Don't know if this could be a reson for not eating but I found whenever I had to put an adf in a small tupperware, they wouldn't eat. Also, those silly froggers have horrible eyesight and if I dangle a worm right in front of them, they ignore it but if I do that an inch or so away, they go after it. Just me experience. But, Mac is right (of course :) ) your guy needs to build up his strength.

Mac, do you think it is possible to put him in a critter keeper or something similar and keep the water lower so he has some room to swim around if he wants and there is room for some hidey places?