It is the perch, the marauders of the lake, on a hunting expedition!
They go together in a large company, like soldiers in an army, rows of them above, beside, and behind one another. There are hundreds upon hundreds of them, and yet a single unit.
With their uppermost layer only a couple of inches below the surface of the water they hasten on. Then all turn at once, changing from the long, narrow marching column into compact formation. A fresh signal, inaudible, imperceptible to all but themselves, and once more, in a trice, the narrow, smoothly-gliding hunting-column is reformed.
Just as they twist and turn in the horizontal plane, so do they in the vertical. They go suddenly and headlong from the surface to the depths, spinning out from their compact mass a long, living thread.
And the thread becomes longer and longer, and thinner and thinner, while they pass through one of the narrows in the submarine mountainous region.
It is the shoal of bleak they are after. Now they are in the valley where it lies.
The lively little freshwater herring as yet suspect no danger; they are in constant motion, occupied in snapping up the fallen, half-drowned insects. Noses are pushed up, and little thimble-like mouths open; the water streams in, and with it the food. An eager interchange from bottom to surface goes on; for when the upper layer is satiated, it likes to enjoy its feeling of well-being in peace, until voracity once more makes them all rivals.
The splash of the waves on the surface lifts the gluttons up and down, while the ground-swell rocks the satiated to rest.
The perch have quickened their pace; involuntarily the speed is increased; they already scent their prey.
Foremost of the company, with a dark-golden, high-backed leader at their head, swim a couple of hundred of the finest perch. They are at their strongest age, and in best possible condition, suffering neither from too great a weight of fatness, nor from the nervous lassitude of insufficient nourishment. They lead, and with frolicsome eagerness push past one another, so as to be the first to arrive.