Breeding guppies: Selective breeding

breeding guppies selective breedingSelective breeding means deliberately breeding guppies with certain traits (such as a particular color or tail shape), and phasing out undesirable characteristics. In order to achieve this, you need to do a reasonable amount of forward planning, ongoing monitoring and record keeping!

First of all, decide upon the traits that you wish to achieve in your guppies, be they pattern, tail shape or color. Begin your guppy lines with good quality parent fish, which display good quality examples of these characteristics.

In this article, we will explain to you how to go about selectively breeding guppies, and how to keep track of your progress.

Line breeding

Line breeding is the term used to refer to the process of mating related guppies together to reliably produce or enhance the desirable traits of the fish.

Subsequent generations of the best examples of the offspring are then mated with other related fish in the line that also possess the desirable traits, to ultimately produce a specialist line that reliably produces fish that display the most prominent and desirable features you are aiming to achieve.

It is entirely possible and often recommended to mate female offspring with the father of the line to achieve good results, yet breeding male offspring with the mother of the line generally fails to produce positive results, and so this is best avoided.

Out crossing

Out crossing refers to breeding a guppy of one line with an unrelated guppy, to provide the additional genetic diversity necessary to support health and good conformation, and reduce the chances of producing fish with faults or deformities, such as curvature of the spine.

Breeding closely related guppies and their subsequent generations over and over again can serve to introduce a range of undesirable factors as well as desirable ones into the line, due to the limited amount of diversity present within the gene pool.

Out crossing is an important part of line breeding, and out crossing your related breeding guppies every few generations will help to maintain the genetic robustness of the line without sacrificing the desirable traits of the strain.

Out crossing can also be used to introduce a new desirable trait into your line, such as a particularly vibrant color or a new tail shape.


Backcrossing refers to mating a guppy from a line back to one if its earlier ancestors, to restore the progression of the line’s traits to a previous state and remove or phase out an undesirable trait that has crept in somewhere along the way.

Often, one deliberate backcrossing is sufficient to correct an undesirable issue, although you may have to undertake the process more than once to achieve success.

Culling guppies

Culling is an important part of selectively breeding guppies, as it removes fish with undesirable or indistinctive traits from the potential gene pool.

Guppies that are deformed, sickly or physically sub-par should be put to sleep, but guppies that are healthy and viable but simply not in line with what you wish to achieve from your line can be sold or given away to other hobbyists or the retail fish trade for pet shops.

Keeping records when selectively breeding guppies

In order to keep track of what is going on with your guppy breeding program, which fish is which and what your matings have achieved, keeping accurate and conscientious records is vital.

If you are not sure what you need to record and how to interpret the information, recording the following details should provide you with everything that you need:

  • Starting with your parent stock, assign each founding guppy pair or trio with a number, so that you can trace and identify the origins of your subsequent fish from each mating.
  • Notate the sex of each guppy, and the color, pattern and tail style to establish the type of strain you produce.
  • Assign a generational figure to each set of offspring: For example “F” for the founders, and “F1,”  “F2” etc for the generation and level of removal from the founders of each subsequent set of offspring.
  • Note any crosses and the relations of each fish to each other; for instance brother to sister, daughter to father, half sibling to half sibling, in order to keep track of the relationship of different fish in your line. This will allow you to identify the relationship of different fish to each other and what desirable or undesirable traits breeding them produces, and if backcrossing or outcrossing will be required.
  • Keep details of the dates that you breed any fish, which fish were mated, and what date the mother delivers the guppy fry.
  • Mark up each of your tanks with what fish are within them, and any pertinent dates in order to keep track of which fish are where, as similar-looking guppies can be hard to tell apart based solely on your written records!

This post is part of our Guppy Breeding series! Read more…


  1. how old does the guppy have to be?

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