possible sick fire-bellied toad

My kids have 4 fire-bellied toads, just today the largest of the four, Frogger, is lying in their pool lethargically. Normally he is such a pig, he begins attacking the other toads before the crickets can even hit the bottom of the tank and today he ate nothing.

His bright green color seems to have faded somewhat, he prefers to "float" in his pool his body almost fully stretched out. I also observed that he appears to inflate his belly with air then let it all the way out, he then repeats the process.

Any ideas? I don't like seeing him like this and I'm also concerned that it could be something that the other toads could contract.

Thanks for your help