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

Abstract: 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. [Copyright &y& Elsevier]