distinguish different fish by observing their shapes, colors and fin features. But when the fish look very similar, this method is prone to mistakes. For instance, although scientists have conducted extensive research on local fish, the known species of fish are still far fewer than the actual existing ones (Zhang et al., 2023). Especially for fish of the same genus or family, the differences in appearance are very small and it is easy to mistake them, which will affect the accuracy of biodiversity research. The differences in the composition of fish species in different sea areas also reflect the flaws of morphological methods. For instance, five shared species were discovered in the northern and southern waters of Hainan Island, suggesting that subtle differences in appearance might have been overlooked, resulting in incomplete species records (Zhang et al., 2023). This problem is more prominent in sea areas with a wide variety of fish species and rapid changes, which also indicates that traditional methods are difficult to accurately reflect the diversity of fish species. 2.2 Expert participation is required and standards are difficult to unify The morphological identification of fish mainly relies on the experience of experts. This method is difficult to formulate unified standards and is not suitable for large-scale investigations, especially in areas lacking professionals. For instance, recording 363 species of fish in the coastal waters of Hainan Island requires experts to identify them for a long time (Luo et al., 2023), and the efficiency is very low. Furthermore, the judgments of different experts may vary, thereby affecting the comparability of the research results. In long-term monitoring and biodiversity assessment, the lack of unified standards is one of the main problems. The fish communities in Hainan Island and the South China Sea change with the seasons and environment, and a unified approach must be adopted to accurately track the changes (Luo et al., 2023). If the identification standards are not unified, effective comparisons cannot be made and effective protection and management measures cannot be formulated. 2.3 Juvenile fish and hidden species are difficult to identify The physical characteristics of juvenile fish have not yet fully developed, making it difficult to accurately identify them using traditional methods. This will lead to incomplete statistics of species numbers and make it impossible for people to understand the growth patterns of fish schools. For example, investigations in the coastal waters and estuaries of Hainan Island may miss or wrongly discover juvenile fish, thereby affecting the study of the living habits of important species (Luo et al., 2023; Luo et al., 2024). Covert species refer to fish that look similar but have different genes, and traditional methods cannot distinguish them. The existence of such species implies that the actual biodiversity may be underestimated (Zhang et al., 2023; Wu, 2024). Therefore, many current studies suggest combining genetic testing and morphological observation to improve the accuracy of fish identification. 3 Application of Molecular Technology in Fish Species Identification 3.1 DNA barcoding technology: fast and accurate species identification DNA barcoding technology (such as COI gene sequencing) has greatly enhanced the identification efficiency and accuracy of fish in Hainan and the South China Sea. Compared with traditional methods, it can easily distinguish fish with similar appearances or at different growth stages (Hubert et al., 2008; Naz et al., 2023) This technology can accurately identify small fish and economic fish species by comparing genetic differences among species (Hubert et al., 2008). After establishing the DNA barcode database, identification becomes more reliable, and new species or covert species can also be discovered (Kyle et al., 2007; Naz et al., 2023). Furthermore, this technology is applicable to the identification of processed fish products and juvenile fish, making up for the deficiencies in morphology and contributing to fishery management and ecological protection (Naz et al., 2023; Seetapan et al., 2024).
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