Gill morphology and sodium influx in the rainbow trout (Salmo gairdneri) acclimated to artificial freshwater environments

Abstract

AbstractBranchial sodium uptake was measured across secondary lamellae (SL) using the isolated‐perfused head preparation. This study was correlated with histological examination.Freshwater trout, Salmo gairdneri, were exposed to various artificial media: distilled water (DW), fresh water (FW: NaCl < 200 μl/1; Ca++ = 1.5 mM/1), FW + 5 mM CaCl2 and FW + 10 mM CaCl2. These environments altered the number and forms of “chloride cells” (CC) located in SL and were related to changes in maximal transport rate of Na+. An increase in a specific type of CC (round) was associated with an increase in Vmax, and a decrease in round cells was associated with a decrease in Vmax.Relative to FW, exposure to DW increased the density of round cells, FW + 5 mM CaCl2 had no effect, and FW + 10 mM CaCl2 produced an initial degeneration of CC followed by restoration and increase in protruding round cells.We conclude that secondary lamellar chloride cells play an important role in Na+ uptake.