Enviromental sex determination.

[Maurice Matla]

Enviromental sex determination. Most people are aware that it occurs in crocodilians were the temperature in the nest determins the ratio of male vs female offspring.

Until this evening i was not aware that it also occors in ,at least some, fish species. I came across a piece of research about this phenonomen in Apistogramma species mainly. In this bit of research they looked at the influance of temp and PH in determining the male/female ratio in these fish. I will post a link too it below.

I was wondering if the same thing is known to occur in Parosphromenus. Or any thoughts on that phenonomen regarding Parosphromenus and ESD.

https://www.researchgate.net/publication/229586281_Environmental_sex_determination_in_Apistogramma_Cichlidae_and_two_other_freshwater_fishes_Teleostei

I am not sure in wich categorie to post this feel free to move if needed.

[Peter Finke]

It is known for quite a long time that the sex of fish individuals (or amphibians or reptiles) is not fixed within seconds by insemination (as in mammals or birds for instance) but by environmental factors as temperature, pH or the degree of humic substances during the first days or even weeks of their lives. The phenomenon has been widely been researched upon by specialists at universities in Germany and other countries and should be taken as well-known by science but not by hobbyists, however. I posted on this years ago in this forum. Often we have very one-sided results in the groups of offspring of Paros (f.i. 60 nagyi all males, 2 females) that are to be explained by one factor or the other. It could prove to be difficult, however, to name the decisive environmental factor in a concrete case, for mostly it is a combination of several factors.
What one should learn by this is that this is one of the important arguments for trying to imitate the natural environmental conditions for breedings as close as possible.

[Gianne Souza]

Although they are not Paros, sex determination in Bettas is still quite a mystery. Many spawns are heavily skewed in one direction or the other (I myself have had spawns that are nearly 100% male or 100% female, and I’ve tried to isolate different variables like pH or temperature – haven’t found anything consistent yet!) It is thought that Bettas rely on environmental cues to determine sex, but the link has not been definitively proven.

Here is a research article that I found extremely interesting. I made an “abstract cartoon” and a summary breaking down the article. A link to the actual article is at the bottom of the page:

http://www.ingloriousbettas.com/sex-determination-in-bettas.html

This article was particularly interesting because females that had their ovaries surgically removed (dubbed “neomales”) were actually able to go on and father viable offspring, notably of both sexes! This argues against an XX/XY system of sex determination. Anecdotal evidence of females spontaneously switching to males are well known among Betta breeders (I in fact witnessed this first hand – a female that actually placed 2nd in her class at one show “switched” in transit to the next show, where s/he placed in a male class!)

I wonder if Paros have a similar sex determination system as Bettas, and if so, what can cause skewing towards one sex or the other. Peter, is it known what the approximate sex ratios typically are in the wild? I know this information would be very difficult to collect properly (ex: perhaps nesting males are more evenly distributed in discrete territories but females roam around in loose shoals, then there could be a collection bias in any one catch. This pattern of behavior is similar to nesting male bettas/roaming female bettas). Would be interesting to see if there are skewed sex ratios in the wild, and when they occur.

Cheers
Gianne

[Maurice Matla]

I´m diving into that article later on.

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