Genetic population structure of red snapper (Lutjanus malabaricus) and orange-spotted grouper (Epinephelus coiodes) in Brunei and Sabah

The genetic population structure of red snapper Lutjanus malabaricus and orange-spotted grouper Epinephelus coiodes in Brunei and Sabah was investigated using allozyme electrophoresis. Samples were collected from three sites in Brunei for E. coiodes and from three sites in Brunei and Sabah for L. malabaricus. A total of 22 loci and 16 loci were scored, respectively. The index of fixation (F(ST) ) for the E. coiodes population was 0.176 but, in general, it lacked within-population structuring. The F(ST) was particularly high between Brunei Bay/Jerudong and Brunei Bay/ Kuala Belait, suggesting genetic subdivision on a small spatial scale. Isolation of Brunei Bay from the South China Sea may constrain the movement of adult fishes and larval dispersal, thereby reducing homogeneity among subpopulations. All variable loci for E. coiodes were in Hardy-Weinberg equilibrium except for MDH* and GTDHP* (P < 0.01), in which two subpopulations showed an excess of heterozygotes (P < 0.01). The study on the L. malabaricus population showed a heterozygote deficit of approximately 60% in variable loci (F(ST) genetic variation within population = 0.45; P < 0.05); however, the mean observed heterozygosity for the population far exceeded L. malabaricus populations in Australia and Indonesia. A F(ST) value of 0.076 revealed moderate genetic differentiation among subpopulations of L. malabaricus. The genotypes were likely to be drawn from the same distribution in Jerudong and Kuala Belait. This study infers that sustainable management of snapper and grouper resources in Brunei waters must take into account the presence of a single stock and two stocks, respectively.