Separating and Sexing Guppy Fry

Why is this important?

I've been importing, buying, swapping and breeding Guppies for years. Unfortunately it's very very difficult to get great fish here in Australia although they are available and some reasonable stocks are available if you are prepared to work the line a bit.

One of my key frustrations is that it is near on impossible to buy virgin females. To me this is one of the single biggest "musts" when breeding in particular if you are trying to improve a line. If you don't know who the father is then it's impossible to know the genetic make up of your fish; who knows what you have!

So, I thought I would tap out an article on the method I use to make sure that I have virgin females available for my breeding program.

Female Guppies have a very big give away that to the trained eye is visible at about 2 to 3 weeks old; the gravid spot. The gravid spot is the darker spot just in front of the anal fin.

I typically try to separate my females as early as possible so start the process as soon as I notice a gravid spot and continue the process util I've moved all the females. Some breeds are easier to spot than others.

My fishes drop of fry are moved to a grow out tank from day 2 (I use hang on the outside breeding boxes for the birth). Obviously at this point it is a mix of gender in the grow out tank. At this stage, if I don't have spare, I cycle a single 20L tank in readiness.

The key to separating is that you only move the female fish. The reason for this is that providing you are 100% sure it's a female you move it away from the males. In this way you know that the female tank only holds females ( by default it's possible that the male tank, the original grow out tank, holds both genders). If you were to move the males you run the risk of missing one and leaving it in with the females!

That's it! In point form:

  • Keep all fry together from birth in a grow out tank which will eventually be the Males tank. (I use 20L tanks)
  • At about 2 weeks see if you can spot any females by identifying the gravid spot. Try using a hand held torch to help. I also sometimes use a magnifying glass or zoom in with my mobile phone.
  • If you are 100% confident you spot a female move her to a second grow out tank, this is now the female grow out tank.
  • Continue the process until all the females have moved across.
  • Get to know your fish as they grow and start identifying your next breeding pair or trio. It's amazing how familiar you become with each individual fish... I don't recommend naming them!
Hover over pic for more info

Female about to drop fry

It's far better to have 5 females then 10 and accidentally move a male across so don't risk it, if you're not sure don't move it is the rule. 

Look for the gravid spot to identify young females