As far as I'm aware, there are no ways implemented. Got no idea because I'm not smart enough for this type of thing. The only solution I could think of is to implement a paywall (I know, disgusting) to raise the barrier to entry to try and keep bots out. That, and I don't know if it's currently possible, but making it so only people on your instance can comment, vote, and report posts on an instance.
I personally feel that depending on the price of joining, that could slightly lessen the bot problem for that specific instance since getting banned means you wasted money instead of just time. Though, it might also alienate it from growing as well.