| From 2009.4 to 2011.4, the cultivation of Chinese mitten crab (Eriocheir sinensis) is observed and surveyed in shuxin, chongming, shanghai, and the ways of ecologically high and stable yields were investigated. The physical and chemical indexs were measured, which include water quality,water temperature,frequency of molting,the frequency distributions of weight of body,the changes of moisture,the content of total lipid and protein,the feed efficiency and output. According to these indexs, we study the ecological effects of bottom aeration during juveniles cultivation, and discuss the changes of physical and biochemical analysis during the molting cycle. The results can provide theoretical foundation for the spread of bottom aeration and good harvest and high output of juveniles, which could boost the sustainable development of crustacean aquaculture.1. The evaluation of comprehensive effects of the bottom aeration to culture water body in juvenile crab pondsIn order to know the effects of bottom aeration to the water quality and dissolved oxygen in the area near the grass of different density, we choose productive aquaculture ponds of juvenile crab, and carry out the configuration and application of facilities. In June, July and August, through control experiment between bottom aeration and absence of aeration in the Eriocheir Sinensis pond, we select the different places, such as the area near the grass of different density and the center of pond, to detect the water temperature, pH, dissolved oxygen, ammonia and nitrite in the surface and bottom of the pond.The results of research indicate that in the twenty-four hours, the formation rule of thermocline in the pond is form—breaked—form once again. In continuous three months, the bottom aeration can effectively break the thermocline, improve the content of the dissolved oxygen, and make the content of the dissolved oxygen stay stable. Besides, in the area near the grass of different density, bottom aeration can also make t the content of the dissolved oxygen stay stable.2. Ecological effects of bottom water layer aeration systems in intensively-reared youngling crabs Eriocheir sinensis pondsIn order to discussed the new processes and technique of high and stable yields in intensively-reared youngling crabs Eriocheir sinensis ponds, we carryed out the bottom aeration configuration and application of facilities. The physical and chemical indexs were measured, which included water quality,water temperature,the duration of exposure,frequency of molting,the frequency distributions of weight,feed efficiency and yields during the cultivation of juveniles. According to these indexs, we studyed the ecological effects of bottom aeration.The results of research indicated that the bottom aeration could effectively break the thermocline, relieve the effects of hypoxia stress and temperature stress to the growth of juveniles, and make the contents of pH,ammonia and nitrite stay in the extent of safety. The duration of exposure of juveniles in experimental ponds was three hours shorter than that in control ponds, but the content of dissolved oxygen was about 3 mg·L-1 higher. By means of bottom aeration, the duration of ten times molting was only 108 days, and the growths of weight,length,width and height of body were relatively obvious. The frequency distribution of weight of juveniles in experimental ponds was mostly 5.5-6.5 g, which was obviously higher than that 2.5-3.5 g in control ponds. The average standard of juveniles in experimental ponds was 7.81 g, the total yield was 3090 kg, the yield every 667 m2 was 257.5 kg, the rate of prematurity was 4.8 %, and the feed efficiency was 1.82. However, the average standard of juveniles in control ponds was 5.56 g, the total yield was 1500 kg, the yield every 667 m2 was 125 kg, the rate of prematurity was 15.6 %, and the feed efficiency was 2.90. The indexs in experimental ponds were obviously higher than that in control ponds.3. Changes of morphometry and biochemical composition of juveniles eriocheir sinensis in the bottom aeration pondsUsing the way of physical measurement and biochemical analysis in juvenile crab, the changes of the physical indexs and chemical indexs were compared during the ten molting periods in the bottom aeration ponds. The physical indexs include the body weight,length,width,height,L♀1,L♂1,L♀2 and L♂2. The chemical indexs include the moisture,total lipid and protein.The results showed that during the periods of four month growth, the grow curves between weight,length and width is approximately by the equations: W= 0.6*10-3*L3. With the changes of age, the grow curves between growth of weight and age is by the equations: W=aTb . The grow curves between the growth of length,width and height and age is by the equations: L=a+bT. The quadratic equations between the ratio of L♀1 /L♀2 and the ratio of L♂1/L♂2 and age is below: Y=aX2+bX+c, and for this reason we can speculate whether the crabs of male and female had the trends of prematurity. During the ten molting periods, the content of the moisture and protein had no obvious changes. However, the variety of the content of total lipid is not obvious, only about 5% in the previous seven times, and it increase to 9% in the later three times. Maybe with the growth of body, the content of hepatopancreas in the body is gradually increasing, which at last leads to the increasing of the content of total lipid. 4. Changes of biochemical composition and energy research of juvenile eriocheir sinensis during the molting cycleThis study investigated the changes of hepatosomatic index(HSI) and biochemical composition during the molting cycle of juvenile Eriocheir sinensis(about 2.0g).The results showed that in the twenty-four days of molting cycle, the HIS was gradually increasing while the moisture content of hepatopancreas and muscle was gradually dropping. The total lipid content of hepatopancreas was first dropping and then increasing. The total lipid levels and protein content of the muscle were gradually dropping. The main energy of molting was provided with fat of hepatopancreas. The main fatty acids in hepatopancreas were C16:0,C18:1n-9 and C18:2n-6. The main fatty acids in muscle were C16:0,C18:1n-9,C18:2n-6 and C20:5n-3. The levels of C20:5n-3,C20:4n-6 and C22:6n-3 in muscle had a big difference from that in hepatopancreas. Maybe that the fatty acids in different tissue were different. |
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