Chaetoceros debilis

High resolution image of Chaetoceros debilis. 2001 Photo courtesy of Brian Bill, Northwest Fisheries Science Center.

Chaetoceros is a diatom that has a cell wall made of silica. The cells occur in chains held together by long spines called setae that extend from the corners of the cells. It is possible that these setae help the cells stay afloat in the water since, like most diatoms, they have no way of moving themselves. Some kinds of Chaetoceros with very strong spines kill fish when the cells and spines become lodged in the fish gills, irritating the gill tissue so the fish produce large amounts of mucus that suffocate the fish. Chaetoceros has been associated with fish kills in the Pacific Northwest at least since 1961.