4.1 Genetic diversity
Haplotype diversity (H d) and nucleotide diversity (π ) are two important indicators to measure genetic diversity, and πrepresents the proportion of each haplotype in the populations, which can reveal the polymorphism of mtDNA in the populations more accurately (Chen et al., 2022). Grant & Bowen (1998) concluded thatH d was higher than 0.5 and π was greater than 0.005, which indicated higher species diversity. This study revealed high levels of haplotype and low levels of nucleotide diversity, which is common among some marine fish species (Avise et al., 1987; Zhang et al., 2006).
High genetic diversity plays a crucial role in the exploitation and restoration of fishery resources (DeWoody et al., 2021). Assessing genetic diversity is an effective approach the adaptability and survival ability of species in response to environmental changes (Schmitt and Hewitt, 2004), which is essential for species management and conservation. The fish of L. spadiceus is an economic species and has been caught for a long time. Compared with other marine fishes in the same sea area, L. spadiceus had a lower nucleotide diversity (Yi et al., 2021; Niu et al., 2019; Xu et al., 2021), reflecting that the L. spadiceus population in the South China Sea has a fragile genetic diversity and requires conservation as well as a sustainable development planning from fishery management.