Metabolic responses of Nephrops norvegicus to progressive hypoxia

Abstract

This work studied some of the metabolic responses of Nephrops norvegicus to a progressive reduction in water oxygen tension (PwO₂) at 12 °C. Experiments were designed to simulate water quality conditions that may occur during the trade of live crustaceans. Oxygen consumption rates and ammonia efflux rates were found to be constant over a wide range of PwO₂ values (20.4-5.9 kPa). A similar result was found for the difference between post-branchial and pre-branchial oxygen concentrations (20.4-2.6 kPa), obtained from a separate experiment. Anaerobic pathways, however, were activated after PwO₂ reached 6.3 kPa, as blood lactate and glucose concentrations increased from 1.24 ± 0.08 and 1.17 ± 0.19 (T₀ values) to 10.55 ± 8.99 and 3.63 ± 0.89 mg · 100 mL⁻¹ respectively. N. norvegicus was able to maintain blood pH levels at relatively constant values despite a drop in water pH levels and the accumulation of lactate observed at low PwO₂. Heart rates also remained stable during PwO₂ reductions, but scaphognathite beat rate increased considerably, probably as an attempt to maintain steady weight-specific oxygen consumption rates. N. norvegicus appeared to be well adapted to cope with progressive hypoxia as may occur during holding and transportation procedures.