Skinny FBT

[KDK241]

I've had 2 of my FBTs for about a year now and I recently picked up 2 more. It was then that I realized the 2 I got were HUGE compared to mine and one of mine looks really skinny. They are in a 38 gallon tank with 50/50 land and water and I feed them gut loaded and dusted crickets twice a week and a couple earthworms once a week. The skinny one is definitely at the bottom of the pecking order and it was that way when it was just the 2 of them but I always watched to make sure he was getting enough food. He has always eaten as much as the others, if not more and he's always the first one there when food goes in the tank

He's active, calls frequently and appears healthy, just skinny. He isn't picked on by the other frogs and I made sure there are plenty of spaces where they can get away from each other but he hangs out in the water with everyone else. The other one I got with him is also a little thin compared to the new ones but not nearly as thin as this guy. (The new ones are seriously fat, lol) Is there something else I should be feeding him to help him bulk up a little or is that just how he is? I looked at some pictures from when I first got him and he was definitely a little bigger but not by much.