> But how often do we see natural hybrids even when several species of
Rainbowfish co-occur.
Okay, but the thing to remember her partly too is that mates are easy to
find. Do you think that if someone dropped some australis into the
Brisbane River as males only, that they wouldn't cross with the local
fish? It doesn't have to be a different species either, it could be a
Mary River duboulayi that gets dumped in the Brisbane River. Even in
nature hybrids start becoming more frequent when one of the species
becomes rarer. A example of this is thought to be between Murray cod and
trout cod. It is only in recent times that definite hybrids have been
collected between the two in nature in the Murray River below Lake
Mulwala. This is thought to be because the trout cod aren't finding
mates as easily as they may have once did. It could also just be that
we never recognised any hybrids where they were present before too. Now, if
someone dumped a few hundred australis in they would probably be less
likely to cross. But you can never ultimately predict this with any
certainty.
> So there are ecological preferences that tend to stop cross-breeding
but I'm sure there are many other factors also - such as colour
patterns, display performances, temperature preferences for spawning,
time of day preferred to spawn etc etc. I guess a lot of these factors
could be ascertained by a good observant aquarist or scientist. Some are
already known for some species e.g. some species of Ambassids are
evening spawners while others are early morning spawners
Does the difference in spawning time in ambassids occur in non sympatric
populations though? ie, does the morning species only spawn in the
morning when in isolation from other ambassisids? Often these things
"evolve" in some populations and not others because each community in
unique in its own little way. There are many examples of where a species
will behave differently in the absense or presence of another species.
> Also in undisturbed habitat the existing species are much more likely
to be more exquisitely adapted to that particular habitat and are more
likely to succeed there. >
Sure, introduced fish are far more likely to succeed in disturbed
habitats. How natural is the Brisbane River these days and many of the
large coastal Qld rivers?
Tootles
Peter Unmack