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Aug 6, 2021
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I’ve recently been searching on the web about methods of yielding more male/female Guppies from batches of fry. I’ve read that softer water with lower PH yields more females, harder water with higher PH yields more males. I’ve read that even the temperature can affect the ratio of sexes. Has anyone tested these methods and can say they are true? Or is this all a myth? I would like more males in my batches when the time comes, since they are so colourful and mesmerising to look at!
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pH can affect the sex ratios on some fish. I did experiments using Apistogramma dwarf cichlids, Epiplaty and Aphyosemium killifish, Australian and New Guinea rainbowfish, and had a much higher % of male offspring compared to females. In most cases I ended up with 80-90% male.

The pH varied between 7.0 & 8.6 and the higher the pH, the more males.

Temperature and GH make no difference to sexes, but will make a difference to the number of eggs that hatch (for egg layer species). In cooler water with a temperature below 22C not many eggs hatched. When the temperature was 24-30C, most if not all of the eggs hatched.

If the GH was high (above 200ppm), very few killifish or Apistogramma eggs hatched. Best hatch rates occurred when the GH was below 100ppm for these species. The rainbowfish eggs hatched regardless of the GH, which varied between 0ppm & 350ppm.
Temperature affects sex ratios in reptiles but I have not heard of any reports of fish (wild or domestic) sex rations being affected by temperatures.

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