Skewed sex ratios (was: New subscriber)

[Fredrik.Ljungberg@saab.se]

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On Jan 8, 10:38am, EXT AVS; Thomas Soelter wrote:
>Ed Pon wrote:
>
>> Uwe Romer wrote about the sex determination of apistos being largely
>> dependent on temperature and ph.
>
> I heard about that but canīt believe. My last A. cactuoides fry had only 10 %
> female. Hatching was done artificial by (taking them away after swimming
free).
> The tempeature in the spawning tank was 25 C the pH about over 7. I thought
that
> would cause masses of female - but didnīt. Maybe the reason is the hatching
> temperature which was higher 28 C ??
>

According to Romer and Beisenherz the first month determined the sex. A
hatching temp of 28 C (the first week) and then keeping the fry in 25 C
would be close to the recommended mean temp of 26 C.

Check out the archive, this is a popular topic.
http://www.rwcp.or.jp/people/ocarroll/Personal/apisto/

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). For territorial
fish the situation would be different but maybe crowdedness has some
importance???

Any thoughts welcome,

Fredrik

PS A recent spawn of Ap. gephyra, raised in pH 6,2 and T 24-26 C
looks as if it's 75% females, T. candidi raised in slightly more
acidic water was 80% males. Ap. agassizii under ideal circumnstances
(6,5 and 26 C) was 90% males. Go figure. DS

- -- 
Fredrik.Ljungberg@saab.se
Saab Ab 
Flutter and Loads Department
voice +46 13 18 54 60, fax +46 13 18 33 63

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