The influence of water pH on the perivitelline fluid of perch (Perca fluviatilis) eggs

The diameter, trans-chorion potential difference and perivitelline-fluid pH of the eggs of perch (Perca fluviatilis) have been measured in a range of water pH (8-4.5). The water used was relatively nutrient rich. Eggs transferred from pH 8 to pH 4.5 shrink; probably as a result of loss of water from perivitelline fluid. Trans-chorion potential differences are close to zero over the range of pH. Mean perivitelline-fluid pH is higher than external water pH at pH 6.7 and above. Below pH 6.7, mean perivitelline-fluid pH is approximately the same as external water pH. The results suggest a non-Donnan distribution of hydrogen ions. The results are compared with data on salmonid eggs in nutrient-poor waters.