Derek Broughton wrote:
Oh, _that's_ why we aren't raising sharks in our ponds :-)

But there are at least a few people in my area that are raising sturgeons
in ponds, but that's another story, heh.

As for the OP, check out fancy goldfish and see if any bear resemblance to
your mutated fellows. The described changes would be consistent with many
fancy goldfish forms. I've seen a few "common" goldfish for sale that
appear to actually be a cross to a fancy (body shape is off for a common
or comet) or perhaps they're a milder form of a similar mutation. After 10
years of potential inbreeding, you could be seeing recessive genes come to
light from some such past crossing. Or it could also be a recessive
mutation that has just finally reached a high enough level in the
population to be expressed, again this is usually due to inbreeding.