Erythrocytic magnesium in freshwater fishes.

Erythrocytic magnesium in rainbow and speckled trout (Salmo gairdneri, Salvelinus fontinalis) carp (Cyprinus carpio) and goldfish (Carassius auratus) was examined by correlation analyses involving weight, hemoglobin content, plasma magnesium, erythrocytic sodium, potassium, calcium, chloride and unidentified anion concentration and chloride equilibrium potential, and in relation to possible diurnal and seasonal variation as well as with respect to constant, diurnally cycling and progressively increasing temperature conditions. Given that magnesium is not actively transported, cellular concentrations appear to reflect processes influencing membrane potential and may also be related to maintenance of cellular electroneutrality. No evidence of significant diurnal variation was encountered under either constant or diurnally cycling temperature conditions. Variations in relation to temperature, season and weight were, however, consistent with the suggestion that these animals have the ability to alter erythrocytic magnesium concentrations. It is hypothesized that by adjusting magnesium in relation to organophosphate, the availability of the latter to hemoglobin may be influenced and in this way contribute to adaptive regulation of hemoglobin-oxygen affinity.