Well you've stir my interest. I don't think we can avoid this to a
certain degree. Many wild caught fish are very difficult to reproduce.
Subsequent generations seem to be much easier to reproduce. Where
originally you had to match their natural water conditions quite
closely, the later generations would spawn and produce viable fry in a
much larger range of water conditions. I don't think we're generally
fixing a trait of only viability in a different from natural water
conditions but selecting for fish that can handle a wider range of
water conditions and diets. Those tilapia that are now surviving the
winter in greater numbers, can no doubt do quite well back in their
native warmer habitat.
I think for the most part if we don't overly inbreed the species,
we're selecting for fish that are better able to survive differing
water conditions. An aquarium just doesn't maintain the types of
conditions a waterway will. Besides the predation factor I think the
waterway has a much more stable and healthy environment Aquariums
select for fish that can handle greater extremes of water quality.
I'm not saying its impossible to develope a strain that can't handle
it's old native conditions. But it would be more a case of inbreeding
brother to sister without crossing out to cousins in the population
group. Thats the habit that will fix a trait.
Cary Hostrawser
Minnesota Aquarium Society
http://www.mn-aquarium.org/
Rainbowfish Study Group of North America
http://home.earthlink.net/~sbuckel/index.html