The foundation of quantitative genetics theory was developed during the last century and facilitated many successful breeding programs for cultivated plants and t- restrial livestock. The results have been almost universally impressive, and today nearly all agricultural production utilises genetically improved seed and animals. The aquaculture industry can learn a great deal from these experiences, because the basic theory behind selective breeding is the same for all species. The ?rst published selection experiments in aquaculture started in 1920 s to improve disease resistance in ?sh, but it was not before the 1970 s that the ?rst family based breeding program was initiated for Atlantic salmon in Norway by AKVAFORSK. Unfortunately, the subsequent implementation of selective breeding on a wider scale in aquaculture has been slow, and despite the dramatic gains that have been demonstrated in a number of species, less than 10% of world aquaculture production is currently based on improved stocks. For the long-term sustainability of aquaculture production, there is an urgent need to develop and implement e- cient breeding programs for all species under commercial production. The ability for aquaculture to successfully meet the demands of an ever increasing human p- ulation, will rely on genetically improved stocks that utilise feed, water and land resources in an ef?cient way. Technological advances like genome sequences of aquaculture species, and advanced molecular methods means that there are new and exciting prospects for building on these well-established methods into the future.

Although aquaculture as a biological production system has a long history, systematic and efficient breeding programs to improve economically important traits in the farmed species have rarely been utilized until recently, except for salmonid species. This means that the majority of aquaculture production (more than 90 %) is based on genetically unimproved stocks. In farm animals the situation is vastly different: practically no terrestrial farm production is based on genetically unimproved and undomesticated populations. This difference between aquaculture and livestock production is in spite of the fact that the basic elements of breeding theory are the same for fish and shellfish as for farm animals. One possible reason for the difference is the complexity of reproductive biology in aquatic species, and special consideration needs to be taken in the design of breeding plans for these species. Since 1971 AKVAFORSK, has continuously carried out large scale breeding research projects with salmonid species, and during the latest 15 years also with a number of fresh water and marine species. Results from this work and the results from other institutions around the world have brought forward considerable knowledge, which make the development of efficient breeding programs feasible. The genetic improvement obtained in selection programs for fish and shellfish is remarkable and much higher than what has been achieved in terrestrial farm animals.

The foundation of quantitative genetics theory was developed during the last century and facilitated many successful breeding programs for cultivated plants and t- restrial livestock. The results have been almost universally impressive, and today nearly all agricultural production utilises genetically improved seed and animals. The aquaculture industry can learn a great deal from these experiences, because the basic theory behind selective breeding is the same for all species. The ?rst published selection experiments in aquaculture started in 1920 s to improve disease resistance in ?sh, but it was not before the 1970 s that the ?rst family based breeding program was initiated for Atlantic salmon in Norway by AKVAFORSK. Unfortunately, the subsequent implementation of selective breeding on a wider scale in aquaculture has been slow, and despite the dramatic gains that have been demonstrated in a number of species, less than 10% of world aquaculture production is currently based on improved stocks. For the long-term sustainability of aquaculture production, there is an urgent need to develop and implement e- cient breeding programs for all species under commercial production. The ability for aquaculture to successfully meet the demands of an ever increasing human p- ulation, will rely on genetically improved stocks that utilise feed, water and land resources in an ef?cient way. Technological advances like genome sequences of aquaculture species, and advanced molecular methods means that there are new and exciting prospects for building on these well-established methods into the future.

This book describes the basic elements in the theory of animal breeding and inheritance of quantitative economic traits and the way in which this technology can be implemented in selective breeding programs for aquaculture species. The role and the implementation of molecular genetics in modern selective breeding programs is also addressed. The booka (TM)s main objective is to stimulate development of efficient selective breeding programs in aquaculture, the worlda (TM)s fastest growing industry for animal protein production.

Considerable genetic gain from selection has been demonstrated for several aquatic species in traits like growth rate and survival. AKVAFORSK and allied institutions have demonstrated the value of selection in Atlantic salmon, rainbow trout, Nile tilapia, rohu carp and the shrimp Penaeus vannamei. Presently, however, less than 10 % of total world aquaculture production is based on genetically improved animals. The urgent challenge to the industry is to implement and start selective breeding programs in order to make the aquaculture industry more competitive and sustainable, through improving the utilization of feed, land and water resources.

The text has been written by scientists at AKVAFORSK, Akvaforsk Genetics Center and co-workers in order to summarise present knowledge in the field, and to encourage implementation of selective breeding programs for economically important fish and shellfish species around the world.