The seas surrounding the British Isles provide a home for a large number of different fish.
Although not so varied as tropical seas, at least 50 different species of fish can be discovered in pools at low tide. Many of these fish will be young of larger fish or others that get trapped by the ebbing tide.
This article will explore the fish that are often found in pools and under rocks on the shore.
Photograph by Luke Richards (IOW)
This little green fish is found on rocky shores the length of the British coastline. It is a very common fish that hides under rocks and in crannies when the tide is out. It is called by other names as well, and is well known as the Shanny and the Sea-frog. The latter name may be because of its habit of basking on weeds out of the water and jumping back into the pool with a plop when it is disturbed. The Blenny has slime-covered skin. It also has sharp comb-like teeth which it uses to crunch barnacles off rocks and to attack dead crabs and pieces of carrion that it cannot swallow whole. The adults are up to 16 cm long and they come inshore to breed during early spring, where the adult male can be found guarding eggs in the large pools. However, it is the young fish that are much more common under rocks and even in holes in the rocks. Blennies swim with an undulating snake-like motion. They can be distinguished from the gobies by a continuous dorsal (top) fin that runs the length of the body.
There are two other blennies
that can be found between the tides. The larger and fiercer Tompot Blenny
gattorugine is brownish-orange and has two distinct tentacles on
its head. The Montagu's Blenny,
galerita, is similar, but is covered in pale blue dots, and has
a flap of skin on its head. Montagu's Blenny is only found in the south-west
The gobies are the other
family of fishes that are common on the shore. There are several species,
but the Rock Goby is the one that is often discovered under rocks when
the tide goes out. The adults grow to 12 cm long and are almost black in
colour. However, if they are living on sand they may be much lighter. Young
fish are much more common than adults on the shore and may only be 45 mm
in length. All the gobies have two dorsal fins and a pelvic (underneath)
fin that is fused into a weak suction cup. They have small scales. The
Goby, Gobius niger, looks very much like a Rock Goby. The Rock
Goby is not found on the east coast. Rock Gobies eat tiny shrimps and worms
and rarely tackle anything they cannot swallow in one go.
Drop a pebble into a shallow sandy pool and lots of very small fish will dart rapidly in all directions before coming to rest. They are difficult to see because they are coloured to blend in with the sandy bottoms on which they rest. The Common Goby will be found on rocky shores where there are sandy pools. It is a small fish that only attains a length of 64 mm. Like all gobies it has two dorsal fins. It feeds on small crustaceans.
The Common Goby only lives
for one year and the male guards the eggs that will be deposited on the
underside of a rock or seashell. This fish also lives in estuaries. There
is an almost identical, but larger, fish called the Sand Goby, Pomatoschistus
minutus, which is found in pools nearer the low tide mark. It comes
inshore to breed in the late summer.
Even longer and thinner,
the Butterfish or Gunnel looks like a snake and swims, or rather wriggles
along the bottom, in an undulating snake-like fashion. During spring and
autumn small specimens of this orange-brown fish can be discovered in small
water-filled hollows under rocks when the tide recedes. It can be easily
recognised by about 13 large spots spaced out along the top of its body.
These are false-eye spots, and may fool hungry fish into thinking it is
a much bigger fish and not a tasty worm. The Butterfish gets its name because
it is so slippery. It is almost impossible to pick up in your hand and
it is best to use a net. Butterfish reach a length of 25 cm, but shore
specimens are usually smaller and feed on small crustaceans. The adults
eat worms. The male fish guards the eggs that are laid in shallow water.
The bronze coloured Rockling
is unusual in several ways. The first dorsal fin consists of a single small
ray, followed by a fringe of tiny rays in a slot. These rays vibrate and
may help the Rockling to find its food. This rockling has five barbels
on its head that it uses to find worms buried in the sand. The 5-Bearded
Rockling grows to 25 cm long, although fish found on the shore are usually
smaller. It can be discovered both in pools and under rocks. Eggs and sperm
are released into the sea where fertilisation takes place. The larvae are
silver and live with the surface plankton. They are known as 'Mackerel-midges'.
In mid- summer they move inshore and change colour from silver to brown.
Several other species occur, of which the Shore Rockling, Gaidropsarus
mediterraneus, has only three barbels.
Seen from above, this fish
looks like a rock, while it waits in ambush for a prawn or small fish to
swallow in its expandible mouth. In the larger pools, this fish can be
a very common predator. It is known by lots of different names like Rockfish,
Clobberhead and Sea Scorpion in different places. It can be many different
colours to match the background where it lives. However, the most usual
is a patchwork brown and cream. Adults grow to 18 cm long. Fish of this
size will only be found in the large pools. Smaller and younger fish are
common during the summer months in the company of the prawns on which they
feed. Like most of the shore fish, the Bullhead lacks the buoyancy organ
called the swim bladder. It is heavier than water, so when it stops swimming
it must rest on the bottom.
