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Re: Sex Ratio
Hi Wright, I have Riv Xiphidius PK15. I had heard this fish was known to throw almost all males. When I asked the breeder how he was doing with the sex ratio, he said it had started very bad. Of the 30 fry he raised up, 29 were males. He was then fortunate enough to get that one female he raised up, to spawn, and then those fry raised up to be about 2:1 ratio. I took a couple prs of those and the fry I am currently raising up, are still 2:1 ratio. These fry are just about spawning size now, so I'll see how the next generation does. Does anyone know if the bad sex ratios being discussed continue on each successive generation? Or is it so bad, that you can't even get 1 fish of one of the sexes?
alt email: ron02886 at cox_net
On Fri, 13 Dec 2002 11:21:27
Wright Huntley wrote:
>I'd like to see more discussion of this topic, as I find it fascinating.
>Real facts seem hard to get.
>In RIVs, temperature in the first few weeks is reported, by some, to be most
>significant, but the late Paul Vormbaum also reported equal ratios by
>putting only two newly-hatched babies to each container. They always seemed
>to become a pair.
>In some species (and my impression is that many Aphyos/Diapterons are in
>this group) males are very jealous of territory and can kill all smaller and
>weaker ones, so the ratio of females to males is often very high. This might
>happen with Nothos, too, but my rough guess is that the slaughter is usually
>less sex based with them.
>The role of pH is very confused, as most of those using it as a critereon
>seem ignorant of the relationship between pH and the rest of their water
>chemistry, particularly alkalinity. My WAG is that water hardness or
>alkalinity are either/both more likely to influence sex ratios than pH, but
>too few hobbyists bother to actually measure them for us to build up much
>Here is a point on the curve. *Rivulus xiphidius* Crique Blanche G2000 were
>hatched and raised in my too-soft Modesto water, with enough added salt to
>get tds up over 100, but 0 degrees KH and GH. pH was unknown, but could be
>almost anything in that water. Best guess is that it was about 7-8. It was
>summer, so my temps were in the high 70s, most of the time. [We had the AC
>set to 80, but the tanks stayed a bit below that.]
>At a couple of months, I divided them and gave a little over half to Tim
>(the actual owner). I selected carefully for a range of sizes to each of us,
>in hopes we would both have pairs. That may have been about when I started
>adding some "Equilibrium" to reconstitute my water, for the salt alone had
>been killing plants. My GH and KH were therefore probably no longer "0."
>I ended up with 100% males, and IDK what Tim's have turned out to be. His
>were subsequently raised in far colder water (SF Peninsula and not Modesto)
>and grew a lot slower, so could not be sexed as early as mine.
>This is my first experience with a seriously skewed sex ratio. In Fremont
>and Santa Clara, where I had harder water with stable buffering, I never was
>conscious of any sex ratio that was strongly off from what chance would give.
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