Masters ThesisStreptococcosis is a zoonotic disease of fish reported to cause significant losses in aquaculture, it is caused by bacteria from three major groups; Streptococcus, Lactococcus and Vagococcus. This study aimed to establish the occurrence and antimicrobial resistance of Streptococcus and Lactococcus species in farmed Tilapia in Morogoro. A questionnaire was administered to fish farmers to acquire information about management practices of fish ponds in relation to occurrence of Streptococcus and Lactococcus species. Three hundred and fifty two fish were collected from 22 different ponds to establish occurrence of the bacteria. Fish biodata and water quality parameters were recorded during sampling. Bacterial isolation was done by culturing on blood agar at 37°C. Biochemical tests were performed for preliminary identification of Streptococcus and Lactococcus species, genus specific PCR used to confirm Streptococcus species. A multiplex PCR was set to simultaneously detect Streptococcus iniae, Streptococcus agalactiae and Lactococcus garvieae. Antimicrobial resistance testing was done by disc diffusion method. Majority of the farmers followed appropriate pond management practices. Water parameters were in a desirable range (6.48 - 11.03, 2.08 - 13.6 mg/L and 21.7 - 36.68 °C for pH, dissolved oxygen and water temperature, respectively) in most ponds. Multiplex PCR detected L. garvieae from 6 fish samples. There was no statistically significant association between fish weight and sex with occurrence of L. garvieae (p = 0.09 and 0.14, respectively). All isolates were sensitive to tetracycline and ciprofloxacin. Fifty percent of the isolates were resistant to chloramphenicol and sulfamethoxazole. All isolates were resistant to ampicillin, penicillin and gentamycin which are common used antibiotics in humans and animals. This study indicated the presence of antimicrobial resistant zoonotic L. garvieae among farmed tilapia in Morogoro. Removing dead fish in the ponds, quarantining fish with abnormal behaviors and exchanging water regularly are some of the means to prevent an outbreak. In an outbreak, the most effective antibiotics are tetracycline and ciprofloxacin.