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How Guppy Fry Sexing is Determined


Cinnebuns
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I often hear about people having all male or female fry for periods of time. Sometime people have a hypothesis that this is determined by temperature. I have yet to see any evidence of this and infact have seen it go opposite many times. It doesn't seem to me to be a valid way guppy sex is determined. I still remain open to this hypothesis if any evidence does come up but I have yet to see one. 

I have a new hypothesis that came to me one evening. Guppy females have incredible control over their reproduction. They are able to start and stop their delivery of fry, abort them if they feel unsafe, and become pregnant on their own in the absence of a male. If that isn't amazing enough they are also able to give effectively choose which male's sperm has a better chance of being used or even completely flush out a male's sperm if she doesn't like him enough. (Read up on cryptic female choice. It's fascinating.)  This got me thinking. What if females are able to increase the number of males or females they produce based on the fish around them?  Would a female giving birth in an all female tank produce more males?  

I am an armature scientist. I have a minor in psychology and have taken courses that go over basics of designing an experiment and analyzing data but I have never taken the full course in it that psychology majors took. While talking with a friend, we are considering setting up and experiment to test this. It wouldn't happen for a couple of months but I would still like some input now on making this as accurate as possible and trying to minimize variables. 

My ideas is this:

2 pregnant females who are direct sisters and look identical so genetic variables are at a minimum. Both must be virgin before mating. 

Place 1 male (unrelated? Related?) in with both females alone for a day. 

Put female A in a tank with other females. All other females must be virgin so to be sure all fry are hers. 

Put female B in a tank with 1 male. I'm not entirely sure how best to deal with this tank tbh. More than 1 male and she would get harassed too much. Put in other females and they might get pregnant and drop fry. Keep her alone and she might not drop fry herself. 

Control tank?

Seperate fry in 2 grow out tanks. At 5-6 weeks old sex all fry, count and document. 

I know there are holes and it's not perfect but that's why I come here!  Any ideas?

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I've done a good bit of research support over the years. Often for grad students and post docs, and professors.

The tanks need to be kept the same manner. Things like light or sound or temp can not differ. Water parms need to be monitored closely and kept the same, but I would not allow the water from one tank to mix with the water in the other tank because of hormones and scents and such. Maybe all tanks should be new, so no prior scents are present? They don't need to be glass rectangular aquariums, they might be jars or plastic containers. These are not display tanks, just identical tanks. The feeding needs to be identical.

It is very nice to have more than 2 subjects. If one dies, you have to start all over again. If you could get close to 30 or more subjects, you statistical proof is much stronger. 30+ in each group is even better.  

Everything needs labels and ID numbers. Doing double blind won't be easy because a tank of only females looks different than a tank with a male and a female., Maybe the person feeding the fish should not be able to see the fish? You could have dark covers with feeding holes.

If the identical females spend a day with a male then one female remains with that male and the other female joins one virgin female, then both "schools" of guppies are the same size. This would also allow for smaller tanks. Which to leads to more subjects. 

You would probably want to set this set up a few times to see how the tank set up etc work for the guppies. If the set up doesn't work for 2 or 4 subjects it is cheaper to find out before you make 30 or 60 setups.

Constantly tracking lots of data fields is always helpful for statistical analysis. Sometime things you assume would have no effect can turn out to have a major effect. Things you can not control, but can record include weather conditions and pressure changes or moon phase. 

I could go on and on, but I will let you tell me if you want more of this sort of detail.

I love research !

 

You might want a sprig of identical artificial floating plant material in each tank for fry to hide in.

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Oh another good source for design ideas is scholarly journals. You can read where an experiments design worked and where it didn't work as well. It don't have to be a fish journal. Any journal that talks about experiment design can give you good examples.

 

And you don't need to do all the subjects are the same time. If you are limited on space, you can do sets of say 6 subjects and replicate the study 5 times. 

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On 1/23/2023 at 12:57 AM, KittenFishMom said:

I remember reading the sex in snapping turtles is determined by temperature at certain points during incubations of the eggs.  So it might not be as far fetched an idea as it sounds.

I know temp is a factor is many reptiles not just turtles but I'm not convinced it is in guppies. I don't doubt it because it seems far fetched but because I don't see any evidence for it. I see it go both ways in both temps for many different people. I will believe it if I see evidence for it but currently I have seen none. Only Facebook gossip. 

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im sure no expert, but ive always doubted the validity of claims guppies are born a certain sex based on water temp. my reasoning being, i keep lots of guppies, and i do so in unheated tanks that year round average 68-72 degree's, and i get plenty of both sex fry. whenever ive seen folks comment on temps affecting sex with guppies its below 74, or above 74, well im always below 74, and get both. totally non scientific, but based on 25+ years of observation keeping guppies.

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An experiment is always fun and may be informative. We all want ways to make more males! 

I think lots of the "all my fry are female!" statements are made by folks who don't realize it may be 4+ months before male fry show their true colors and/or gonopodium.

The rate of fry development in my own experience varies so much according to tank size and water changes. Youtuber Kaimuki backyard raises guppies in large outdoor tubs where in addition to any water changes he may do, rainfall provides additional water changes. I've seen him in videos taking fish to the LFS who are sexually distinguishable at I think 4 months old.

