RESPIRATION 161 



Among lamellibranchs, Arctic or boreal cold-water species have a higher 

 metabolism than warm-water Mediterranean species, when measured at 

 the same temperature. Thus Cardium ciliatum from East Greenland has an 

 oxygen consumption twice that of C. edule from the Mediterranean, 

 determined at 5°C. In specimens of one and the same species, Mytilus 

 edulis, from different latitudes the same metabolic rate was recorded in the 

 Mediterranean at 15°C as in Danish waters at 5°C. Curves of oxygen con- 

 sumption versus graded temperatures are displaced towards the left in 

 some but not all cold-water as compared with warm-water species. Thus 

 graphs of 2 uptake for prawns Panda /us montagui show that Kristineberg 

 animals have a higher metabolic rate than those from Plymouth, when 

 measured at the same intermediate temperature (10°C). 



These relations are brought out in detailed studies on a wide series of 

 arctic and tropical fish and crustaceans investigated in Alaska and Panama. 

 The environmental sea temperatures of the arctic species ranged from 

 — 2°C to 9-4°C (mean 6-8°C). Sea temperatures in the Canal Zone showed 

 a range of 25-6°C to 30 C C. In all the arctic aquatic forms (amphipods, 

 isopods, decapod crustaceans, teleosts), the 2 consumption curves were 

 displaced to the left, toward cold temperatures, when compared with 

 tropical species (Fig. 4.12). The arctic animals, at the normal temperature 

 of their habitat, O C, have metabolic rates from three to ten times less than 

 tropical species at a habitat temperature of 30C. When the corresponding 

 metabolic curves of tropical species are extrapolated to O c C, the metabolic 

 rates of these animals would be lowered from thirty to forty times (Fig. 

 4.13). Consequently in the arctic species examined there is a very appreci- 

 able amount of metabolic adaptation to low temperatures (142). 



Metabolism of isolated tissues sometimes reflects the same temperature 

 influence measurable in the intact animal. In a study of Mercenaria 

 mercenaria, excised gills from cold-water animals showed a higher Q 02 than 

 gills from warm-water animals (at 20°C and 25°C). Of the same nature 

 are results obtained from a comparison of the metabolism of brain and 

 liver tissue of the polar cod Boreogadus saida and golden orfe Idus melano- 

 tus. The former is an arctic fish living at environmental temperatures of 

 around 0°C, the latter a freshwater temperate fish having an environmental 

 temperature of 25 C C. Polar cod tissues showed a higher respiratory rate 

 over a temperature range of C C-25 C C, and a relatively much greater rate 

 below 10°C (79, 125a). 



Interrelations of Oxygen Consumption and Oxygen Tension. The 

 relations between oxygen consumption and oxygen tension are complex. 

 A convenient generalization divides animals into those which maintain a 

 steady respiratory state over a wide range of external oxygen tensions and 

 those in which the amount of oxygen consumed is directly dependent on 

 the oxygen tension of the environment. Among those factors which deter- 

 mine relative independence are: size of the animal, existence of an efficient 

 circulatory system and magnitude of diffusion distances ; degree of loco- 

 motory activity and effect of temperature variations; ability to regulate 



M.A. — 6 



