well, the silver sharks they sell at my lfs are about 6cm long. and the store i go to has a grow n' trade system. basically, you buy a fish and if it grows relatively big since your last purchase, you can trade it in for other smaller fish.
For example, I had a small comet i had won at a royal exhibtion. He was about 5cm when i had him first, and i didn't really notice he had grown to about 15cm after a while. I traded him in for 10 neons which i infact sold about half a year later. income!

but about 2 years later i returned to the store and he was for sale! at $50 Aust.

He was about 20-25cm! well, i was happy he was still alive.

He seemed to be traded around alot in his life.
Anyway back to the point, so kossy, or anyone listening, the silver sharks will be happy alone?