Two populations of killifish, Fundulus heteroclitus (L.) were studied, one from a high environmentally impacted site (Saw Mill Creek) exposed to pollutants, heavy metals and infected with parasites, the other from a habitat that was far less affected (Lemon Creek), on Staten Island, New York. The rodlet cell counts in the gills of each population were compared and correlated with the number of gill parasites. A comparison of rodlet cell numbers was also made between mature males and females within each population. Although the parasite infestation was significantly higher in the Saw Mill Creek population, the rodlet cell counts did not differ between the two groups. There was no statistical correlation between the parasite number and number of rodlet cells or between standard length and rodlet cells in each population. Also, the number of rodlet cells did not differ between males and females in either group. Furthermore, EM observations showed no difference in the activity of these cells. Our findings suggest that in F. heteroclitus, rodlet cells are not dependable biomarkers for evaluating the fish’s response to parasites and environmental stressors. In addition, the sexual status of the fish does not appear to affect the number of rodlet cells.