With their trumpet-like snouts,
all pipefish suck in their food of fish larvae and small crustaceans. The
Great Pipefish can be recognised quite easily by its brown and white banded
body. During the late summer they follow the tide in. The Worm Pipefish,
lumbriciformis, can be mistaken for a thin strip of brown weed wedged
under a rock. It needs a practised eye to spot it, but in the south-west
it is a common fish at low tide. However, it likes warm water and is absent
from the north and the east coasts of Britain. Like the sea-horses, which
belong to the same family, it is the male pipefish that looks after the
young in a special pouch along his belly. In the shallow seas where the
bottom is sandy, the Lesser Pipefish, Syngnathus rostellatus, is
The wrasse are a large family
of colourful fishes. Five species breed around Britain. Of these it is
the Corkwing that lives in the shallow water offshore where it breeds,
building a nest amongst weeds. Most rock pool fish are squat or elongate,
and adapted for a life in amongst the rocks, but wrasse are ordinary-looking
fish and are covered in scales. The colour is greenish-brown with black
horizontal lines and a black spot just in front of the tail fin. However,
when resting, or caught in a net, the lines and spot are obscured by black
vertical bars. In late summer the young are very common in the lower shore
pools feeding on tiny crustaceans. The adults are aggressive with sharp
teeth to attack hard-shelled crabs and prawns. Corkwing Wrasse can grow
to 25 cm in length. The Corkwing is found all around the coast of Britain
apart from parts of the east coast. It could be mistaken for the much rarer
Rock Cook, Centrolabrus exoletus, or confused with very young Ballan
Wrasse, Labrus bergylta, which are about one in every hundred of
the young wrasse caught inshore.
Photograph by Luke Richards (Isle of Wight)
This small goby is unusual
as it does not rest on the bottom but hangs motionless in mid- water on
the fringes of the weeds. Small shoals can be found in intertidal pools,
and if there are no large fish present they can be seen in the clear water.
It is the most attractive of the common gobies of the shore. In some areas
it is an orange colour. It is only 6 cm in length when fully grown. There
is a clear black spot just in front of the caudal fin; the second spot
on the side is less clear.
Photograph by Luke Richards (IOW)
As thin and as long as a
pencil, the Sea Stickleback is very fierce and may attack fish larger than
itself. It reaches 15 cm long and has a pointed snout with sharp teeth.
There are 15 spines in front of the single dorsal fin. The Sea Stickleback
is brown on the upper side, silvery underneath, and has a prodigious appetite
for small crustaceans and fish larvae. It can become trapped in the larger
pools at low tide. The male builds a nest of weed in summer.
Whilst searching for sea anemones at the very low tide I saw for the second day running in the same location a male Lumpsucker, Cyclopterus lumpus, part out of water on its side with its mouth just submerged in the water. With the incoming tide it just righted itself but remained swimming in the same vacinity.I believe it must have been protecting its eggs. Length 24 cm. Shallow pool created between the spokes of an old cartwheel. Location of fish: Creeksea on the River Crouch approx. 6 miles inland.
Photos in album River Crouch Fish.
The larvae of almost any fish can get trapped in pools as the tide goes out. Adult fish that live in the shallow water often venture into the lower pools, and adult specimens of the sandy coloured Dragonet, Callionymus lyra, the orange Montagu's Sea Snail, Liparis montagui, and the Cornish Sucker, Lepadogaster lepadogaster are all part of the shore fauna. On the east coast the Eelpout, Zoarces viviparus hides under rocks at low tide. It gives birth to live young instead of laying eggs. A small flatfish called the Topknot, Zeugopterus punctatus, clings to the underside of rocks in pools in the south-west.
Field Key to the Shore Fishes of the British Isles by Alwyne Wheeler. (Field Studies journal Vol. 8 No. 3 p 481-521).
Key to the Fishes of Northern Europe by Alwyne Wheeler [Warne 1978] ISBN 0-7232 2064 6 Limp edition.
ESSENTIAL PURCHASE *****
Collins Pocket Guide to the Fish of Britain & Europe Link
BRITISH FISHES by Frances Dipper
This book is favoured by Divers as it arranges the fish in habitats where they are found.
Underwater World Publications 1987
ISBN 0 946020 113 2
Rock Pool Database
Use these links if your are familiar with the scientific classifications of marine life