I have seen fish fit in the in the most insane place so small it crazy I used to think they had a death wish. I lost 2 tiger barbs in a row to a power head that had an opening no larger then 3/8 of an inch. I had a 3 inch bala shark sucked into a canister filter that had an opening maybe the same 3/8 and the tubing in the canister was only 5/8 ID, he lived because I noticed it in time. I looked in the tank and was like where is he, tore the tank apart and thought wth. I gave up thinking he jumped out and died behind the stand where I couldn't get to him. Then about 10 minutes later a voice told me to check the canister, I almost ignored it because there was no way he could fit.