Oxygen consumption and ventilatory frequency responses to gradual hypoxia in common dentex (Dentex dentex):: Basis for suitable oxygen level estimations

This study established different oxygen level categories (optimal, sub-optimal, dangerous and lethal) for Dentex dentex according to ventilatory frequency (V-f) and oxygen consumption (MO2) in response to gradually decreasing dissolved oxygen levels for different fish masses (117-745 g) and water temperatures (13.9-28.1 degrees C). Initial and maximum ventilatory frequency (V-f0 and V-fmax, respectively) and oxygen saturation at which ventilatory frequency was altered (S-Vf) ranged from 31.3 to 71.3 beats/min, 58.0 to 129.7 beats/min and 48.1 to 81.7%, respectively. D. dentex maintained a constant MO2 rate, until a critical oxygen saturation (S(cri)t) was reached. The S(cri)t and lethal oxygen saturation (LS50) ranged from 26.5 to 40.6% and 12.3 to 18.9%, respectively. V-f0, V-fmax, S-crit, and LS50 were correlated positively and significantly with temperature, but only V-fmax was correlated with body mass, pointing to a higher V-f response in small than large fish. In the range of fish masses and temperatures tested, our findings suggest an optimal dissolved oxygen saturation of above 70-75% (constant V-f and MO2), a sub-optimal value of between 70 and 35% (altered V-f but not MO2), with anything below 35% being dangerous (altered V-f and MO2). We conclude that suitable oxygen levels for D. dentex are similar with respect to other species of interest in aquaculture. (c) 2006 Elsevier B.V. All rights reserved.