LD5o of the bacteria Aeromonas hydrophila to matrinxã, Brycon amazonicus

Abstract

In order to determine the lethal dose (96-h LD 50 ) of the bacteria Aeromonas hydrophila to matrinxã, Brycon amazonicus, to be applied in challenge tests, 90 fish (63.23 ± 6.39 g) were divided into five treatments, with different bacterial solutions: T 1 -Control (0.9% NaCl saline solution); T 2 (4 x 10 11 cells/ mL); T 3 (5 x 10 11 cells/ mL); T 4 (1.36 x 10 12 cells/ mL) and T 5 (3.06 x 10 12 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 LD 50 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 (T 1 = 0%; T 2 = 16.66%; T 3 = 44.44%; T 4 = 72.22% and T 5 = 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 LD 50 value of A. hydrophila to matrinxã is 6.66 x 10 11 cells/ mL. Keywords: Aeromonas hydrophila, 96-h LD 50 , matrinxã, tropical fishes DL 5o da bactéria Aeromonas hydrophila para o matrinxã, Brycon amazonicus resumo Para determinar a dose letal (DL 50 96-h) da bactéria Aeromonas hydrophila para o matrinxã, Brycon amazonicus, com aplicabilidade para testes de desafio, foram utilizados 90 peixes (63,23 ± 6,39 g), divididos em cinco tratamentos, com diferentes soluções bacterianas: T 1 -Controle (solução salina 0,9% NaCl); T 2 (4 x 10 11 células/ mL); T 3 (5 x 10 11 células/ mL -1 ); T 4 (1,36 x 10 12 células/mL -1 ) e T 5 (3,06 x 10 12 células/ mL -1 ). Os peixes foram previamente anestesiados com benzocaína (60 mg L -1 ), inoculados na cavidade peritoneal com as suspensões bacterianas e distribuídos em 15 aquários de vidro de 80 L de capacidade, com aeração constante. O experimento teve duração de 96 h, no qual foram monitoradas a mortalidade e a qualidade da água. O delineamento experimental foi inteiramente casualisado com três réplicas e a DL 50 96-h foi estimada de acordo com o método Spearman-Karber. Durante o experimento os parâmetros físico-químicos da água permaneceram dentro das condições consideradas adequadas para o desenvolvimento e saúde dos organismos aquáticos. A mortalidade dos peixes aumentou nas concentrações crescentes de A. hydrophila (T 1 = 0%; T 2 = 16,66%; T 3 = 44,44%; T 4 = 72,22% e T 5 = 100%), contudo, as primeiras mortalidades ocorreram em 57 h após a inoculação das concentrações bacterianas, sendo observados os primeiros sinais de infecção em 24 h após a inoculação. Os resultados indicam que o valor da DL 50 96-h da bactéria A. hydrophila para o matrinxã foi igual a 6,66 x 10 11 células/mL de solução salina. PAlAvrAs-chAve: Aeromonas hydrophila, DL 50 96-h, matrinxã...

Evaluation of Efficacy of Oxytetracycline Oral and Bath Therapies in Nile Tilapia, Oreochromis niloticus against Aeromonas hydrophila Infection

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