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Spiny dogfish: the small shark with two venomous spines that hunts in schools from Norway to the Black Sea

It is small for a shark, rarely comes alone and defends itself with two venomous spines: the spiny dogfish or spurdog, *Squalus acanthias* — German Dornhai, Spanish mielga or galludo, Italian spinarolo, French aiguillat commun, Portuguese galhudo or galhudo-malhado, Dutch doornhaai, Danish pighaj, Swedish pigghaj, Norwegian pigghå, Finnish piikkihai, Russian катран or обыкновенная колючая акула, Turkish mahmuzlu camgöz, Greek ακανθίας or κεντρόνι, Croatian kostelj, Albanian peshkaqen gjëmbor (GBIF) and Japanese アブラツノザメ (Wikidata). For Slovenian and Arabic we found no confirmed species name in GBIF or Wikidata. Here is how you recognise it, where it lives, what it eats, how it reproduces, how you handle it at the boat — and why it is now considered vulnerable.

A shark whose name means its spines

Carl Linnaeus described it in 1758 in the tenth edition of his *Systema Naturae*. It belongs to the family of dogfish sharks (Squalidae) in the order Squaliformes; according to the English Wikipedia, the species name *acanthias* refers to its spines. For a long time it was considered to occur worldwide — but according to FishBase, since a paper by Ebert and colleagues in 2010 the animals of the North Pacific belong to a separate species, the Pacific spiny dogfish *Squalus suckleyi*. The German Wikipedia considers it possibly the most abundant shark species of all.

How to recognise it

  • Body: slender and elongated, with a pointed snout; back and flanks, according to the German Wikipedia, dark grey to brown with white spots, the belly pale.
  • Spines: one spine in front of each of the two dorsal fins; according to the German Wikipedia, a groove runs from each spine to a venom gland. There is no anal fin — as in all dogfish sharks. That is how you tell it from the catshark, the smooth-hound and the tope, which all carry an anal fin.
  • Size: according to FishBase usually around 100 cm; females grow larger than males. How big and how heavy it gets at most is disputed — see the contradictions below.
  • Maturity: males according to FishBase at 60 to 70 cm, females at 75 to 90 cm; the English Wikipedia gives an age of around 10 years for males and 16 years for females.
  • Age: FishBase gives a maximum age of 75 years; most animals would reach 20 to 24 years. Here too the sources contradict each other — see below.

What it eats — and how it hunts

According to FishBase, the spiny dogfish eats comb jellies, squid, mackerel, herring, bottom fish, shrimp, crabs and sea cucumbers; the English Wikipedia lists squid, fish, crabs, jellyfish, sea cucumbers and shrimp. FishBase gives it a trophic level of 4.4 — it stands far up the food chain. What is special is the way it hunts: according to the English Wikipedia it travels in schools that can run into the thousands; the German Wikipedia speaks of enormous schools in which it used to occur. Whoever has a spiny dogfish on the hook therefore often soon has the next one.

Where it lives: from Norway to the Black Sea

According to FishBase, the spiny dogfish lives around the globe in cold and temperate seas, at water temperatures of 7 to 15 °C, over the shelf and the upper continental slope; it often enters enclosed bays and estuaries and tolerates brackish water, but fresh water, according to FishBase, only for a few hours. The English Wikipedia names, among others, the north-east Atlantic, the Oslofjord, the Adriatic and the northern Aegean, the US east coast and New Zealand. In the Black Sea Wikidata lists it as a separate subspecies, *Squalus acanthias ponticus* — there and in Turkey it is called katran. How deep it usually stands is described differently by the sources — see the contradictions. According to FishBase it migrates over long distances at sea.

Reproduction: the longest gestation of any cartilaginous fish

The spiny dogfish lays no eggs: according to the German Wikipedia, the young hatch from egg capsules inside the mother and are born alive. Mating, according to FishBase and the English Wikipedia, takes place in winter, in open water. The gestation period, according to FishBase, is 18 to 24 months — the longest of any cartilaginous fish; the German Wikipedia gives 18 to 22 months. At birth the young are 18 to 30 cm long according to FishBase, 20 to 30 cm according to the German Wikipedia; the sex ratio, according to FishBase, is one to one. How many young a female has is disputed — see below. According to FishBase, the species has very low resilience: a population needs more than 14 years to double. That is why this shark recovers so poorly from overfishing.

The spines — and how you handle it at the boat

The spines are a weapon. When the spiny dogfish is grabbed, according to the English Wikipedia it arches its back and stabs at the attacker; in doing so the spines release a mild venom, and FishBase lists the species as venomous. For you at the boat that means: never hold the fish up by the tail, never press it against your body, wear gloves and grip it firmly with both hands behind the head and in front of the tail, so that the two spines point away from you. Remove the hook with pliers, not with your fingers. A sting is painful but not life-threatening; if you get stung, clean the wound and see a doctor if it swells or reddens.

