Taxonomic Implications of Meristic Variation in North Atlantic Cod Populations

Abstract

It is commonly accepted that genetic differences across populations are reinforced by environmental influences 
on phenotypic expression, leading to gradient variation in morphological features. We evaluated the 
morphological features of two Atlantic cod (Gadus mohua) populations. When nurtured in the same laboratory 
setting, juveniles from the two groups showed remarkable variations in shape. Nevertheless, there was no 
difference in the two populations' juveniles body forms grown in the wild, showing that the genetic variances 
between the populations were concealed by the competing influences of the varied environmental variables faced 
in the wild. We hypothesize that stabilizing selection for the same ideal phenotype may account for a considerable 
percentage of the genetic variation in fish body structure, leading to genetic divergence throughout populations 
under various environmental stressors. This article summarises studies on the diversity in the mitochondrial DNA 
sequence found in Atlantic cod (Gadus morhua) in the North Atlantic and its environs. The population genetic 
architecture of the Barents Sea, Northeast, and Northwest Atlantics has seen significant modifications. Compared 
to populations from the Northwest Atlantic, which are all dominated by a single common genotype and show 
little diversity in haplotype and nucleotide content, samples from Norway and the Barents Sea support many 
genotypes at intermediate frequencies and exhibit far more genetic variety.