Preliminary Experimental Study On Swimming Behavior Of Crucian Carp

The sustained growth of fishing capacity has brought heavy pressure to the fishery resources in our offing. At meantime, exhausting of resources emerges in nearly all the inshore fisheries in varying degree. The growing decline of fishery resources causes the inshore fishing fishery unsustainable. Therefore, developing the culture fishery and adopting selective fishing equipment and fishing method have become a major issue on developing our fishery economy. As one of our traditional farmed fishes, crucian carp spreads all over China for its omnivorous habit, adaptive capacity, reproductive ability, biological stress and disease-resistant ability. It is also a popular food fish species in China because of its nutrition and good tasty. Research on swimming behavior of crucian carp is representative and the experimental results not only may enrich behavior ecology research of crucian carp, provide the reference for improving the fishing equipment , fishing method and the enhancement technology, but may also provide some data and methods for swimming behavior research on other aquatic organism.As early as in the late 1960s, people carried out much research on applying fish swimming behavior to fishing technology as the swimming speed of fish and its avoidance from fishing equipment is closely related. The maximum sustainable swimming speed of aquatic animals (ie critical swimming speed) may be a key parameter for trawl design. When the escape direction from the trawl of the target fish is the same as the towing direction, the towing speed must be bigger than the maximum sustainable swimming speed of the fishing target to be able to achieve the catch effect. Recently, for the need of reproduction and the protection of fish, the parameter of fish swimming ability has been applied into improving the design for cultivation system, developing better deep water anti-storm cage and getting higher security and efficiency for the fish way and fish ladder. Related research on swimming behavior of fish is also applied in the bionics and so on. The research enriches the contents of fish behavior, fish physiology and fish ecology theoretically, as well as becomes an important theoretical principle for improving fishing technology and aquaculture. Research on swimming behavior of fish is also closely related with the protection and management of fishery resources.In this paper, we studied the swimming behavior in crucian carp using new fishing circulated water tank at 18～20℃. Based on the measurements of critical swimming speed and rheotaxis behavior, we researched the effects of water velocities on critical swimming speed rheotaxis, tail beat frequency, swimming performances and the relationships of body length and critical swimming speed, rheotaxis frequency and tail beat frequency, water velocities on swimming performances in crucian carp. The results were as follows:(1)A total of 15 individuals with body length 19.45±1.40 cm,weighting 200.88±35.22g was sampled for the measuring critical swimming speed. The absolute average critical swimming speed of 92.59±52.98 cm / s, maximum up to 145.57 cm / s. Absolute critical swimming speed increased with body length increasing;relative average critical swimming speed of crucian carp was 4.73±2.30 BL/s, maximum up to 7.03 BL/ s;,relative critical swimming speed increased with body length increasing.(2)A total of 24 individuals with body length 21.40±5.13 cm,weighting 208.68±53.32g was sampled for the measuring rheotaxis behavior under water velocities (0,20,40,60cm/s) for 90min. The results indicated that rheotaxis frequencies and tail beat frequencies of crucian carp increased with increasing water velocities from 0 to 40cm/s,but decreased at 60cm/s with time in 90 min. Results showed that the swimming directions of fish were random in water at a velocity of 0 cm/s. However, there was extremely strong rheotaxis by fish above 40cm/s (ie. 40cm/s and 60cm/s).The time of swimming performances varied obviously at different water velocities. At 0 m / s,the fish kept moving and downstream for almost the whole 90min,that's more than 99% of the experimental time. For the other three water velocities, the crucian carp were in fixed positions against the current ( FP) mainly. The time of FP increased from 51.0% to 78.5% when the water velocities rose from 20cm/s to 60cm/s. The time of moving backward against the current (MB) reached the maximum at 20 cm/s,accounting for about 13.4% of the experimental time.,but time of moving forward against the current ( MF ) decreased from 21.6% to 5% in 90min. The time of downstream ( DS) accounted for 14.0%,8.6% and 12.2% of the experimental time at water velocities of 20cm/s,40cm/s and 60cm/s,respectively. During the experimental time groups of 0~10min,10~30min,30~60min,60min ~90min,the rheotaxis frequency and tail beat frequency of the groups of 20cm/s,40cm/s and 60cm/s were significantly higher with time at four time groups than those of the 0cm/s group. And the rheotaxis frequency and tail beat frequency are the highest of 40cm/s group, 60cm/s group is the second highest.At 40cm/s and 60cm/s groups (higher water velocities), the rheotaxis frequency and tail beat frequency didn't vary significantly during the course of 90 minutes,but varied significantly at 0cm/s and 20cm/s(lower water velocities). Results showed a significant positive relationship between tail beat frequency (TBF) and rheotaxis frequency (RF). The regression relations formula was followed as : RF = a + b TBF , with a range from 0.85 to 0.93 , b from 8.27 to 11.04 , and R from 0.85 to 0.93 .