Water quality influences the presence ofStreptococcus agalactiaein cage cultured red hybrid tilapia,Oreochromis niloticus × Oreochromis mossambicus

Abstract

Attempts were made to identify the association between water quality parameters and the presence of Streptococcus agalactiae in cage cultured red hybrid tilapia, Oreochromis niloticus × O. mossambicus. Fish from commercial floating net cage‐culture systems in a river and lake were randomly sampled over a 24‐month period. Swabs from the brains, eyes and kidneys were streaked directly onto blood agar to isolate S. agalactiae. Water temperature, dissolved oxygen, pH, clarity, ammonia, nitrite, sulfide, rate of water flow and depth of water at sampling sites were measured at the same time of fish sampling. The prevalence of fish that were cultured positive to S. agalactiae was significantly higher in lake compared with river. The length and weight of the infected fish were between 9 and 33 cm, and between 20 and 760 g respectively. There was a significant and positive strong correlation between the presence of S. agalactiae and fish mortalities in lake. All water quality parameters showed significant differences between river and lake. However, only water temperature, clarity and pH of lake and the ammonia, temperature and dissolved oxygen in river showed significant correlation with the presence of S. agalactiae in the cultured fish. It was concluded that several unfavourable water quality in the fish farm influencing the presence of S. agalactiae in cultured red hybrid tilapia.

Infection and pathology in Queensland grouper, Epinephelus lanceolatus, (Bloch), caused by exposure to Streptococcus agalactiae via different routes

“…Other studies have similarly shown that unfavourable water quality in fish farms can influence the susceptibility of cultured red hybrid tilapia to infection with S. agalactiae (Amal et al . ,b). Moreover controlled studies have corroborated this effect, also in tilapia (Evans et al .…”

“…; Amal et al . , ,b; Lusiastuti et al . ) and Gilthead seabream, Sparus aurata Linnaeus in Kuwait (Glibert et al .…”

On the origin of Group B Streptococcus from disease outbreaks in wild marine fish in Australia

“…Environments with different hydrodynamic conditions can also contributed to the presence of a pathogen. Prevalence of cultured red hybrid tilapia (Oreochromis niloticus x Oreochromis mossambicus) positive for GBS was higher in lake compared to river, and that unfavourable environmental factors such as ammonia, temperature, water clarity, pH, and dissolved oxygen were positively correlated with the presence of GBS in infected fish (Amal et al, 2013a).…”

“…So whilst we can transfer infection by immersion in a relatively high concentration of bacteria, it appears that better water quality reduces stress in a cohort naïve fish sufficiently to prevent initial colonisation, or reduce shedding in challenged fish. A combination of unfavourable water quality in fish farm can influence the presence of S. agalactiae and the susceptibility of cultured red hybrid tilapia to the bacteria (Amal et al, 2013a). As the environmental drivers for the recent and ongoing mortalities in wild Queensland grouper is unknown this aspect of susceptibility to infection is worthy of further investigation in a controlled study.…”

“…Outbreaks caused by streptococcal infections in several fish species have been associated with changing environmental conditions, including increased ammonia levels, warm and cold water temperatures, osmolarity changes and low dissolved oxygen (Amal et al, 2013a;Bromage and Owens, 2002;Evans et al, 2006c;Evans et al, 2003;Sepahi et al, 2013). Whilst exposure for 24 hr with a sub lethal dose of un-ionized ammonia UIA (0.32-0.37 mg L -1 ) did not significantly cause more mortality in Nile tilapia (Oreochromis niloticus) after injection with 750 colony-forming units (cfu) of S. agalactiae per fish, when exposed to high level of UIA (2.0-4.0 mg L -1 ) and no subsequent challenge, fish experienced 93-100% mortalities within 24 hr (Evans et al, 2006a).…”