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 Su b-Antarctic Nototheniids, Eleginops maclovinus, Patagonotothen tessell ata, and Paranotothenia magellanica, cardiocirculatory features that m ay reflect interspecific differences in organismal performance, which in rum may explain aspects of evolutionary and ecological diversity. H aematocrit values were similar in all three species (between 28 and 3? ), being in the range of that observed in other red-blooded Notothenio ids. In all species, the heart ventricle was fully trabeculated (Type I ventricle) with P. tessellata and P. magellanica having higher relat ive ventricle weights than E. maclovinus. The latter species was chara cterized by unique spindle-shaped ventricle, apparently caused by the insertion of a pair of respiratory muscles on either side of the peric ardial cavity. Intrinsic cardiac performance was assessed using an in vitro isolated and perfused heart preparation working under loading co nditions. Common trends in the three species were a) the intrinsic hea rt rate higher than that shown by the Antarctic counterparts, b) strok e 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 loa ding than under pressure loading. There were clearly defined interspec ific differences in cardiac mechanical performance between the two Not otheniinae and E. maclovinus. The heart of the latter differed from th ose of the Nototheniinae, particularly in its incapacity to maintain c onstant 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.