By, Al Savastio, ALA, taken from :

Aside from all the negative press associated with the word. aquarists may not know the benefits of selective inbreeding, I went through some genetics books to gat a working definition of the term. They define inbreeding as the mating of related individuals. The different genes at a common locus on a chromosome are called alleles. If a fish has two identical aIleles it is a homozygote. Related fish share alleles through one or more common ancestors. I suppose you could get homozygous fish from unrelated fish, but inbreeding greatly increases the chance of this happening. In and of itself inbreeding is neither good or bad. It can be abused and it can certainly be used constructively

Most of us are aware that domesticated swords and platies were produced by hybridization. In these breeding schemes hybridization is almost always followed by inbreeding. In the second step the hybrids are often bred brother to sister or back to one of the parents. The only exception to this is when the hybrids are sterile. For instance, the only way to get mules is to mate horses with donkeys.

As hobbyists we can make use of a type of inbreeding called Linabreeding. I use this technique whenever I come across an outstanding male swordtail. First, bread this male to a virgin female to be assured he is the father of the resulting fry. Than bread this male back to his descendants - in other words back to his daughters and grand-daughters. This is done because the animal you’ve chosen is so outstanding you want his descendants to resemble him closely. This is how you create a strain of outstanding males as opposed to random mating where a good fish pops up every now and then. Every time you breed your best male back to his descendants you are increasing his contribution to the gene pool. Livestock and fish hatchery managers often go this route.

Our goal should be to produce show quality strains. not just show quality individuals.. Someday I would like to sec a show where entrants are required to bring in a dozen of their best fish. A species maintenance approach to domesticated livebearers would tie in nicaly with this goal.

Reproduced from the ALA Magazine Livebearers Issue 98 March/April 1988