That's a very cute concept and will be very beautiful with the flowing fins.
As someone who has dabbled in the art of tattoos, I would recommend that you determine what kind of style you're looking for and then have a tattoo artist that is very good at that style help you design it. Take the time to scrutinize different artists and explore their different portfolios. Even if you draw out the tattoo EXACTLY how you want it, there will be an artist out there who may be able to enhance it even more. If you can find someone who is very good at koi and flowing dresses or material, chances are they will help you design a very stunning betta tattoo! Also, don’t settle. If the design is not to your liking 110% and it doesn’t knock you off your feet, figure out why and have them change it. It is your money and your body. If you’re working with a good artist, they know this and will work it until it makes you happy. Good luck!
*Steps off soapbox*
"All men are equal before fish." - Herbert Hoover
My work crew: Beast - M. Deltatail
My home boys: Merlin - hmpk
RIP - Domino, Lumier, Kraken & Makara