International Journal of Aquaculture, 2025, Vol.15, No.3, 116-134 http://www.aquapublisher.com/index.php/ija 123 not have completely stopped. One thing to pay special attention to is that human activities are affecting this differentiation process. For example, some places will artificially release fish fry, or fish from farms will escape. These behaviors may cause the originally separated groups to re-contact and mix, and the process that was originally heading towards "differentiation" may be "pulled back". On the other hand, if the habitat becomes more and more fragmented and the environment changes, it may also cause the groups that were originally able to communicate to be separated, and this will accelerate differentiation. Therefore, studying the differences within the population is not just for academic research, it is also related to how to protect the species and even affect future management strategies. For marble goby, its various regional populations should currently be regarded as different populations (ESUs, evolutionarily significant units) under the same species. Although there is no reproductive isolation between these populations, they have shown unique genetic composition and adaptive potential, and should be protected and managed separately. For example, in aquaculture, it is not advisable to randomly mix and breed marble goby from different regions, so as not to destroy the genetic purity and unique adaptability of local populations. Similarly, at the species protection level, it is possible to consider demarcating protection units for marble goby in different water systems in the distribution area to maintain their genetic diversity and evolutionary potential. By paying attention to intraspecific divergence, we can take measures before the species has truly differentiated, prevent the loss of its genetic diversity, and reserve space for possible speciation in the future. 4 Species Definition and Taxonomic Clarification 4.1 Limitations of morphological taxonomy of marble goby Traditional morphological taxonomy faces many challenges in identifying marble goby and their closely related species. The morphological differences among species in the genus marble goby are relatively subtle, mainly in qualitative or counting traits such as body color patterns and the number of fin rays, which often have individual variation and environmentally induced plasticity. This leads to different researchers giving inconsistent descriptions of the same species. Fisheries personnel in some areas cannot even distinguish marble goby from other similar fish species and refer to them as "marble goby" fish (Figure 2) (Nhi et al., 2010). Morphological identification is particularly difficult in the juvenile stage. Many fish larvae cannot be accurately classified due to their incomplete development of characteristics, and their species identity cannot be determined based on morphology alone (Syaifudin et al., 2021). For example, marble goby larvae are very similar in appearance to larvae of another closely related small Channa family fish, and confusion often occurred in the past based on morphology alone. For example, adult marble goby in different habitats may have differences in body color and pattern, but these differences are not enough to serve as a basis for the classification of new species, but may mislead classification judgments. Figure 2 Marble goby (Oxyeleotris marmoratus) (Adopted from Nhi et al., 2010)
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