Moore. — Plants in Pond Fish Culture 151 



The algas may be regarded as the piece de resistance of the 

 chironomid larvae which are sought after by the young fish foraging 

 in the upper strata of the pond waters. Unfortunately, through 

 lack of appreciation of their worth in the economy of the pond 

 and the tendency of the scums to be regarded as untidy and a 

 nuisance, they have often been ruthlessly discarded from the pond 

 waters. In one stroke, by the injudicious use of chemicals, the 

 vegetation upon which these organisms subsist may be destroyed, 

 and in that stroke the "meat supply" of the young fish. 



By referring to the tables* again on the food content of the 

 advanced fry and finger lings, we find that the water fleas, or 

 cladocerans, are conspicuous in the food of the young pond fish. 

 The various investigators of the habits of the water fleas have 

 contributed to our knowledge of the food habits of these small 

 organisms, the most important contribution being that of Dr. 

 E. A. Birge, in his "Plankton Studies of Lake Mendota, " II, 

 Trans. Wis. Acad. Sci., Vol. 11, 1896-7. 



I have found that the water fleas often feed upon a single 

 type of alga in the ponds, the algas, of course, being extremely 

 minute to be accommodated by these small organisms. At 

 Fairport, la., one of the ponds developed a heavy culture of the 

 Blue-green alga, Aphanozomenon, and simultaneously with it 

 there arose an almost pure culture of Daphnia pulex, which fed 

 upon the Aphanozomenon during a period of six weeks at least 

 when it was under my observation. It was a remarkably interest- 

 ing sight to observe the daphnia under a microscope winnowing 

 into the food cavity a continual stream of this plant and to take 

 it with such apparent relish ! This myriad host of daphnia doubt- 

 less contributed to the large output of young Channel Cat which 

 had been spawned in the pond, but whose dietary was not deter- 

 mined in the early stages of growth. 



At other stations similar observations on the food habits of 

 cladocerans were made. At Louisville, Ky., in one of the ponds, 

 daphnids were feeding on a heavy culture of a minute alga known 

 as Botryococcus and in another pond on the disorganizing sub- 

 stance of a heavy growth of Ceratium. At the Bullochville, Ga., 

 station the daphnids were at one time utilizing the extremely 



* Published Report. Loc. cit. 



