Genetic diversity and population structure of giant trevallies (Caranx ignobilis Forsskål, 1775) in the Philippines with implications to management.

The giant trevallies (Caranx ignobilis) is a globally important fish species that is at risk from overexploitation. In this study, 150 C. ignobilis from six provinces in the Philippines were collected for genetic analyses. For each province, five representative specimens of C. ignobilis were subjected to DNA barcoding and revealed high interspecific K2P distances of 9.58% and 17.29% when compared to other species of Caranx and Carangoides, respectively. On the other hand, all 150 C. ignobilis specimens were subjected to population genetic analysis using the mitochondrial cytochrome b region. In the studied population of C. ignobilis, 33 unique haplotypes were observed, and the population exhibited high haplotype (h = 0.831) and nucleotide (π=0.930%) diversity. Pairwise F_ST values between the six study sites indicated limited genetic differentiation among the studied populations. The limited genetic differentiation may be due to the oceanic currents in the Philippines facilitating larval dispersal as observed in the results of the Lagrangian dispersion model. Data from neutrality tests, mismatch distribution, and Bayesian skyline plot revealed that the population may have undergone demographic expansion. This study provides valuable genetic information on C. ignobilis that can be used for formulating sustainable fishery management strategies.