Apisto borellii opal sex ratio of fry

[JeffInKentucky]

I have had several batches of fry that when mature are about a 6:1 female to male ratio. I read somewhere once that water parameters influence that ratio, but I cannot recall what those parameters were. My water is soft, with a ph around 6.5 and temps around 78. Can anyone advise what the parameters should be to result in more males AND if when the sex is determined? Is it upon the spawn, hatching, or grow-out? Thanks in advance.

 

[MacZ]

General tendency for fish, amphibians and reptiles: The warmer the more males.
At 25°C the ratio should be more towards 1:1.

that when mature are about a 6:1 female to male ratio

What size/age are we talking? Is it possible you tried to sex them too early? (Trying to rule out any mistakes here.)

AND if when the sex is determined?

Between fertilisation and hatching.

 

[JeffInKentucky]

General tendency for fish, amphibians and reptiles: The warmer the more males.
At 25°C the ratio should be more towards 1:1.


What size/age are we talking? Is it possible you tried to sex them too early? (Trying to rule out any mistakes here.)


Between fertilisation and hatching.

Thank you very much! Except for the latest batch (which I had turned the heat up) all were sexed as adults. Another month or so and I should know if my last attempt with a higher temp worked. Appreciate it!

 

[MacZ]

Allright, good luck.

For the wellbeing of the parent fish you should not exceed 27°C for longer than a few weeks, otherwise the risk of bacterial infections rises a lot.

 

[Mike Wise]

Look up Römer & Beißenherz's paper on temperature and sex ratios in the search engine here. A. borellii was one of the species in the study. 26°C/79°F resulted in a 50/50 ratio. Realize that they made strict counts of numbers of eggs/numbers of adults. Any batch <90% survival were discarded from their statistics. Unless you do the same your results will vary from theirs. pH also has some bearing on sex ratios, but less than temperature. Lower pH values produced slightly more males. If I had the same problem as you I would raise your temperature and lower the pH slightly.