Divalent cations enhance ammonia excretion in Lahontan cutthroat trout in highly alkaline water

The Lahontan cutthroat trout lives under highly alkaline and saline conditions in Pyramid Lake, Nevada (pH 9.4; 0.2 mmol 1−1 Ca++; 7.3 mmol 1−1 Mg++). These experiments were conducted to study the possible roles of water Ca++ and Mg++ concentrations on ammonia excretion in the Lahontan cutthroat trout under highly alkaline conditions. The basic protocol of the experiments was to determine ammonia excretion rates during the following three exposure periods (each of 3‐h duration) in sequence: (a) in normal lake water; (b) in soft lake water with the divalent cation concentrations reduced; and (c) in the soft lake water with either Ca++ or Mg++ (or no divalent cations added) added back at the appropriate lake water concentration. The soft‐water exposure caused a significant reduction in ammonia excretion to about half of the control (original lake water) levels. When either Ca++ or Mg++ was added to the soft water in the third exposure period, the ammonia excretion rates were increased more than twofold back to lake water levels.