Re: NANFA-- Questions about Heterandria formosa.....

unclescott (
Sat, 21 Jun 2003 10:03:54 -0500

> Are female H. formosa able to store sperm like other Poeciliids for
continuous fertilization of eggs or do they require insemination for each
egg(s)? Considering their differing way of gestation of their eggs and
delivery mode I was curious if they differed in this aspect as well.

>I have a group of 52 females from one local population whom I have isolated
in a 40 gallon tank away from any males. Females who were previously
pregnant who have delivered their young do not seem to be gestating any more
young after a period of about five weeks.

If you keep them in the middle 70s F (even though they can go a lot cooler,
gestation slows wayyyy down), give them lots of vegetation to hide in and
lots of meaty food (rinsed, formerly frozen bloodworms, among other things
work well), in time you should have a bunch of fry.

Given the number of fish, I think you are wise to keep them in a 40 gallon
tank. Too often aquarists see a small fish and think "small tank." Their
behaviors are more natural and they are likely to be healthier in quarters
where they have "room to rumble."

A Copeia article several years ago singled out Het. formosa as one of the
most -advanced? sophisticated? unique? - of the poeciliids practicing
superfoetation. Because they are so small (and their fry relatively large),
a female would only have one or two full term fry in her body at a time. But
researchers found quite a series of really tiny eggs ready to go. The
increase in size of the embryo (my memory is straining here) was somewhere
in the neighborhood of 800-1000% ! Clearly there is nurturing from the

One could form the image of quite an assembly line. In our age of extreme
sports, now we have extreme procreation. ;) A remarkable little fish.

All the best,

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