> I guess what I would like to know is (a) what changes can we expect
> genetically and/or environmentally from captive breeding and will that
> change (if one takes place) return once a species is returned to its
> natural habitat.
The only change genetically you will likely see is a loss of alleles. This
can happen throught several avenues including the following.
1/ Genetic drift which is the random loss of rare alleles. This is
thought to be quite important in small populations.
2/ Bottlenecks which are caused by breeding from only a small number of
fishes over one or more generations. Basically, by only breeding from a
few of the fish you don't get a representative sample of all the
variation that is present.
3/ Different selection pressures. Darwin's "struggle for survival" is
quite different in an aquarium vs the wild. Thus you could expect to see
a shift in allele frequencies tending towards the loss of some alleles.
Not sure by what you mean when you say environmentally? My guess would
be behaviourally? With the exception of salmonid studies on hatchery vs
wild fish I am not aware to any studies on non game fish comparing
behaviour when captive fish are released into the wild. If anyone knows
of any, perhaps they could post the references to the list. I'm sure
though that fish raised in semi natural ponds largely independant of a
fishkeeper and fed only live foods would have a better chance of survival
compared to a fish raised in a crowded aquarium on flake foods.
> (b) What number of wild stock would be required to
> maintain a genetically similar stock in captivity. I assume the larger the
> number the better the chances?
Generally speaking the larger the number the better. However, again it
depends upon the species. Some species have more variation than others
thus you need more founders to preserve all the variation present. Also,
within species with geographically isolated populations each
population may have different levels of variation and no one population
is likely to represent all the variation within that species. Some
genetisists quote the number of 500 (250 pairs) as being a relatively
"safe" number of founders. However, in dealing with endangered species
this is not always possible. This is because the fish are endangered for
a good reason, there ain't many of 'em left! I would suggest that most
genetisists would be relatively comfortable with a founding stock of 20-50
fish of equal sex ratio all things considered. This is more fish than an
individual can handle, thus the need for co-ordinated group effort.
> If you read one of my earlier replies to Peter Unmacks comments, you will
> see some extracted comments by the researchers on captive populations of
> the Eachamensis Rainbowfish in their study. There was only two collections
> of these fishes from the wild and both were very small in number. They were
> then bred in captivity over 10 to 12 years without any _Planned Program_
> and yet the results showed little genetic variation over wild stock. Can
> we assume that similiar results will apply to other Rainbowfishes?
No.
The other problem with the eachamensis tale is that we really don't
know how much variaition was present before the fish went extinct. (You
quote "little genetic variation over wild stock", however, this is other
M. s. splendidas and eachamensis populations, ie not those from Lake
Eacham itself is it not?) Thus, compared to other populations the
captive stocks have comparitive levels of variation. But, we really
can't know how successful we have been unless we knew the original
variation in the fish from Lake Eachem proper.
Tootles
Peter