*i. ™ ecaase most of the ox 5 r 2 en used *V respiring organisms possessing 

 the Tt-A cycle is for the oxidation of TCA-cycle intermediates, uptake 

 of oxygen may be used as a measure of the activity of this cycle. Numer- 

 ous investigations have been undertaken to relate overall oxygen con- 

 sumption of fish tissues to various physiological factors* 



Vernberg and Gray (1953), working with 17 species of marine tele- 

 osts, found a positive correlation between the activity of each species 

 and the oxygen consumption of excised brain tissue. Based on consumption 

 of oxygen, these fish could be arranged into three groups that related to 

 their activity: active species, characterized by constant swimming move- 

 ments; species of intermediate activity j and sluggish, bottom-dwelling 

 species. The brain tissue of more active fishes, such as menhaden, had 

 a higher % 2 than did bottom dwellers such as the toadfish. In addition, 

 these Qo 2 values could be correlated to various physiological indices of 

 activity such as concentration of hemoglobin, level of blood sugar (Hall 

 and Gray 1929 and Gray and Hall 1930) and ratio g£ gill area to body 

 weight (Gray 19U7). Menhaden, for example, has higher concentration of 

 hemoglobin and level of blood sugar and has 10 times more gill area per 

 gram of body weight than has toadfish. Menhaden and other active fish 

 also have a greater number of immature circulating erythrocytes than have 

 less active species (Dawson 19!>3). A later comparison of Qq 2 values of 

 brain, liver, and muscle of the toadfish, scup, and menhaden again showed 

 a definite correlation between activity of the species and consumption of 

 oxygen for brain tissue; however, this relationship did not hold for liver 

 and muscle tissue (Vernberg 195U). No positive relationship of activity 

 to body size was noted. The oxygen consumption of excised brain of large- 

 mouth bass was found to be less than was that of slices of rat cortex 

 (Fuhrman et al. 19uU)» 



Other workers have investigated consumption of oxygen with respect 

 to acclimatization to temperature (Freeman 1950 and Peiss and Field 1950) . 

 Freeman held goldfish at temperatures ranging from U° to 37.5° 0. for 1 to 

 2 weeks, after which time the influence of this thermal acclimatization on 

 the rate of oxygen consumption of excised brain tissue was noted* Uptake 

 of oxygen measured at a given temperature was highest for fish acclima- 

 tized at the lowest temperatures. This finding supports the idea that the 

 brain probably plays a major role in determining the level of oxygen con- 

 sumption of fish, as indicated above by the work of Vernberg (195u). 

 Peiss and Field demonstrated adaptation to cold by comparing the respira- 

 tory activity of minced or sliced brain and liver preparations of Arctic 

 cod, which lives normally at -1.5° to 2.0° C, to that of golden orfe, 

 which lives at 25° C. Uptake of oxygen, measured over a temperature range 

 of 0° to 2^°, increased with temperature. As was found by Freeman (1950), 

 however, respiratory activity showed an inverse relationship to the ens- 

 vironmental temperature to which the animal is acclimatized; that is* 

 uptake of oxygen at any given temperature was greater for the preparations 

 of Arctic cod than for those of golden orfe. Similar results were obtained 

 with the mud sucker Gillichthys mirabilis acclimatized to high and low 

 temperature (Wells 1935 ) . In addition, the temperature coefficient of 

 brain and liver of Arctic cod remained essentially constant over the en- 

 tire experimental range of temneratures, whereas it increased sharply in 

 the orfe tissues from 0° to 10© C. Novikov (195U) found a low activation 

 energy for the dehydrogenation system of minced carp muscle. By means of 

 the Thundberg technique of methylene blue reduction, he compared the 



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