Polar Biol (1992) 12:141 - 145 ~_~ Springer-Verlag 1992 Haematological studies on Aethotaxis mitopteryx DeWitt, a high-Antarctic fish with a single haemoglobin* Andreas Kunzmann 1, Angela Fago 2, Rossana D'Avino 2 and Guido di Prisco 2 1Institut ffir Polar6kologie, Universit~it Kiel, Olshausenstrasse 40 60, W-2300 Kiel, Federal Republic of Germany 2Institute of Protein Biochemistryand Enzymology,C.N.R., Via Marconi 10, 1-80125 Naples, Italy Received 5 August 1991; accepted 9 November 1991 Summary. The haematological parameters (haematocrit, erythrocyte number, haemoglobin concentration, MCHC, MCH, oxygen-carrying capacity, pH, Pl/2, ~, pCO2, pO2) of the Antarctic fish Aethotaxis mitopteryx DeWitt are reported. The erythrocyte number (0.39"1012/1) and the haemoglobin concentration (27.8 g/l) were found to be among the lowest values known for red-blooded Antarctic fishes. Among the species of the family Nototheniidae, this is the only one found so far to have a single haemoglobin in its blood. The results have been analysed in comparison with those of other Antarctic species, in an effort to establish correlations between the physiology of this pel- agic-benthopelagic fish and its ecology. From the haema- tological parameters in this study and the functional properties of haemoglobin outlined in the following paper, it is suggested that A. mitopteryx has an extremely sluggish mode of life. Introduction The origin of the suborder Notothenioidei dates back to the lower Tertiary, about 50 million years ago (Andersen 1984). Low temperatures have pervaded the Southern Ocean for some 40 million years (Kennett 1977) and have led, in combination with the isolating effect of the polar Frontal Zone, to a high degree of endemism and steno- thermy (DeVries and Eastman 1981). The family Nototheniidae separated into three groups around 20-25 Ma. In the Miocene, less than 10 Ma, the most advanced group amongst them, the Pleuragram- miini, divided into the three monospecies genera Pleura- gramma antarcticum, Cryothenia peninsulae and Aetho- taxis mitopteryx (Andersen 1984). There are indications that special adaptations (e.g. neutral buoyancy, antifreeze, blood characteristics) may * Data presented here were collectedduring the European Polarstern Study (EPOS) sponsored by the European Science Foundation Offprint requests to. A. Kunzmann be of relatively recent origin (Andersen 1984), and could be assigned to 'recent' changes in mode of life. Antarctic notothenioids derived from primarily benthic perciform fishes and the development of pelagic larvae and pelagic adults is also to be seen as a fairly recent process. The evolution of pelagic (or benthopelagic) species, such as P. antarcticum or A. mitopteryx, should be seen in context with the increase in productivity of the water column. It appears that there has been an advantage in being able to explore the pelagic niche, at least during parts of the year (Hubold 1990). A. mitopteryx was first described by DeWitt (1962) from McMurdo Sound. DeWitt underlined the close affin- ities to the pelagic genus Pleuragramma in body shape and general appearance. He predicted a pelagic lifestyle on the grounds of several morphological similarities to Pleura- gramma, and identified the continental slope as its major habitat (DeWitt 1970). Between 1962 and 1981 only a few specimens of A. mitopteryx are recorded, mainly by Soviet authors (Permitin 1969; Andriashev and Neyelov 1978; Kotlyar 1979; Gerasimchuk and Piotrovsky 1981), includ- ing one - rather doubtful - record from sub-Antarctic islands. The rather late identification and the repeated attribute 'rare species' in the literature might be an indi- cation for either a restricted distribution or a poor density of stocks. Respiratory properties of blood, especially the oxygen- carrying capacity and oxygen affinity, respond to evolu- tionary selective pressure (Wells et al. 1980). In fishes, we find special adaptations, which fit into a particular mode of life in a particular environment. Active, pelagic fishes, for example, living in well oxygenated waters, tend to have oxygen equilibria favouring unloading of oxygen to the tissues (Wells et al. 1989). Sluggish, benthic fishes tend to have equilibria favouring oxygen uptake at the gills. In Antarctic notothenioids, a special pathway of evolu- tion has brought forward a variety of adaptations in their oxygen transport system (Wells et al. 1980). The general trend to reduce the number of erythrocytes and haemo- globin has been reported in all notothenioid families, and data on the blood physiology of about 30 of approxim-