A frozen stock-culture of S. iniae (ARS 98-60) from an outbreak of streptococcal disease in Nile tilapia was grown in tryptic soy broth (TSB) at 25 °C with shaking at 100 rpm for 24 h. The concentration of the culture was adjusted to an optical density of 1.0 measured on a Shimadzu UV-1601 spectrophotometer at 540 nm to give a S. iniae concentration of 1×109 colony forming units (CFU)/mL