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Re: Notho sex changes
Yes, it is true that there are fish that actually change sex
(fertile female to fertile male or vice versa), however this is not
what I have observed with Nothobranchius. My experiences have been
more in line with what Joe Bulterman described in that a *pair* of fish
sold or purchased turns into 2 males.
My take on this is that in such cases the *pair was always 2
males, but the subordinate fish has maintained the juvenile phenotype
(looks like a female). How might this happen? In the literature (on
diapause in Nothos: see papers by Levels) it has been suggested that
adults of both sexes are releasing hormone and/or steroids into the
environment that induce diapause in the eggs. This is hypothesized to
be a sort of signal to the eggs that there are still adult fish (and
assciated predators) in the pond so chances of surviving long enough to
reproduce if you hatch now are quite slim.
I would suggest that hormones and/or steroids produced by
mature males have a similar effect on males that have not yet sexed
out. If the density of males in the pond is sufficiently high it makes
little sense for an immature male to become mature at that time. In
the wild, the gaudy colors of mature males can make them more
succeptable to predation than the more drab females. With this in mind
it may make more sense for an immature male to bide his time until the
density of mature males drops due to predation or *burnout*.
FWIW with a tank full of Nothos that are starting to sex out I
tend to notice more identifiable males within a day or 2 of a
major water change. More frequent water changes may aleviate this
problem (and a lot of others) altogether, but for me anyway it's
easier to talk about more frequent water changes than to actually do
them. Just my .02, your milage may vary...
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