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What is happening in the Florida Keys?
FWC says abnormal spinning and small-scale fish mortalities were first reported in fall 2023. Critically endangered smalltooth sawfish were among the affected animals, making the event both a wildlife and conservation emergency.
FWC’s update page records more than 275 unique reports since December 2023. Reports were most frequent in winter and spring 2024, declined during summer 2024, and continued at lower levels in 2025. Those counts describe reports, not a confirmed total of individual fish affected.
The official position remains cautious: “The cause of the spinning fish behavior and sawfish deaths in the Florida Keys is still unclear,” the Florida Fish and Wildlife Conservation Commission says.
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What does spinning mean biologically?
Spinning is a visible neurological sign, not a diagnosis. FWC describes the Florida behavior as consistent with effects on the central nervous system. Damage or dysfunction in the brain, spinal cord, or the membranes around them can interfere with balance, orientation, and controlled swimming.
The same outward behavior can arise from very different mechanisms, including a neurotoxin, an infection, a structural lesion, or severe environmental stress. Observing circles or spirals therefore tells investigators where to look, but not which cause is responsible.
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Why are harmful algal blooms the leading hypothesis?
Investigators found several harmful-algal-bloom species capable of producing neurotoxins in water samples from the area. They also detected toxins in fish tissue. Neurotoxins could plausibly produce the disorientation and abnormal swimming that witnesses describe.
That evidence supports further investigation rather than a solved case. FWC states: “Presence does not prove cause, and more research is needed to determine if these algae and toxins are responsible.” A toxin may be present without being concentrated enough, biologically active enough, or timed correctly to explain the deaths. Multiple toxins or changing water conditions could also be involved.
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Is red tide killing the fish?
Red tide was investigated, but testing had not established it as the cause. An Associated Press report summarizing FWC information in March 2025 said tests for red tide, parasites, bacteria, viruses, and more than 250 chemicals had not produced a definitive explanation.
“Red tide” is therefore a possibility examined by scientists, not a confirmed answer for the Florida Keys event.
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What can documented fish diseases teach scientists?
Past disease cases explain why researchers are examining both pathogens and tissue damage, while also showing why comparisons cannot prove what happened in Florida.
Spinning disease in Atlantic menhaden
A U.S. Geological Survey study found that Atlantic menhaden with “spinning disease” carried high loads of Vibrio (Listonella) anguillarum O3, especially in the brain. The fish also had hemorrhagic meningitis and encephalitis—bleeding and inflammation affecting the protective membranes and tissue of the brain.
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Spiral swimming in salmonids
An older USGS account linked spiral swimming in salmonids to Cytophaga psychrophila infections. Cranial and vertebral lesions compressed tissue near the medulla, a region involved in essential nervous-system functions. The historical hatchery observations, from 1963 through 1987, involved 2% to 10% of affected underyearling salmonids.
These examples demonstrate that infection or a lesion can cause spinning in other fish. They do not show that either bacterium caused the Florida Keys deaths, and they do not replace direct pathology from the affected sawfish and other local species.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How do the main explanations compare?
| Explanation | Possible mechanism | Evidence in the Florida Keys event | Certainty |
|---|---|---|---|
| Harmful-algal-bloom neurotoxins | A toxin disrupts the central nervous system, causing disorientation and uncontrolled swimming. | Potentially neurotoxic algae were found in water, and toxins were detected in fish tissue. | Leading hypothesis, not proven causation. |
| Bacterial or viral infection | Infection or inflammation damages the brain, spinal cord, or surrounding membranes. | Known to cause spinning in other species; Florida testing had not established a definitive pathogen. | Possible, but unconfirmed in this event. |
| Structural lesions | Injury or compression interrupts neural pathways controlling balance and movement. | Documented as a mechanism in other fish diseases; a matching Florida lesion has not been established publicly. | Biologically plausible, evidence unresolved. |
| Oxygen, chemical, or other environmental stress | Severe water-quality stress impairs nervous-system function or causes secondary injury. | More than 250 chemicals were tested without a definitive cause reported by March 2025; conditions may change over time. | Not ruled into a single confirmed explanation. |
Why has the investigation not reached a conclusion?
The event may involve one toxin, several toxins, an infectious process, changing environmental conditions, or another neurological stressor. Detecting a substance in water or tissue establishes exposure, not that the substance reached a lethal dose or caused the observed behavior. Conversely, a short-lived contaminant or rapidly degraded toxin could be difficult to detect after a fish dies.
FWC describes the work as a collaborative, ongoing investigation. The state allocated $1.75 million to Bonefish & Tarpon Trust research during the 2024–2025 state fiscal year, reflecting the scale of the effort rather than a confirmed diagnosis.
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Yes. FWC’s update records reports continuing at lower levels during 2025 after the larger peak in 2024. Because reports and hypotheses can change, current status should be checked through FWC updates rather than inferred from an older post or a single video.
Quick Recap
What should people do if they see one?
- Report the sighting through the current Florida Fish and Wildlife Conservation Commission or NOAA reporting channel, including the date, location, species if known, and photographs or video.
- Do not capture, handle, transport, or attempt to treat a spinning fish. Smalltooth sawfish are critically endangered, and handling can add stress or injury.
- Do not assume a single dead or disoriented fish proves red tide, poisoning, or infection. A report helps investigators combine observations with water, tissue, and pathology results.
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