Freshwater cats, at least big yellas, do the same thing. The babies will usually swim around the mama in a big swirling ball until, somehow, they know that its time to hide and in they go! Kinda strange the first time you see it happen........giant swirling mass of tiny baby whiskerfish and then all of a sudden they all disappear! I had no idea that hardheads did the same thing.
Pretty cool stuff!