Help with my Asian Water Monitor?

Not to be rude, but your setup needs some work. I would get rid of the glass tank (it is way too small to get a good temp gradient) and get a wood cage. He needs a basking spot of 130 degrees and ambients of 85-90. At least 6" of dirt/soil for him to dig and burrow in. Humidity in the 80-85% range.

How are you feeding, tongs or setting the food in and leaving him alone to eat?

Thank you for the input, James.

I am setting food down and leaving him alone to eat. He is far too distressed to eat when he sees me.

Tank looks fine to me for now. Like another said hotspot of near 130 but area that he can cool down in the 80's. These little ones are very shy. I would stop the handling untill he settles in and starts eating. Since he likes fish try getting a pinky mouse and rub some of the fish he is eating all over the mouse- sort of marinate the mouse with the fish. place it near him in the cage and leave him be. He should eat in due time.
Hot spot- plenty of hides and no handling and he should come around.