Water temp VS sex of fry

John7 · Post by **John7** » 14 May 2007, 19:26

I have heard that the temperature of the tank water affects the sex of the fry when incubating eggs. Is this true?

I have a spawn of hi fin paleatus and there seem to be more males than females. Does it happen with all fish?

If so, which temp produces more females versus males?

apistomaster · Post by **apistomaster** » 14 May 2007, 22:02

The effects on sex determination on developing eggs or fry is advanced among the breeders of Apistogrammma species and Killifish quite a bit. Either because of water temperature or pH, sometime in combination.

I raise both and have been since 1968. I have experienced entire batches of Killies that were all males or females. I have had many batches that were ~50/50. I have had many experiences where I only had two or three hatch from a bag of stored peat moss and I ended up with a pair. I think, over time it evens out. The problem is with killies, especially annuals, it can only take a one time event of all of one sex to end your continued breeding without reaching out for some fish of the opposite sex.

I have seen the same thing among the fry of other breeders of Apistogramma that are heavily skewed towards one sex or the other. Never as absolute as with Killies, I have not had this experience among my Apistogramma. I believe the balance has been close enough to being even as to still be normal.

I have not heard of this among Corydoras.

It never seemed like a good explanation of the skewed sexes "problem" to me. I have been taught that sex is determined at the moment of fertilization and has a 50/50 probability, excluding the effects of artificial conditions where hormones are deliberately used. I don't understand how pH and/or temperature can be the determining factor(s). Something else is going on that is more complex than these explanations. IMO.

Post by **Silurus** » 14 May 2007, 23:16

Temperature dependent sex-determination (TSD) is a well-known phenomenon in reptiles. The exact mechanisms are unclear, but it has been suggested that the sex-determining genes are sensitive to temperature (i.e. they can be switched on or off depending on the ambient temperature).

Bas Pels · Post by **Bas Pels** » 15 May 2007, 10:57

Approximately a year ago I heard an inverview on the radio about sex determining factors within animals.

Mammals do have a simple systen (males XY, females XX) birds also have quite a understandeble systen (males X_, females XX) however, females can be turned into functioning males (or vice versa)

Within fish, either no sex determining genes excist, or a very complicatess system excists. As Larry explained, within Killies and Apistogramma the situation is well known - some pH and/or temperature effect does play some role. Within lifebearers (closely related to killies) a temperature effect is known in some species.

However, not all fishes depend on pH / temperature. Barlow reported (I borrowed the book

I can't give any reference) about midas ci chlids, where appartently social stress influenced the gender.

Smaller fish developed into females, bigger into males.

So quitre a lot sill remains to be discovered

apistomaster · Post by **apistomaster** » 20 May 2007, 22:49

I would have to agree. Sex change and/or indeterminate sex of reef fish Pomacentridae, damsels and clowns is well known.

I have suspected that the subdominant Apistogramma sometimes turn out to be mostly female yet many retain female appearance and size yet remain functional males.
Also a dominance related outcome is that in at least aquariums, Apistogramma males often out compete the less aggressive females resulting in male skewed result at maturity. It isn't clear cut what all the factors go into sex determination of fish.

Catfish don't usually have as complicated social behaviors as the Cichlidae and therefore fewer clues.
Much yet to be learned about on this topic.

I'll be darned, I've found a way to discuss THAT other group of fish without the asterisk letter substitution.

sabbath · Post by **sabbath** » 21 May 2007, 01:06

When I first started breeding there was an old-timer in my club that advised me on these issues with apistos.
I had this with A. maulbruter, and A. diplotaenia in particular.

I had 2 female diplotaenia that would spawn within a day or two of one another, and decided to experiment.
one would spawn, and I'd steal the wigglers, and raise them hot (low 80's), and do the smae with the next batch but raise them in cool water (low 70's). I'll be darned if I didn't get all females in the cool water, and all males in the warm water. I rased quite a few batches like this, and because i could guarantee pairs it was pretty profitable as well.

I with the maulbruter, I did the same thing, but i had to split the fry I stole. Perhaps you can give this a try with the cats and see what happens?

Being that S. barbatus (the only cory I have worked with) requires cool water that is what I raised them in, and the sexes were a little heavy on the male side, but not terribly.

Rich