KIM L. JEFFERSON, Daniel B. Warnell School of Forest Resources, University of Georgia, Athens, Georgia 30602, USA

MICHAEL J. VAN DEN AVYLE, Georgia Fish and Wildlife Cooperative Unit, University of Georgia, Athens, Georgia 30602, USA

VICKI S. BLAZER, National Fish Health Research Laboratory, Leetown Science Center, U. S. Geological Survey, Biological Resources Division, Kearneysville, West Virginia 25430, USA

ROBERT E. REINERT, Daniel B. Warnell School of Forest Resources, University of Georgia, Athens, Georgia 30602, USA

Biomarkers are often used to assess environmental degradation and effects on fish populations. Macrophage aggregate size, number, and pigment distribution are potential biomarkers for fish health and environmental degradation. Pigment distribution of macrophage aggregates may be representative of exposure to certain types of contaminants. In a laboratory study, fish were fed 0, 50, 200 and 800 (ppm) arsenic and 0, 0.01, 0.10, 1.0, 10.0 and 25.0 (ppm) dieldrin in their diet. Liver, spleen and head kidney were removed from each fish for macrophage aggregate analysis. A preliminary evaluation of these tissues found that there were significant dose-dependent increases in pigment distribution of macrophage aggregates. These findings may be comparable to field studies in detecting contaminants in fish populations.