Sexing Guppy Fry - The Planted Tank Forum
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post #1 of 4 (permalink) Old 03-12-2003, 07:18 PM Thread Starter
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At what point should you be able to tell the difference between male and female guppies? I have two batches of fry in my tank, one is 3 weeks old and approaching 1/2 -3/4 of an inch long, the other batch is 1 week old and still under 1/2 inch. The older batch are both half black and i cannot see any difference in tail size or coloration, none of my males are that color but one of my females is. The second batch of fry are completely clear which again matches the coloration of one of my females. At what point do the males start displaying their colors and are they nessicarily the colors of the breeding male or female?

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post #2 of 4 (permalink) Old 03-12-2003, 08:29 PM
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First, you will need a two-gallon aquarium and a piece of black cardboard that can cover the back of the aquarium. Cut a hole about 1/2 inch in the center of the cardboard and place it on the back of the aquarium. Place a small lamp with a frosted 100-watt bulb directly behind the hole. Using the water from the aquarium containing the new fry, fill the two-gallon tank. Carefully remove two or three fry from the tank and put them in the sexing tank. Wait until early evening when the sun is dim, and using a magnifying glass, observe the guppy as it swims through the beam of light. Under these specialized conditions, the gravid spot of the females can be detected. Males will not have this spot. Segregate the males and

I found the above on the net. To me, sexing them is a pain in the butt!
You can wait till they get a little older than what it says above, when the males come to sexual maturity. They will develop a gonopodium(sp) it is a nifty third fin thing on their abdomen, that they use to deliver sperm to the female. Usually you can see the gravid spot on the females by then too.
Only thing is, if you wait that long to sex them, then some of the females may have already been impregnated.

Have fun! I don't envy you, LOL. :lol:

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post #3 of 4 (permalink) Old 03-12-2003, 08:57 PM Thread Starter
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Having them breed is not a concern, i could care less about maintaining a "Pure" line as it is just a kick to have them breeding all the time, i am gonna give the extra to my friends/family/and any local fish stores i can conive into giving me credit for 8)

Though in refrence to color patterns how is it determined what a male will look like? is the color of the male or the color of the female?

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post #4 of 4 (permalink) Old 03-12-2003, 09:08 PM
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I personally think its easier to see if there is an anal fin or lack of anal fin to determine sex, because the gonopodium is a smaller organ. So, if there is an anal fin its a female.

About breeding guppies, you want to make sure the male and the female have around the same tail color, shape, and characteristics you want, otherwise you will have more of a mix group.

Here is a site for more information on breeding if your interested:


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