Line breeding is a form of interbreeding used to “fasten” desirable traits in a breed or strain. Compared to close interbreeding, which also serves to fasten desirable traits, careful line breeding involves a lower risk of undesirable traits showing up in the breed or strain. Line breeding tilapia is thus safer than engaging in close interbreeding.

What is close interbreeding?
When relatives that aren’t separated by more than one generation mates with each other and produce offspring, it is called close interbreeding. Examples of such relatives are mother-son, father-daughter, and brother-sister. Close interbreeding will concentrate desirable traits in a breed or strain, but it also quickly concentrates undesirable traits.

Responsible tilapia breeders usually only let their fish interbreed in very special circumstances where line breeding won’t work. Close interbreeding should not be carried out over and over again since that is associated with rigorous genetic problems in the offspring. It is also important to keep your fish in an environment where it is easy for you to severely cull the resulting batch.

What is line breeding?
When two individuals of a particular line are separated from each other by more than one generation it is called line breeding if they mate with each other and produce offspring. Just like close interbreeding, line breeding is used to “fasten” desirable traits. If you have a tilapia fish with a highly sought-after trait, you can use line breeding to preserve and concentrate that trait in its offspring.

One example of line breeding is the mating of first cousins. First cousins share a common ancestor (grandmother or grandfather or both) but are separated by more than one generation. This separation is what makes line breeding much safer than close interbreeding. It is however important to keep in mind that even line breeding will limit the genetic diversity in the offspring. You will probably not notice any problems at all in the first and second generation, but if you continue to line breed without adding any new genetic material the gene pool can rapidly become small enough for various hereditary problems to manifest.

Line breeding tilapia
As mentioned above, line breeding should not be carried out for several generations without adding new genetic material. Among tilapia breeders, it is common to widen the gene pool of the tilapia strain by practising so called outcrossing. Outcrossing involves letting unrelated individuals mate with members of your strain in a controlled fashion and will decrease the risk of genetic problems in future offspring. By carefully combining linebreeding and outcrossing, it is possible fasten desirable traits without have a lot of undesirable traits showing up in the offspring.

To avoid genetic problems in your tilapia population, it is important learn about basic genetics and the genetics of tilapia before you attempt line breeding. Understanding concepts such as dominant and recessive genes will make line breeding safer and easier for you. It is also important to learn about genetic health issues known to occur in tilapias and how these problems are passed on to new generations.

Before attempting line breeding it is also important to set up a system that will work not only today, but many fish generations into the futures. Planning ahead and keeping a detailed log of your endeavours is strongly recommended. Don’t fall into the temptation of focusing to narrowly on one or two desirable traits, because not paying attention to the overall health of a strain from the start will come back and cause problems for you several fish generations from now.