Research Product

Although numerous investigators have noted changes in macrophage aggregates (MA) when comparing contaminated and reference sites, there is little information available as to the factors which may affect the accumulation of these structures. We are interested in assessing their usefulness as indicators of environmental stress as well as in examining the effects of other factors such as fish species, age, and parasite load. The use of splenic and hepatic MA parameters was evaluated in estuarine and freshwater systems. Estuarine fish were collected during the Environmental Protection Agency’s Environmental Monitoring and Assessment Program (EMAP). A variety of fish species are collected from numerous sites every year for histopathological analysis. At each site physical, chemical and biological data, including 110 sediment and 55 tissue contaminant levels, bottom dissolved oxygen, benthic and fish abundance, are also collected. Using image analysis we measured the number and mean size of MA per mm2 of splenic tissue. From these analyses the amount of tissue occupied by MA was calculated. An increase in MA number and percent of tissue occupied by MA was observed in most species from contaminated sites. MA of gafftopsail catfish were the best indicators of elevated tissue contaminants while both catfish and spot MA were good indicators of elevated sediment contaminants. Yellow perch, brown bullheads and rock bass were collected from five sites in Lake Champlain, VT-NY. Three of these sites are known to have sediment contaminant problems. In this study fish were aged. When comparing fish of similar ages, MA of rock bass and brown bullheads were good indicators of sediment contamination. Significant differences in yellow perch MA parameters were not noted between reference and contaminated sites. Correlations between age and MA number (r=0.69) and percent of tissue occupied by MA (r=0.70) were observed in yellow perch collected at the reference sites. However, this relationship was not evident at the contaminated sites, indicating some factor was influencing their accumulation. In this study we also evaluated mean intensity (as a measure of pigment content) and shape factor of MA. Preliminary results indicate measurement of these parameters may be useful in increasing the specificity of these structures.