8 Big Game Fishes 
medium; hence the fishes are said to be cold- 
blooded. But in the tuna, bonito, and others the 
movements are so energetic that the temperature 
is higher than that of the water. When a fish 
is taken out of the water; it gasps and opens its 
gills, and doubtless is killed in part by too much 
oxygen, the reverse of the drowning process. 
The digestive organs of fishes are simple. The 
prey is not chewed, the teeth being intended to 
hold the victim, which is swallowed entire at one 
or two gulps, though the tuna often crushes its 
prey. Food is quickly digested, and the capacity 
of some fishes, as the tuna, bluefish, and others, is 
remarkable. The mouth and teeth are modified 
or adapted to the requirements of the fishes. 
Those which live on oysters, as the sheepshead, 
have crushing organs. The shark, not a true fish, 
cuts its food or tears it. The fish is enabled to 
hold its position at various levels without effort 
by the aid of its air or swimming bladder (vz), 
possessed by most individuals. This is a silvery 
air sac or balloon lying directly beneath the verte- 
bra, longer or shorter according to species, absent 
in some. It contains gas, principally nitrogen, 
and by it the fish is enabled to retain a certain 
specific gravity. 
