Hi, my name is Nic and I would appreciate advice on how to increase the number of males in a guppy brood?

Welcome to the forum Nic.
There is no reliable way to increase the number of males. If you run your tanks a bit cooler than usual,there are often more males compared to the number of females but that does not mean that you end up with more males. The reason is that a cooler tank will also mean slower metabolism for the fish and slower development of the fry before birth. With less being born, a larger percentage of males may very well mean significantly less females and a few less males. I suppose it depends on why you want to influence the sex distribution of the fry.

I am not aware of any way to do this either. Their might be some type of chemical out there that would affect the production of hormones in the developing fish. You might be able to alter the production of males through selective breeding. What I mean is to pick young for the next generation from females that have produced more males than females. The other option is to just get rid of the females,,,and wallah youve got more males I think you are the first person to want more males from their fish though. Most people end up having strains that are male heavy.

Thank You for your advice Michael. I have also read that the females sense how much space is available and the broodsize and number of females are then more. I am conducting a little experiment, maybe it will work.
Nic

Good luck Nic, let us know how your experiment turns out.

When selecting pairs, ruthless culling of stock to only those males that seem to provide higher percentages of males should be bred. Temperature also helps, but seclive breeding is a major component.

Hi Nic,It took me awhile to find the info you were looking for.I know I had read it somewhere before ,but had to go and find it again.There is chapter, in a very good book I own on Genetics,Polygenic Sex Determination,the book is Genetics for aquarists by Dr.J.Schroder.Its one of the books that never leaves the top of desk.In the picture are some of my favorite books.

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The following passage taken directly from the link provided might help. The fact that the sexual gender is inherited by a simple XY-system is essentially correct, but a smplyfied way of explanation. It has been known for a long time now, that there are also a large number of autosomal genes with some effect on the defining of sexual gender. When these become accumulated to a neccessary amount, pointing towards a certain gender f.ex. female, the XY-system can be "suppressed" and a XY-individual can become a fully functional female. The other way around, autosomal genes can produce a fully functional XX-male of an XX-individual. Such a male mated with a normal female, produces 100% daughters. But a XY-female produces 25% daughters, 50% normal sons as well as 25% YY-males! These (fully functional and vital) YY-males produce only 100% male offspring, a fact that has rendered great interest among commercial breeders in Singapore.

In research laboratories there has even been produced a functional YY-female, which within a test-mating with an XX-male produced 100% male offspring. It was argumented, that such females would be a suitable match for matings with YY-males in order to produce enough amount of YY-males for commercial purposes ... There are since a long time well elaborated methods to force the whole batch to become either 100% female or 100% male, through feeding gravid females with either oestrogen-enhanced or testosterone-enhanced food. But genetically seen, these batches are still a blend of XY-individuals and XX-individuals.

Here is the link http://hem.passagen.se/mikeno/english/texter/esge.htm

OK NYC, what I get is that you can get weird expressions of gender by pushing huge doses of estrogen or testosterone without actually having the correct genetic material in the fish. I suppose that is OK for the crap foreign breeders that have brought us the 100% male dwarf gouramis and similar anomalies. It is nothing that I would want to become involved with and is certainly nothing I would ever suggest to a hobbyist who wants to get real males and real females.

OK NYC!!!!!! Who are YOU to say what people should or shouln't do!!!!!No one is asking you to get involved with anything.You have to have an open MIND this is an open forum for everyone.You should be more careful what you say ,there might be a young boy or girl out there who is on this site who happens to like Dwarf Gouramis or baloon mollies.You should not be too quick to condem anything or anybody.Here from NYC ...