Ion-exchange phenomena regulate the environment of embryos in the eggs of freshwater fish

Abstract

1. 1. Calcium-selective microelectrodes have been used to measure the activity of calcium in the perivitelline fluid of brown trout eggs, exposed to water with a range of Ca 2+ concentrations. Trans-chorion potential differences were also measured. 2. 2. These values are compared with those predicted by a model based on ion-exchange theory and the Donnan equilibrium. The model allows for partial-dissociation of acid-groups in both the perivitelline fluid and the chorion, and the effects of external pH and ion concentration on this dissociation. The ion-exchange properties of perivitelline fluid and chorion were determined by acid-base titration. 3. 3. The model has the potential to predict the effects of external pH and ion concentration on the distribution of many ions in fish eggs; especially in nutrient-poor waters. It is particularly relevant, therefore, to studies of acidification and metal pollution.