Fwd: Skewed sex ratios (was: New subscriber)

["Ed Pon" <edpon@hotmail.com>]

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

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.

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