Inbreeding is the mating between relatives or between fish that are more closely related by ancestry than the average population and is an important breeding program that can be used to improve population structure. However, if this is done without control and planning, it can destroy the population under the term "Inbreeding Depression". Inbreeding depression reduces growth and survival and increases anomalies. Most aquaculturists have been told that inbreeding can cause problems that should be avoided at all costs. This view is valid only if the inbreeding is unfavorable. Since inbreeding has been a powerful and valuable way to produce superior animals and plants for years. In order to genetically manage a population, a breeder or a breeding center manager must know how to use inbreeding to improve fertility. He needs to know the benefits of inbreeding as well as the time to avoid inbreeding in order to prevent inbreeding depression that reduces profitability and productivity. Inbreeding is one of the three most common breeding programs that have been used by breeders for centuries to breed plants and animals. This method is used to produce faster and better animals, and this technology has increased our ability to produce and use bloody fish to improve a population or for research purposes. This method is used in order to produce animals with faster growth and better characteristics and this technology has increased our ability to produce and use inbred fish to improve a population or for research purposes. Inbreeding: Inbreeding is the mating of organisms closely related by ancestry. From a genetic point of view, inbreeding increases levels of homozygosity in offspring. An increase in homozygosity (having the same pair of genetic information) is due to having commonalities among fish in one or more alleles (different types of genetic information in a particular gene location). This means that parents may have inherited an allele from a common ancestor. When inbred mating occurs, the alleles received from common ancestors can mate in offspring. In this case, the genetic purity is more likely to be present in one or more locus (chromosomal sites) in offspring. Inbreeding methods: Inbreeding is usually the third choice (after selective breeding and cross breeding) in population genetic modification programs and is similar to a double - edged sword that can severely damage the population. However, if used properly, it can be an effective breeding program. If animals with superior traits are used in inbreeding, animals with outstanding traits can be created. Development or creation of new species: The inbreeding is used if a new breed, species or variety emerges. The new breed can be the result of a random hybridization or created by an individual with unusual or desirable appearance traits. When the breeds are new and small, inbreeding is inevitable. At the beginning of the emergence of new species or breeds, there may be a small number of males, one superior to the other. In this case, the male reproduces with many females and a significant percentage of female offspring (daughters and granddaughters) in order to produce a similar population. Creating a particular breed is done in this way and when the goal is to develop a breed, only one or two male offspring (son) of a male animal are used. Line breeding: Line breeding is when closely related individuals such as parent and offspring mate. In fact, line breeding is a type of breeding in which the hereditary characteristics of an ancestor or a line of ancestors are concentrated in the herd. Usually, only one male reproduces with several females. If there are animals with outstanding traits, it is possible to use line breeding to develop a new breed or to create a new species. Line breeding is used to increase the participation of an individual with outstanding traits in a population, especially when that animal is so prominent that it is unlikely to be found better than that animal. Therefore, line breeding is an inbreeding program to achieve the goal of producing animal with outstanding traits. Use of superior male fish: This type of program is a line breeding program in which the breeder usually buys a superior male animal and uses it instead of one male population, meaning that this fish is the only male in the population. This fish mates with all the females and many of their female offspring. This mating program is used to raise a population and meet the phenotypic standards of superior male fish. This breeding program produces populations with high levels of inbreeding. Therefore, some breeders use multiple male populations to minimize inbreeding and reduce inbreeding depression. Use of inbreeding in order to identify and eliminate harmful genetic information: Inbreeding can be used as a form of the "Progeny testing" to identify harmful recessive genes and eliminate families that contain these genes. At the progeny testing method, fish with dominant appearance traits are mated with a standard fish (fish with a homozygous recessive gene) to identify the heterozygosity and maintain homozygosity. By inbreeding and developing families with high levels of inbreeding, the breeder can identify harmful recessive alleles and at the same time isolate the families that carry the hidden genetic disorders. This technique is expensive, but it is a breeding program that can produce animals with outstanding traits in terms of appearance quality over several generations. Inbreeding in order to improve the results of selective breeding between the families: If the amount of heritability is low for a trait, inbreeding can be used to improve the results of selective breeding. For the low degree of heritability, inbreeding can be used to create inbred fish families that later reinforce hereditary differences between families. Creating inbred lines for cross breeding programs: One of the most important applications of inbreeding is the development of inbred lines which are used in cross breeding programs to produce prominent hybrids.