Outbreak of natural Streptococcosis in hatchery produced silver pomfret (Pampus argenteus Euphrasen) larvae in Kuwait

• Published in: Aquaculture 2012-02, Vol.330-333, p.15-20
• Main Authors: Azad, I.S., Al-Marzouk, A., James, C.M., Almatar, S., Al-Gharabally, H., Qasem, J.A.
• Format: Article
• Language: English
• Subjects: anorexia; Aquaculture; bacteria; blood; brain; epithelium; Fish; fish culture; Fish hatcheries; fish larvae; fisheries; Gram-positive bacteria; hatcheries; Histopathology; mariculture; melanization; morbidity; Mortality; Pampus argenteus; PCR; polymerase chain reaction; rearing; seawater; Silver pomfret; Smears; Streptococcosis; Streptococcus agalactiae; summer; tanks; temperature; transmission electron microscopy; water supply; Water temperature
• ISSN: 0044-8486; 1873-5622
• DOI: 10.1016/j.aquaculture.2011.12.010

Hatchery-produced silver pomfret (Pampus argenteus) in the Mariculture and Fisheries Department's fish culture facilities suffered infection due to Streptococcosis during the summer months of 2007. The fish larvae showed anorexia, thinning, gradual darkening and morbidity. The rearing tank water and the supply water were found to harbor Streptococcus agalactiae. The blood and body fluid smears revealed the presence of Gram positive Cocco-bacilli with characteristic aggregated distribution. The bacterium was recovered from the brain of moribund fish. Cumulative mortalities increased with a raise in the seawater temperature from 25 to 29°C reaching over 50% by 24dph. Light and transmission electron microscopy also showed the presence of the bacterium in the granular layer of the brain. The bacterium measured 2.6×1.8μm (l×w). The TEM sections of the fish brain showed typical capsular bacterium and heavily melanized skin epithelium. The API-strep (Biomeurex, Germany) and the biochemical properties of the isolate also confirmed the identity. The isolate was further tested positive through PCR for its identity revealing a species specific amplicon of 220bp. Samples of brain of moribund larvae at 15, 20, 25, 30 and 35dph showed positive amplicon for the presence of S. agalactiae. ► We study disease outbreak in Silver pomfret, Pampus argenteus. ► We examine susceptibility of the fish to the bacterium Streptococcus agalactiae. ► Histopathology and PCR-based molecular diagnosis confirm S. agalactiae infections. ► Mortalities of silver pomfret were directly influences by the summer water temperature.