At Samaesan Island, which is in Chon Buri Province, the Upper Gulf of Thailand, in 2018 we found skunk anemonefish (Amphiprion akallopisos) previously only known from the Andaman Sea that have been establishing their populations in the area at a 4-m depth

Genetic diversity and population connectivity of brownstripe red snapper (Lutjanus vitta) from different petroleum platforms located in the north (N1, N2, N3, and N4), central, and south regions and two coastal locations, Songkhla and Samaesarn (Gulf of Thailand), were examined using the control region (CR) polymorphism. In total, 59 haplotypes of CR were found, and 42 of these were private haplotypes (found in only one geographic location). The haplotype no./sample size (N_H/N) found in the central (0.800), south (0.741), and north (0.733) platforms was greater than that in the coastal populations (0.643 in Samaesarn and 0.682 in Songkhla). Haplotype diversity of north, central, and south platforms and coastal populations were comparable (Hd = 0.943–0.982). Nucleotide diversity within populations was estimated. The lowest and highest nucleotide diversity was observed in the north (1.293%) and south (2.850%) platforms. Larger genetic divergence was found between north–central (0.096%) and north–south platforms (0.069%) than between coastal populations (0.007%). A lack of nucleotide divergence was found between central–south platforms and between platforms and coastal populations (north–Samaesarn, central–Songkhla, and south–Songkhla). The F_ST estimate did not reveal significant population differentiation between all pairwise comparisons (p > 0.01 after the sequential Bonferroni’s adjustment). AMOVA confirmed a lack of intraspecific population structure of L. vitta in the Gulf of Thailand (p > 0.05). Genetic connectivity between fish from different sampling sites was noticed based on haplotype network, phylogenetic analysis, and population structure analysis. Demographic statistics revealed that L. vitta went through a sudden population expansion.