The nucleus of the lapillar otolith discriminates the early life stages of Boreogadus saida and Arctogadus glacialis
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Polar cod (Boreogadus saida) and ice cod (Arctogadus glacialis) are sympatric on continental shelves of the Arctic Ocean. The larvae and early juveniles of the two species are similar, and discrimination based on morphology and pigmentation is uncertain. We present a discrimination criterion based on the difference in lapillus nucleus size between genetically identified B. saida (n = 441, 4.2–55.0 mm standard length) and A. glacialis (n = 82, 8.6–45.5 mm). The product of the shortest and longest diameters of the nucleus (SN × LN) was 58 % larger in A. glacialis than in B. saida. The logistic regression (Ln[p/(1 − p)] = 0.02687SN × LN − 17.5466), where p is the probability that the fish is A. glacialis, correctly reassigned 501 of the 523 fishes (96 %) used to build the model to their genetically determined species (99 % of B. saida and 80 % of A. glacialis). The same regression correctly classified 97 % of 189 fish sampled in 2002 and 2003 and not used in building the model (99 % of B. saida and 89 % of A. glacialis).
KeywordsArctic gadids Ice cod Polar cod Otolith microstructure Species identification
We thank the numerous colleagues who contributed to field sampling, as well as the crew of the research icebreaker CCGS Amundsen. H. Cloutier, S. Puckett, and E. Rondeau provided technical assistance. S. L. Talbot at the Alaska Science Center, U.S. Geological Survey, Anchorage, Alaska, USA, designed the primers used in the amplification of Cytb. This study is a contribution to the programs of Québec-Océan at Université Laval, the Network of Centres of Excellence ArcticNet, and the Canada Research Chair on the response of marine arctic ecosystems to climate warming.
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