Metabolism of marbled spinefoot siganus rivulatus at various oxygen and salinity concentrations -

Abstract

The present study was carried out to: (1) assess the oxygen requirements of juvenile Siganus rivulatus and its tolerance to short-term hypoxia, (2) establish standard metabolic rate of marbled spinefoot juveniles, (3) investigate the response of S. rivulatus to hypoxia, and (4) study the effect of salinity on metabolism of marbled spinefoot. In the first experiment, juvenile rabbitfish (15 fish per tank) were maintained for one hour in waters of various oxygen concentrations. They were then transferred to well-aerated tanks and observed for 72 hour. Survival was evaluated, fish behavior at low oxygen concentrations observed and recorded, and a broken-line analysis performed on the data. In the second experiment, a series of flow-through respirometry experiments were performed to estimate the standard metabolic rate of marbled spinefoot at 27 °C and 35 ppt. In the third experiment, a series of closed respirometry experiments were performed during which dissolved oxygen was allowed to drop to 0.5 mg-L. Oxygen consumption rates were calculated at 11 intervals along a declining continuum of oxygen concentrations and a broken line analysis was performed through the average respiration rates at every oxygen concentration to determine the critical oxygen tension Pcrit. In the fourth experiment, fish were maintained at salinities of 25, 30, 35 and 40 ppt for 2 weeks. Flow-through respirometry was performed to measure respiration rates, with up to ten replicate runs per treatment. Results of the first experiment suggest that Siganus rivulatus can survive for one hour at oxygen concentration of 1.44 mg-L (100percent survival) but not at oxygen concentrations below 0.65 mg-L (16percent survival) where fish exhibited aquatic surface respiration. Results of the broken-line analysis performed on all data suggested a breakpoint of 0.69 mg-L. In the second experiment, we estimated a mean standard metabolic rate of 0.57 ± 0.02 mg O₂-g fish-h for marbled spinefoot. Results of the third experiment show that S. rivulatus is a