186 BULLETIN OF THE BUREAU OF FISHERIES. 
held as a most important responsibility of the station to stimulate and to guide the 
development of fish farming as a more widespread industry. This function as a fish- 
cultural experiment station should rightly be regarded as second to none.”’ 
On page 398 of the same report he stated: “It is manifest that the assembly of 
fish-cultural ponds, supplied originally with water from the Mississippi, but permitted 
to develop essentially pond conditions, stocked with abundant aquatic vegetation 
and rich in entomostraca, insect adults, and larve, together with the customary variety 
of smaller animal forms that thrive on the bottom, amidst the vegetation or in free- 
swimming condition, offer favorable opportunities for biological and physiological 
studies bearing upon problems of fish food, as well as for investigations of more par- 
ticular scientific interest.”’ 
One feature of the environment, especially well developed at Fairport, and which 
will always be present in the pond culture of food fishes, is the presence of a greater 
or less number of dragonflies and damselflies which pass their larval life in the waters 
of the ponds and their adult life in the immediate vicinity. It becomes, therefore, of 
considerable importance to know whether the presence of these larve and adults is 
beneficial or injurious to the fishes. The ecology of this problem forms the main theme 
of the present paper, to which is added a list of such species as have been obtained 
at or near the station during three years of collecting. 
The observations here recorded were made during the months of July and August, 
together with the last week in June and the first week in September. Some species 
emerge earlier in the year, but they usually have a second period of emergence within 
the limits just mentioned, and hence it is believed that the present observations cover 
all species of real importance. 
GENERAL DESCRIPTION OF THE PONDS AND THEIR ENVIRONMENT. 
The position and arrangement of the ponds of the Fairport station are clearly 
shown in the accompanying map. For convenience of manipulation they have been 
divided into six series called, respectively, A, B, C, D, E, and F, the ponds in each 
series being numbered independently. Series A and C are small cement ponds or out- 
of-doors aquaria for the temporary keeping of fish and mussels under experimentation 
and do not concern the present discussion at all. Series E and F are dirt ponds filled 
for the first time in July, 1916, and used the remainder of that summer and ever since. 
But owing to their newness when the present investigation on dragonflies and damsel- 
flies was begun, they were given no attention. During the summer of 1917, however, 
some of the observations on the food of odonate imagos were made around the shores 
of these ponds. Some of the young fishes also, the food contents of whose stomachs 
were examined during 1917, came from these ponds. This leaves only series B and D, 
the former south of the railroad and within 200 feet of the river bank, the latter north 
of the railroad and much farther from the river. Series B is made up of six small 
dirt ponds, the largest only 0.19 of an acre in extent, all of them heavily filled with alga 
and water vegetation of various kinds. 
Series D, on the other hand, contains nine large ponds with a total area of nearly 
6 acres and presents admirable conditions for an ecological study of their environment. 
This is the series upon which the present study is based; they are all dirt ponds of the 
usual construction, having wide embankments thickly covered with vegetation, and 
