GENETIC DIVERSITY AND POPULATION INSIGHTS OF KAWAKAWA EUTHYNNUS AFFINIS (CANTOR, 1849) IN MALAYSIAN BORNEO REVEALED BY MITOCHONDRIAL DNA CYTOCHROME B GENE

Abstract

Kawakawa (Euthynnus affinis) is a commercially valuable pelagic species with a broad distribution across tropical and subtropical waters of the Indo-Pacific region. Despite its economic importance, limited knowledge of stock structure, management, and conservation in Malaysian and adjacent waters has raised concerns regarding overexploitation and population depletion. Comprehensive molecular assessments of population structure are therefore critical for informing effective fisheries management strategies. This study investigated the genetic diversity and population structure of E. affinis in Malaysian waters using the mitochondrial cytochrome b (Cyt b) gene. A 522 bp fragment of the Cyt b region was sequenced from 120 individuals collected from eight geographically distinct populations in Malaysian Borneo. Genetic divergence among populations ranged from low to high, accompanied by high overall haplotype diversity (Hd = 0.9260) and moderate nucleotide diversity (π = 0.0325). A total of 32 unique haplotypes were identified across all sampled populations. Phylogenetic reconstruction based on Neighbor-Joining analysis, together with haplotype relationships inferred from a minimum spanning network, revealed the presence of two distinct genetic clades. Analysis of molecular variance (AMOVA) demonstrated strong and statistically significant genetic structuring among populations (F_ST = 0.902, P < 0.05). Neutrality tests further indicated a historical signal of population expansion. This study constitutes the first comprehensive Cyt b–based molecular assessment of the genetic structure of E. affinis in Malaysian Borneo and provides essential baseline information to support sustainable fisheries management and conservation planning.