STREPTOCOCCOSIS

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One of the major species of Streptococcus affecting fish and causing severe economic losses to fish farmers is Streptococcus iniae. It is a Gram-positive cocci in pairs or chains and is catalase negative and oxidase negative.

Clinical Presentation and Epidemiology

Streptococcus iniae is the specie of Streptococcus first recovered from a freshwater Dolphin (Inia geoffnensis) before it was later associated with disease outbreak in fish, specifically Tilapia (Perera et al., 1994).

In rainbow trout, Streptococcus iniae causes lethargy, discoloration, bilateral exophthalmia, and corneal opacity Internally, ocular haemorrhaging, haemorrhages on spleen and adipose tissue of the intestine are observed. (Lahav et al., 2009).

Diagnostic Consideration

Inocula from harvested diseased organs could be taken under sterile condition to streak on Brain heart infusion agar (BHIA) supplemented with thallium acetate and oxalinic acid. With this supplemented agar, Streptococcus iniae can be recovered from brain, intestines, and kidneys of diseased fish (Nguyen and Kanai, 1999).

Management and Treatment

In some parts of the world, commercially available vaccines are used as a means of preventing disease outbreaks. In most cases, the Veterinarian would need antibiotics to treat during outbreaks. Drugs like florfenicol, streptomycin or gentamicin may be administered via feed at 20mg/kg body weight for up to 7 days for treatment.