Hemichromis sp. Bangui, sex ratio

[jfk]

Hello!

in the practice of my colleagues it was noticed that you can find just 1-2 females per 50-80 young males of Hemichromis sp. Bangui.
I would like to discuss is this an accident caused by the selection at a fishfarm, or this situation is usual for further breeding in aquaria.

I appreciate any your comment!

[Bas Pels]

fully unexperienced in African cichlids, my thoughts go out to Apistogramms, which are known to be pH dependend in sexratio - low pH gives more females

As many of these breed at very low (dangerously low, due to a lack of buffer capacity of the water) most breedser breed them atmax possible pH - thus get many more males than females

perhaps this is also the case for Hemichromis???

[Darrell Ullisch]

Actually, the only controlled study done on sex ratios in Dwarf Cichlids (I really need to write the name down, as I keep forgetting it) concluded that Apistogramma are controlled by temperature rather than pH. Pelvicachromis, however, were shown to be pH dependent, with some species requiring pH as low as 5.0 just to get an even split on the sexes. Six weeks of age seems to be the point where sex was determined in most Dwarf Cichlids. I've seen similar results in Killifish, though strictly anecdotal, that South American species are generally temperature dependent, while West Africans appear to be pH dependent as to sex ratios.

Since Hemichromis are West African, I would also wonder about the pH, but I wanted to make sure the correct reason was given.

[Lab]

fully unexperienced in African cichlids, my thoughts go out to Apistogramms, which are known to be pH dependend in sexratio - low pH gives more females

As many of these breed at very low (dangerously low, due to a lack of buffer capacity of the water) most breedser breed them atmax possible pH - thus get many more males than females

perhaps this is also the case for Hemichromis???

It was thought that this was so, but research has shown a much higher correlation with temperature, although pH seemed to influence a little bit in some cases. High temp. yields more males and low more females with a 50/50 ratio about 26 degrees celsius. This is of course an average and will not always work since there are probably also some individual differences (Personally I suspect that the temperature effect could really be an effect of oxygen content, because temp. and oxygen are obviously closely connected. Naturally it is much more feasible for the hobbyist to control temperature, so this has no real practical importance). The experimental work in this area was published as follows: U. Römer and W. Beisenherz, 1996: "Environmental determination of sex in Apistogramma (Cichlidae) and two other freshwater fishes (Teleostei)". Journal of Fish Biology (1996) 48, 714-725.
I have the paper as PDF, and will gladly mail it to anyone interested.

As for "westies" I think that in many species pH actually does determine sex ratio. At least this is what I read to be true for some Pelvicachromis spp. I have never heard sex ratio to be a problem for Hemichromis spp., but then again I don't know a whole lot about West African cichlids.

[jfk]

thank you for comments!

I agree that this sex ratio shift can be driven by temperature or pH. I agree also that some reports about killies are controversial, I can remember that one aquarists reported about more males, while one other reported more females in the same condition for the same species. I even suspect that some sex ratio shift can be driven with the social organisation of the flock...

But in the case of Bangui I would like to get more facts about breed generation to find either this shift was accidental or it is usual. Therefore it would be great to ask the keepers of Bangui did they face the same problem?