A man watches fish and sharks swim at the Miami Seaquarium on Wednesday, in Miami, Florida. Founded in 1955, it is one of the oldest oceanariums in the US. Photo: AFP

 You never know what you'll get when you go fishing in Florida. You might accidentally catch an alligator, a snake - or, for one man, the oldest grouper on record.

Researchers estimate that the Warsaw grouper, caught in December, was 50 years old.

The fish is "the oldest sample collected for our ageing program," the Florida Fish and Wildlife Conservation Commission (FWC) Research Institute said Friday.

Biologists in the FWC Age and Growth Lab calculated the grouper's age by examining its otoliths, also known as "earstones," which are hard calcium structures located behind the brain in bony fish.

Otoliths allow scientists to estimate a fish's age.

The FWC accompanied the post with a photograph of Jason Boyll, an amateur fisherman from the southwestern Siesta Key who caught the 160- kilogram grouper.

In the photo, Boyll is standing next to his catch, which is taller than he is.

Boyll caught the grouper off the west coast of Florida on December 29, at a depth of 182 meters, according to the FWC.