科研之友
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摘要
in order to determine the lethal dose (96-h ld50) of the bacteria aeromonas hydrophila to matrinxˋ, brycon amazonicus, to be applied in challenge tests, 90 fish (63.23 ㊣ 6.39 g) were divided into five treatments, with different bacterial solutions: t1 - control (0.9% nacl saline solution); t2 (4 x 1011 cells/ ml); t3 (5 x 1011 cells/ ml); t4 (1.36 x 1012 cells/ ml) and t5 (3.06 x 1012 cells/ ml). fish were previously anesthetized with benzocaine (60 mg l-1), inoculated in the peritoneal cavity with the bacterial suspensions and then distributed into fifteen 80-l test chambers, where the water variables were monitored and fish mortality was observed. the experiment was randomly designed in three replicates and the 96-h ld50 was estimated according to the trimmed spearman-karber method. water quality variables remained within adequate ranges for fish health and performance. fish mortality rate increased with the bacterial concentrations of a. hydrophila (t1 = 0%; t2 = 16.66%; t3 = 44.44%; t4 = 72.22% and t5 = 100%), and the first mortalities were observed after 57 h, although the signs of the bacterial infection were already observed 24 h after the inoculation. the results indicate that the 96-h ld50 value of a. hydrophila to matrinxˋ is 6.66 x 1011 cells/ ml.
