The natural foods of fishes are either produced in the pond or are washed or fall into the pond from the surrounding area. Food produced in the pond has its origin in the nutrients that are dissolved in the water and in the pond bottom. A variety of plants utilize these nutrients to grow. These plants may be microscopic algae that give a green color to the water or they may be large rooted plants that grow in shallow water areas. Plant material in turn is food for a variety of small animals such as insects and microscopic zooplankton. These small animals are eaten by fish such as bluegills and young bass. Large fish like the bass will feed mainly on small fish, crayfish, and tadpoles. The chain of events leading to the production of large fish can follow different routes. It can follow a “food chain” from nutrients, to algae, to zooplankton, to small fish, to large fish, or it can go from nutrients, to rooted plants, to insects, to small fish, or large fish. In reality, food chains have more links or steps than mentioned here and there are considerable crossing over between the various chains. What really exists is a “food web.”
All ponds contain nutrients, which ultimately produce food for fish. The amount of nutrients present depends upon the productivity of the watershed. The amount of fish that the pond can support is called the “carrying capacity.” This is comparable to a pasture’s capacity to support only a certain amount of cattle or a garden’s ability to produce only a certain amount of vegetables. In Kansas, mixed species ponds typically support between 100 and 400 pounds of fish per acre if supplemental feeding is not provided. The average pond supports about 250 pounds of fish per acre. Populations can comprise many small individuals or fewer large individuals, but the total weight of fish will depend upon what the pond can support. The amount of fish food a pond will produce is limited by the amount of nutrients and will be shared by the existing fish community. By managing for fewer fish, larger fish can be produced.