EFFECTS OF ACCELERATION MODES ON MAXIMUM SWIMMING SPEED AND ACTIVITY METABOLISM IN MEGALOBRAMA AMBLYCEPHALA AND SILURUS MERIDIONALIS

To explore the effects of acceleration modes on the locomotor performance and metabolism characteristics in swimming for the species with different ecological habits and to evaluate the applicable methods for determining the critical swimming speed (U_crit), burst swimming speed (U_burst) and maximum metabolic rate (MMR) for M. amblycephala and S. meridionalis, maximum swimming speed (V_max) and oxygen consumption rate (MO₂) of the experimental fish during their swimming processes and metabolic recovery after the exhaustion were measured under four different acceleration modes. The results showed that under the acceleration mode with velocity increment (ΔV) of 20 cm/s and duration of each acceleration (Δt) of 2min, V_max and proportions of anaerobic metabolism in swimming process for both species were significantly higher than those under the other three modes, respectively (P<0.05). And their burst swimming should occur. Under the other three modes (ΔV=10 cm/s, Δt=20, 40, and 60min), the proportions of anaerobic metabolism of both species were below 12% and there was no significant (P>0.05) difference among the three values for the same species. There was no significant difference for the V_max of M. amblycephala among the three modes. Meanwhile, V_max of S. meridionalis under the mode with ΔV of 10 cm/s and Δt of 20min was significantly higher than those under the other two modes (P<0.05). MO₂ of M. amblycephala and S. meridionalis both increased with increasing swimming speed for all acceleration modes. However, MO₂ showed different trends with the increasing swimming speed in U_burst measurements for the two species. The inflection point of correlative curve for MO₂ with swimming speed occurred at velocity of 100 cm/s for the M. amblycephala and MO₂ did not change significantly with increasing velocity in the subsequent acceleration process. But such “plateau period” of MO₂ appeared when the velocity was above 20 cm/s for the S. meridionalis. Under all acceleration modes, the maximum oxygen consumption rates (AMO₂) of the two species during swimming process were significantly higher than the maximum value (DMO₂) during the metabolic recovery period (P<0.05). The AMO₂ measured by U_crit method was higher than that observed by U_burst method for M. amblycephala, and the value for S. meridionalis showed an opposite trend. It was suggested that it should be applicable to determining U_crit of M. amblycephala by the acceleration modes with ΔV of 10 cm/s and Δt of 20—60min, but only Δt of 20min with ΔV of 10 cm/s was the applicable mode for S. meridionalis. The maximum MO₂ measured during swimming process should be used as MMR for both species. In addition, U_crit method should be applicable to MMR measurement for M. amblycephala, and U_burst method be applicable to that for S. meridionalisis. The strong sustainability of swimming for M. amblycephala is accompanied by the weak ability of acceleration in burst swimming, and S. meridionalisis shows the opposite trend. Such differences between the species might reflect the trade-off effect in adapting to their ecological habits.