It could be a size/visual thing, but likely he really just hasn't noticed them there yet. You could make the water more shallow so the fish splash around a bit. Once he knows there's a possibility of fish there he will check his water bowl for them I thought it was odd that my captive bred babies never hung out in the water bowl like my wild caught adult did. That was until they had their first live fish meal... now they periodically check the water bowl and will even go through the fishing/hunting motions when there's nothing there