Scientists who examined nine species of Betta from Thailand and Indonesia have revealed that Betta sp. "Mahachai" is a distinct species and have identified several other overlooked species.
The results came after scientists used a molecular technique to examine two regions of mitochondrial DNA from nine different species of Betta.
Based on the results of the molecular study and an analysis of the fishes' morphological features, the team confirmed that the currently undescribed Betta sp. "Mahachai" from central Thailand is a distinct species, not just a form of Betta splendens as some had suggested.
The results also demonstrated the probable existence of two overlooked Betta species from the Khorat plateau basin, and found that Betta smaragdina, appeared to contain three different lineages which might represent previously overlooked species.
For more details see the paper: Sriwattanarothai N, Steink D, Ruenwongsa P, Hanner R and B Panijani (2010) - Molecular and morphological evidence supports the species status of the Mahachai fighter Betta sp. Mahachai and reveals new species of Betta from Thailand. Journal of Fish Biology, Volume 77, Issue 2, pages 414–424, August 2010. DOI: 10.1111/j.1095-8649.2010.02715.x