virulence and histopathology
of vibrio anguillarum like (val) bacterium isolated from hatchery
produced juveniles of lates calcarifer (bloch)
I.S. Azad, A.R. Thirunavukkarasu, M. Kailasam, J.J.S.
Rajan-2004
Asian Fisheries Science, 17(1-2): 101-110
Abstract:
Hatchery produced Asian sea bass Later calcarifer
(Bloch) juveniles (120 days post hatch) maintained in a fish hatchery,
Central Institute of Brackishwater
Aquaculture (CIBA), were used in the present study. Diseased and moribund
fish showed haemorrhages at the bases of dorsal, pectoral and anal fins. The
affected fish stopped taking food. Bacteria isolated from the aseptic kidney
samples drawn from the moribund fish belonged to the genus Vibrio as
evidenced through selective growth on TCBS agar. Colony morphology, growth
and the biochemical characteristics suggested that the bacterium was Vibrio
anguillarum-like (VAL). This VAL bacterium, injected at varying doses in
Liza macrolepis and Oreochromis mossambicus revealed LD50
end points of 104.17 and 105.47
CFU, respectively. Exposure of L. calcarifer juveniles to graded
levels of virulent bacterium via injection and bath showed that a cell
density of 104.5 CFU/fish and 106.3 CFU per ml,
respectively, can kill half of the exposed population. Investigations
carried out on the histopathology of the infected fish indicated severe
necrotic degenerative changes in the gills, with mild to extensive lamellar
fusion and hyperplasia of naturally infected seabass juveniles, while that
of the experimentally infected fish showed no discernible changes. Natural
infection showed wide spread chronic histopathological manifestations while,
the experimental infection accounted for acute phase pathogenesis –
related manifestations.
(Central Institute of Brackishwater Aquaculture
(CIBA), 75, Santhome High Road, R.A. Puram, Chennai-600 028, India)