Feeder fish in China definitely carries more parasites due to the dirty water people using to raise them.Sponge is not good in my mind for 3 reasons.First owners would have to wash the sponge and change the water every day or every other day,or bacteria would breed very quickly which may cause pacman edema,also the frequent washing would disturb and stress the frogs).Secondly,frogs like burrowing,there is nothing to burrow if using the sponge, then they may destroy the sponge and get hurt.Thirdly,using sponge would make it harder for a new pacman to adjust themselves.