British Marine Life Study Society

Photograph by Luke Richards (IOW)

Photograph by Luke Richards (IOW)

Common Name(s):
Butterfish, Gunnel 
Rock Eel (USA) Rock Gunnel (USA)
Notes on names
Scientific Name:
Pholis gunnellus

Usual Size:  to 25 cm

Fishbase entry


Photograph by Andy Horton

Small eel-like fish. Distinguished by a row of ocellated (eye) spots (9 - 15) underneath the long dorsal fin that runs the length of its body. Orange-brown. Ocellated spots often not clearly visible in small specimens. 


Portrait (Link)
Similar species:  Common Eel  Anguilla,  and Eelpout  Zoarces viviparus.
Breeding:  Winter - spring. Eggs guarded by the male fish, intertidally (north) to 25 metres depth. 

Habitat: Benthic, shallow seas, intertidal except summer. 
Worms, small crustaceans like amphipods. 
Adults probably eat the Hermit Crab commensal ragworm Nereis fucata. (pic
It was really fascinating to watch the small South-clawed Hermit Crab, Diogenes pugilator, moulting inside its shell. Alas the predatory Butterfish, Pholis gunnellus, was much too quick and it had the soft-shelled hermit crab for dinner in a fraction of a second. The Boar Fish, Capros aper, paid little heed. 
Butterfish show an predatory interest in the activities of hermit crabs, including the Common Hermit Crab, Pagurus bernhardus,  with the ragworm Nereis fucata residing inside.
All British coasts. Common in the north and only occasionally found intertidally in the extreme south-west. Very common off some Scottish coasts. Atlantic coast of North America. 
Sussex: frequent in spring and autumn intertidally on rocky shores. Rarely in large pools (On Sussex shores, 1 in a 1000+ only).

Additional Notes:
Northern fish so unable to tolerate living on the shore during the summer, where it is common under stones in the spring and autumn. Often infected with the Black-spot disease Cryptocotyle lingua
Eaten by otters off Scottish coast. Mucus covered scale-less body is very slippery, hence its common name. Impossible to grab hold of by the inexperienced.

Butterfish, Pholis gunnellus, infected with the Black-spot parasite Cryptocotyle lingua.
Life style of the trigenetic parasite Cryptocotyle lingua.

Further Observations and Discussion (Marine Wildlife of the North-east Atlantic Ocean Group)

A very red Butterfish (photograph and discussion)

More photographs of Butterfish

Some books misidentify this fish as the Eelpout  Zoarces viviparus.

The scientific species name gunnellus probably came from the word "gunwhale" or "gunwale" pronounced gunnel. AH


October 1999.  Butterfish located in Loch Creran, Argyll, Scotland. (56° 31' N, 5° 23'W).
Prevalent.   Identified using various text and advice of a senior lecturer. Peter R Haylock, Heriot-Watt University. 
April 2000: under Selsey Lifeboat Station, West Sussex coast (Paul Parsons). Clay bedrock with loose rocks. 
Frequently discovered at Kingston Beach, Shoreham-by-Sea, spring and autumn. Rarely (1 in a 1000) in pools. 
30 September 2000:
Someone brought in a small Butterfish, Pholis gunnellus, found in a crab trap in the River Exe. Jenny Nunn, (Axmouth Sea Discovery Centre)
>Hi Andy........Pholis gunnellus are rare in Swansea and Gower.....the odd one found maybe in Pembrokeshire they are quite common in Spring and rarely found in summer,  but always under stones everywhere, often with young river Eels..........never in pools.  Jim Hall
February 2001
Neil Watkins discovered these fish on Auchmithie beach in Angus, Scotland.  They range in size from about 6 cm to approx 15 cm. 
I did research on this fish back in 1969, at the Marine Lab on Hayling Island. Fish were numerous in Langstone Harbour, Hants. I have also regularly found them on the stony beach at Lyme Regis, where I ran a field studies course for many years, still present in 1999. Also present just offshore at low tide from Charmouth to West Bay, Dorset. Determining factor certainly seems to be substrate. I rarely found them in conditions that tended towards anaerobic, ie, mud or muddy sand. Most commonly they were below MTL, and I have discovered them most months of the year, certainly in the summer months. Martin Torbett
I saw a Butterfish while diving under Trefor Pier  (Snowdon, Wales) Sunday 27th May 2001.  Gianfranco Unali
I spotted several Butterfish at St Abbs (shore dive heading for Cathedral rock), SE Scotland on the 21st Sept 2002. Simon Mardle.

October 2002
I had a sighting of  a Butterfish whilst scuba diving on a wreck in Scapa flow in the Orkney Islands in October 2002. 

March or April 2003
I thought I should write to report the capture of a butterfish in the Holes bay area of Poole harbour, Dorset. A friend ,while netting prawns along the quay wall, caught this very attractive small eel. After identifying it from a book, he brought it to me for my marine aquarium where it is now residing together with a wrasse and some blennies. During the search for more information on this species I came across your website.
Report by Nick Bainton.

6 August 2003
Me and my Dad found a butterfish in a rock pool in Gardenstown Beach in the Moray Firth, Scotland. At first we thought it was a baby moray eel when we studied it in the net we had caught it in, but later identified it as a Butterfish once we referred to your website.

For some time now (the past three years) I have been occasionally spotting this uncommon eel where I work. I usually find it inside of clusters of seaweed I have to pull out of the water. I have taken photos of it in order to show it around to try and have someone identify it for me. To no avail. Then, just by sheer accident, I saw it's picture on your website. It's a Rock Gunnel. Finally, mystery solved. Thank you.

Tom Lewis, Dockmaster / Club Steward, Ipswich Bay Yacht Club, Ipswich, Massachusetts, U.S.A.

Information wanted: Please send any records of this fish, with location, date, who discovered it, how it was identified, prevalence, common name and any other details to 
Shorewatch Project   EMail 
All messages will receive a reply. 

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False eye spots obscured in this pale specimen