The secondary lamellae of the gills of cold water (high latitude) teleosts. A comparative light and electron microscopic study.

The fine structure of the secondary lamellae of gills was examined in two cold-water marine teleosts, the winter flounder, Pseudopleuronectes americanus, and the antarctic cod, Trematomus borchgrevinik. In both species the overall lamellar fine structure is similar to that of other marine teleosts. The major variations in cellular organization involve the distribution of both the "chloride cells" and the mucous cells on the secondary lamellae of P. americanus. At winter water temperatures of +2.5 degrees C, significantly more chloride and mucous cells are present than in summer with water temperatures of +15.2 degrees C. Both cell types are routinely present throughout the length of a secondary lamella as far as the lamellar tip. The chloride cells on the secondary lamellae are always situated in the inner layer of epithelium deep to the outer pavement cells. T. borchgrevinki shows no apparent difference in the distribution of mucous cells either at its normal water temperature of -1.9 degrees C or at a temperature of +4 degrees C, the upper limit of its thermal tolerance to which some specimens were adapted in the aquarium. Chloride cells were never observed on the secondary lamellae of T. borchgrevinki. This suggests that low environmental water temperatures may be related to the distribution of mucous cells and chloride cells on the secondary lamella of the teleost gill.