The nonlethal sampling methods tested in this study, especially venipuncture
and kidney aspiration, proved applicable for obtaining samples
from Nile tilapia for use in microbiological and molecular diagnosis
of S. agalactiae. However, the handling is considered a risk factor to
streptococcosis in tilapia (Zamri-Saad et al., 2014) and the execution
of nonlethal sampling methods might cause stress to the fish and increase
their susceptibility to streptococcal infection. Previous studies
evaluated the effect of induced stress in carrier fish on the development
of disease and on increase of transmission of pathogens after using a
corticosteroid drug (Antonio and Hedrick, 1994) and heat stress
(Hunter et al., 1980), however, there are no studies which demonstrate
induced stress in fish by the use of nonlethal sampling methods. In this
study, there was no mortality and no signs of infection observed in fish
subjected to the sampling methods tested, which demonstrates that
these methods can be used to safely obtain tissue and body fluids
from Nile tilapia.