46 U. S. BUREAU or FISHEEIES. 



rations that will apj^ear later that it is equally effective in the nu- 

 merous ])onds, dams, lakes, and other bodies of Avater in which it is 

 abundant. 



In Broomall's Dam, near Media, Pa., most of the shore is clean and 

 nearly free from dense growths of vegetation. Frequent examina- 

 tions, especially in the early morning and evening, invariably found 

 large numbers of small suiifish of this species exploring and feeding 

 to the very edge of the water. At one point is a shallow area which 

 was covered by a rather dense growth of saw grass, tearthumb, Sagit- 

 taria, and other plants. Much light drift material had collected here 

 and blocked a zone about 40 yards long and from 8 to 2 feet' wide. 

 Within this area fishes were seldom seen. Another area at the inlet 

 was silted up and obstructed by stranded logs, brush, etc., brought 

 down by floods, so that fishes could not enter freely. At another 

 point a large flat-bottomed scow was so stranded in a shallow cove 

 that a pool behind it was completely cut off from the lake. 



Throughout the three summers covered by this investigation the 

 history of this pond was followed closely. Except for an occasional 

 egg boat or larva sheltered behind an obstruction practically no 

 breeding was ever detected round the open shores of the pond fre- 

 quented by the sunfishes, but in each of the obstructed areas referred . 

 to breeding continued just as long as they were barred to the fishes. 

 In the first mentioned there was alwa^^s light breeding of Culex 

 pipie7is, together with a few Anopheles larvae. In the other two, as 

 well as within the boat itself, there was heavy breeding of Cvlex 

 pipiens only. When the boat was moved and the other areas opened, 

 sunfishes immediately entered and devoured the larva? and pupas witli 

 avidity. In the plant-gi^own area breeding was never entirely 

 stopped except during a period of about six weeks in 1919. A few 

 larvae of both genera could always be found behind shelters, and in 

 little shut-oif pockets breeding was sometimes dense. 



During the summer of 1919, while some repairs were being made, 

 the level of the water was lowered sufficiently to entirely drain this 

 area. Under these conditions the fishes could penetrate to every part 

 of the water, and while they were deprived of the shelter of the 

 plants no mosquito larvae whatever were found in any part of this 

 pond. This was in marked contrast to conditions in some check pens 

 constructed on one side of the pond and separated from its waters 

 by earth embankments not exceeding 2 feet in thickness. In these the 

 breeding of Culex prpiens would often run up to 30-f- per dipper and 

 some Anopheles could always be found. When, however, sunfishes 

 were introduced into one of these pens the number of larvae quickly 

 fell to one-third per dipper. 



This pond is deep and cold, being fed by springs, and fish food 

 is not overabundant, while sunfishes are very plentifid, so that 

 they are probably chronically hungry, as is indicated by the eager- 

 ness with, which they will take alrnost any kind of liait. Not all of 

 the credit for keeping this pond so nearly free from wrigglers should 

 be given to the common sunfishes, for there were also long-eared 

 sunfishes, calico liass, and roach present. Except for the last, how- 

 ever, the common sunfishes were by far the most plentiful, and the 

 area of freedom from mosquitoes corresponded exactly with the 

 observed area of their activities, while it did not agree so closely 



