Controlling Sex Ratios In Plant Spawning Killies
by, Gary Elson
Tell me if you’ve heard this before. You collect eggs, painstakingly. You hatch them, and carefully raise your fry.
You have plenty, and as they grow, you begin to look forward to sharing pairs of your exciting new species with killie
keeping friends.
As the juveniles develop, you realize you have all males. Or all females. Before you know it, you lose your breeders.
You have 50 fish, but you have lost a species. Yup, it happens, and it does so all too often. A very unsatisfying statement.
I suspect we can influence sex ratios in most killies. We just don’t know how. And since humans love answers,
systems, and to have a sense a control over our world, the fact this problem remains an unresolved question can drive us
crazy.
We have many anecdotal recipes for controlling sex ratios in killies, but precious little independent proof they work.
There have been reports that fry raised to adulthood in a small container holding just two fish will give you one fish of each
sex. I’ve been told it, and read it. I have tried it several times with fish that were giving me terrible ratios, and they gave me
terrible ratios. Here, it didn’t even come close to working. That’s not the magic bullet, at least for the fish I keep.
I have learned that my Aphyosemion zygaima will give females in extremely mineral poor water, a decent ratio in
moderately soft water and huge numbers of males in water of 140 ppm. I’ve had that fish here for 21 of the past 23 years,
and I can manipulate ratios with water hardness. I just produced a tank of 100% males beside a tank of 100% females, just
by hardening my soft tap water for the former.
Eureka? Nope, not even close. A. zygaima is an ogoense group killie, and none of my other ogoense have
responded in the least like this. I used to get bad ratios on Aphyosemion ogoense. Hardness did nothing to help. I could not
get my results from zygaima to repeat.
Friends told me to try raising fry at different temperatures. I did. No luck, beyond standard random results. Our
home experiments are always with few tanks and small numbers of fish – we don’t have unlimited resources. It’s enough to
make any statistician cringe. And it greatly affects our ability to claim results.
Even when I have had success, I don’t know why. My A ogoense 80-24 are giving me great ratios now, almost even
ones. Is it minerals? Is it specific, unidentified minerals? Or temperature working with minerals? Or diet? Could it be that
when I work in the fishroom, I have been listening to more punk than blues these days? Is it magic? If you picked up this
article looking for answers, all I have is questions.
What next?
There are environmental triggers for the gens controlling sex in our killies. We see it all the time, unfortunately. Life
would be so much easier if we got nice 50/50 ratios.
It makes sense. Different environmental pressures have shaped and created a wide range of wonderfully diverse
killies, and more has to be different in them than color. Every species we look at is the product of a long and ancient story
we can’t read. If they don’t all develop the same shapes and colors, how can we expect them to develop the same sex ratio
triggers?
Try every trick. Divide those wonderful lots of eggs. Try to use different containers, with different water. Keep notes.
Try different temperatures. Keep track of ratios across seasons, if you get temperature changes in your fishtanks at different
times of year. Count fry hatching to compare them to fry maturing, to see if males are killing each other before we can tell
them apart. Change diets. Seek patterns, and above all, share your observations. We killie keepers are too reticent about
sharing info, because we have a tendency not to take our discussions far enough. We’re generally a modest bunch.
Be wary of easy solutions that seem to be “one size fits all”. You may well discover a solution to this old problem, for one
species of plant spawner. Don’t expect it to work for all species.
Hey, answers get boring fast. Questions are what we need anyhow! And when it comes to providing us with
questions, killies are very generous creatures! ...