Re: Skewed sex ratios

[Fredrik.Ljungberg@saab.se]

On Jan 8,  8:54am, EXT AVS; \Ed Pon\ wrote:

> >From what I recall of the research data, a combination of temperature
> and ph were recorded as having effects on sex ratios.

You're right, pH is important as well.

Does anyone have the article? I'd really like to read it. Temp and pH
is what all are talking about but other factors may be important (I
know hardness wasn't) population density, amount of light?, anything?

> Fred wrote:
> >For killies there is a strong belief (my belief) that also population
> >density can affect sex ratio. I've had Epiplatys growing up in various
> >numbers in various sized tanks and my strictly unscientifical (and not
> >always exactly accurate) observations indicate that low density (few
> >fish and/or large tank) give more females and vice versa. A plausible
> >explanation would be that given more space a species would seize the
> >oppurtunity to increase population (taking more of the available space
> >and increasing survival of the species in the long run).
>
> This sounds like it would be a positive survival trait, and something
> that's consistent with evoltion.  It's also known that if you buy any
> two young clownfish, they will develop into a male and female.  The
> sames is said to be true of Crenicara Puntuata (did I spell that
> right?).  Another type of salt-water fish (can't remember which) exists
> in schools with one male and the rest of the group being female.  If the
> male dies, one of the females turns into the male of the group.
> Anyway--late determination of sex in fish is not unusual, and
> determination by environmental and social factors is also not unusual.
> I've heard of a couple of hermaphroditic killifish,  I wonder when
> they'll discover a hermaphroditic apisto.
>

I remember Ingo Koslowski writing about observations of Apistos
changing sex. The impression I got was that these were isolated events
and I haven't found anything more about it since (mid 80's). Maybe all
fish have this ancient sex-changing ability, coming from frogs as we
all are? Some have lost it, some haven't. Or it may be as Ed said a new
trait evolving in some species.

Research in this field must have been done for food-fish, salmon, trout,
Tilapiines (spelling?), etc?

Fredrik



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