It seems to me that
CaptainSpam is misunderstanding
ymelup's argument.
Eir
argument is not `these two things in the same enviroment are
different, so
evolution is stupid and wrong'. Eir argument seems to me to be `These two things, in the same environment, somehow ended up vastly different. The
Darwinian theory of evolution does not, and cannot, predict what the
angelfish and
eel look like---for, whatever explanation you might give to explain how protofish evolved into an angelfish in this environment is going to be completely different from the explanation for the eel's
characteristics. ymelup's conclusion from this is not that they obviously could not have evolved by the same process---rather, it is that a theory that allows them both to evolve could not predict the characteristics of both, and is thus not a useful theory.
ymelup isn't saying evolution doesn't happen---e's saying that it is not that scientific a theory---which may well be true.
As for ymelup's first argument, just try to construct an experiment that will demonstrate to a reasonable degree of certainty that long-scale Darwinian evolution actually occurs. Chances are, you can't. It's certainly a useful model, though---much more so than scientific creationism. If you're an instrumentalist or a positivist, that's all that matters, anyway.