Following your heart: Comparing ventricle weight of two ecotypes of Atlantic cod (Gadus morhua) found in Icelandic waters.
As a part of a search for parameters that can be used to distinguish between the two different ecotypes of cod (frontal and coastal) in Icelandic waters, ventricle weights were compared among cod collected in deep and shallow waters of the West coast of Iceland in mid-winter 2013. Fishes display a high degree of cardiac plasticity in form and function as a response to a number of environmental and biological factors. We hypothesized that the relative weight of the ventricles would differ between ecotypes due to different behaviors and occupation in distinct habitats. Frontal cod undertakes long migrations after spawning to the cold deep waters at the edge of the continental shelf towards the thermal fronts while coastal cod remains relatively sedentary and rarely enters waters deeper than 200 meters. This difference in migration strategies of the two ecotypes might affect their cardiac morphology as lower temperatures and physical exercisehas been shown to cause cardiac hypertrophy in fishes. We verified the behavior of the cod using a discriminant function based on their otolith morphology. We found that frontal cod had significantly higher relative ventricular mass (RVM) than same size coastal cod caught in shallow waters. This is most likely a physical response to the different life history strategies of the two ecotypes. This study is yet another confirmation of phenotypic differences in the Icelandic cod stock.