It's all in the gills: evaluation of O2 uptake in Pacific hagfish refutes a major respiratory role for the skin

Abstract

Hagfish skin has been reported as an important site for ammonia excretion and as the major site of systemic oxygen acquisition. However, whether cutaneous O₂ uptake is the dominant route of uptake remains under debate; all evidence supporting this hypothesis has been derived using indirect measurements. Here, we used partitioned chambers and direct measurements of oxygen consumption and ammonia excretion to quantify cutaneous and branchial exchanges in Pacific hagfish (Eptatretus stoutii) at rest and following exhaustive exercise. Hagfish primarily relied on the gills for both O₂ uptake (81.0%) and ammonia excretion (70.7%). Following exercise, both O₂ uptake and ammonia excretion increased, but only across the gill; cutaneous exchange was not increased. When branchial O₂ availability was reduced by exposure to anteriorly localized hypoxia (∼4.6 kPa O₂), cutaneous O₂ consumption was only slightly elevated on an absolute basis. These results refute a major role for cutaneous O₂ acquisition in the Pacific hagfish.

Keywords: Agnathan; Ammonia; EPOC; Exercise; Metabolic rate; Respiration.