Study of streptococcosis/lactococcosis in some farmed rainbow trout in Fars province, Iran

Objective: Streptococcosis/lactococcosis caused by Gram positive cocci bacteria is one of the emerging bacterial diseases in both freshwater and marine aquaculture industry worldwide. Although, a number of Gram positive cocci/rod bacteria have been identified as the causative agents of disease outbreak in different species of fish, more studies are required to identify the bacterial species involved in the disease outbreak in different regions. This study was undertaken to identify the main bacterial species involved in some affected farmed rainbow trout in Fars Province, Beaza region which is one of main contaminated regions in Iran. Also, the possible predisposing factors were studied. Method & Materials: Six hundred samples were collected from four affected farmed trout showing clinical signs of disease during summer 2005 and 2006. Tissue samples of kidney, brain and liver were cultured on blood agar incubated at 25◦C for 72 hours and the grown colonies were characterized phenotipically using routine bacteriological works. Water quality criteria were also checked each sampling time. Results & Conclusion: The bacteriological studies resulted in the isolation and characterization of totally 480 Gram positive cocci strains of which 390 strains were identified as Streptococcus iniae and 90 strains as Lactococcus garvieae. Also, in some cases some Gram negative bacteria identified as Aeromonas hydrophila were identified. High water temperature exceeded 19◦C and poor health management such as overcrowding, over handling, unsuitable feeding and negative environmental impact of tourism activity were also identified as the main predisposing factors for developing and consistency of streptococcosis/lactococcois in this region.

Keywords:

Streptococcosis/ lactococcosis , Streptococcus iniae , Lactococcus garvieae , rainbow trout , Fars Province , Aeromonas hydrophila