It is known that some bacterial pathogens that are detectable in internal
organs are not detectable in blood samples (Noga et al., 1988).
Thus, tissue sampling of diseased fish after euthanasia is important for
the determination of the etiologic agent involved in disease outbreaks on fish farms. However, euthanasia is impractical for health monitoring.
Biopsies are considered alternative methods of tissue sampling for diagnostic
assays, but due to the large anatomical variation between different
species of fish, a specific biopsy technique for Nile tilapia becomes
necessary. Kidney biopsy is an effective technique for diagnosing enteric
red mouth disease in rainbow trout (Oncorhynchus mykiss) (Noga et al.,
1988) and to detect persistent nervous necrosis virus infection in Atlantic
cod (Gadus morhua) (Korsnes et al., 2009). However, there are no
studies that demonstrate the efficacy of kidney biopsy samples for the
detection of S. agalactiae in any fish species. Therefore, the current
study is the first to evaluate the association of kidney aspiration with
different diagnostic methods to detect the presence of S. agalactiae infection
in Nile tilapia, and is also the first study to compare the detection
of S. agalactiae by means of lethal and nonlethal sampling in fish.