IMPOUNDING WATER TO CONTROL BREEDING OF MOSQUITOES. 17 



Table 8. — List of fishes taken in 12 collections in the impounded area. Bayou 

 Walnut, Mound, La., 1916-11, Ijy F. M. Barnes, U. 8. Bureau of Fisheries. 



Species. 



Gambusia aflinis 



Lepomis cyanellus 



Lepomis humilis 



Lepomis pallidus 



Lepomis isch^Tus 



Lepomis symmetricus 



Lepomis megalotis 



Pomoxis annularis 



Pomoxis sparoides 



Ameiurus nebulosus 



Dorosoma cepedianmn. . . 

 Notemigonus crvsoleiicas - 

 Apliredoderus say anus . . . 



Microptenis salmoides 



Micropterus dolomieu. . . . 

 Chaenobrj'ttus gulosus . . . 



Common name. 



Number 

 of collec- 

 tions. 



Top minnow 



Green sunflsh 



Sunfish 



Blue-gUl sunfish 



Sunfish 



do 



do 



Crappie 



Calico bass 



Common bullhead 



Hicliory shad 



Roach, shiner 



Pirate perch 



Large-mouth black bass . 



Warmouth bass, "goggle-eye' 



IM umber 

 of speci- 

 mens. 



163 



95 



89 



1 



1 



1 



1 



103 



25 



43 



15 



151 



3 



2 



3 



12 



In the comparison of the rxumbers of the top minnows found per 

 collection in the natural bayou and in all other classes of surface 

 Tvater it was seen that for all classes of water there was an average of 

 63 Gambusia per collection and for the natural bayou 25 specimens 

 per collection. From the figures in Table 8 we find an average of 

 14 specimens of Gambusia for the 12 collections made in the im- 

 pounded water. Just as the comparison of the numbers of these 

 fish in the natural bayou and in all other classes of water is influenced 

 by the fact that some of the collections in the latter case were made 

 in locations where the fishes were highly concentrated, so in the 

 impounded water, as compared with the natural bayou, we must con- 

 sider the effect of great dilution in the former. It is sufficient for 

 the practical results of the work to note that the Gambusia survived 

 in important numbers the effects of the impounding, and that the 

 presence of the game fishes in the area serves the purpose of keeping 

 the top minnows along the margins where they are useful in the 

 marginal control of mosquito breeding. 



FACTORS PREVENTING MOSQUITO BREEDING IN THE IMPOUNDED 



WATER. 



The nonbreeding of Anopheles in the impounded water is due to a 

 number of factors which have not as yet been definitely measured. 

 In general, as has been stated, the important difference between the 

 impounded section of the bayou and the natural bayou is just the 

 difference between lakelike conditions which do not favor the de- 

 velopment of Anopheles and swamplike conditions which do favor 

 such development. The factors which are considered to operate 

 against mosquito development are the greater freedom for action 

 on the part of the predators, the fish and the aquatic insects ; wave 

 action; depth, which influences temperature of the water; absence 

 110446"— 22 2 



