EFFECTS OF LAMPRICIDES ON THE GILL ULTRASTRUCTURE OF LARVAL SEA LAMPREYS AND RAINBOW-TROUT FRY

Larval lampreys (Petromyzon marinus) and rainbow trout fry (Oncorhynch us mykiss) were exposed to toxic solutions of the lampricidal chemical s TFM (3-trifluormethyl-4-nitrophenol) and Bayer 73 (5,2'-dichloro-4'- nitrosalicylanilide). Both species were exposed to their 9-h LC(100) f or 9 h or until they were near death. The respiratory lamellae of the gills were then studied with transmission electron microscopy. In lamp reys, damage was confined to presumed ion-uptake cells. Both lampricid es produced similar changes in these cells: cell rounding, enlargement of mitochondrial profiles, vacuolization of the cytoplasm, and wideni ng of the intercellular spaces. Bayer 73 caused a greater incidence of necrosis of ion-uptake cells than did TFM. Exposure to lethal TFM/Bay er-73 mixtures (containing 0.4-1.6% Bayer 73) affected lamprey gill la mellae in the same way as did Bayer 73. Unlike lamprey gills, trout gi lls were entirely unaltered by levels of the lampricides lethal to tro ut. These findings suggest that (i) disruption of ion-regulating cells contributes to the mortality of lampreys exposed to lampricides and t o the high susceptibility of lampreys to TFM; (ii) the mechanisms of c ytotoxicity of TFM and Bayer 73 are similar