Streptococcosis in Tilapia
Streptococcosis is the leading cause of mortality in commercial tilapia farms worldwide — 30–80% losses in untreated outbreaks, with characteristic erratic spiral swimming, unilateral exophthalmia, and a clear link to water temperatures above 27°C.
Clinical signs
- Erratic spiral swimming, corkscrewing and loss of equilibrium — the most distinctive field sign
- Unilateral or bilateral exophthalmia (pop-eye), often with corneal opacity and intra-ocular haemorrhage
- Darkened skin, especially the dorsal surface, in moribund fish
- Haemorrhages at the base of fins, around the mouth and on the operculum
- Abdominal distension from ascites; enlarged spleen and dark red liver on necropsy
- Mortality 30–80% over 2–4 weeks in untreated outbreaks; chronic losses persist if not addressed
Transmission
- Horizontal via water — bacteria shed from skin lesions, eyes, faeces and dead fish into the pond column
- Cannibalism of dead and moribund fish is a major amplification route
- Vertical transmission from carrier broodstock to fry is documented for S. agalactiae
- Temperature-driven — outbreaks accelerate sharply above 27°C and peak at 30–32°C
- Stress triggers: high stocking density, low DO (below 4 mg/L), handling, grading and transport
- S. agalactiae is the dominant strain in most Asian tilapia farms; S. iniae dominates in the Americas and parts of Africa
Diagnosis
- Field: spiral swimming + unilateral pop-eye in tilapia above 27°C water is highly suggestive
- Bacterial culture from brain, kidney or eye on blood agar — small white α-haemolytic colonies in 24–48 hours
- Gram stain shows Gram-positive cocci in chains (the genus Streptococcus is defined by this pattern)
- PCR for cfb (S. agalactiae) or lct (S. iniae) genes — distinguishes the two main species in 4–6 hours
- Antibiogram on every confirmed isolate — resistance to amoxicillin, erythromycin and tetracycline is increasing across Asia
Treatment & emergency response
- Amoxicillin in feed at 40–80 mg/kg body weight/day for 10 days — first-line treatment where the strain is sensitive
- Florfenicol in feed at 10 mg/kg body weight/day for 10 days — common second-line where amoxicillin resistance is documented
- Always run an antibiogram before second courses — resistance develops within a single cycle in poorly managed farms
- Observe statutory withdrawal periods before harvest — typically 21–42 days depending on antibiotic and jurisdiction
- Lower water temperature where feasible (deeper water, aeration, partial shading) to slow bacterial replication
- Remove dead and moribund fish at least twice daily — each carcass releases 10⁸–10⁹ cfu/mL into the pond
- Stop all handling, grading and transport for the duration of treatment and 14 days after
Prevention
- Vaccinate fingerlings against S. agalactiae and S. iniae before stocking — commercial injectable and oral vaccines reduce mortality by 60–85%
- Keep stocking density within species-appropriate limits (typically below 25 kg/m³ in cage culture, below 4 kg/m² in ponds)
- Maintain DO above 5 mg/L at all times — install paddle-wheel or diffused aerators sized for peak biomass
- Minimise handling during the high-risk window (water above 28°C) — schedule grading for early-morning hours
- Source fingerlings only from hatcheries with documented broodstock screening for S. agalactiae
- Add a 90-day vaccinated-only stocking policy after any confirmed outbreak
- Monitor and log water temperature daily — flag any sustained 28°C+ reading for intensified surveillance
Biosecurity checklist
- Vaccination certificate on every fingerling batch before stocking, retained for the full cycle
- Twice-daily removal of dead and moribund fish — never leave them overnight
- Foot baths and net disinfection (KMnO₄ 10 mg/L or 200 ppm chlorine) at every pond entry
- Daily water temperature + DO log per pond with documented thresholds (action above 28°C, urgent above 30°C)
- Dedicated nets per pond; colour-code to prevent cross-pond use
- Antibiogram on every confirmed isolate; never repeat the same antibiotic without sensitivity data
- Written outbreak response plan including vaccine programme, treatment protocol and notification contacts
Regional prevalence
See where Streptococcosis is being reported right now across India and Southeast Asia, with weekly trend lines and per-district drilldowns.
Open the heatmap →Frequently asked questions
What causes streptococcosis in tilapia?
Streptococcosis in tilapia is caused primarily by two Gram-positive bacteria: Streptococcus agalactiae (dominant in Asian farms) and Streptococcus iniae (dominant in the Americas and parts of Africa). Both produce the same clinical syndrome — spiral swimming, pop-eye and 30–80% mortality. PCR is needed to distinguish them, but treatment principles are similar: antibiotic on antibiogram, vaccination, lower density, and DO above 5 mg/L.
Why do my tilapia have pop-eye?
Unilateral pop-eye (exophthalmia) in tilapia is the classic field sign of streptococcosis. The bacteria invade the brain and eye, causing inflammation behind the eyeball. In a pond running above 27°C with spiral-swimming fish and dorsal darkening, streptococcosis is the working diagnosis until culture or PCR proves otherwise. Other causes (gas-bubble disease, severe nutritional deficiency) are far less common.
Can streptococcosis be prevented in tilapia?
Yes — vaccinated fingerlings combined with strict water-quality management reduces mortality by 60–85%. Commercial injectable and oral vaccines are available for both S. agalactiae and S. iniae in most major tilapia-producing countries. Pair vaccination with stocking density below 25 kg/m³ in cages (or below 4 kg/m² in ponds), DO above 5 mg/L, and minimised handling during the high-temperature window.
What antibiotic treats streptococcosis in tilapia?
Amoxicillin in feed at 40–80 mg/kg body weight/day for 10 days is the first-line treatment where the strain is sensitive. Florfenicol at 10 mg/kg/day for 10 days is the common second-line option. Always run an antibiogram on a confirmed isolate before treating — resistance to amoxicillin, erythromycin and tetracycline is rising across Asian tilapia farms. Observe statutory withdrawal periods (typically 21–42 days) before harvest.
Is tilapia with streptococcosis safe to eat?
S. iniae is zoonotic and can cause invasive infection in immunocompromised people who handle live fish with open skin wounds — properly cooked fish has not caused documented human cases. S. agalactiae strains infecting tilapia are different from human-pathogenic clones and have not been linked to foodborne disease. As a rule, never harvest fish under active antibiotic treatment or within the withdrawal period, and never sell visibly moribund fish.
How does water temperature affect streptococcosis outbreaks?
Streptococcosis is strongly temperature-driven. Outbreaks accelerate sharply above 27°C and peak at 30–32°C. Below 25°C, the same strain may circulate without clinical disease. Any sustained water-temperature reading above 28°C should trigger intensified surveillance — daily mortality counts, behaviour checks for spiral swimming, and immediate sampling at the first cluster.
Catch Streptococcosis before it costs a cycle
CAMARON's Disease Vision module flags Streptococcosis from a single farm photo, ties findings to the regional heatmap, and walks you through the protocol.