| The red swamp crayfish (Procambarus clarkii, Girard1852), native to the southern USA and northern Mexico, is a freshwater economic crustacean. The crayfish was introduced to China in1929. Because of its deliciousness and rich nutrition, the red swamp crayfish is very popular in the international aquatic products markets and is welcomed by the majority of consumers. The crayfish has become one of the most important species in international freshwater shrimp aquaculture industries. In this paper, we studied on the effects of starvation, salinity and density on behavior and physiological functions of red swamp crayfish, and analyzed the variation of behavior and physiological functions of red swamp crayfish under environmental stress. Our results will contribute to enriching the behavioral and physiological data and providing basal data for the cultivation of red swamp crayfish. The main results are summarized as follows:1. Under laboratory conditions,"Y" water maze was used to investigate the effects of starvation (0d (control)),1d,2d,4d and8d) on the behavior of red swamp crayfish. The results showed that starvation had significant effect on food intake, feeding time, feeding frequency and locomotion rate of red swamp crayfish (P<0.05). As starvation time extended, the food intake, feeding time, feeding frequency and locomotion rate first increased significantly and then decreased. Searching time of red swamp crayfish was not affected by starvation (P>0.05), and it began to decline and then increased as starvation time extended.2. The effects of starvation (0d (control)),1d,2d,4d and8d) on major digestive enzymes (gastrointestinal pepsin, hepatopancreatic lipase and gastrointestinal amylase) and antioxidant enzymes (serum superoxide dismutase SOD and hepatopancreatic CAT) of red swamp crayfish were investigated at20±1℃. The results showed that the activities of gastrointestinal pepsin and hepatopancreatic lipase decreased gradually as starvation time extended. On the groups of1,2and4day’s starvation, the activities of gastrointestinal pepsin were approximated to those of the control group (P>0.05). While the downtrend of the hepatopancreatic lipase activity was very significant. The groups of2and4day’s starvation were significantly lower than those of the control and the1day’s starvation group (P<0.05). The gastrointestinal pepsin and hepatopancreatic lipase activities after8days’ starvation were12.162U and47.426U/g prot, showing a significant difference from the control group (16.160U and109.980U/g prot)(P<0.05). The gastrointestinal amylase activity increased at the beginning of the starvation, and then decreased as the starvation time prolonged, with its peak on the4th day of starvation (reached1.889u/mg prot). The starvation also significantly influenced the antioxidant enzyme activities of red swamp crayfish:the activities of serum SOD and hepatopancreatic CAT began to rise and drastically decreased after1day’s starvation. The serum SOD activities after2,4and8days’starvation decreased by7.649%,20.366%and28.665%than that of the control group, and the hepatopancreatic CAT activities dropped by36.512%,45.777%and63.624%on the2nd、4th and8th day of starvation compared with that of the control.3. Under laboratory conditions,"Y" water maze was used to investigate the effects of different salinities (0‰(control)),10‰,20‰and30‰) on the behaviour of red swamp crayfish. The results showed that salinity had significant effects on food intake, feeding time and locomotion rate of red swamp crayfish (P<0.05). Food intake, feeding time and locomotion rate of red swamp crayfish decreased significantly as salinity increased. Searching time and feeding frequency of Red swamp crayfish was unaffected by starvation (P>0.05). As salinity increased, searching time of red swamp crayfish increased gradually, while feeding frequency decreased gradually.4. The effects of different salinities (0%o (control)),10‰,20‰and30‰) on major digestive enzymes (gastrointestinal pepsin, hepatopancreatic lipase and gastrointestinal amylase) and antioxidant enzymes (serum SOD and hepatopancreatic CAT) of red swamp crayfish were investigated at20±1℃, and sampled randomly from each test group at1st,4th,8th,12th,24th and48th, respectively. The results showed that:at the same stress level, the activities of gastrointestinal pepsin and hepatopancreatic lipase decreased gradually as experiment time extended; the activities of gastrointestinal amylase, serum SOD and hepatopancreatic CAT increased at the beginning of salinity stress, and then decreased as experiment time extended. At the different stress levels, the activities of gastrointestinal pepsin, hepatopancreatic lipase, gastrointestinal amylase, serum SOD and hepatopancreatic CAT decreased gradually as salinity increased.5. Under laboratory conditions,"Y" water maze was used to investigate the effects of different density levels (20individuals/m2,40individuals/m2,60individuals/m2,80individuals/m2and100individuals/m2) on the behaviour of red swamp crayfish. The results showed that food intake and feeding time decreased gradually as density increased. Food intake of Red swamp crayfish reared at40indviduals/m2,60indviduals/m2,80individuals/m2and100individuals/m2were significant lower than20indviduals/m2(P<0.05), but there was no significant difference between80individuals/m2and100individuals/m2(P>0.05). The downtrend of feeding time was not obvious, and there were no significant differences among each treatment group (P>0.05). Feeding frequency of red swamp crayfish began to rise, and then decreased as density increased, with its peak at60indviduals/m2(reached4.200times/hour), but there were no significant differences among each treatment group (P>0.05). Density had significant effect on gross food intake, attacking frequency and locomotion rate of red swamp crayfish (P<0.05). Gross food intake, attacking frequency and locomotion rate of red swamp crayfish increased gradually as density increased.6. The effects of different density levels (20individuals/m2,40individuals/m2,60individuals/m2,80individuals/m2and100individuals/m2) on major digestive enzymes (gastrointestinal pepsin, hepatopancreatic lipase and gastrointestinal amylase) and antioxidant enzymes (serum SOD and hepatopancreatic CAT) of red swamp crayfish were investigated at20±1℃. The results showed that the activities of gastrointestinal pepsin, hepatopancreatic lipase and gastrointestinal amylase of red swamp crayfish were unaffected by density (P>0.05). And the activities of gastrointestinal pepsin, hepatopancreatic lipase and gastrointestinal amylase fluctuated as density increased. The changes of the activities of serum SOD and hepatopancreatic CAT were obvious at different density levels. As density increased, the serum SOD activity decreased gradually (P<0.05), while the hepatopancreatic CAT increased significantly (P<0.05). In sum, our results could be concluded as follow:1) at the beginning of starvation, food intake, locomotion rate and function of antioxidant system of red swamp crayfish increased, but digestive function decreased. As the degree of starvation increased, food intake, locomotion rate, digestive and antioxidant system function decreased.2) Under salinity stress, food intake, locomotion rate, digestive and antioxidant system function of red swamp crayfish decreased.3) Under density stress, food intake and function of antioxidant system of red swamp crayfish decreased, and attacking frequency increased, while no significant change in digestive function. |
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