This topic was debated at some length on this list quite some time back and
that discussion is still available on the archives ( I think).
I think that both pH and temperature both scored well as likely factors as
well as a couple of other factors. I think that lacustrine species
(theoretically anyway) having evolved in a more stable environment may be
more susceptible to being influenced by these factors if they are
significantly different to the preferred levels. e.g. G. incisus seems to
throw more males at pH around 7 but ratios equal at 7.6.
Records, if kept are fairly seldom published and most of this information is
at best anecdotal but may still be valuable. I personally am guilty of
failure to keep records as well as being quick to state impressions based on
my anecdotal experience. Most hobbyists keep their fish for fun and too much
record keeping tends to dilute the "fun factor".
On the other hand many "serious" breeders, through trial and error (rather
than accurate record keeping) have developed a set of "rules" for each
species that "works" for them under their local water and climatic
conditions.
As to how it works Larry, all I can use as an example is the human analogy
based on a lot of published infertility work. The chemical nature of an
individual woman's vaginal secretions (pH is only one factor) can
selectively influence the chances of survival of the y-chromosome containing
sperm over those containing the x-chromosome and thus increase the chances
of the offspring being male. I guess that such a mechanism could also be
operating with fish too bit there are many other possibilities as well as
many other stages along the line of development that may be significant.
Regards,
Bruce.
Bruce Hansen, A.N.G.F.A., Advancing Australian Aquatics.
Bruce Hansen, ANGFA, caring for our aquatic ecosystems.
Please visit us at http://www.ozemail.com.au/~fisher/angfa.htm
-----Original Message-----
From: Simon, Dan <dan.simon at attws.com>
To: 'RSG mail' <rainbowfish at pcug.org.au>
Date: Wednesday, 4 November 1998 15:51
Subject: [RML] pH and sex ratios
>Exactly what pH does one need to keep a fry tank to ensure more males
>(or females for that matter) . I've read to lower it for more males,
>but to what extent ? Is there any sort of guidlines ?
>
>Dan
>