CRUSTACEA AS FOOD FOR YOUNG FISH. 17 



with crustaceans, and so on. It was stated that this method was 

 extremely simple and convenient. 



Concerning the raising of Entomostraca, Seal (1892) wrote that 

 stagnant waters everywhere, and especially those destitute of fishes, 

 abound with certain kinds of Entomostraca, but principally with 

 Daphnia and Cyclops. Water-cress beds and masses of other aquatic 

 plants are alive with other kinds of crustaceans, such as " water hog " 

 or "Asel " (Asellus), and "fresh-water shrimp" (Gammarus). 

 Masses of dead leaves in the waters of springs or spring streams 

 harbor them in great numbers. But the conditions in nature that 

 promote their development are not nearly so favorable as they can 

 be made by combining the natural and artificial. There is no neces- 

 sity for the introduction of any foreign material to stimulate a pro- 

 duction of the crustaceans. It appears that in raising Entomostraca 

 at the Gremaz establishment secrecy was maintained and nothing 

 was revealed concerning some essential principle. This secret was 

 offered for sale. Mather (189T) stated that it was some system of 

 ordure in which he had no faith. Evidently referring to the Gremaz 

 method, previously mentioned, Seal went on to say that there was no 

 necessity for driving fish from one pond to another, as the food 

 could easily be caught and transferred to the fish basins. Seal sug- 

 gested spreading the water from a spring so as to make a shallow 

 pond and planting it thickly with water cress, stating that nature 

 would speedily stock it with animal life. 



The foregoing remarks by Seal would seem to apply more par- 

 ticularly to conditions suited to the scuds (Gammarus) rather than 

 to Daphnia. However, he added that the advantage of an artificial 

 system over purely natural conditions in the production of Crustacea 

 is the same as in the propagation of fish, sajdng that when exposed to 

 the ravages of fish themselves, the multiplication of the crustaceans 

 would be slow, if not wholly averted, owing to the destruction of the 

 breeders as well as the others. In separate basins, however, there 

 would be no restriction on the production and " their fecundity is so 

 great, the accumulation is enormous." " Thus," he says, " while one 

 basin is being depopulated others can be repopulated." As at first a 

 more extensive but in the long run most economical provision for rais- 

 ing Entomostraca (and probably other crustaceans), Seal suggested 

 making wood or cement-lined trenches, covered with " sash like hot- 

 beds," through which the waters of springs could flow, the inlets and 

 outlets to be protected by wire gauze. 



Raveret-Wattel (1898) described the methods of raising Ento- 

 mostraca at a small fish-cultural establishment at Rouen, France. 

 The fish-cultural operations were limited to 2,000 or 3,000 fry and 

 the number of older individuals that resulted from that many fry. 

 The fry were fed for a while exclusively upon Daphnia and other 

 Entomostraca incidentally present. The entomostracan food was 

 then gradually replaced by finely minced horse meat. A sufficient 

 supply of Daphnia was maintained as follows : A cask was filled with 

 water in which a light basket weighted with rocks and containing 

 some stable manure, from which all straw had been removed, was 

 sunk. Some Daphnia were then introduced, which in a little while 

 multiplied sufficiently to provide a constant supply for the fry. 



