1/2, 9 handed

Villain is on a heater. He seems pretty bad. Saw him call down a tight player when he had 3rd pair ( happened to be good). Also saw him bluff off his stack earlier with 2nd pair (if he was bluffing, not sure).

Otth:
Hero raises to 10 from middle/late position with AJ ($285)
Villain calls ($600). Hes calling about 50% of hands here
Co calls
Button calls
Bb calls

Flop $51
JJQ

Hero bets $27, only villain calls

Turn $105
JJQ4

Hero bets $50, villain calls

Check is my default here, but thought this villain could call with worse with a lot of his range.

River $205
JJQ42

Hero? Awkward $200 remaining at this point. Hero bets $50. Villain raises to $135.

Need to be right 18% of the time here. Fwiw earlier i saw villain make a smallish river raise like this when he rivered the nut flush. Wasnt a paired board tho. This villain was capable of 3betting so QQ is heavily discounted here. So I lose to QJ (3) and all flushes. I shouldnt beat much and I obviously think im behind. Small river raise doesnt look like a bluff... At the same time, im still ahead of 90% of his preflop calling range if he is clicking buttons post flop here sometimes...thoughts??

When he bluffed off his stack, I assume it was a much larger bet? This small river raise doesn't look bluffy to me.

I don't see your average 1/2 player bluffing here. He'd either have to be calling you down with air to get to this river (unlikely); or else he'd have to be turning a Q into a bluff (also unlikely at this level, but see below).

Assuming you're right in your read that this guy is a fish, the one thing that might make me call would be the chance that he could be going for value with a worse jack or with your same hand. I could see a fish betting AJ, KJ, TJ, J9, J8, or J7s here and thinking he's good. And he has all of those hands, since he's calling preflop with 50% of hands. That's a lot of combos. But you have to discount them a lot because most fish see a flush board and get scared.

I'm also slightly skeptical of your description of this guy as a fish. The examples you give involve him calling down with 3rd pair correctly, and then later turning second pair into a bluff, which is often a higher level play. And since he's the type to turn second pair into a bluff, might he do that with a Q on this runout when you make a weak-looking bet into him? Maybe AQ with the ace of diamonds?

If your read is correct and he's just a fish on a heater, rather than a good player playing really loose preflop, then I think it's a fold. But only needing 18% equity, I don't think it's a big mistake either way.

Bet more on the flop. JJQ with a suit connects with a ton of hands Villains would have called with pre. I think $40 is about right here.

Turn bet is ok'ish, but it leaves awkward stack sizes. I think I prefer a check/call line here. If Villain checks back we can bet river for value.

River is definitely a check/call here. The only thing that might check behind that we could get value from is a Q. KT missed, and V will surely bet his own J if we check to him.

As played I think it has to be a river call as we are getting 5 to 1. You;re probably toast but I think there's at least a chance villain is turning KT into a bluff or overvaluing a J. Gross though.