This water chemistry
was chosen to match that used in efflux experiments (see
below). In order to determine the impact of water chemistry on
influx, an identical trial was also conducted using constantly aerated
aquarium water (ionic composition (mol L−1): 375 Na+, 574
Ca2+, 0.022 Cu+, 119 Mg+, 29 K+, 310 Cl−; total hardness: 70 mg L−1;
ammonia: 1.5 mol L−1;total alkalinity: 52 mg L1; pH: 6.7). To each
container, 10 L of 22Na isotope (∼5 Ci L−1; Perkin Elmer) was
added. Triplicate 1 mL initial water samples were taken for measurement
of total water Na+ and radioactivity levels. After 1 h, final
triplicate 1-mL water samples were taken, fish were washed in a
high Na+ rinse (1 M NaCl) with a lethal dose of 3-aminobenzoic acid
ethylester (MS-222, 1 g L−1). Th