Pathogenicity of Aeromonas hydrophila in Silver Carp Hypophthalmichthys molitrix and its Control Trial

Abstract

Pathogenicity of Aeromonas hydrophila, previously isolated from kidney of apparently healthy silver carp, was tested in silver carp Hypophthalmichthys molitrix. Trials were also made to control the pathogen in the experimentally infected fish. Before artificial infection the morphological, biochemical and physiological characters of A. hydrophila were studied. The infection was done by intramuscular (IM) injection method. Two different doses viz., 2.8 × 10 5 and 2.8 × 10 6 CFU/fish were used. In all the injected fish external pathology appeared. Reddish lesions on anal region and fin bases were observed. Injected A. hydrophila was re-isolated from liver, kidney and intestine of the challenged fish. It was understood that the isolate was highly virulent pathogen for silver carp. To control the infection by antibiotics, oxysentin 20% (oxytetracyline HCL BP), acimox (amoxicillin trihydrate BP) and oxy-D Vet (oxytetracycline 20% and + doxycycline 10%) were tested at lower, recommended and higher doses of the pharmaceutical companies, respectively. The antibiotic treatments were conducted for 10 days and the fish were observed for 15 days. Among the three antibiotics, acimox and oxy-D Vet at recommended dose showed the best result where 100% fish were recovered. But, oxysentin 20% at higher dose showed best results.