Abstract:
The floating cage cultured seabass (Lates calcarifer) at the site of Valaichchenai
lagoon in Batticaloa District, East coast of Sri Lanka was reported acute mortality
within a short period of stocking the fish in the cage. The present study was focused to
study the etiology caused by an infection on culturing sea bass at the site. Gross
pathological and histopathological examinations were carried in moribund and
naïve fishes. Bacteriological, and mycological screening and antibiotic sensitivity
test for isolated bacteria were performed to find out the pathogen. Water and feed
quality and their management were assessed at the time of mortality. Investigations
primarily revealed that infection was initiated with the flooding due to heavy
monsoonal season and sudden fluctuation in salinity. The gross pathological signs
were a change of skin color, large irregular hemorrhages on the body surface,
cloudy eye, ulcers on the skin, lamellar fusion, fin rot, and tail rot as well as
histopathological findings such as necrosis in muscles, liver, and kidney tissues,
cyst formation by secondarily infected pathogens proved that pathogen was bacteria.
Gram staining also offered a clear indication of gram negative rod shaped bacteria
and, the particular pathogenic bacteria was confirmed as Aeromonas hydrophila
through further analyses such as Oxidative test, Indol test, and antibiotic sensitivity
test. Antibiotic sensitivity tests also point out that Tetracycline is one of the
effective antibiotics for the Aeromonas hydrophila infection. The improper feeding
management and sudden salinity fluctuation pave the path for acute infection of
A.hydrophila and ultimately lead to high mortality in cage culture.
