Technically it's bet' tah (because of the double 'T' and after the scientific name 'betta splenden'

but it's been mispronounced for so long I think both are widely accepted. Personally though, I am impressed when I hear the proper pronunciation and I think if you work in the aquarium industry, you should probably pronounce it correctly.
When I hear Bay-tah I think there must be something rudimentary and unfinished about my fishie. I know my bettas are definitely the full and complete version.
