576 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



attempts have been made to use portions of such shallows for the rais- 

 ing of marketable species. 



It is well known thatthe growth of the troat, as a genus, is peculiarly 

 affected by large supplies of food in salt-water. Thus, the salraou-smolt, 

 which goes to the sea weighing a few ounces, returns as a grilse of three 

 or four pounds. Our brook-trout, so long as it is confined to the meager 

 insect diet of a shallow mountaiu-rill, scarcely grows beyond the size of 

 one's finger ; but, with access to salt-water in late winter and in spring, 

 it takes on a s'ilver coat, and with surprising rapidity attains a weight of 

 one or two pounds. 



The experiments of Professor Rasch have shown that these desirable 

 results may be attained without allowing the fish to wander in the open 

 sea. It suflices to inclose a space of brackish or salt water, and to keep 

 the trout within those limits. There are two essentials: (1.) A brook 

 emptying into salt-water. (2.) A narrow cove, inlet, or fiord making 

 the continuation or mouth of such brook. If this inlet has a pinched 

 place in it, so much the better, because there will be the economical 

 spot to throw across a dam, or a grating, to bar the passage to the open 

 sea. Usually some form of dam is desirable, so that when the tide ebbs, 

 a certain depth of water shall be held back in the salt-pond thus formed. 

 The barrier should not be of uniform height, because then tlie pond, 

 becoming quite stagnant on the bottom, would gradually fill with mud 

 brought down by the brook. To obviate this, a vertical cut should be 

 left open to keep up the bottom current, (Plate XIX, Fig. 1 a.) The 

 width of this cut must be such as to discharge the flow of the brook ; 

 otherwise it would rise and pour over the whole of the dam crest, and 

 the fish would pass over also. Further, to provide against such an acci- 

 dent and to give free passage to the flowing and ebbing tide, an 

 ample waste-way, lower, of coarse, than the dam-crest, must be built 

 next to, and continuous with, the cut, (&.) As to the crest of the dam, 

 it must be raised higher than the level of the highest tides. It 

 must be built, of course, solid, and of such material and with such 

 foundations as its situation demands. If, as often occurs, there is a 

 stratum of salt-mud, the foundations must be built quite close, to pre- 

 vent musk-rats from working through ; for one hole is enough to let 

 out the greater -pavt of the fish. The waste-way should be of ample 

 width not only to let out the water of the brook in case of a flood, but 

 to freely admit the tide, which brings in food. It must be carefully 

 grated, together with the cut, which is sunk lower. It requires some 

 calculation so to arrange gratings that they will not get clogged with 

 drift material. They must be arranged on the principle of coarser and 

 finer sieves. On the pond side, and well out from the waste-way, the 

 first grating may be put, with stout bars,^five inches apart, (Figs. 2, 3, 

 c c;) within this a second, with bars two inches apart, (Figs. 2, 3, d d;) 

 after this, a central grating, which is the important one, intended to 

 stop the fish, (Figs. 2, 3, e e.) It should be carefully made of one-quar- 



