Abstract:

 Natural population of grass carp， a species of Cyprinidae commonly found in China， has been declining in recent years Interruption of free flowing river by dams is one of the important factors The degree of fatigue influences fish swimming capability and determines whether the fish could pass the fishways To understand the effect of  fatigue degree on swimming capability of grass crap， a laboratory study was conducted in a flumetype respirometer equipped with a high speed video camera system to [JP2]record swimming behavior The fish， body length （BL） ranging from 80 to 97 cm and body mass ranging from 96 to [JP]134 g， were selected in experiment The critical swimming speed （[WTBX]Ucrit [WT]） was 711±06 BL/s [JP]in the control group A power function accurately describes the relationship between oxygen consumption rate （MO2） and swimming speed （U）.The function was [WTBX]MO2=4705+419U123 （R2=0976）[WT]， showing oxygen consumption increased with swimming speed The critical swimming speeds after  activity cost （[WTBX]Upcrit[WT]）were compared futher Four kinds of different previous activities cost （06/08/10/12 [WTBX]Ucrit [WT]， in one hour） were measured at the 18±1oC The [WTBX]Upcrit[WT] was found to be 725±135， 633±060， 626±080， and 560±042 BL/s， respectively It is found that [WTBX]Upcrit[WT] was mostly smaller than [WTBX]Ucrit[WT]，while the cost speed was greater than 08 [WTBX]Ucrit[WT]. The fish fatigue at high flow rate used great proportion of anaerobic metabolism and led to a large number of lactic acid accumulation， resulting in a big percentage of anaerobic metabolism This would [JP2]damage the swimming system The function of oxygen consumption rate was described as： MO2=38269+[JP]465U144，MO2=44526+4223U146，MO2=46611+4790U149 and MO2=60034+3883U151 The speed exponents indicate that the efficiency was becoming lower with increase of velocity during activity cost period It is therefore suggested that continuous swimming would not be harmful to swimming capability when the swimming speed was lower than 08 [WTBX]Ucrit[WT] This investigation is expected to provide the basic science of fish swimming behavior and the data required for the design of fishways The fishways depending on special fish could bring a better passing rate.[HJ1][HJ]