Thornback Ray Copyright JDScuba

Sunfish Mola mola_Copyright NRW marine monitoring team

Bull huss on reef Copyright JDScuba


Marine fish can be categorised into:

  • Bony fish, which have an internal calcium skeleton (such as herring and plaice).
  • Cartilaginous fish, whose skeleton is primarily made of cartlidge and represent the oldest surviving jawed vertebrates. The sharks, skates and rays fall into this category and are collectively known as elasmobranchs.
  • Jawless fish (lampreys and hagfish). These distinctive, elongated fish do not have jaws, fins or stomachs and have a distinctive elongated shape and feed by suction with a round muscular mouth and rows of teeth.

The number of fish in Wales is difficult to estimate accurately – up to 500 species have been recorded from the UK and Ireland, with at least 250 found off the Welsh coasts. The majority of these are bony fish, with approximately 25 species of cartilaginous fish (skates, rays, sharks) and 3 jawless fish (lampreys and hagfish).

Marine fish occupy a wide variety of niches in Wales. Many inhabit nearshore areas and are familiar to us as inhabitants of rockpools, like the blennies, gobies and shannies. These contrast with species such as bluefin tuna Thunnus thynnus, which can grow to over 400 kg and are found seasonally off the south west coast of Wales. The 10m basking shark is a species which also undergo large migrations and are occasionally seen off the west coasts of Wales feeding on plankton between May and September.

Marine fish exhibit a huge variety of body diversity, from slender elongated pipe fish and eels to the distinctive flattened shape of the bony flatfish (e.g. plaice) and skates / rays. There is an equally vast array of life history behaviours and reproduction strategies within marine fish. Benthic fish, found on the seabed, can be relatively sedentary; the cling fish has a modified sucker allowing it to stick to the underside of rocks, the male will stay under a rock to guard their eggs. This contrasts with pelagic species such as herring and sandeel, which shoal in large numbers and spawn over huge areas of the seabed. Skates and rays are famously known for producing intricate ‘mermaids’ purses’, these are tough egg cases attached to the seabed where the embryos of the young develop. The empty cases can often be found washed up on beaches. The iconic long snouted seahorse Hippocampus guttulatus is rare in Wales. Males famously brood the eggs in their ventral pouch, and they have the ability to rapidly transform colour patterns to blend with their immediate surroundings.

Some fish species are migrants to Welsh waters, seen especially in south and West Wales, these include iconic species such as the Ocean Sunfish Mola mola, the heaviest bony fish in the world. They are usually encountered whilst drifting on the surface, with their dorsal fin visible flopping side to side.

Some Welsh fish are diadromous, spending part of their life cycle in freshwater environment and part in the marine environment. Fish that are hatched in freshwater, live most of their life in the marine environment and then migrate back to freshwater to spawn are known as anadromous. These include Atlantic salmon Salmo salar, river and sea lampreys Lampetra fluviatilis and Petromyzon marinus and allis and twaite shads (Alosa alosa and Alosa fallax). The European eel Anguilla Anguilla has a similar but reversed pattern, it hatches in the sea, and travels to rivers where it spends most of its adult life stages before it returns to the sea to breed. These diadromous species face threats to their movement up and downstream and a number of initiatives are ongoing to remove barriers and make passage easier. Both Atlantic salmon and European eel are under particular threat in Wales and have experienced huge declines in the last 30 years.

Tompot Blenny_Copyright Natural England Ross Bullimore

Nursehound eggcase_Copyright Natural England - Anglea Gall

Juvenile Angelshark on surface Copyright JDScuba

Conservation / protection of fish in Wales

Marine fish in Wales are protected under a number of pieces of legislation. Both bony and cartilaginous fish are listed on the Environment (Wales) Act Section 7 list.

