Effect Of Dissolved Oxygen Level On The Metabolic Interaction Between Digestion And Locomotion In Juvenile Southern Catfish (Silurus Meridionalis Chen)

To investigate the effect of dissolved oxygen level ([O2]) on maintenance metabolism, feeding metabolism, aerobic swimming performance and their metabolic interaction in juvenile southern catfish (Silurus meridionalis Chen), we measured the following: (1) the resting oxygen consumption rate (MO₂rest) over a range of water [O2] and from this we calculated the critical oxygen tension (Pcrit) of fasting fish; (2) the postprandial MO₂ response (10% body mass meal size) at water [O2] of 1, 2, 4 and 8 mgO2 L?1; and (3) the swimming performance of fasting and digesting fish at water [O2] of 1, 2, 4 and 8 mgO2 L?1 at 25°C.The results as follows:1. The MO₂rest remained constant over a broad range of water [O2] but then dropped markedly associated with reaching the Pcrit. The Pcrit value was 1.31 mgO2 L?1 (16.4% saturation) at 25°C, and the calculated value of resting MO₂ at Pcrit was 138.41 mgO2 kg?1 h?1.2. After force-fed with a10 % body mass size of freshly killed loach (withoutbone, viscera, head and tail), the MO₂ increased significantly after feeding in every experimental group, then reached the MO₂peak during 13-30 h and decreased significantly to the pre-fed level in every dissolved oxygen level group. The peak time values were 30.4±5.3,13.0±1.5,14.4±1.2,11.6±0.9 h at 1,2,4,8 mg.L-1, respectively. The MO₂peak values were 224.3±2.2,310.2±3.7,298.3±2.8,326.2±3.1 mgO2 kg-1 h-1, respectively. Compared to normoxia group, hypoxic groups presented lower peak postprandial MO₂ (MO₂peak) (1 mgO2 L?1group), larger energy expenditure and longer digestive process (both 1 and 2 mgO2 L?1) than those of normoxic groups.3. Both critical swimming speed (Ucrit) and the active metabolic rate (MO₂active) of fasting fish remained unchanged over a decrease in water [O2] from 8 to 4 mgO2 L-1 and then decreased significantly with further decreases in water [O2], while these parameters in fed fish decreased pronouncedly as water [O2] decreased from 8 to 1 mgO2 L-1. Feeding caused a significantly lower Ucrit in the 2 mgO2 L-1 water [O2] group, a significantly higher MO₂active in both the 2 and 8 mg L-1 water [O2] groups and a significantly higher metabolic scope (MO₂active - MO₂rest) in both the 2 and 4 mgO2 L-1 water [O2] groups compared to fasting fish(p<0.05).4. The MO₂ increased greatly with swimming speed in the higher water [O2] groups, whereas it leveled off as swimming speeds approached the Ucrit in the lower water [O2] groups. Within all water [O2] groups, feeding caused a higher MO₂ compared to fasting fish when fish swam at the same speeds, except in the 1 mgO2 L?1 group.The indications as follows:1. This finding showed that the critical water [O2] for maintenance of metabolism, digestion, swimming and postprandial swimming increased sequentially due to the increasing O2 demand, which challenges respiratory capacity.2. With the administration of the medium-sized meal that was used in this study, the metabolic mode of juvenile southern catfish changed from an additive mode during normoxia to a digestion-priority mode under moderate hypoxia and to locomotio-priority mode under hypoxia.