8 MISC. PUB. 528, U. S. DEPT. OF AGRICULTURE 
The large number of species in these Illinois lakes was attributed 
to floods and indiscriminate stocking. Regardless of the cause, the 
figures are somewhat representative of the fish population in the aver- 
age pond—a great number of species and individuals, with the undesir- 
able kinds composing a large percentage of the standing crop. Often 
it is impossible to get any appreciable number of usable fish from such 
ponds because the competition for food is so great that the game and 
pan fish that are present cannot grow to an acceptable size. For suc- 
cessful management, these ponds usually require that the existing fish 
population be removed and the pond be stocked with the correct species 
and numbers. ; 
In order to obtain edible fish of sufficient size, the kinds and the 
number of individuals in a pond must be limited. Neither forage nor 
carnivorous fish can be raised to as large size alone as when they occur 
together. A pond stocked only with bluegill will, soon after the first 
spawning, be filled with thousands of small bluegill. Since these 
young fish compete with the older fish for food, all stop growing and 
the older bluegill lose weight (27). Ponds with such populations do 
not produce fish of a usable size. A pond must contain sufficient forage 
fish te support the carnivorous fish, and there must be enough carnivo- 
reus fish to prevent the forage fish from overpopulating the pond. 
The determination of the species combination and the number to be 
planted are essential parts of pond management. 
It is often difficult to improve the fishing in old ponds. Poor fishing 
may be due to several factors: (1) Too many fish, (2) the wrong kinds 
of fish, (3) low fertility, and (4) a congestion of aquatic rooted plants. 
Before anything can be done to improve old ponds, the existing fish 
population must be sampled. This may be done by hook and line fish- 
ing but is better done by seining. Fishing often does not show up 
the numbers of small and rough fish in correct proportion. 
If the pond contains pan and game fish most of which are small and 
thin, it is overcrowded and steps must be taken to reduce the popula- 
tion. If no bass are present, they should be added at the rate of 100 
fingerlings per acre of fertilized pond or 30 per acre of nonfertilized 
pond. If bass are present, the number of bluegill should be reduced 
by seining or heavy fishing and the food increased by fertilization (25). 
If most of the bluegill are large and most of the bass are small, the 
number of bass should be reduced by seining or fishing, and the food 
increased by fertilization (25). 
If a pond contains a large number of carp or other undesirable 
kinds of fish, all the fish should be removed by draining the pond. 
It may then be correctly stocked. Most old ponds with an existing 
fish population can be brought into efficient production more quickly 
by draining and proper stocking than by any other method. 
Rotenone is sometimes used to destroy fish in a pond that cannot 
be drained (77). This poison does not render the fish inedible nor 
is it injurious to air-breathing vertebrates in concretions useful for 
this purpose. Poisoning is accomplished by drawing sacks of derris 
root (5-percent rotenone) through the water, and 0.25 parts per mil- 
lion are required. Ponds should not be restocked for at least a month 
after application of this material. Rotenone should not be used 
without the approval of the State fish and game department. 
