Controlling Sex Ratios In Plant Spawning Killies

by, Gary Elson

Tell me if youíve 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 donít 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. Iíve 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 didnít even come close to working. Thatís 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. Iíve 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 Ė we donít have unlimited resources. Itís enough to make any statistician cringe. And it greatly affects our ability to claim results. Even when I have had success, I donít 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 canít read. If they donít 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. Weíre generally a modest bunch. Be wary of easy solutions that seem to be ďone size fits allĒ. You may well discover a solution to this old problem, for one species of plant spawner. Donít 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! ...