| Summary: | With a 100 billion NOK export value, Atlantic salmon (Salmo salar L.) has become one of the most important export products for Norway. A highly intensified production in recirculating aquaculture systems (RAS) has pushed the physical limits to achieve the fastest growing fish for the market, which has led to problems concerning early sexual maturation of males. New gene editing technology such as CRISPR/Cas9 could solve the maturation problems that the industry is facing, by creating frameshift (FS) mutations that lead to a lack of function. An interesting gene that has been linked to maturation in vertebrates is vestigial-like protein 3 (vgll3). Researchers have studied this gene for nearly a decade and believe that vgll3 plays a key part in the age of maturation for Atlantic salmon. The objective of the research presented in this thesis was to explore whether fish with two mutated copies of the vgll3 allele (FS/FS, i.e. vgll3 knockout) differ in their timing of maturation in modern production environments, compared to fish with two unedited copies of the vgll3 wildtype allele (WT/WT), or heterozygous fish that have one mutated and one unedited vgll3 allele (FS/WT). This was accomplished by having four families of gene edited male salmon with different vgll3 genotypes (FS/FS, FS/WT and WT/WT) reared in a common garden experiment, following a typical intensive “large smolt” production environment of stable 13 °C water temperature with continuous light from first feeding, up until the fish reached 1.4 kg. Maturation was characterized by the combined use of ultrasound, testes histology, testes weight (the gonadosomatic index, GSI), and the plasma levels of the main androgen in salmon, 11- ketotestosterone (11-KT). The vgll3 knockouts (FS/FS) had the lowest maturation levels (39%) of the three groups, followed by wildtype (73%) and heterozygous (96%). There were growth and performance differences between the groups when the fish were 30-40 g, knockouts being significantly smaller, and condition factor was ...
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