Gill ventilation and O2 extraction during graded hypoxia in two ecologically distinct species of flatfish, the flounder (Platichthys flesus) and the plaice (Pleuronectes platessa)

Abstract

Gill ventilation, breathing frequency, breath volume, oxygen extraction from the ventilatory water current and oxygen uptake through the gills were measured in flounder, Platichthys flesus, and plaice, Pleuronectes platessa, at water O2 tensions ranging from 35 to 155 mm Hg at 10° C. Ventilation volumes were similar in the two species at high water O2 tension. Exposure to hypoxic water elicited a larger increase in ventilation in the flounder. The per cent extraction of O2 from water decreased slightly in both species as water O2 tension was lowered. At comparable levels of ventilation O2 extraction was higher in flounder. At the higher levels of water O2 tension, O2 uptake across the gills of flounder was stable, the critical O2 tension being between 60 and 100 mm Hg. The plaice behaved as an oxygen conformer over the entire range of O2 tensions investigated. The superior ability of the flounder in maintaining OZ uptake across the gills during a reduction in water O2 tension may in part explain why the species, unlike plaice, inhabits very shallow waters with large fluctuations in dissolved oxygen.