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RESEARCH PRODUCT

Structural and Mechanical Characteristics of the Heart of the Icefish Chionodraco hamatus (Lönnberg)

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description

The absence of haemoglobin from the blood of icefish, antarctic teleosts of the family Chaenichthydae, has stimulated important physiological mechanisms which serve to compensate for the absence of the respiratory pigment. In view of the central role played by the circulation in meeting the oxygen demands of the tissues, it is not surprising to find that the cardiocirculatory system has been extensively remodelled in icefish. These adaptations include: (1) increases in blood volume, from two to four times larger than that in many teleosts (Hemmingsen and Douglas 1970; Holeton 1970); (2) increases in blood flow associated with lowered oxygen demands (Hemmingsen and Douglas 1970; Holeton 1970); (3) corresponding increase in cardiac output by means of very large stroke volume (6–15 times greater than in other teleosts) at low heart rate and at relatively low ventral aortic pressure (Hemmingsen and Douglas 1972; Hemmingsen et al. 1972); (4) gill blood vessels (Vogel and Koch 1981) and muscle capillaries (Fitch et al. 1984) which have larger diameters compared to other teleosts; (5) increased vascularity in the skin and in the fins (Walvig 1960; Jakubowsky 1982); (6) impressive cardiac enlargement resulting in a relative heart weight similar to that of small mammals (Johnston et al. 1983; Feller et al. 1985; Tota et al. 1990). The interrelationships between these compensatory adaptations are illustrated in Fig 1.