Join Date: Mar 2007
Location: Colorado Front Range
Goldfish probably aren't the best companions for Bettas. They are coldwater and Bettas are tropical. In addition, some of the fancy varieties with flowing fins presents a challenge for the betta.
I also wouldn't put a betta in with most sharks. Bala Sharks would be my only thought as they are slow growers and pretty placid. Rainbow, RTS, and such get too nippy. The other problem is most sharks move considerably quicker than most bettas, which can cause some problems if they are nippers. Other sharks will outgrow most tanks (such as the irridescant shark which gets 3 feet).
You're better off with community fish with a betta. Tetras, danios, rasboras, ....