18 IT. S. BUREAU OF FISHERIES. 



A further quotation from Doctor Pond, in reference to Cerato- 

 phyllum, is of interest in this connection. This nonrooted phmt 

 he shows to be dependent primarily upon the nutrient saUs in solu- 

 tion in the water, and thus a competitor of many of the small forms 

 of life which derive their sustenance from the same source. A 

 pond filled with Ceratophyllum, therefore, would be expected to con- 

 tain fewer of these forms and, consequently, of the forms that live 

 upon tliem. From this it would seem to follow that the water best 

 suited to Ceratophyllum would not contain sufficient food for young 

 fish if that plant were the predominant species, and if this reason- 

 ing is correct the value of Ceratophyllum would depend upon the 

 presence of sufficient rooted vegetation to offset the effects of com- 

 petition. Such may have been the conditions at the Fish Lakes, 

 where there were an unusually large number of species of rooted 

 plants, above all of which, however, the superintendent believed 

 Ceratophyllum to be the best. 



No particular species of aquatic plant can be said to be always de- 

 sirable. The endless interrelations of plant and animal life and 

 physical surroundings make the problem a special one for each lo- 

 cality. It should be noted, however, that according to the data 

 here presented great caution should be used as to the introduction of 

 pondweeds, waterweed, water clover, water lilies, frogbit, and 

 cat-tail. The last two can not be regarded as desirable in any fish- 

 pond. Chara, indigenous at some stations, is in most cases so much 

 in favor as a food producer that, notwithstanding its objectionable 

 characters, it is considered the best plant for fish-cultural purposes. 

 It should be borne in mind, however, that at the stations where this 

 plant is a favorite the ponds are of more recent construction than 

 at Wytheville, for instance, where Chara became especially trouble- 

 some. 



The introduction of the water lily {Castalia odorata) into the 

 ponds at Wytheville, with the result of apparently crowding out 

 two other aquatic plants, and the somewhat similar experiences at 

 San Marcos, Tex., and at Mill Creek, Mich., suggest that the partial 

 elimination of one species by the introduction of another may at 

 times be advantageously attempted, and that with a full knowledge , 

 of the effects of given combinations of species a desirable balance 

 of vegetation could be maintained by this means. This question also, 

 however, enters the broad field of plant physiology. 



Heretofore some of the lower forms of vegetation, algal growths, 

 frequently described as " frog spittle," " water moss," and " slime," 

 have entered into pond culture only as an element of water supply, 

 their effect upon fish life being regarded as negligible. Observa- 

 tions ® of Dr. Emmeline Moore, in behalf of the United States Bureau 

 of Fisheries, demonstrate that this view as to tlie value of some 

 species of algse is entirely erroneous, and that in the early stages of 

 the young fishes — particularly the first two or three weeks — their 

 food consists largely of animal life whose food during the same 

 period consists largely of certain species of algae. This opens a 

 broad field of investigation. The spirogyra, so obnoxious to the 

 fish-culturists, is not included in Doctor Moore's list of food-pro- 



5 Dr. Emmeline Moore : The Food Which is Eaten by tlie Food Which the Pish Eat. 

 Paper read at the Fortv-ninth Annual Meeting of the American Fisheries Society, Louis- 

 ville, Ky., Oct. 10, 1919. 



