K.A. Glover of the Institute of Marine Research in Nordnes and co-authors have published a paper on their investigation into the genetic diversity within and among Atlantic cod (Gadus morhua) farmed in marine cages. The proof-of-concept study for the identification of escapees is soon to be published in the journal, Animal Genetics. The results suggest that this method can be used to trace individuals to their farm of origin and also to identify escapees.
The researchers explain that their study presents a molecular genetic characterisation of Atlantic cod reared in commercial marine farms. Samples consisted of approximately 47 fish collected from nine cages located on four farms throughout Norway. In addition, 28 farmed escapees were recaptured in the sea (443 fish in total).
Nine microsatellite loci and the Pan I gene were analysed, revealing a total of 181 alleles. Each sample contained 43 to 63 per cent of total allelic variation.
Comparing variation with published data for wild cod indicates that lower genetic variation exists within single cages than in wild populations. Significant linkage disequilibrium was observed amongst pairs of loci in all samples, suggesting a low number of contributing parental fish. Global FST was 0.049, and the highest pair-wise FST value (pooled loci) was 0.085. For single loci, the Pan I gene was the most diagnostic, displaying a global FST of 0.203. Simulations amongst the samples collected on farms revealed an overall correct self-assignment percentage of 75 per cent, demonstrating a high probability of identifying individuals to their farm of origin.
Identification of the 28 escapees revealed a single cage as the most likely source of origin for half of the escapees, whilst the remaining fish were assigned to a mixture of samples, suggesting more than one source of escapees.
Reference
Glover K.A., G. Dahle, J.I. Westgaard, T. Johansen, H. Knutsen and K.E. Jørstad. 2010. Genetic diversity within and among Atlantic cod (Gadus morhua) farmed in marine cages: a proof-of-concept study for the identification of escapees. Animal Genetics. 10.1111/j.1365-2052.2010.02025.x
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