Bony fish listed on the Section 7 list

Species name Species common name Welsh species name
Ammodytes marinus Sand-eel Llymrïen
Clupea harengus Herring Pennog
Gadus morhua Cod Penfras
Hippocampus guttulatus Long snouted seahorse Morfarch myngog
Lophius piscatorius Sea monkfish Cythraul y môr
Merlangius merlangus Whiting Gwyniad môr
Merluccius merluccius European hake Cegddu
Molva molva Ling Honos
Pleuronectes platessa Plaice Lleden goch
Scomber scombrus Mackerel Macrell
Solea solea Sole Lleden chwithig
Trachurus trachurus Horse mackerel Marchfacrell

Diadromous bony fish listed on the Section 7 list

Species name Species common name Welsh species name
Alosa alosa Allis shad Herlyn
Alosa fallax Twaite shad Gwangen
Anguilla anguilla European eel Llysywen
Lampetra fluviatilis River lamprey Llysywen bendoll yr afon
Petromyzon marinus Sea lamprey Llysywen bendoll y môr
Salmo salar Atlantic salmon Eog
Salmo trutta Brown / Sea trout Brithyll / Siwin

Cartilaginous fish listed on the Section 7 list

Species name Species common name Welsh species name
Cetorhinus maximus Basking shark Heulgi
Dipturus batis Common skate Morgath
Galeorhinus galeus Tope shark Ci glas
Lamna nasus Porbeagle shark Corgi môr
Prionace glauca Blue shark Morgi glas
Raja brachyura Blonde ray Morgath felen
Raja clavate Thornback ray Morgath styds
Raja undulata Undulate ray Morgath donnog
Rostroraja alba White or Bottlenosed skate Morgath wen
Squalus acanthias Spiny dogfish Ci pigog
Squatina squatina Angel shark Maelgi

Four species of marine fish found in Wales have additional protection under Schedule 5 of the Wildlife and Countryside Act 1981. These are the basking shark, angelshark, white skate and long snouted seahorse.

There are also five fish (with a marine component to their life history) included on Annex II of the EC Habitats & Species Directive that occur in Wales; sea lamprey, river lamprey, allis shad twaite shad and Atlantic salmon.

Other fish found in Welsh marine waters and on the OSPAR list of species but not listed above, include bluefin tuna, the diadromous species European sturgeon Acipenser sturi, the deep sea leafscale gulper shark Centrophorus squamosus and gulper shark Centrophorus granulosus.

Action for marine fish in Wales

Sharks, Skates and Rays (elasmobranchs)

Relatively little is known about sharks, skates and rays as a group, however, they have a significant cultural and conservation importance in Wales. Project SIARC (Sharks Inspiring Action and Research with Communities) is specifically delivering a fisher-integrated research programme to gather data on elasmobranchs and their associated habitats in two Special Areas of Conservation in Wales. Project SIARC is a multidisciplinary project, focussing on elasmobranchs of conservation importance, including the Critically Endangered (IUCN red list) Angelshark Squatina squatina. Combining both social and biological sciences the project aims to address critical data gaps in the ecology of elasmobranchs, diversify opportunities for marine conservation, generate a greater appreciation for the underwater environment and inspire the next generation. The project is led by the Zoological Society of London (ZSL) and Natural Resources Wales (NRW) and is being completed in partnership with six delivery partners and 13 collaborative partners.

Migratory fish

A number of projects in Wales are the focus of removing barriers to fish migration, allowing easier passage from marine environments into the upper reaches of Welsh rivers for spawning. The LIFE Dee River project is a £6.8m project focussed on the Dee in east Wales, which is focussed heavily on improving the numbers of salmon and lamprey, which includes removing constraints to fish migration and installing fish passage solutions.

Another LIFE project called ‘Four Rivers for LIFE’ is underway on four rivers designated as Special Areas of Conservation in south Wales (Teifi, Cleddau, Tywi and Usk) which likewise aims to restore protected diadromous fish species throughout their riverine habitat.

Afonydd Cymru also have projects ongoing to remove barriers to migration, especially for salmon.

Species in Wales

Amphibians & Reptiles



Terrestrial Mammals



Helping Wildlife

Wildlife Gardening