The acid-base status of prenatal pups of the dogfish, Squalus acanthias, in the uterine environment.

The acid-base status of late-term Squalus acanthias L. pups in the uterine seawater environment was examined. Blood values for pH, total CO2, partial pressure of CO2, urea and sodium concentrations in late-term pups were not significantly different from those of the mothers. Haematocrit was slightly lower, while total plasma lipid and ammonia concentrations were several times higher. The uterine environment in which these pups reside and maintain normal acid-base status is nevertheless quite remarkable. In the later months of gestation, up to six pups (approx. 60 g each) reside in each horn of the uterus, in about 100 ml of seawater, in which they ventilate. While the major ion concentrations of the uterine fluid resemble normal seawater, the pH may be as low as 5.9, and the ammonia concentration as high as 22 mmol l-1. This system provides a unique opportunity to study acid-base balance, respiration and nitrogenous waste excretion in developing elasmobranchs under quite unusual conditions.