Effects Of Four Physical Environment Factors On The Movement And Feeding Behavior Of Sea Cucumber Apostichopus Japonicus (Selenka)

Sea cucumber (Apostichopus japonicus, Selenka) is the largest aquaculture speciesin China by output value. However, there are several problems existing in the bottom-sowing culture of sea cucumbers, including the choosing the bottom-sowing spot, lowrecapture rate caused by the lost A.japonicus after being launched, and the high risk andlow efficient of diving capture. Therefore, it is crucial to solve the problems above tostudy for the characteristics of A.japonicus in behavioral ecology, including its movementbehavior, feeding behavior, territorial behavior, habitat selection behavior, etc. So far, thestudy of the behavior of sea cucumber in China is still at the starting stage---the researcharea of the study is mainly descriptive---and still needs to be further improved in theoryin terms of the breadth and depth of the research. In this study, four physical factors,including magnetic field, sound wave, pressure and flow velocity, were selected relatingto the movement and feeding behaviors of A.japonicus. With help of the self-developedA.japonicus aquaculture facilities, we observed and recorded the effects of these physicalfactors on the movement and feeding behaviors, as well as on the habitat selection, growth,morphology, larval development of A.japonicus. The main results of this paper are asfollows:1. Effects of magnetic field on the behavior and growth of A.japonicusBehavior and growth experiments of the large, medium and small sizes of the seacucumber A.japonicus were conducted in the simulated farming environment withdifferent magnetic field intensities built by the permanent magnets. The results showedthat under the experimental condition, the rate of oxygen consumption (Roc) and therate of ammonia excretion (Rae) of A.japonicus in the magnetic field intensity500mTgroup were lower than those in control (P<0.05). The specific growth rate (SGR) of the large size A.japonicus in800mT and0.05mT groups was significantly lower than thatin400mT group (P<0.05). There is no significant difference in SGR in differentmagnetic field intensities for the medium size A.japonicus, while for the small sizeA.japonicus, SGR in800mT and400mT groups was significantly lower than thatin.0.05mT group (P<0.05).Magnets have a significant attractive effect to A.japonicus in experimentalconditions. The mean attractive rate of large size A.japonicus in800mT group wassignificantly higher than that in0.05mT (P<0.05). Similar pattern occurred to the mediumsize of A.japonicus that the mean attractive rate in800mT and400mT groups wassignificantly higher than that in0.05mT (P<0.05). However, for the small sizeA.japonicus the mean attractive rate shows no significant differences in the three magneticintensities. However, after being tested in natural sea area for two months, the self-developed magnet trap device for sea cucumber did not show a significant attractive effecton capturing A.japonicus.2. Effects of sound and ultrasound on the distribution of A.japonicusThe mean probability distribution was used as a statistical index and (ultra)soundwaves at various frequencies emitted by underwater speakers and ultrasonic vibratorswere tested in the laboratory to determine their effects on the movement characteristicsof A.japonicus at different sizes. The experimental results showed that low-frequency(100Hz) sound waves attracted medium and small A.japonicus (<10g/ind.), whereashigh-frequency sound waves (10000Hz) and ultrasonic waves (28000Hz) repelled allsizes of A.japonicus.3. Effects of water depth on the movement and feeding behavior of A.japonicusIn natural sea area, sea cucumber A.japonicus larvae of different developing stageswere put in the ecological culture nets. The distribution and the development of theselarvae under different depths of the water (0-4.5m) were observed and the results showedthat A.japonicus larvae mainly stayed at the depth of3-4.5m under water. With the helpof the self-developed device called “Observable pressure-regulating water case forexperiments”, the pressure of water within the depth of50m can be simulated indoors.Accordingly, the movement behaviors of different sizes of A.japonicus under differentwater depths and pressures can be observed and it showed that A.japonicus can adjust tothe pressure within the depth of0-50m, by showing themselves to move and feednormally without significant physical damage. 4. Effects of flow velocity on the movement and adhesive of A.japonicusWith the help of the self-developed device called “Experimental water flowsimulation device capable of adjusting flow velocity”, the velocity of flow range0from30cm/s can be simulated indoors. Accordingly, the movement and adhesive behaviors ofdifferent sizes of A.japonicus under different flow velocity can be observed and it showedthat:(1) With the slow flow (~5cm/s), A.japonicus moved more distance than in the stillwater, and hardly moved in the riptide (~30cm/s);(2) The adhesive capacity ofA.japonicus is related to the flow velocity and attached time. A.japonicus were able toattach the bottom after any attached time in the slow flow, after10s in the medium flow(~15cm/s) and after60s in the riptide (~30cm/s). And the large size of A.japonicus hadthe strong adhesive ability.