Thats what I was thinking at first but the tanks are relatively small maybe the size of a 10 gallon if that and the other two fish in the tank are larger than he is so I wouldn't think he would bother them I do know that eels are jumpers but the top of the tank is closed well and can only be opened by pushing in from the front ill ask them there reason for doing this the lady checking me out wasn't friendly and didn't seem to give a dam and I was in a rush to get home so i didn't bother to fight with her. I think that they could have done a little better though than a hamster ball the eel looked miserable in the thing.