Lethal dose and clinical signs of Aeromonas hydrophila in Arapaima gigas (Arapaimidae), the giant fish from Amazon.

Aeromonas hydrophila is causing substantial economic losses in world aquaculture. This study determined the tolerance limit (LD 50-96h ) of A. hydrophila in Arapaima gigas , and also investigated the clinical signs after intradermal inoculation. Arapaima g igas fingerlings were inoculated intraperitoneally with 0 (control), 1.0 × 10 5 , 1.0 × 10 6 , 1.0 × 10 7 , 1.0 × 10 9 and 1.0 × 10 10 CFU/mL of A. hydrophila for the determination of LD 50-96h , which was 1.8 × 10 8 CFU/mL. In another trial with intradermal inoculation of 1.8 × 10 8 CFU/mL A. hydrophila , there was a 91.6% of mortality between 8 and 23 h, and several clinical signs were found. As follows: depigmentation in the tegument, lesions in the tail and fins, loss of balance, reduction of respiratory movements, hemorrhagic foci, necrotic hemorrhages in the kidney, liver and swim bladder, splenomegaly, ascites in the abdominal cavity and hyperemia, enlargement of the gall bladder, among other clinical signs observed. The results showed that A. gigas has a relative tolerance to A. hydrophila when compared to other Neotropical fish species. [ABSTRACT FROM AUTHOR]