If you have seen the fish make a habit of calling flops/turns, I would take advantage of his frequency and bet close to pot on both the flop and turn. I'm sure you already know, but this would have made the river an easier shove.

Although you said he calls down the flop/turn lightly, I can't see him continuing with any random Ax. The only Ax he probably has in his range by the river would be A2. Given this, I'd probably shove expecting him to call rather lightly with his pocket pairs (also see: Zeebo's theorem).

By the by, how does he respond to 3bet/squeezes?