Abstract
Kawakawa (Euthynnus affinis) is a widely distributed epipelagic tuna, considered among the most economically significant species in the subtropical and tropical waters of the Indo-Pacific region. However, the lack of comprehensive information on the stock structure, management, and conservation of E. affinis populations in Malaysia raises concerns of potential overfishing and depletion of this marine fish. To ensure effective and successful species management, it is imperative to conduct a molecular- based assessment of the stock structure. In the present study, the genetic diversity and population structure of E. affinis in Malaysia and its surrounding waters were investigated using mitochondrial DNA cytochrome oxidase I (COI) and cytochrome b (Cyt b) genes. A total of 390 (COI) and 414 (Cyt b) individuals of E. affinis were sampled from 20 distinct locations situated within five geographic regions: the Straits of Malacca, South China Sea, Sulu Sea, Celebes Sea, and the Arabian Sea. The results revealed that the genetic divergence among 20 populations of E. affinis varied from low to high. The average haplotype diversity (Hd) and nucleotide diversity (π) for COI were calculated to be 0.5131 and 0.0043, respectively. On the other hand, the average haplotype diversity (Hd) and nucleotide diversity (π) for Cyt b were found to be 0.7450 and 0.0162, respectively. The analysis of haplotype distribution revealed that a total of 20 distinct haplotypes were identified for both the COI and Cyt b genes across 20 populations of E. affinis. The analysis of the Neighbor-Joining (NJ) tree and the Minimum Spanning Network (MSN) revealed the formation of three distinct clades among thesamples. AMOVA analysisshowed a significant genetic structure among the 20 populations of E. affinis, as indicated by the COI: FST = 0.5364 (P < 0.05) and Cyt b: FST = 0.9521 (P < 0.05). The neutrality test and mismatch distribution analysis indicated that the E. affinis specimens underwent a period of population expansion. This study marks a significant milestone as the first comprehensive documentation of genetic diversity and population structure of E. affinis across various locations in Malaysia, with an additional pioneering investigation conducted in the waters of Yemen.
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