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2 MISC. PUB. 528, U. S. DEPT.) OF AGRICULTURE 
comparatively few kinds and numbers of fish, and are fertilized. The 
elimination of rooted plants is perhaps the most revolutionary of these 
practices, for it has long been felt that such plants were essential to the 
production of fish. In this publication are presented some of the 
underlying principles of fish culture in farm ponds and an outline of 
management methods that have been tested and proved. 
PRODUCTION AND YIELD 
There has been little uniformity in the manner of discussing fish pro- 
duction. It is therefore important that the various terms be under- 
stood before comparisons are made. The production of fish hatcheries 
has been customarily stated in number of fry or fingerlings * per sur- 
face acre of water. Some population studies have also been expressed 
in number of fish of specified lengths per acre of water. Such figures 
are approximations since fish of identical length may vary greatly in 
weight. The weight of a fish depends upon the amount of food that 
has been available (24). 
Some production figures have been stated in weight of fish per unit 
volume of water. This procedure is laborious and may be misleading 
since in ponds the depth of water has little effect upon the per-acre pro- 
duction (24). The results of most of the recent studies in pond-fish 
production have been stated in weight per acre of surface area and 
this is the standard used here. 
In fish culture, the terms “production” and “yield” have been loosely 
apphed. Each has been used to mean: (1) The amount of fish produced 
in a given period of time, usually a year, after a pond is newly stocked ; 
(2) the amount of fish in a pond regardless of elapsed time; and (3) 
the amount of fish that may be harvested from a pond without ad- 
versely affecting the breeding stock. Obviously, these are three very 
different things. Correctly the first is the production, usually stated 
as an annual average; the second is the standing crop; and the third 
is the harvestable crop. 
THE AQUATIC ENVIRONMENT 
The aquatic environment provided by the small pond is rather 
complicated, yet it lends itself readily to investigation and manage- 
ment. The plants and animals in a pond are dependent upon water 
for their survival and their wanderings generally are restricted to it 
or its environs. All are dependent, directly or indirectly, upon the 
gases and mineral nutrients in the water and in the soil that forms 
the bottom of the pond. One may, by various means of sampling, 
determine at any time the species and approximate numbers of the 
organisms living in it. The composition of plant and animal species 
may be altered by selective removal or addition and by other manage- 
ment practices. The fertility may be increased by adding fertilizers. 
Often a pond may be drained and all the aquatic organisms, except 
those with special means for withstanding desiccation, removed or 
destroyed; when the pond is refilled such plants and animals as are 
desired may be returned to it, and much can be done toward prevent- 
*Fry are very small newly hatched fish; fingerlings are young fish roughly the size 
of a finger. 
