Are the eggs fertile but failing to hatch or infertile from the start?
Is you can get the fertile eggs it should be quite easy to experiment
on the eggs without risking the parents. But if its true this is only
occurring with subsequent generations the solution is going to be a
bit trickier. Diet, inbreeding, lack of natural selection by the
native environment? Unfortunately I don't think enough is know about
how they reproduce in the wild to extrapolate on. Maybe they even need
poorer water conditions to trigger proper maturation of sperm and
eggs. If anybody should have an idea of the annual water conditions
cycle you should, or at least know who to talk to Peter. Its hard to
believe that alleles could have degenerated in so few generations, as
to make the species nonviable. Particularly a species living in such
limited numbers in such small water holes.
Just a thought, has anybody documented a case in fish where siblings
cannot produce viable offspring? What I'm getting at is some species
of plants cannot self pollinate even when they have both pollen and
eggs ripe at the same time. It must come from another plant. Could a
similar mechanism be acting species with small population to insure
some type of genetic diversity? Could too many alleles being identical
create a smaller percentage of fertile eggs (ie second or third
generation of brother sister mating), while cousins would create a
higher level of fertility. If such a mechanism was in effect, it could
explain why some species go through this die out phase in captivity
after a few generations. It could also explain how small populations
in small environments manage to maintain some genetic variability.
I wouldn't think it would be too difficult to set up a test for this
hypothesis. That is since we seem to have a species suffering from
fertility problems after just a few generations.
Cary Hostrawser
Minnesota Aquarium Society
http://www.mn-aquarium.org/
Rainbowfish Study Group of North America
http://home.earthlink.net/~sbuckel/index.html