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Sexing young fish smaller than 100 grams is not easy. Seeing that tilapia are the most popular fish in aquaponic systems worldwide, we will focus on how to sex them visually. 

Please note that the representation of the sexes shown in the image above is for illustration purposes only and is not 100% anatomically accurate. Urinary orifice and sexual organs on left and anus on right, assuming fish’s head is pointing right. 

Below are some close up photos of a male and female Rendalli tilapia, both over 500 grams each. As can be seen, the sexual organs are quite distinct between male and female. With practice you will learn to pick this up.

The female has an oviduct, from which the eggs are released. 

The male sex organ is called the papilla. 

Mr Nick James, a South Africa Ichthyologist and possibly the leading exponent on T. rendalli in the World adds:

  • At breeding time, the female T. rendalli turns much darker red ventrally than the male, which often has an almost white ventral region. Both sexes show distinct dark vertical bands. For fish of the same age the males are much larger than the females and have longer dorsal and anal fins edges.
  • T. rendalli are actually typical of their genus (Tilapia) in that they are substrate-spawners. It is only the genusOreochromis (mosambicus, niloticus etc) that have female mouth-brooders and do not form pair bonds like Tilapia do. OtherTilapia, like T. sparrmanni are also pair-bonded substrate-spawners.
  • T. rendalli eggs are adhesive, and the female will stick them on a smooth rock or slate in a tank without sand.

In our particular setup they burrowed a nest in the river sand at the bottom of the tank.

If you sex them correctly and create the right environment for the breeding pair, you will soon have a lot of these little guys (see below).

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