A fish gill system for quantifying the ultrastructural effects of environmental stressors: methylmercury, Kepone®, and heat shock

In previous histopathological studies, fish gills have been used to study nonspecific responses of tissue to injury; however, such studies have revealed little about the specific effects of different toxicants on cells. Here, we used transmission electron microscopy plus a morphometric technique (stereology) to determine how several types of gill cells are specifically altered by three stressors: methylmercury, heat shock, and the insecticide Kepone® (chlordecone). Larval sea lampreys, Petromyzon marinus, were exposed to various concentrations of waterborne stressor (ranging from the incipient lethal concentrations to a 24-h LC50) for different periods (half a day or 3 weeks). Methylmercury increased the volumes of gill epithelial cells and their nuclei and mitochondria, presumably by inducing ambient water to leak into these structures. Heat shock, by contrast, decreased the volumes of most cells and their organelles, presumably by causing cells to shed pieces of cytoplasm. Kepone had almost no effect, but the few changes that were recorded (increased mitochondrial volume in one cell type) are consistent with known actions of Kepone® (alteration of mitochondrial respiration). The results prove that a fish gill can be used to probe the specific actions of different toxicants and pollutants.