182 



THE BIOLOGY OF MARINE ANIMALS 



brates), warming raises t u and t { values, promoting unloading in the tissues 

 (57). 



Functioning of Haemoglobin in Marine Fishes. Marine fishes live in a 

 fairly constant environment, where the 2 tension is high ( 1 00-1 60 mm Hg), 

 and the C0 2 tension generally less than 1 mm. The blood in passing through 

 the gills is brought into equilibrium with the sea water in the branchial 

 cavity. The haemoglobins of many teleosts have high values of t u and t t 

 at the summer environmental temperatures to which the fish are normally 

 exposed. There is some correlation between habits of the fish and haemo- 

 globin characteristics. Active pelagic teleosts such as mackerel (Scomber), 



s - 



<1 



e 



100 

 90 



80 



10 



60 

 50 

 40 

 30 

 20 

 10 







10 20 30 40 50 60 10 80 90 100 110 720 

 Oxygen Tens ion (mm Hg) 



Fig. 4.17. The Effect of carbon dioxide on Oxygen 

 Dissociation Curves of Mackerel Blood (Scomber scombrus) at 20 c C 



Curve 1 for 1 mm C0 2 ; curve 2 for 10 mm C0 2 ; curve 3 for 25 mm C0 2 tension. 

 (From Root, 1931.) 



which have bloods of relatively high oxygen capacity, possess haemo- 

 globins with low oxygen affinities, whereas sluggish species such as the 

 toadfish (Opsanus), with bloods of low oxygen capacities, have haemo- 

 globins with high affinities. Other fish are intermediate in these respects, 

 e.g. scup (Stenotomus). The Bohr effect is often quite pronounced, an 

 increase of C0 2 raising loading tension and reducing oxygen affinity 

 (Figs. 4.17, 4.18). There is, however, considerable interspecific variation 

 in this respect, haemoglobins of sea-robin (Prionotus) and mackerel 

 (Scomber), for example, being much more sensitive to C0 2 than tautog 

 (Tautoga) and toadfish (Opsanus). Reduction of 2 affinity with rise in 

 acidity and C0 2 tension would be advantageous in promoting unloading 



