Initial relative mass (WR, low v. high) and energetic trajectory in time (starved v. fed) were experimentally manipulated in bluegill Lepomis macrochirus. Fed fish starting at low WR grew more and gained more WR than fed fish starting at high WR. Similarly, starved fish starting at high WR lost more mass and WR than did starved fish starting at low WR. Temporal changes in other variables did not consistently match that of WR, but, by the end of the experiment, proximate composition showed a high correlation to WR. Regression slopes of WR on proximate composition increased with time in the laboratory. Differences between wild and laboratory fish appeared to result from relaxation of environmental stress. When excess resources are available such that L. macrochirus grow, condition indices will increase, but individual response will depend on initial values and thus past environmental experience.