576 REPOET OF COMMISSIONER OF FISH AND FISHERIES. 



animals, wherefore, even from practical considerations, in tlie artificial 

 fish-culture so zealously carried on in our time, they certainly ought not 

 to be left entirely out of consideration. They will especially recommeml 

 themselves as wholesome and efficient nourishment for the still delicate 

 young fishes, just as, also, certain species deserve to be planted in larger 

 fish-ponds. These small animals play a still more imj^ortant role in the 

 great economy of nature by filling all the stagnant pools and swamps 

 with their countless multitudes." 



The recommendation suggested by the professor concerning the culti- 

 vation of these crustaceans as food for fish-fry was about the same, prac- 

 tically, as that attem]3ted by Mr. Sanvedon in the vicinity of Paris in 

 1864, '65, ^GG, and '67, and has comi)letely answered the purpose.* 



The aquatic insects which, after passing through the larval condition 

 in the water, take on a winged form, it will perhaps be difficult to trans- 

 port from one place to another ; it will, however, be worth the trouble 

 to attempt it. The animals of the extensive crustacean or crawfish 

 family, which live in mud or among the stones at the bottom of the wa- 

 ter — which by common people are called Grundaat, because they destroy 

 fishing implements placed on the bottom — easily admit, on the contrary, 

 of being transported from one bodj^ of water to another; and since they, 

 with little care, multiply with great rapidity, there will be no difficulty 

 in making a supply of this nourishment amj^le in the basins which may 

 serve as abiding places for the younger fishes. Since these basins must 

 stand empty at certain intervals, it is easy to provide that a new after- 

 growth of such crustaceans shall take place when the basin again is to 

 be used, if the quantity of these should be improperly reduced by a pre- 

 ceding stock of fishes. IIow far the free-swimming crustaceans, which 

 sometimes occur in countless quantities even in the most elevated 

 mountain streams and throughout the larger rivers, will admit of being 

 introduced to waters where they do not occur, is a question well worth 

 examiuatioD. I have seen the Yormen so full of these animals that it 

 appeared as if there were one to two animals in each cubic inch of water, 

 at least nearest the surface. 



They think they have discovered in Scotland that the fatness and the 

 flavor of the fish in certain waters was really to be attributed to a mol- 

 lusk, a icater-snail, which lives in these waters in great abundance, and 

 this species of snail has, therefore, already been introduced into this coun- 

 try, but is hardly distributed as far as it is desirable it should be. The 

 introduction of these animals into new waters in which they can live is 

 not difficult, and since their fecundity is very great, a great wealth of 

 food will very quickly be produced for fish whose cultivation may be 

 attempted by their introduction. 



Of the species of fish which belong as well to salt as to fresh water 

 there are only three, the salmon {Salmo salar), the sea- trout {Salmo 

 eriox and trutta), and the eel [Murcena anguilla). 



* Bulletin de la Soci6t6 d'Acclimatation, December, 1867. 



