My porcupine puffer has been trying to eat but it appears that he can't open his mouth to get the shrimp. He is actively swimming and water parameters are fine. there doesn't seem to be any type of fungus around his mouth. Its just when he goes to try and get the shrimp he can't open his mouth. Please help, is there anything I can do for the little guy? I have been feeding him "Omega" freezer dried shrimp.