Sex ratio?

[dconnors]

I am beginning to understand that pH can affect sex ratio in some Nanochromis/Pelvicachromis species...could someone please explain this to me? I have a pair of N. parilus that are going bonkers and I just want to do all I can in my power to get as even number of males to females that I can. Thanks in advance for any answers!
Dave

 

[aquaticclarity]

In general terms for fish with off spring that can have their sex influinced by pH...

higher pH = more males

lower pH = more females

Here are some ball park examples for spawning and raising some West African cichlids under diffrent pH conditions and the results (not exact pH to sex ratio numbers but close) The fun part is that other factors like raising conditions and temperature as well as the size difference in male and female (some females my not live because they are out competed by larger male siblings) can also effet the end sex ratio results.

Pevicachromis pulcher
6.5pH 25% male 75% female
7.0pH 50/50 ratio
7.5pH 75% male 25% female

Pelvicachromis rubrolabiatus
(very ball park here as I'm only working off of a few spawns)
5.0pH 25% male 75% female
5.5pH 50/50
6.0pH 75% male 25% female

Nanochromis parilus
6.3pH 25% male 75% female
6.8pH 50/50 ratio
7.3pH 75% male 25% female

 

[dconnors]

Wow, just like reptile eggs and temperatures then...Thanks Jeff!

 

[peterK]

Nice reply Jeff. Do you have any experience with P. t. "Wouri"? In pH 6.5 I got 1 female and 7 males...

 

[jmtrops]

I wish it was that simple. My wild P. sacrimotis spawned at a pH of 7.8 and 550 us and it looks like I have a good sex ratio, maybe a couple more females than males. I had a batch of taeniatus that were hatch in florida and were moved up here to mass with me at 1 week old and were raised in the hard hi pH water and the M/F ratio was 40/60. Now the pulchers that spawned in that water were 90% males.

When I was in Florida I used a 10 to 1 RO tap water mix. It was 100 us and the pH started at 7 and slowly dropped. Signatus spawns were 50/50, taeniatus were 50/50, my wild pulchers were 50/50 and my other pulchers, several pairs aquarium strain were 10/90.

I moved the fish again and now my tap water is very soft 95 us so I will see what they do now. I have a couple spawns growing now.

 

[dconnors]

Ok so I guess my next question would be at what stage of the fry development does this occur? At fertilization or as the fry develop?

 

[aquaticclarity]

With Apistos the sex seems to be determined in the first few weeks of life. I don't know that any studies/tests have been done on Pelvicachromis though.

 

[ste12000]

When Romer did his tests on Apistogramma and temp vs sex ratios he averaged the results of many spawnings, ive not read it in detail for a few years but im sure the final results were averaged over 25-50 spawnings.. It may of been that at a certain temp 50% of spawns were 100% males, in the other 50% 100% females making a split of 50% sex ratio at that temp..

While i do beleive that PH and temp may well have a subtle effect my own previous experiences have shown that 1 spawn can be heavy in males and without changing anything the sex ratio can shift in the next spawn and be either balanced or even heavy in the other sex, i personally have never been able to pinpoint any one temp or PH that would provide a reliable 50/50 sex ratio.

Also, does it make evolution sense to have the sex ratio determined by something as simple as Temp or PH??? What if a population was blocked off from the main population in a area of high temps and low PH, if the research is 100% true then that population would cease to exsist in a very short time if all resulting fish were male!
Collectors have spoken of shallow pool habitats having temps of 90+ degrees, would this not spell the end for the fish if this area remained isolated and hot and only males were produced??

As you can most likely tell.. Im a little Skeptical thats its as clear cut as is sometimes written!!

 

[Mike Wise]

Pelvicachromis and Apistogramma are 2 very different genera, both in genetics and habitat. I don't think you can compare the environmental effects on sex ratio of one genus based on the effects on the other. In apistos, temperature does seem to have a noticeable effect on sex ratios in a controlled environment. Observations by Römer in the Rio Negro also seem to show this. In the wild there is a gradation in temperature due to water depth. In these biotopes, the most dominant females defend territories in the ~26°C/79°F zone, while less dominant females defend territories in higher (warmer) and lower (cooler) zones. All breed and produce fry. If temperature-based sex ratios hold true in the wild, them dominant females produce equal numbers of both sexes, females in warmer zones produce more males, and females in cooler zones produce more females. Over the entire population, I would expect the sex ratio of surviving fry to be close to 50:50. This should change with maturity. More females will tend to survive because they live within the larger territories of dominant males (together with other females). The dominant male defends not only himself but the the females in his territory. These dominant males are out defending their territory and more subject to predation. This isn't a problem, since non-territorial males will replace them. Males without territories will also be out in the open more, looking for and fighting for territories, and more likely to become prey than females. Therefore I would expect more females to survive in the wild than males. We often don't see this in fish shipments because males, either looking for or defending a territory, are more frequently collected than female hiding with eggs or fry.