PRACTICAL FISH-CULTURE. 577 



ter-incli vertical rods placed, with one-half-iuch gaps, iii a liard-piue 

 frame, and braced with horizontal wires, (Fig. i, full size.) On the sea- 

 ward side one screen, (Figs. 2, 3,/,) made like d, will be sufficient; and 

 the stout screen c may be omitted where there is no fear of floating logs 

 or branches. As the crest of the dam must be higher than the highest 

 tide, so also the bottom of the waste- way must be lower tban the lowest 

 flood-tide, in order to insure the entrance of tbe sea-water at every flow. 

 The changes of level produced by this dam will be understood through 

 Fig. 5. The dark portion is a section of the old bottom, the marsh in 

 the center and the upland rising on each side ; the deep depression in 

 the middle is the old bed of the brook. In its natural state, the brook, 

 at low tide, would only fill its banks to the line A B ; at high tide, the 

 water would be backed up to the line E F. When the dam is built, 

 the water, at low tide, would be as high as the line D, because the 

 deep cut a is narrower than the natural bed of the brook ; at high 

 tide the level would be the same as without a dam, namely, E F. The 

 advantages gained are: first, that while a flow of water is still kept up, 

 the depth and surface are much increased by raising the level ; and, 

 secondly, the fish, by means of the grated cut and waste- way, are pre- 

 vented from wandering. A brackish pond thus made would have a 

 brook (Fig. 6, G) running in at its upper end, where the water would be 

 shallow and fresh, E; while at the lower end it would be deep and more 

 or less salt, F; and the deeper the better, for this breeds big fish. The 

 Salmo lacustris of Western Europe, and the great thirty-pound trout in- 

 habiting the Norwegian lakes, some of which are three hundred fathoms 

 deep, are considered by Professor Rasch as only overgrown individuals 

 of the common European brook-trout, jSalmo fario. Our own brook- 

 trout, Sabno fontinalis, is known to attain to twelve pounds in our Maine 

 lakes, where the water is deep and food plenty. In water brackish, or 

 nearly salt, and crowded with Crustacea and small-fry, the depth does 

 not count for so much ; and a trout will pass from one to two and from 

 two to three pounds rapidly, although he may nowhere find holes more 

 than five feet deep. 



Two such ponds as have just been described were laid out by Profes- 

 sor Rasch in 1869; theonecoveringsomeseveuty-flve acres, at Sandvigen, 

 near Ohristiania ; the other of two hundred and seventy acres, and with a 

 maximum depth of thirty-eight feet, not far from Frederickstad. The 

 tide in the last ramifications of these Norwegian fiords is ver^^ slight, 

 not exceeding one foot ; so that a low and cheap dam is sufficient. In 

 a rough slab shanty, twelve feetsquare, he hatched 80,000 salmon-eggs in 

 one season. The apparatus inside was equally primitive ; only a set of 

 narrow board troughs, arranged step-fashion, and emptying into each 

 other by notches cut in alternate ends. Some gravel was placed in the 

 bottom of these troughs. A wooden pipe brought in the water from a 

 neighboring spring. There were no filters, stop-cocks, or tanks. 



Professor Easch collects the eggs, dry, in a basin, which has simply 

 S. Mis. 74 37 



