FISHING LOCOMOTION.

Timaru Herald, Volume XIIC, Issue 14057, 15 November 1909, Page 7

FISHING LOCOMOTION.

Leaning over the parapet of some old stone breakwater or pier-head, and watching the fish playing about in the clear green depths below, perhaps the last thought which is likely to occur to any of us is that we are looking on at a really astonishing thing. That a fish is able to propel itself through the water in. any desired direction is in no way surprising; but that it can change its level at will, rising or falling without the use of its fins, and instantly assuming a horizontal or vertical position according to the mood or need of the moment, is a fact that a little reflection will soon develop into prime motive for wonder. For it is clear that the fish must be able at will to vary its weight in relation to the water it displaces. When it sinks to the bottom, as the young whiting are now doing continually before your eyes ,it must have suddenly rendered itself heavier than the medium it inhabits; each time it rises to the surface like a released cork, head first, tail pointing almost vertically downwards ,it must not only have transformed i tself into something lighter than the water, but must have become lighter in its fore parts than in its tail. The mystery, for such it undoubtedly is on a casual survey, resolves itself immediately we come to study the nature and functions of the so-called airbladder in fishes. By this contrivance all these intricate movements of the fish are brought about. The bladder, however, contains, not air, as in commonly supposed, but gas, which is discharged or regenerated by certain organs of the fish, according to whether upward or downward movement is necessary. Also, either the whole length of the bladder, or only its front or near portion ,can be inflated. Thus the fish is able to swim level, or, by altering its centre of gravity, to raise or lower either head or tail at will.