Some species of fish require specific bottom material to reproduce. Largemouth bass and bluegill are generalists and will spawn on about any type of bottom material, but the channel catfish is more particular. It requires some type of cavity such as a hole in the bank or solid structure in the form of a stump or rock for nest establishment. As stated several times previously, catfish reproduction is not desired in catfish-only ponds, so nesting structures should not be provided.
When species other than bass, bluegill, and catfish are desired in a pond, it is necessary to know their reproductive requirements in order to determine whether they will be able to maintain a population.