The identification of carrier fish is one of the main issues affecting
the control and prevention of infectious diseases at the farm level
(Altinok and Kurt, 2003). The carrier state for streptococcosis has been
found under natural conditions, and it has been shown to be induced
by antibiotic therapy (Evans et al., 2002; Faria et al., 2014). The results
of the current study support the hypothesis that the carrier state occurs
in Nile tilapia, and this may have a negative health impact on farms as
the bacterium can be maintained within culture systems. Currently,
there are no standardized methods available for the diagnosis of
S. agalactiae in carrier fish. Herein, it has been demonstrated that carrier
fish detection was possible using both lethal and nonlethal sampling
methods in conjunction with bacteriology, PCR, and qPCR methods.
The possibility of clinical outcome in a carrier fish submitted to the nonlethal
sampling should be considered, and can be monitored along the
use of this method in field conditions.