With those water perams I doubt he's stressed out. He might be bullied while eating by the sa cats they're generally more aggressive eaters. But like I have said before sometimes they just stop eating for awhile nothings wrong they just stop eating for a few days. When mine did that sometimes he'd even come to the top and take his fillets like normal go back to the bottom and spit them out. So if it's not bullying it's prob just a hunger strike. You cOuld treat for paricites just to cover your bases