naive question...

As those of you who read my last post know, I was lucky enough to be in
possession of a Black Moor fish for a month - before I killed the poor
little guy, but that's another story - and am currently scouting around
aquariums looking for some replacements, to arrive once my tank has cycled.

However, I was a little freaked out as the moors they had in the shop were a
good six inches in length (mine was an inch), and to be honest kinda freaked
me out a bit - I'm looking for a small fish, not a monster... what's more,
the goldfish they had were 7 or 8 inches long, much bigger than I expected
they'd ever grow.

Anyway, basic fish questions:

1) I assume the big fish were a few years older than mine was, and will grow
to that size if you keep them alive and healthy in a tank? Who'd want to buy
a fish that size unless they were tossing it in a garden pond?

2) Is that old story true about fish only growing as big as the tank you put
them in? I really don't want to end up with my 21 litre hexagonal tank full
of sea bass-sized critters....

Methinks I need to do a marine biology course...

best

R