you can only have ten in your possesion at any given time UNLESS you have a receipt(which needs to have date, name, address, phone #, and quantity) from the supplier BUT those fish you bought are only good for SEVEN days. After the seventh day you have to empty the tank down to ten...
The seven days wasn't explained but I am sure it is to prevent someone from buying 50, then catching more on their own and keeping a pen full of 50 on the same receipt...