In vitro cardiac performance in the sub-antarctic notothenioids Eleginops maclovinus (subfamily eleginopinae), Paranotothenia magellanica, and Patagonotothen tessellata (subfamily nototheniinae)

There is lack of information concerning species diversification in the Non-Antarctic Nototheniid fish both in relation with their variation in organismal performance and in the morphofunctional characteristics underlying this variation. This work was designed to study in three Sub-Antarctic Nototheniids, Eleginops maclovinus, Patagonotothen tessellata, and Paranotothenia magellanica, cardiocirculatory features that may reflect interspecific differences in organismal performance, which in rum may explain aspects of evolutionary and ecological diversity. Haematocrit values were similar in all three species (between 28 and 3?), being in the range of that observed in other red-blooded Notothenioids. In all species, the heart ventricle was fully trabeculated (Type I ventricle) with P. tessellata and P. magellanica having higher relative ventricle weights than E. maclovinus. The latter species was characterized by unique spindle-shaped ventricle, apparently caused by the insertion of a pair of respiratory muscles on either side of the pericardial cavity. Intrinsic cardiac performance was assessed using an in vitro isolated and perfused heart preparation working under loading conditions. Common trends in the three species were a) the intrinsic heart rate higher than that shown by the Antarctic counterparts, b) stroke volume positively related to preload and inversely to afterload, c) pressure work exhibiting higher cost (in terms of oxygen consumption) than volume work, and d) higher mechanical efficiency under volume loading than under pressure loading. There were clearly defined interspecific differences in cardiac mechanical performance between the two Nototheniinae and E. maclovinus. The heart of the latter differed from those of the Nototheniinae, particularly in its incapacity to maintain constant stroke volume and cardiac output under pressure loading. This finding may be relevant for evaluating organismal performance in light of Notothenioid diversification. (C) 1997 Elsevier Science Inc.