126 The Lije Story of the Fish 



from beneficent. Most widely publicized is the "explosion'* 

 of fish from abyssal depths when brought to the surface by 

 scientists. This is, of course, caused by the expansion of the 

 air-bladder when released from pressure. Its occurrence is 

 much rarer than is popularly supposed because many deep- 

 sea fish do not have air-bladders, and their tissues, composed 

 largely of water, are so incompressible that they do not ex- 

 pand. Less spectacular is the Great Lakes fish known as the 

 pike-perch. When brought up in a net from a depth of one 

 hundred feet, it swells so that it floats helplessly at the sur- 

 face. If a hollow needle is inserted through the flesh into 

 the air-bladder, the hiss of escaping gas can be heard, and 

 the fish is able to resume normal swimming. The pike-perch 

 is obviously supersensitive in this respect, for we all know of 

 other fish which can come up from greater depths with no 

 such alarming manifestations. The swordfish is a famous 

 diver, but when we get it to the top it is by no means a help- 

 less floater. 



So far our glimpses of the air-bladder have been far from 

 reassuring. To the fish which we have mentioned, it seems 

 to be about as pleasant a possession as we should find a hand- 

 grenade which we had to carry around in our pockets, 

 equipped with a barometric fuse which would set it off and 

 blow us to pieces if we climbed a high hill or went up in an 

 express elevator. However, we have been considering arti- 

 ficial conditions — abrupt, man-made changes. On the Pacific 

 Coast the rock cod lives at a depth of lOO feet. Bring him to 

 the top, and he is helplessly bloated, but let him spend a 

 week in an aquarium, and he can reduce himself to normal. 

 Another set of Pacific Coast residents, the lantern-fishes, 

 have a family habit of spending the night at the surface of 

 the sea but going down to depths of 600 feet for the day. 

 Now, the pressure at 600 feet is nearly twenty atmospheres. 

 If you bring them suddenly up from that depth, they are in 



