The Food Turnover of a Bluegill Population

Abstract

The growth rate of populations of aquatic organisms has become a dominating topic of limnological research, constituting the production problem. The trophic-level concept of Lindeman ( 1942) cut through the maze of data on aquatic food relations and pointed out the possibility that the quantitative aspect of production could be attacked by considering the energy content of the organisms and the energy flow from one trophic level to another. Lindeman's ideas have been justifiably criticized by Ivlev (1945), but, despite certain inadequacies, remain a significant contribution. The concept of production is still undergoing an evolution and is now in the process of refinement. Macfayden (1948) has traced the development of this concept and of closely associated ideas. Clarke (1946) considerably sharpened the working definitions of production rate, standing crop, and yield; as a result, terminology is becoming more stabilized. The writer is particularly interested in fish production, feeling that investigation of this part of the aquatic ecosystem will contribute' significantly to the general problem. The intrinsic biological interest of fishes and their considerable economic value are incentives to a more complete understanding of this part of the production process. Ricker (1946) accelerated the study of fish production by reviewing past achievements in this field and by pointing out areas for profitable research. The present work on the food turnover by a fish population was stimulated by Ricker's analysis of the subject. The supply of food is one of the major, basic factors controlling the density and production of fishes. To understand more clearly the relationship between the fish population and its food supply, the efficiency of food conversion by sunfishes of various ages has been investigated in the laboratory. Experimental feeding of longear sunfish (Lepomis megalotis) and green sunfish (Lepomis cyanellus) was begun in 1950, and the results of these experiments have recently been published (Gerking 1952). The experiments have been continued, using the bluegill (Lepomis macrochirus) because it is widely distributed in