16 BULLETIN 10^8, U. S. DEPARTMEXT OF AGRICULTURE. 



It is seen that the collections are confined to the sections of the 

 bayou below the dam and to the backwater above the impounded 

 zone. Xo specimens were taken in the collections in the impounded 

 area proper. The section of the bayou above the impounded area 

 was clear for a distance of about ^ mile and the backwater gave 

 favorable conditions for nonbreeding in this distance with the ex- 

 ception of a limited area just above the last station where a ridge 

 crosses the bed of the hajou and where the aquatic grass {Zizaniopsis 

 lyiiliacea) persisted, as shown in Plate IX, Figure 2. The maximum 

 depth where this grass survived was about 1 foot. Below this point 

 to the dam, a distance of nearly a mile, an average depth of 3^ feet 

 was maintained which was sufficient to suppress this grass as well 

 as all other vegetation in the channel. Another location of Ano- 

 pheles breeding found above the impounded zone was some distance 

 above the growth of grass mentioned, among willows and other 

 vegetation characteristic of natural bayou conditions. This location 

 is shown in Plate IX, Figure 3. 



FISHES IN THE IMPOUNDED AREA. 



A survey of the fishes in the impounded area in Bayou Walnut, 

 the results of which are given in Table 8, shows that the top minnow 

 {Ga/rnbusia afjfinis) finds no difficulty in establishing itself under the 

 conditions of deeper and open water. The fish collections in this 

 water also show that the larger fishes of the region, those of value 

 for food, have found their way to the impounded area in some num- 

 bers. The more valuable of these for food are the crappie or " white- 

 perch" {Pomoxis annularis), the calico bass {Pomoxis sparoides), 

 the large-mouth black-bass or "trout" {2Iicropterus sahnoid^s) , and 

 the warmouth bass or "goggle-eye" {Chaenohryttus gulosus). 

 These game fishes are largely predacious and of course take their 

 toll from the Gambusia. but this feeding of these larger fishes upoii 

 the little top minnows must not be viewed so much in the light of tL 

 reduction of the mosquito-eating minnows as from the standpoin 

 that the patrol work which they do serves to keep the little fishe. 

 in the shallow water along the margins. In the open water of the 

 impounded area there is no mosquito breeding and since the salva- 

 tion of the Httle fishes depends upon their remaining along the 

 margin to escape the larger fishes, the value of the larger fishes as 

 an indirect aid in mosquito control is seen. 



