Flounder (Platichthys flesus) are the most commonly caught flatfish by UK shore anglers in estuaries, tidal rivers, and sheltered inshore waters. They are arguably the most accessible sea fish in the UK – found in enormous numbers in virtually every estuary in England, Scotland, Wales, and Ireland, catchable on simple tackle with basic bait, and available throughout the year with peak activity in autumn and winter.
Flounder are not celebrated for fighting ability or size. A typical flounder weighs well under 1lb and their flat, pancake body offers minimal resistance in the water. But their abundance, widespread distribution, and the fact that they enter fresh water (making them catchable far upstream from the sea in tidal rivers) make them a species that many UK anglers encounter before any other.
[Image placeholder: A flounder lying flat showing its dull brown upper surface with orange spots and rough, bumpy skin texture, held just above the water at an estuary]
Identification
Flounder identification from other common flatfish:
Flounder key features: – Brown to olive-green upper surface with scattered orange or reddish spots – the spots are not always present and vary between individuals – Rough, bumpy skin: The flounder’s skin has small prickly tubercles (bumps) along the lateral line and near the fin bases. Running your hand against the direction of the fin rays reveals the roughness. This is a reliable tactile identifier. – Small tubercles at the base of the dorsal and anal fins – Usually right-eyed: Both eyes are on the right side of the body (like plaice), but flounder can occasionally be left-eyed (unlike plaice which are almost always right-eyed) – Lateral line: Slightly curved over the pectoral fin (less curved than plaice) – Size: Minimum landing size 25cm in English waters – verify with MMO
Similar species: – Plaice: The most common confusion. Plaice have smooth skin and bright orange-red spots; the spots on a plaice are distinct and vivid. Plaice lack the rough prickly skin and tubercles that flounder have. Also, plaice are almost exclusively marine (offshore sand), while flounder are estuarine and tidal river fish. – Dab: Much smaller, rough skin on the upper surface but no tubercles at fin bases; highly curved lateral line over the pectoral. – Sole: Oval body, tiny eyes, very different body proportion; not confused by experienced anglers
Hybridisation: Flounder and plaice hybridise naturally in UK waters, producing intermediate fish that confuse species list claims. Flounder-plaice hybrids are recorded from many UK estuaries.
Distribution
Flounder are found in UK waters throughout the range: – Every estuary in England, Scotland, Wales, and Ireland – Tidal rivers, sometimes many miles upstream (flounder enter completely fresh water and have been recorded in the Thames and Severn well above the tidal limit) – Sheltered bays and harbours with soft muddy substrate – Sandy beaches with estuarine influence
They are not offshore fish. Deep, open sea fishing does not produce flounder. The further into the estuary and sheltered shallow water, the more likely you are to find flounder.
Behaviour and Habitat
Flounder are bottom-feeding predators that hunt worms, crustaceans, and small fish by lying on the bottom and ambushing prey. They are particularly associated with: – Muddy and sandy substrates in estuaries – Creek channels at low tide, moving onto flats as tide floods – Areas with fresh water run-off (they tolerate low salinity very well)
Tidal movement: Flounder feed on the tide. The flooding tide brings fresh water, food, and cover. Estuary anglers fish the flood and ebb through the creek channels as fish move with the water.
Winter: Flounder move to deeper estuary water and are less caught from the tidal flats. But they remain in the estuary through the coldest months and are often the only sea fish catchable from estuarine shore marks in January.
Fishing for Flounder
Shore fishing
Tackle: Light beachcasting or spinning tackle is adequate. A 10-12ft light beachcaster or a 9-10ft LRF (light rock fishing) rod with 10lb braid and a 15lb fluorocarbon leader. Leads of 1-3oz are usually sufficient in estuaries.
Rigs: A simple two-hook paternoster or a running leger. The hooks are small by sea fishing standards – size 2-6 is appropriate for flounder. Long hook traces (12-18 inches) allow the bait to move naturally on the bottom.
Roving and searching: The most effective flounder approach is to keep moving. Cast, wait two or three minutes, and if no bite occurs, retrieve and cast to a different spot. Flounder bite decisively when present but there is no value in waiting at a blank mark. Cover the estuary methodically.
Bait: – Ragworm (king rag or harbour rag): The primary flounder bait. Present on a fine-wired size 4-6 hook, full worm or tipped with a small section. – Harbour ragworm (maddies): Small red ragworm, exceptional flounder bait in estuary conditions. – Lugworm: Works but not as good as rag in most estuary conditions. – Peeler crab: A small piece of peeler crab presented on a small hook is very effective, particularly from April to June when crabs are available. – Mussel: Effective on some estuary marks, particularly where mussel beds are present. – Sandeel: Flounder will take a small sandeel on some marks.
Lure fishing for flounder
Flounder take small lures, particularly small soft plastic worm imitations, small shads, and gold or silver blade lures on some estuary marks. This is more of a Scandinavian approach that is gaining some traction in UK LRF (light rock fishing) circles. Small jig heads (2-5g) with worm-style soft plastics.
Minimum Landing Size and Retention
The minimum landing size for flounder in English waters is 25cm (total length). Most flounder caught from UK estuaries are below or close to this limit. Return undersized fish immediately. Many UK flounder anglers practise catch and release regardless of size.
Frequently Asked Questions
Do flounder live in fresh water?
Flounder can tolerate fresh water and are regularly recorded in completely freshwater sections of tidal rivers. They are euryhaline (can survive in a wide range of salinities). This is unusual for a flatfish and distinguishes flounder from most other UK flatfish species that are strictly marine.
What is the best time to fish for flounder?
Autumn and winter (September to February) produce the best flounder fishing from UK estuaries. Fish move inshore and into estuaries as sea temperatures drop. Summer flounder fishing is possible but numbers are typically lower.
What is the British record for flounder?
The British record flounder stands at 5lb 11oz (Andy Wolfe, Hayle Estuary, Cornwall, 1956). Verify current records with the British Record Fish Committee. A flounder over 2lb from any UK mark is a very good fish today.
Can you eat flounder?
Yes, flounder is edible and the flesh is white and delicate. However, they are typically small and produce limited flesh per fish. Many UK flounder anglers return all fish. Where retained, flounder should be above the minimum landing size and consumed fresh.
Why are flounder called flounders?
The name comes from an Old Norse or Scandinavian root (Scandinavia has long had a flounder-fishing tradition). The species is widespread across northern Europe from Portugal to the White Sea.