@Tonikill1 It depends. Researchers do it with government backing, using it just to temporarily stun fish, gather data, and release them. For people doing it just 'cause they want to, they'd have to check their local laws. It might either be illegal in and of itself or get categorized as poaching which could vary in how severely it's treated. Or, maybe not. Someone could live somewhere that won't have even had a reason to consider outlawing it until they catch someone doing it.
@Tonikill1 I mean, you could basically say that about anything, really. I just meant that you can't break a law if they haven't made it one yet, but after they see someone doing this they might think "There oughta be a law" and boom, you're the reason why electrofishing is illegal. That's also why some places have some very oddly specific laws that if you end up reading them you just think "Okay, wonder what happened to set this precedent."