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Abnormal Fish Behavior Event 2023-present

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About the Event

A man and two women are standing outside next to a large metal table that is holding a large dead sawfish.

The Florida Fish and Wildlife Conservation Commission (FWC) continues to document and investigate the cause of abnormal fish behavior (spinning) and small-scale fish mortalities in the Florida Keys that were first reported in fall of 2023. The critically endangered smalltooth sawfish are among the species that have been seen spinning, and while fish have not generally been dying in large numbers, sawfish mortalities have been documented at unprecedented levels.  

The cause of the spinning fish behavior and sawfish deaths in the Florida Keys is still unclear. FWC and its partners are investigating various potential causes, but the best evidence so far points to harmful algal blooms (HABs) and their toxins. In late 2024-2025, we have the added complexity of a red tide bloom that impacted the Lower Keys. The spinning behavior is consistent with effects on the central nervous system such as could be caused by exposure to neurotoxins produced by some HAB species. Several HAB species capable of producing neurotoxins were found in water samples and toxins have been detected in fish tissue samples. Presence does not prove cause, and more research is needed to determine if these algae and toxins are responsible. 

Reports of this abnormal behavior peaked in winter and spring of 2024 and then decreased during the summer of 2024. Although numbers in 2025 have been much lower overall, FWC continues to document cases submitted through the Fish Kill Hotline and the Sawfish Hotline.  

The FWC continues to work collaboratively with universities, environmental groups, and government agencies at all levels to investigate and respond to the spinning fish event.

FAQs

Over 80 species impacted (some unconfirmed) including

Angelfish, Atlantic Blue Tang, Atlantic Threadfin Herring, Ballyhoo, Barracuda, Bermuda Sea Chub, grunts (including Bluestriped, French, and White Grunts and Porkfish), Bonefish, box/trunk/cowfishes, puffer, catfish, Orange Filefish, flying fish, glass minnow, Goliath Grouper, Gray Triggerfish, jacks (including Bigeye Scad/Goggle-Eye, Blue Runner, Crevalle Jack, Yellow Jack, Leatherjacket, Lookdown, and Permit), lionfish, mojarras (including Silver Jenny and Yellowfin and Stripped Mojarra), needlefish, parrotfishes (including Stoplight and Rainbow Parrotfish), Pilchard/Scaled Sardine, Pinfish, pipefish, porgy, Rays and relatives (including Atlantic and Southern Stingray, Spotted Eagle Ray, skate, and Smalltooth Sawfish) Red Drum, remora, Sailfish, Sand Perch, Sargent Major, Sharks (including Blacktip, Bonnethead, Bull, Caribbean Sharpnose, Lemon, Nurse, and Tiger Shark), Sheepshead, silversides, snappers (including Cubera, Dog, Gray, Lane, Mutton, and Yellowtail Snapper) Snook, Spadefish, Spanish Mackerel, Tarpon, Toadfish, Tripple Tail, and White Mullet. 

 

Invertebrate Species: 

Infrequently, a small number of invertebrate species were also reported from the area to be swimming abnormally or dead, but evidence for them being affected directly by whatever is causing the problem with fish is minimal. Some described behaviors were within the normal range for given species (e.g., lobsters were reported walking in single file) and isolated low dissolved oxygen events may also have occurred (e.g., as suggested by crabs gathering in numbers in shallow water around the shoreline of an enclosed basin). Invertebrates reported dead or behaving abnormally include Blue Crab, Spiny Lobster, Horseshoe Crab, Spider Crab, and Stone Crab. However, generally invertebrates like shrimp, mysids, and crabs appeared to behave normally when encountered by FWC biologists at locations with actively spinning fish. 

All fisheries in the Florida Keys that are open, remain open. Please be sure to follow all rules and regulations when you head out on the water.

Harvesting distressed or dead animals is not advised under any circumstances. For more advice on consumption or to report a suspected fish-related illness, please contact your local county health department https://www.floridahealth.gov/index.html or call the Florida Poison Information Hotline 1-800-222-1222.

 

Swimming where there are dead fish is not recommended. Please report any fish kills to the Fish Kill Hotline, 800-636-0511 or MyFWC.com/ReportFishKill.