I have fry who are every bit of 6 months old before they grow a gonopodium or are colored up as males in my overcrowded 10 and 20 gallon tanks. If I was determined to take them to the LFS to sell at 4 months, they'd all be "female" looking. Of course, if I was really breeding for profit I'd do more water changes and feed BBS to get them grown and gone--but maybe the "all my fry are female!" folks are casual like I am and therefore their fry are slow to sex out.

Edited by PineSong
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On 1/26/2023 at 8:04 PM, PineSong said:

An experiment is always fun and may be informative. We all want ways to make more males! 

I think lots of the "all my fry are female!" statements are made by folks who don't realize it may be 4+ months before male fry show their true colors and/or gonopodium.

The rate of fry development in my own experience varies so much according to tank size and water changes. Youtuber Kaimuki backyard raises guppies in large outdoor tubs where in addition to any water changes he may do, rainfall provides additional water changes. I've seen him in videos taking fish to the LFS who are sexually distinguishable at I think 4 months old.

I have fry who are every bit of 6 months old before they grow a gonopodium or are colored up as males in my overcrowded 10 and 20 gallon tanks. If I was determined to take them to the LFS to sell at 4 months, they'd all be "female" looking. Of course, if I was really breeding for profit I'd do more water changes and feed BBS to get them grown and gone--but maybe the "all my fry are female!" folks are casual like I am and therefore their fry are slow to sex out.

That makes me wonder if temperature has anything to do with growth rate or age of maturation, and the apparent effect in sex ratio is an illusion caused by the actual effect on growth. Maybe their metabolisms speed up in warmer water? It seems to work that way for cherry shrimp. But I've never kept livebearers, so I'm just speculating.

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On 1/26/2023 at 7:42 PM, Rube_Goldfish said:

That makes me wonder if temperature has anything to do with growth rate or age of maturation, and the apparent effect in sex ratio is an illusion caused by the actual effect on growth. Maybe their metabolisms speed up in warmer water? It seems to work that way for cherry shrimp. But I've never kept livebearers, so I'm just speculating.

with this, i think you are on to something. keeping cooler temp tanks, i tend to get longer lifespans that what you normally see quoted for many different species of fish.

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On 1/25/2023 at 9:59 AM, TheSwissAquarist said:

What I wonder about is wether the guppy fry are a neutral sex at birth, and then become one or the other in function of the M/F ratio in their tank.

Random Hypothesis, I could also be totally wrong! 😅

Oh thats an interesting thought and quite possible. My thoughts came about because of how much control we already know the female has over reproduction but that's entirely possible too. 

 

On 1/26/2023 at 7:04 PM, PineSong said:

it may be 4+ months before male fry show their true colors and/or gonopodium

You can still usually tell if it's a late bloomer male or a female before then however that takes experience to know. 

 

On 1/26/2023 at 7:42 PM, Rube_Goldfish said:

That makes me wonder if temperature has anything to do with growth rate or age of maturation, and the apparent effect in sex ratio is an illusion caused by the actual effect on growth. Maybe their metabolisms speed up in warmer water? It seems to work that way for cherry shrimp. But I've never kept livebearers, so I'm just speculating.

It does. Warmer water makes them grow faster but also shortens their lifespan by half if high enough. 

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Edit to lead with love and support not criticism 🤩

 

@Cinnebuns unfortunately you're approaching the scientific method incorrectly. If your hypothesis is that sex ratio in the tank determines sex ratio of birthed babies, you have to eliminate all the alternatives (or as many as you can). So you design your experiment to test for those alternatives (controlling for all other variables if possible), not for what you actually want to see or prove. 

In a way, this might make your test easier. Take temperature for example. If you think sex ratio of birthed babies is due to the sex ratio of adults in the tank, but it's possible that it's due to temperature, you might have two "treatments" of varying temperature, controlling for as many unrelated variables as possible, and see if the different temperature treatments yield different sex ratios. Let's say you go through all that, and find that tanks at 65F have the same birth sex ratios as tanks at 80F. You won't have proved your hypothesis about adult sex ratios, but you will have disproved that temperate is actually the driver. This is the scientific method: you disprove all the alternatives, and what's left is truth, fact, or whatever you want to call it. 

Also I agree with what @KittenFishMom wrote about replication. Having just 2 tanks weakens the power of your analysis, and weakens any conclusions/inferences you make. You want (say) 10 high temp tanks and 10 low temp tanks. 

Then, after you have eliminated temp as the driver, you ask what other factors might drive birth sex ratios, and test for them the same way. Could it be light or day length? Amount of fat or protein in diet? Presence of predators? Water quality? You have to isolate each alternative, replicate your sample sizes, measure outcomes, and possibly rely on mathematical analyses to know if the findings are real or not. 

How will you ensure you are getting all these virgin females, in a species that can often become pregnant before they're reliably sexable (to non-experts like most of us)? The answer is to go down the betta rabbit hole. Take a spawn of guppy babies (or work with endlers, which are smaller), and raise individuals in cups from a very young age. Now you're going to need a lot of cups, and a breeding setup to facilitate water changes. Oh joy, the rabbit hole just got deeper. 😛

Before you do all that, however, head over to Google (not the most scholarly of search engines, but at least its available to most of us) and search for "Poeciliid sex ratios". You'll find a lot of hits, and it's possible that some of the research there will disprove some of the alternative hypotheses. A lot of the hits relate to adult sex ratios, but I didn't look too deep. I did see evidence that temperature and pH are known to drive offspring sex ratios in some fish. You could also replace some of the search terms to broaden your search, eg "livebearer sex ratios". 

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