The Fourth International Stock Enhancement & Searanching

Theme E: Interactions between wild and released animals and their ecological and genetic implications

26. GENETIC TAGGING OF FARMED ATLANTIC COD (GADUS MORHUA L.) AND DETECTION OF ESCAPEMENT FROM A COMMERCIAL COD FARM


Knut Jørstad , Cvan der Meeren T, Dahle G, Paulsen O, Svåsand T, Otterå H
Institute Of Marine Research
knut.Jørstad@imr.no

Farmed fish are escaping from the aquaculture industry and this is considered a risk for negative genetic impacts on native gene pools. A genetic tagged Atlantic cod (Gadus morhua L.) strain was developed to identify escapees from commercial cod farms and to investigate the potential interbreeding between farmed and wild cod. The genetic tagged cod are homozygote for a rare allele in the GPI-1*30 locus expressed in white muscle tissue. Large quantities of offspring were produced from this strain in 2007 and 2008, and 500 000 juveniles of each year-class were transported to a cod farm in western Norway, where they were raised under commercial conditions. A comprehensive monitoring fishing program was established to detect escapees during the farming period. All cod captured around the farming facilities and in the adjacent fjord areas were screened for the genetic tag. The first farmed cod escapees, identified to the 2008 year-class through the genetic tag and body size, were found around the farming locations and in the adjacent fjord area in November 2008. The second and larger escapement of the same year-class was detected during the natural spawning season in early April 2009. A third escapement was detected in November 2009, and this time the farmed cod were identified to the 2008 year-class. The escapees of the 2008 year-class were spreading in the whole fjord system, including local spawning sites for wild cod. Detailed examination of the escaped cod revealed substantial degree of sexual maturation, and 869 cod larvae were therefore collected through spring 2009. The genetic analyses identified 8 larvae as offspring from the escaped farmed cod, demonstrating successful reproduction under natural environmental conditions. But so far, no significant signal for interbreeding has been detected.