No abstract

Environmental influences (temperature and oxygenation) on cod metabolism and their impact on the ecology of this species were investigated. Limiting oxygen concentration curves (O 2 level ranging between 15 and 100% air saturation) were established at 2, 5 and 10°C. The standard metabolic rate (SMR), the maximum metabolic rate and the metabolic scope were then modelled as functions of temperature and/or oxygen saturation. The mean SMR at 2, 5 and 10°C were 19.8±4.9, 30.8±6.1 and 54.3±4.1 mg O 2 h −1 kg −1 , respectively. Between 2 and 5°C, the active metabolic rate of cod almost doubled from 65 to 120 mg O 2 h −1 kg −1 , to reach 177 mg O 2 h −1 kg −1 at 10°C. In terms of metabolic scope (MS), the temperature rise from 2 to 5°C resulted in a twofold increase from 45 to 89 mg O 2 h −1 kg −1 , with MS reaching 123 mg O 2 h −1 kg −1 at 10°C. Our proposed model describing the impact of temperature and oxygen level provides new insight into the energetic interactions which govern the relationship between Atlantic cod and its environment. We reexamined published experimental and field studies from the angle of the regulation of metabolic power. We suggest that, when faced with heterogeneous or unstable hydrological conditions, cod tend to behaviourally maximise their metabolic scope. Through this adaptive response, fish reduce energy budgeting conflicts and presumably increase the probability of routinely operating away from lethal boundaries.

During their spawning period (June to mid-July) in the Gironde estuary, meagre Argyrosomus regius produce two distinct sounds: regular long grunts, the most common calls, and sometimes also short grunts. It is suggested that long grunts serve the formation of spawning aggregations and short grunts announce the beginning of courtship behaviour. The meagre's long grunts include long series of 30-112 closely spaced pulses placed into call units. Each pulse produces multiple and rapidly decaying swimbladder vibrations with a dominant frequency varying between 336 and 444 Hz.