Abstract

Rodlet cells, though described among teleost fishes for over a century, are poorly understood regarding function and significance. This enigmatic cell is now widely believed to be endogenous, playing a role in homeostasis and response to physiological insult. The Northern snakehead fish (Channa argus) is an invasive species currently found in Virginia and Maryland tributaries of the Potomac River near Washington, DC. A recent survey of snakehead from this region was undertaken to screen these fish for pathogens and for determination of other health-related parameters. Histological examination of tissues from twenty-three fish, approximate age range of 1-5 years, revealed the presence of rodlet cells among various tissues. The abundance of rodlet cells seemed age-dependent, and greater among fish three years and older, based on subjective observation. Rodlet cells were observed in all but one of the 1-year old fish; however, they were not observed in any of the additional eight snakehead fry collected. Rodlet cells were observed primarily along the endothelium of blood vessels located throughout the spleen, kidney, mesentery and pancreatic tissues, as well as the endothelium of the cardiac ventricle and bulbus arteriosis. In some instances, particularly in the ventricle and bulbus arteriosis, rodlet cells were amassed into multifocal aggregates along the endothelium and in the lumen; this pronounced aggregation of rodlet cells is an unusual presentation among teleosts. Rodlet cells were also present diffusely throughout the connective tissue of the bulbus arteriosis in some fish. No morphological differences were apparent among rodlet cells from different organs or tissues based on standard light microscopy, and further studies are underway to characterize these cells ultrastructurally. Grossly, fish were unremarkable, except for the occasional presence of helminths in the coelomic cavity. No other abnormalities were detected among the fish histologically, with the exception of the sporadic presence of encysted parasites or mesenteric granulomas of undetermined origin. No obvious correlation was noted between the presence of parasites or granulomas and rodlet cell distribution or abundance.