Cultural practices which either contribute nutrient materials to the ecosystem or accelerate detrition by induced recirculation of nutrients within the system result in environmental changes which persist after the practices have been discontinued. The effects of environmental modification were found to be reflected in species structure of native fish populations. The percent of centrarchids within the total population was found to occur in direct proportion to the percent of productive bottom. Macroinvertebrate organisms used as food by centrarchids were' found to be restricted to certain bottom types. These studies confirm the conclusion of Eggleton (1933) that forces inherent in the substratum itself bend and shape all other forces and thus condition the reaction of both plants and animals. The role of submersed and floating vegetation as a substrate for invertebrate organisms is discussed. The harvest of fish as a means of reducing lake fertility (Thomas, 1965) was found to have merit. An estimated 24,352 pounds of phosphates as P04 was removed in the 1,151,161 pounds of fish harvested from Lake Harris, Lake County, Florida, during a 15 month population control study. Phosphorous removed from the lake in the harvested f,ish would have been equivalent to removing all phosphates from 91,207 acre feet of water at a 0.1 ppm concentration.