In Thailand, there are currently five recognized species members of the bubble-nesting Betta genus, namely Betta splendens, B. smaragdina, B. imbellis, B. mahachaiensis and B. siamorientalis. In 2010, we indicated the possibility, based on COI barcoding evidence, that there might be two additional species, albeit cryptic, related to the type-locality B. smaragdina in some provinces in the northeast of Thailand. In the present study, after a more extensive survey of the northeast, and phylogenetic analyses based on COI and ITS1 sequences, the B. smaragdina group may be composed of at least 3 cryptic species members. The phylogenetic positions of these B. smaragdina group members in the bubble-nesting bettas' tree together with those of their congeners have been consolidated by better DNA sequence quality and phylogenetic analyses. With a better supported tree, the species statuses of B. siamorientalis and the Cambodian B. smaragdina-like fish, B. stiktos, are also confirmed.

Betta mahachaiensis, a new species of fighting fish belonging to the Betta splendens group, is described. The fish inhabitsspecifically sites with brackish water and nipa palms in the Samut Sakhon Province, Thailand. It is distinguishable from othermembers of the B. splendens group in having an iridescent green/bluish-green appearance on the brown-to-black bodybackground. The opercular membrane has brown-to-black colour without red streaks or patches. The opercle has two paralleliridescent green or bluish-green vertical bars. Its dorsal, caudal, and anal fin rays are brown to black, contrasting with theiridescent green or bluish-green of the interradial membrane. Black transverse bars are present on at least the proximal two-thirds of the dorsal fin, but not on the caudal fin. The colour of the pelvic fins is brown to black with an iridescent green/ bluish-green front margin and a white tip. Females possess similar characters but are less colourful than males.

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Air-breathing fish species of the genus Trichopsis have been reported in Cambodia, Lao PDR, Indonesia, Malaysia, Singapore, Thailand and Vietnam. It is only in Thailand that all three recognized species (Trichopsis vittata, Trichopsis schalleri and Trichopsis pumila), as judged by distinct external features, are found. Cambodia and Lao PDR harbor two species each. The present work involves first-time DNA sequencing and analysis based on mitochondrial (COI) and nuclear (RAG1) DNA of numerous specimens of these species and specimens of a controversial Phetchaburi (Thailand) fish population with a mixed outward appearance. In addition to confirming the morphologically clear-cut taxonomic division of the three fish species, our DNA results show that whereas the T. pumila populations form one single species, there are cryptic species in the T. vittata and T. schalleri populations and possibly a new one in the latter. Members of the putative Phetchaburi fish population have been proven to be hybrids between T. pumila and T. vittata. In addition, a new the phylogenetic tree indicating ancestral relationships is also presented. This study should generate further research to find new/cryptic species of the genus Trichopsis in all countries harboring the fish.

Betta siamorientalis sp. n., a new species of fighting fish belonging to the Betta splendens group, inhabiting four provinces in the eastern Thailand, is described. The combination of slender body shape with reddish vertical bars on the black opercle and an apparent black body distinguishes the new species from other congeners especially B. imbellis. The blacker appearance relative to B. imbellis is due to a higher proportion of black body area relative to that occupied by blue/green iridescence of the scales. Based on morphological similarity and fin colour pattern and vertical bar colour on the opercle, the new species appears to be more closely related to B. imbellis and B. splendens than other members of the B. splendens group.