Isolation and Identification of Aeromonas salmonicida Associated with Furunculosis in Cultured Sablefish (Anoplopoma fimbria)

Abstract:

Sablefish (Anoplopoma fimbria), also known as black cod, is a sleek, black-skinned and valuable cold water benthic fish species that lives in the north Pacific Ocean. They possess high content of unsaturated fatty acids. Sablefish have been cultured in British Columbia of Canada, and in recent years, they were introduced into the aquaculture industry in Shandong Province in north China. In this study, we reported the observation of furunculosis found in cultured sablefish in China. AF-1, a strain of bacterial pathogen was isolated from the diseased sablefish. Sablefish infected with this bacterium showed typical symptoms of furunculosis such as subcutaneous hemorrhage in the abdomen and the fin, abscess, ulcer and liver congestion. AF-1 was confirmed to be the pathogen of sablefish furunculosis through the artificial injection experiment, in which the injected fish showed the same symptoms. A series of methods including biochemical and biophysical tests and phylogenetic analysis of 16S rRNA and gyrB genes were used to identify the pathogen. The API ID32E results showed that AF-1 belonged to Aeromonas sp. The 16S rRNA and gyrB genes were amplified and sequenced, and the submission numbers were KU359246 and KU362567. Phylogenetic analysis of gene sequences showed that AF-1 was Aeromonas salmonicida. The chemotherapeutant sensitivity test showed that AF-1 was resistant to 13 antibiotics such as penicillin, amoxicillin and cephalothin, but was sensitive to another 16 antibiotics such as fumequine and florfenicol. According to the antibiotics sensitivity test result, florfenicol was added into diets to control furunculosis in sablefish. Our study indicated that A. salmonicida could infect cultured sablefish in our country, and provided information on the disease control in cultured sablefish.