I would raise again and try to go broke pre. I don´t like the call option and let a hand like A7 materialize part of his equity letting him see the flop. Stats show him playing maniac enough to make this an EV+ 5bet hand.

I think it´s very explotative line against recreational players raise half of our stack and ovbiously we are commited in any flop texture, i found a lot of calls pre + folds flop with this line against big maniacs like this one.

my first question would be if the reg is aware of the fish beein a fish?....even though i agree that a fish-iso is always a good spot to bluff4bet i guess positions really aint. 

and do i miss somethin? how you described the situation the fish foldet? If so we´re purely 5betbluffing with TT or do we 5bet for value? 

Both doesnt sound good to me, even though folding seems meh...would prefer A5s stuff for that but given positions and sort of deep....meh...

and with the fish still to act i wouldnt interprete too much in his sizing. He could just want the fat falue out of the fish

i would fold as i don't think CO is cold 4B so light with 3 players behind and huge fish who may be getting it in or calling more often - this is way different than if you 3B BUTvCO and BB cold 4Bs

having to fold to 4B at very high frequency is the cost of 3B iso-raise with such a wide range with 4 players still to act

I don't like calling because we'll be playing a large multiway pot OOP with TT against an aggressive reg. 

We could 5b (Assuming that we believe that the reg understands that UTG is a fish and we're 3-betting light and is capable of 5b bluffing), however, if we get 6b AI we'd have to fold. In my opinion, I don't like the 5b line because we make too many assumptions that must be true to be profitable and I don't think even a reg at this stake is putting that much thought and a 4b is simply strength. 

We could fold. I think this is the best option. Make a note and if the reg keeps 4betting us every time we iso-raise the fish 5bet get it in next time. 

We could 5b (Assuming that we believe that the reg understands that UTG is a fish and we're 3-betting light and is capable of 5b bluffing), however, if we get 6b AI we'd have to fold.

5bet/fold? I think juancopani was advising to 5 bet get it in. I think putting in 50% of your stack and then folding pre would be really bad..

OP - we also don't know what UTG did? I think you left out part of the hand right? Was juancopani assuming that UTG called?

Agree with buddha ...

UTG/fish folded.

I agree with you on folding but what would you  do if you were the CO?

Would you have a 4-betting range there?

Would you usually 4-bet with AA-QQ, AK?