Are you sure that your collecting method isn't preselecting for one gender over the other?
Years ago, when I was angling for longear sunfish and bringing them home, I noticed that I had more males and females. My thinking-in-the time was that since males were a little more agressive than females they tended to get to the bait first.
>From: Bruce Stallsmith <fundulus-in-hotmail.com>
>Date: Tue May 16 20:02:41 CDT 2006
>To: nanfa-l-in-nanfa.org
>Subject: NANFA-L-- Skewed Sex Ratio in Shiners?
>I've been writing up work I've done on the reproductive biology of two
>shiner species, Notropis asperifrons (burrhead) and N. stilbius
>(silverstripe). We collected a number of individuals of both species from
>Borden Creek in Alabama in 2004. One thing that has struck me is that by
>random sampling we collected 29 male and 42 female burrheads, and 70 male
>and 66 female silverstripes. A chi-square test doesn't quite show
>statistically significant difference from a 50/50 ratio for the burrheads,
>and in truth it's a fairly small sample to work with. But it's still
>intriguing.
>
>My question for the list is, has anyone encountered sex ratio skew in North
>American cyprinids before, either in your own observations or in the
>literature? I haven't come across any such information in my own experience
>or searches. With the diversity of freshwater species in North America I'm
>surprised that no species have evolved a reproductive strategy involving
>some kind of skewed sex ratio such as has been observed in a variety of
>marine species.
>
>--Bruce Stallsmith
>along the still dank Tennessee
>Huntsville, AL, US of A
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