Effects Of Ecological Manipulation On Mariculture Ecosystems

Aquaculture is an economical activity that is threatened by the repeated appearance of diseases. So far, antibiotics have been intensively used as preventive and curative measures, but such practices are now questioned because regular use of these chemical products has led to the appearance of drug-resistant bacteria and can also have harmful effects on the environment. The need for alternative strategies for control of the microbial conditions in the cultivation of marine rearing, is therefore essential for further progress in aquaculture. Because crustaceans have no specific immune system, suitable techniques for stimulation of the non-specific immune defence may become important in marine rearing. Methods have been proposed, such as the use of probiotic bacteria, immunostimulants or the improvement of the larval quality via the nutrition, and zootechnical progress has been made. Approaches to a strategy of addition of probiotics for microbial control and stimulation of the immune system in marine larval rearing have been presented, but considerable efforts of research will be necessary to develop the applications to aquaculture. The added probiotics and antibiotic's influence on cultivating microbial factor dynamic change was studied by adopting enclosure ecology method. At the same time, population structure and genetic diversity change of bacteria in sediment were also studied by 16S rDNA PCR-RELP method in molecular biology technology. The main results of this dissertation are as follows:1. Influences on physical and chemical factors in water: During the whole process of experiment, variation of physical and chemical factors in different treated group was significant. From the second week of the experiment, N, P, and COD nutrient contents in water of antibiotic treated group hoiked and their content was significantly higher than that of group added probiotics and control group. By contrast, contents of dissolved oxygen(DO) and pH in antibiotic group was lower than that of probiotics treated group and control group. During the experiment, changes of the N, P nutrient content in water of probiotics group was basically relatively stable, which maintained the same level as that at the beginning of the experiment.