A nested-PCR for detecting S. agalactiae in frozen and paraffin-wax-embedded tilapia tissue was thus successfully used for identifying S. agalactiae in naturally infected adult red tilapia. Tilapia having less than 20 g bodyweight (larvae and fry) proved negative for the presence of the S. agalactiae 16S-23S rRNA gene, thereby confirming our previous observations regarding the absence of S. agalactiae infection in such animals. The results also supported the hypothesis that establishing tilapia breeding farms which are free of this pathogen would be a feasible goal as a first prevention and control measure against the infection and disease. The nested-PCR used here is a highly reliable technique for research, diagnosis and epidemiological studies.