16 BULLETIN 1098, U. S. DEPARTMENT 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. No 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 4 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 bayou and where the aquatic grass (Z72zaniopsis 
miliacea) 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 34 feet 
was maintained which was sufficient to suppress this grass as well 
as all other vegetation in the channel. Another location of Anc- 
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 38. 
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 
(Gambusia affinis) 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” (Pomowis annularis), the calico bass (Pomoxis sparoides), 
the large-mouth black-bass or “trout” ((/tcropterus salmoides) , and 
the warmouth bass or “goggle-eye” (Chaenobryttus gulosus). 
These game fishes are largely predacious and of course take their 
toll from the Gambusia, but this feeding of these larger fishes upon 
the little top minnows must not be viewed so much jn the light of the 
reduction of the mosquito-eating minnows as from the standpoint 
that the patrol work which they do serves to keep the little fishes 
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 little 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 contro] is seen. 
