A TweedStart Resource
Key to the Freshwater Fish Species of the Tweed
Catchment
Look at the two pictures of fish above. Use the Family key pages 1, 2
and 3 to identify the family the fish belongs to. Then go to the page
shown for that family to identify the species of fish.
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Family Key
The Lamprey Family
Page 1
No eyes
Lampreys are thin “snake like” like fish.
They look like eels but have no eyes
and no fins immediately behind the head.
no fins behind the head
Go to page 4
Has eyes
The Eel Family
Eels are thin “snake like” like fish.
They look like Lampreys but can be told
apart as Eels have eyes and have fins
immediately behind their head.
fins behind the head
Go to page 5
The Carp Family
Dorsal fin
The dorsal (back) fin varies in size but is mostly towards the
rear of the fish. If barbels are present on the mouth there will
be less than five.
Go to page 6
The Loach Family
Small fish with several barbells around the mouth.
They generally are a “mottled” colour.
Go to page 7
Barbells
2
Page 2
Family Key
The Pike Family
Dorsal fin
Long slender fish with a large head and mouth.
The dorsal (back) fin is located towards the tail
end of the fish.
Go to page 7
The Salmon Family
Adipose fin
Small, fleshy adipose fin present, mouth in middle
of head.
Go to page 8
Dorsal fin
Adipose fin
The Grayling Family
Small, fleshy adipose fin present, mouth on underside
of head. Very large dorsal (back) fin.
Go to page 9
The Stickleback Family
Three spines
Small fish with three spines on its back.
Go to page 9
3
Family Key
Page 3
The Goby Family
Small fish with very large head and mouth. Pectoral fins (just
behind the head) large and rounded.
Go to page 9
The Perch Family
Large dorsal (back) fin with numerous spines.
Fins on underside of fish are often orange
coloured.
Go to page 10
The Flounder Family
Fish completely flattened with both eyes on the one side
of the head.
Go to page 10
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Species Key
Page 4
Lamprey Family: Petromyzontidae
There are three different species of Lamprey in the
River Tweed system; River, Brook and Sea Lampreys.
River and Brook Lampreys can’t be told apart without
the use of a microscope. However Sea Lampreys can
be distinguished from River & Brook Lampreys by
looking at the tail.
The fin around the end of the tail is
clear/yellowish = River or Brook Lamprey
The fin around the end of the tail has black
pigment spots = Sea Lamprey
Sea Lamprey
Petromyzon marinus
Native
River Lamprey or Brook Lamprey
Lampreta fluviatilis or Lampreta planeri
Both Native
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Page 5
Eel Family: Anguillidae
There is only one species of Eel
in the Tweed system – The
European Eel.
European Eel Anguilla anguilla
Native
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Page 6
Carp Family: Cyprinidae
Roach Rutilus rutilus
Introduced
Obvious, large scales visible. Fins on underside
of fish are orange.
Tench Tinca tinca
Introduced
Has a “greenish appearance”. No obvious, large scales.
Common Gudgeon Gobio gobio
Introduced
Has Barbells on its mouth, a small dorsal fin and has dark
“patches” on its side.
Common Carp Cyprinus carpio
Introduced
Has barbells on its mouth, a large dorsal fin and no
“patches” on its side.
Dace Leuciscus leuciscus
Introduced
Small fish with large, obvious scales. Fins on underside not orange.
Minnow Phoxinus phoxinus
Probably Introduced
No large obvious scales. Black “stripe” down side of fish.
Males can develop dark red colour around head at spawning time.
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Page 7
Loach Family: Balitoridae
There is only one species from the Loach
Family in the Tweed system – The Stone Loach.
Stone Loach Barbatula barbatula
Introduced
Pike Family: Esocidea
There is only one species from the Pike
Family in the Tweed system – The Pike.
Pike Esox lucius
Introduced
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Page 8
Salmon Family: Salmonidae
Atlantic Salmon Salmo salar
Gill Cover
Adipose fin
Native
Tail very forked.
Usually only one or two large spots on
the gill cover.
Fins usually not orange.
Brown/Sea Trout Salmo trutta
Native
Gill Cover
Tail only slightly forked if at all.
Usually lots of spots on gill cover.
Tail and adipose fins usually have some
orange colouring.
Adipose fin
Rainbow Trout Oncorhynchus mykiss
Introduced
Numerous small spots on tail. Pink stripe runs down
the side of the fish.
Arctic Charr Salvelinus alpinus
Native
Numerous spots all over the body but not on fins.
Males often have an orange belly and white tips to the
fins.
9
Page 9
Adult Grayling
Grayling Family: Thymallidae
There is only one species from the Grayling family in the
Tweed system – The European Grayling.
European Grayling
Thymallus thymallus
Introduced
Juvenile Grayling
Stickleback Family: Gasterosteidae
There is only one species from the Stickleback family in the
Tweed system – The Three Spined Stickleback.
Three-spined Stickleback
Gasterosteus aculeatus
Native
Goby Family: Cottidae
There is only one species from the Goby
family in the Tweed system – The Common
Bullhead
Common Bullhead
Cottus gobio
Introduced
10
Page 10
Perch Family: Percidae
There is only one species from the Perch family in the
Tweed system – The European Perch.
European Perch
Perca fluviatilis
Introduced
Flatfish Family: Pleuronectidae
There is only one species of Flatfish
found in the Tweed system – The
Common Flounder.
Flounder
Platichthys flesus
Native
SCN 2-01a
KS2 Science – classification – give reasons for classifying animals based on specific characteristics.
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