SB is reasonable reg.
CO is fish.

Preflop
SB should 3bet there reasonably linear range - like 5-6%. Calling and playing postflop (alongside with fish) seems attractive. 4betting not so much.

Flop
Dont like Q on the board, its also high board where SB shouldnt really bluff in 3way with fish - so i need to be careful.

Turn
It seemed tricky at the time i played this that SB cbetted this board into 3way and checked turn. I guess i can check or 1/3 and fold to a raise. Both options seems fine. I do need some protection, but not that much - i dont want to see only Q/J/T turns.

River
T is surely not great for me. SB is checking. He should bet majority of his AT+ after we both checked turn. What are my options here?
Fish is left with 10$ to 24$ pot. Should i just bet/fold 10$ to cover his stack? I think its propably most reasonable, since he can call with KQ/worse Ax and he would check most of these versus my check.