Well, following your lead, masta 2009, I called the Fresno, CA, American Society for the Prevention of Cruelty to Animals (ASPCA). The young lady I talked to didn't know and whoever she talked to didn't know if Betta fighting was legal or not. They did naturally consider the practice cruel. That would of course be their position. She didn't seem to be aware that it is a practice in Fresno, CA.
As to whether there is ever a response to animal cruelty, the SPCA I believe will look into reports of cruelty to mammals.
I am certain that the SPCA and Peta, as well as other animal anti-cruelty and rights orgs, would be opposed to the practice. Whether they take time and resources to actively oppose it is another matter.
Of course, the betting that no doubt is part of the practice, if more organized than the "boys' friendly night out poker game," would be illegal in some states but probably not all.
I am wondering if California and US Fish and Game would know the general attitude. I am inclined to believe that they would not approve of releasing Betta into any local waterways.
I think we have to make a difference between organized Betta fighting and small groups of friends who might fight their Bettas.
I once watched the big horse race in GB on TV where the horses jump barriers. A beautiful horse, that I had spotted and could see it was tiring, was pushed to take a big jump. She fell on the other side of the barrier and broke her neck. I love to watch the Triple Crown in the States. The horses are great hearted athletes. Horses are frequently badly hurt in these sports. Often they are no longer put down if they are valuable studs, but still
As Annie said, these are random thoughts. But we sure have not got this discussion going with much insight offered.