CRUSTACEA AS FOOD FOR YOUliTG FISH. 27 



says that in considering fish foods and the feeding of fishes it is 

 important to keep in mind that habits change with age. It is also 

 quite evident that the feeding habits and food requirements of some 

 species differ widely from those of other species, not only as they 

 increase in size but even in the younger stages. Although it is recog- 

 nized that entomostracans enter largely into the food of the young 

 of many species and that there appears to be but little doubt regard- 

 ing the high nutritive value of crustaceans, it has not been shown 

 that crustaceans of any sort would be at all suitable as food for 

 adults of every species of fish Avhich has been cultivated. 



No experiment or experience has proved that a permanent, constant, 

 and exclusively crustacean food supply is desirable for all stages of 

 any fish, even if practicable, and its practicability has not been 

 demonstrated. None of the experiments in feeding artificially reared 

 fishes with crustaceans has wholly eliminated other forms of food. 

 As Pearse (1918) says, little is known concerning the amount and 

 variety of food required for fishes, and he further pertinently re- 

 marks that the day when we shall know enough to figure out proper 

 rations is far in the future and that in the meantime every effort 

 should be made to provide better food for growing fishes. There is 

 no reason why we should feed flour and liver forever without know- 

 ing why. Eeferring to the raising of trout on fly larvse by Atkins^ 

 Pearse (1918) continues that there is no reason why other natural 

 food should not be fed to growing fishes in hatcheries, adding that 

 entomostracans are easily collected in quantities with pump or townet. 



However desirable " natural foods " may be and however easily 

 collected, the question of raising them is impossible of a solution of 

 general practicable application. What might obtain in one locality 

 or instance might not obtain in another locality or instance; what 

 might suit one kind of fish might be entirely unsuited to another. 

 For instance, it has been stated that one particular species of crusta- 

 cean acts as a secondary host of a parasitic worm which infests small- 

 mouth black bass. It is not known that any other species of fish is 

 affected by this particular parasite, but the same sort of conditions 

 may arise regarding other species of fishes and parasites. 



In a proposition, then, of utilizing crustaceans as fish food in 

 hatcheries, the question becomes specific and local and must be solved 

 by the individual or institution concerned. However, this much is 

 sure: Crustaceans can be cultivated in quantities. The local con- 

 ditions and the kinds of crustaceans will largely determine the extent 

 of operations in this direction. In their cultivation heretofore, 

 while attention has been directed to one or two species, various other 

 forms of crustaceans, insects, etc., have been coincident products. As 

 respects possible undesirability of an exclusive crustacean diet, it 

 may be said that a mixed diet is assured by the usual pond culture 

 method. As heretofore, the culturist need pay special attention to 

 only such forms as he wants for different ages of fishes. Other 

 forms are likely to be present whether he wants them or not. 



It has been seen that certain European fish-culturists, basing their 

 conclusions upon actual operations, regarded the practicability of 

 crustacean culture as successfully demonstrated, and for like reasons 



° Atkins, Charlps G. : Foods for Young Salmonoifl Fishns. Bullotin, U. S. Bureau of 

 Fisheries, Vol. XXVIII, 1908 (1910), pp. 839-851. Washington. 



