Abstract
The half-smooth tongue sole, Cynoglossus semilaevis Günther, is a native of Chinese coastal waters. Its fast growth, low fecundity, and good flavor have resulted in its successful adoption as a cultured species in China. However, owing to the intensive culture, bacterial infectious disease began to occur and resulted in serious losses. Recent years, a disease macroscopically characterized by ulceration of the tail was prevalent in tongue sole fingerlings in China. Tail ulcer disease generally occurs in farmed tongue sole fingerlings of less than 15 cm in length, housed in concrete tanks. Epidemics occur annually, mainly between October and November with associated morbidity levels of 40–50% and mortality levels of 5–10%. Diseased fish were lethargic and low appetitive. The fingerlings (2–3 g) sampled during an epizootic, displayed inflammation and ulceration of the tail. Macroscopic clinical signs included sluggish swimming behavior, anorexia, and tail ulceration. A gram-negative, immotile, short, rod-shaped bacterium, designated ST-01, was isolated from the tail wounds of diseased fingerlings. An infectious challenge test revealed that ST-01 was responsible for development of tail ulcers in half-smooth tongue sole fingerlings. The 16S rRNA of ST-01 was amplified and sequenced. A 1442 bp fragment (EF566900) was produced which shared 99.9% nucleotide identity with that of an Acinetobacter venetianus strain (AJ295007). On phylogenetic analysis, ST-01 was found to cluster tightly with A. venetianus, forming a subgroup clearly phylogenetically distinct from other Acinetobacter species. Based on the evidence above, together with data from morphological, physiological, biochemical and phylogenetic analyses, the bacterium ST-01 was finally identified as Acinetobacter venetianus. The bacterium was sensitive to tetracycline, penicillin G, novobiocin, and nitrofurantoin. Acinetobacter venetianus was first reported as a n-alkane-degrading bacterium.1,4 This is the first report of Acinetobacter venetianus as the causative agent of tail ulcer disease in half-smooth tongue sole fingerlings.2,3
Acknowledgements
This study was supported by the fund of the Department of Science and Technology of Jiangsu Province (No. BS2006029).
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