Flounder

Flounders are known for their unusual flat shape. They usually live in coastal waters but will swim up rivers for some distance.

A flat fish lies on a sandy floor with two bulging eyes on one side of the body.

Flounders are capable of partly changing colour to blend in with their surroundings.

Flounder facts

Scientific name	Platchthys flesus
Family	Bony fish
Diet	Worms, smaller mussels, amphipod crustaceans and gobies
Predators	Eels, pike and fish-eating birds
Size	30cm
Weight	1kg
Record weight	5lb 11oz 8dms
Lifespan	15 years

Flounder and our canals

A bottom living flatfish, flounders are mostly found in river estuaries and have even been recorded swimming through Diglis Fish Pass, near Worcester.

How to identify a flounder

The flounder’s flat shape is unique. Born as a round fish, the flounder flattens out as it matures and settles onto its side on the sea bed.

The side of the flounder without eyes is pale, often white with blotchy markings, while the top side is dark green or yellowish-brown, covered in distinctive hard nodules (known as tubercles).

Lifecycle of a flounder

The flounder has an unusual life cycle. The tiny young start off as a “normal” fish shape but flatten out as they develop, with both eyes ending up on the same side of their body – usually about 50 days after hatching.

Flounder do not spawn in freshwater but migrate between February and May to depths of 20-40m in the sea where spawning takes place. Males mature at three years; females at four years.

Where to find a flounder

Flounders are largely coastal fish and can be found in most estuaries of major rivers, like the River Severn and River Dee.

How to catch a flounder

Finer lines and small hooks will boost your chances of catching a flounder.

Carl Nicholls, fisheries & angling manager

Flounders are fairly common in the UK and easy to catch. The key is to use basic swim-feeder tactics, keeping small baits close to the bottom. These relatively small fish are fond of worms and maggots. To increase your chances of catching one, make sure to use finer lines and smaller hooks, as they’ll be better suited for targeting flounders.