No abstract

Yellow cat¢sh Pelteobagrus fulvidraco (Richardson) is a commercially important ¢sh generally distributed in Southeast Asian countries. The well-known aetiological agent of enteric septicaemia of cat¢sh, Edwardsiella ictaluri, was isolated from diseased yellow cat¢sh P. fulvidraco (Richardson) reared at two commercial ¢sheries in China. The economic losses due to the high mortalities (about 50%) caused by this bacterium have been increasing annually. The a¡ected ¢sh presented two di¡erent, typical symptoms: pale gills, slight exophthalmia and a 'hole in the head' , and haemorrhage on the opercula, in the skin under the jaw, creating a 'hole under the jaw' . These diseases were found frequently in cultured yellow cat¢sh throughout China. The isolates from both outbreaks were all Gram negative, facultatively anaerobic and short rod. Morphological and biochemical tests and phylogenetic analysis based on the 16S rDNA sequences all strongly indicated that these yellow cat¢sh isolates were highly identical to the known E. ictaluri. In addition, the isolates possessed the typical plasmid pro¢le of E. ictaluri. Experimental infection assays were conducted and pathogenicity (by an intraperitoneal injection) was demonstrated in yellow cat¢sh and channel cat¢sh Ictalurus punctatus. The results showed that yellow cat¢sh isolates were quite conservative phenotypically and genetically, and were able to cause two di¡erent, typical symptoms in this ¢sh under unknown conditions and mechanism.

In order to improve the solubility of doped nanoparticles in solutions, Y(2)O(3):Tm(3+)/Yb(3+) nanoparticles were synthesized using the Pechini-type sol-gel method, and their surfaces were modified with amino or carboxylic functional groups using ligand-capped and ligand-exchanging methods. The nanoparticles with modified surfaces were characterized by transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy and zeta potential (ζ), and their photoluminescence was studied by fluorescence spectrophotometry. The results indicate that the upconversion fluorescence of amine- and carboxyl-modified nanoparticles was enhanced after the surfaces of nanoparticles were modified. Compared to the upconversion fluorescence intensity of non-modified nanoparticles, the upconversion fluorescence intensities of amine- and carboxyl-modified nanoparticles were enhanced by 9.4 and 1.4 times, respectively. These results are attributed to the formation of the chemical bonds between Y(2)O(3):Tm(3+)/Yb(3+) core and non-crystalline SiO(2) shell via Y-O-Si bridges, which activate the 'dormant' Tm(3+)/Yb(3+) ions on the surfaces of nanoparticles. The results of the solubility investigations for amine- and carboxyl-modified nanoparticles indicate that severe aggregation can be weakened by adhering amino or carboxylic functional groups to the surfaces of nanoparticles. It is therefore concluded that the good hydrophilicity resulting from active functional groups in solutions and more intense upconversion fluorescence enable the doped core-shell nanoparticles to have great potential to be used as fluorescence biolabels in the future.