Thankyou fr your reply. the 2 fan tails i have got are only really small and seem extreamly happy in the enviroment they are in. I know they will eventualy get pretty big and when that time comes the pet shop i got them from are more than happy to take them bck and keep them in a larger tank. The thing that gets me is how few fish we are 'aloud' to keep for the tank size but yet when ever you go to any pet shop or aquarium the tanks are packed full.......
What are otto's anyway lol. never hurd of them?
It's not about what you are "allowed" to keep in your tank, it's about giving your fish the best home and conditions you can so they lead full and healthy lives.
Comparisons to pet shops aren't really appropriate for a few reasons:
1. The pet shop doesn't need to worry about the adult size of fish as they won't reach the adult size while in the shop
2. Pets shops often have massive filtration systems (Often numerous tanks will be connected to the same filtration system) which are well established. Your filtration at home is much less than that of a pet shop.
3. The fish aren't kept in the shop for that long.
4. Shops are businesses. They have fish to make money. You have fish to enjoy and look after them.
Another thing to think about when keeping goldfish is the filtration. They need higher filtration than tropicals because the are very messy fish and produce a lot of waste. You should have filtration of 10x the volume of the tank (these means for a 15 gallon you need filters which are rated at a total of 150gph (gallons per hour) with lots of media.
If you are not already, I advise you to test ammonia and nitrite regularly to make sure your filtration is keeping up with your goldies' waste.
If it is, you may be able to keep the fish in the tank you have for a while, but eventually you will need to upgrade.