Sodium Regulation in the Crayfish Astacus Fluviatilis

Abstract

1. In distilled water or artificial tap water with a very low sodium concentration, sodium uptake by Astacus is prevented or reduced and 22Na outflux is subnormal. This is accounted for to only a small extent by reduced renal sodium losses. 2. Sodium-depleted animals replaced in artificial tap water regain sodium in a roughly exponential manner. This is shown by 22Na to be the result of a considerable increase in sodium influx coupled with an increased but lower outflux. 3. Sodium outfiux appears to consist of three components: urine losses, passive diffusion losses over the body surface and what may be an ‘exchange diffusion’ component which is high during high influx and minimal in distilled water. This latter component represents about 30% of sodium exchange under normal conditions. 4. Eyestalk removal did not affect the ability of Astacus to absorb sodium. 5. In starved animals the gills take up most of the sodium absorbed and the gut is relatively unimportant. 6. Silver staining of the gills is a passive process and the cuticle of the branchial filaments of the gill stem is selectively stained. This region would be a suitable site for ion uptake mechanisms.