Here's what happened. My sister got a fish at Pet-Smart and it was black and about an inch long and about a half an inch thick. We got it home and it sank to the bottom of the tank for about a half an hour and then it swam to about the middle of the tank then it started to what seemed to be poop but then they started moving. There was about fifteen of them and after all of them were out the momma fish died and so did about six of the babies. Then about three days later all of them died except two. Then about three months later they died as well. Don't know what happened but that's not the question. My question is right when they came out of the mom (well not right after but soon after) they started swimming around. I thought fishes laid eggs that sat there for awhile then hatched. So what happened?