It depends on how big the adult sen is and if the ck hits its full adult size eg: you could keep a 12" sen with a 24" ck but any bigger than that and the sen would probably get eaten.
just make sure u fee dur knife up all i can say also if he did eat 1 could end up with 1 sick knife if u not careful sirchir spikes cant b nice 2 eat =/ so i guess its luck of draw with ea fish