The Effects Of Fluorescent Marking Silver Carp And Bighead Carp On Microflora In Gill And Intestine

Artificial propagation and releasing is a crucial approach for aquatic resources conservation and has achieved ecological and economic benefits in the practice. In the process of artificial propagation and releasing, it is necessary to marking and recapturing releasing fish in order to evaluate the releasing effect. Marking fish with chemical substance is an ideal way for a short period of large-scale marking and releasing fish. The most widely used way is immersing fish in fluorescent substance in order to mark its otolith. Comparing with other marking approach, fluorescent substance marking is more simple and cost-saving, moreover it has less influence on marked organism. The previous result of our lab showed that the tetracycline hydrochloride marking otolith was detected significantly in silver carp, although it had somehow stress in a short time, it could recover to normal level in a certain period. And the result also showed that comparing with the control group, silver carp and bighead carp had a higher survival rate after immersed and the environmental stress tolerance has enhanced. It may be caused by antibacterial act of tetracycline hydrochloride. In order to elucidate the effects on silver carp and bighead carp attached microbial after tetracycline hydrochloride marking, molecular biology method is used for extraction of total genomic DNA of microflora in water, gill and gut of marking silver carp and bighead carp. PCR amplification of16S rRNA gene fragments, denaturing gradient gel electrophoresis, gene cloning and sequencing are also used to identify the type of microflora. By comparing and analyzing of marked effects on silver carp and bighead carp, it will provide the basic data for research on physiological response of marked fish.The research suggests that fluorescent marking decreases the species of microorganisms in water. A lot microorganisms in cyanobacteria, including Calothrix, Oscillatoria, Synechococcus, and also some Hyphomonas, Rhodobacter disappear, and some bacteria of Malikia and Vogesella appear. Because of the great changes of bacterial community structure in the water and the completely filter feeding fish-silver carp and bighead carp has a corresponding change in their gills. The predominant bacteria are proteobacteria gammaproteobacteria Aeromonas and Pseudomonas in the gill of control group silver carp and bighead carp, however after the dispose of tetracycline hydrochloride, some Firmicutes Bacilli, Methylophilus methylotrophus and Microbulbifer add in. After the filter feeding of gill, the water gets into gut and also causes a corresponding change. The control group, especially the bighead carp control group has a lot amount of Pseudoalteromonas, Photobacterium and Vibrio, while after the dispose of tetracycline hydrochloride, they all disappear and only some E.coli and Aeromonas left. Thus, as an antibiotic, tetracy cline hydrochloride can kill various bacteria in the water, achieve the inhibitory effect. While the water living fish are closely related to water environment by feeding and some other activities, so the bacterial community structure in the gills and guts will also change.There are also inherent diversity in the bacterial community structure of silver carp and bighead carp. The causes are not clear and needs further study. It may caused by the diversity of the feeding habits and the interaction between fish and microbial.In the process of artificial propagation and releasing, marking fish responsed to external stress with various physiological and biochemical changes. This kind of stress could continue for a long time, thus the fish immunity will be impaired and sensitive to various pathogenic bacteria, the survival rate will decrease. However, the survival rates of fish with tetracycline hydrochloride marking rise instead of drop. It maybe, as a broad-spectrum antibiotic, tetracycline hydrochloride can inhibit the growth and reproduction of some conditional pathogenic bacteria, such as Aeromonas in the water sample, Pseudomonas and Aeromonas in the gills of and Vibrio in the gut Therefore, except for labeling fish otoliths, tetracycline hydrochloride can also inhibit the outbreak of some conditional disease-causing pathogenic bacteria and reduce the harm of these pathogenic bacteria on the fish. So that increases the survival rate of the stressful fish. It also reminds us that before releasing the fish should be disinfected in order to improve the survival rate.