Oxygen Consumption of Embryos and Parents, and Oxygen Transfer Characteristics Within the Ovary of Two Species of Viviparous Seaperch, Rhacochilus vacca and Embiotoca lateralis
Oxygen tension and content of intraovarian fluid were measured for the viviparous pile perch, Rhacochilus vacca, during middle and late gestation. Oxygen tension decreased with increasing demands of the brood, reaching a minimum of 13.7 mm Hg just prior to parturition. Total oxygen content of the ovarian fluid decreased to a minimum of 22 mg O2, rising thereafter to 54 mg O2 at parturition as the volume of ovarian fluid increased. The in vitro oxygen consumption of the young per unit weight increased 2.5 times during gestation reaching 222 mg O2/kg/hr at birth (mean weight 3.8 g).Oxygen consumption of two pregnant striped seaperch, Embiotoca lateralis, was fairly constant at 70 mg O2/kg/hr early in gestation, increasing later to approximately 107 mg O2/kg/hr at parturition.An oxygen dissociation curve was determined for ventricular blood of pregnant pile perch. The p50 was 12.5 mm Hg. Along with other parameters, this was used to estimate the oxygen transfer characteristics of the brood–ovary exchange system, maximum possible oxygen consumption, and ovarian blood flow rate. The capacity of the system to meet the increasing requirements of the young decreased during gestation, reaching limiting conditions at parturition. It was concluded that transfer of oxygen to the young would be controlled by, and ultimately limited by, ovarian blood flow rate. The brood–ovary system is compared with the mammalian placenta.