The tilapia culture is gaining global prominence by the need to produce good quality tilapia. However, the further enhances the production system activities, the possibility of infectious disease. The aim of this study was to verify the presence of Streptococcus spp. in tilapia sample vaccinated with the vaccine Aquavac® against streptococcose depending on photoperiod of 12 hours light and 12 hour dark (12: 12LD). For this, 180 juvenile tilapia with average weight of 38.06 ± 0.42g were distributed in 2 water tank with 2.300L capacity each, with constant temperature of 28 ° C and maintained for a period of sixty (60) days. The lights turn on at 6:00am and turn off at 18:00pm. At the beginning of the experiment a group of animals were vaccinated and another group received saline (control). Thirty days after immunization, all groups were submitted to a challenge strain of Streptococcus spp. After the experimental period, the animals were anaesthetized with clove oil (Eugenol), euthanized by spinal cord section. Then were collected sample of tissue spleen, intestine and gills for analysis. The procedure of collected was done for 24 hours, at regular intervals of 4 hours. The collected was given by point (time), using 30 fish every point, for a total of six points of procedure of tissue at the following times: 0:00h, 4:00h, 8:00h, 12:00h, 16:00h and 20:00h. The samples were removed, soaked in RNA later solution and stored at -20 °C. The vaccinated fish showed the presence of streptococcus spp in the spleen with a prevalence of 16.7% at 8:00h and 12: 00h and after the beginning of the dark phase at 20: 00h. In addition, this group reported a prevalence of 16.7% in the gills at 20: 00h. The control group showed a 50% prevalence in the spleen, 16.67% in the intestine and gill at 8:00h; prevalence of 33.33% in the spleen, 50% and 16.7% in spleen, intestine and gills 12:00h respectively; prevalence of 16.7% in the intestine and 50% in the gills at 16:00h; and 50%, 16.67% and 33.33% in the spleen, intestines and gills respectively at 20:00h after the beginning of the dark phase of the photoperiod. The results showed that during the dark phase of the photoperiod of points 0:00, 4:00 hasn’t been registered the presence of Streptococcus spp in organs of the groups. After the beginning of the light phase, the animals demonstrated the presence of Streptococcus spp.