Rock salmon, huss, Schillerlocke: the hidden shark on the plate

Hardly any shark has been fished so heavily. In Germany, according to the German Wikipedia, the back pieces were sold as “Seeaal” (sea eel) and the smoked belly flaps as “Schillerlocken”; other trade names were “Kalbsfisch”, “Speckfisch”, “Karbonadenfisch”, “Königsaal”, “Seestör” and “Steinlachs”. In Britain, according to the English Wikipedia, it ends up as “huss” in fish-and-chip shops — the earlier name “rock salmon” is now banned there —, in France it is called “saumonette”, in Belgium “zeepaling”, in Greece it is sold as “galéos”, as a substitute for the heavily threatened tope. According to the English Wikipedia it is caught mainly with bottom trawls and gillnets; world catches fell, according to FAO data, from 31,700 tonnes in 2000 to 13,800 tonnes in 2008. Fins and tails go into cheap shark-fin soup, the rest into fertiliser, liver oil and animal feed. And a warning from the German Wikipedia: the muscle flesh is often heavily contaminated with methylmercury — according to a study by the University of Kiel, a portion of 150 g of Schillerlocken exceeds the tolerable daily dose for an adult tenfold.

Status, bans — and what you can do

On the IUCN Red List, the spiny dogfish is listed globally as vulnerable (Vulnerable). In the north-east Atlantic, according to the English Wikipedia, the IUCN classifies it regionally as critically endangered; European stocks have declined by at least 95 %, and the German Wikipedia gives the same 95 % for the North Atlantic. According to the English Wikipedia, the EU has had a catch quota since 1999, until 2007 only for two North Sea areas; in 2009 a maximum landing size of 1 m came in, in 2011 the quota was set to zero, ending targeted fishing in EU waters; in 2023 the stocks in EU and British waters were again considered recovered enough for commercial fishing. Norway, according to documents of the Directorate of Fisheries (Fiskeridirektoratet), banned targeted fishing in 2007, at first with an exception for small coastal vessels, from 2011 for all; in 2022 it was reopened for vessels under 15 m. On the Norwegian Red List it is listed as vulnerable (sårbar). Since 2010 it has also been in Annex I of the Memorandum of Understanding on the Conservation of Migratory Sharks under the Bonn Convention.

For you at the water that means: in Norway and in the North Sea the spiny dogfish is a frequent bycatch when deep-water fishing for cod, ling or tusk, in the Mediterranean and the Black Sea when bottom fishing. Whether you may keep it as an angler is governed by national rules that change from year to year — for recreational anglers we found no clear, generally valid rule. Ask the local fisheries office or your guide before the trip; if in doubt, release it gently: the species reproduces slowly and is vulnerable.

Five contradictions in the sources

  • How big and how heavy does it get? FishBase: at most 200 cm total length and 9.1 kg. German Wikipedia: about one metre long, up to 10 kg, rarely more. English Wikipedia: females reach about 80 to 84 cm, males 60 to 65 cm — it gives no maximum.
  • How old does it get? FishBase: maximum age 75 years, most 20 to 24 years, in the North Atlantic 35 to 50 years. English Wikipedia: individual animals almost 70 years, on average 30 to 40, by vertebrae and spines 35 to 54 years. German Wikipedia: over 20 years.
  • How many young? FishBase: 1 to 21 young per litter. English Wikipedia: 2 to 12 eggs, usually 5 to 6 young. German Wikipedia: 2 to 11 young, up to 6 eggs per egg capsule.
  • How deep does it live? FishBase: from the surface down to 1,978 m, usually 50 to 300 m, adults mostly 10 to 200 m. English Wikipedia: usually 50 to 149 m, recorded below 700 m. German Wikipedia: 50 to 200 m.
  • When is the IUCN assessment from? FishBase: assessment of 21 November 2019 (version 2025-2). English Wikipedia: 2020, Finucci and colleagues. German Wikipedia: 2017, Fordham and colleagues 2016.

Three traps in the name

  • “Seeaal” is no eel, “Steinlachs” no salmon. Seeaal, Schillerlocke, Königsaal, rock salmon, saumonette, zeepaling, Danish kongeål, Swedish Nordsjöål — almost all trade names of this fish conceal that a shark is lying on the plate. Whoever searches for a species by its market name will not find the animal.
  • “Hundshai” is usually a different shark. The Catalogue of Life also lists “Hundshai” (dog shark) as a German name for the spiny dogfish. In German, however, that name usually means *Galeorhinus galeus* — the tope, a considerably larger shark with an anal fin, to which we have devoted its own article. And the Greek “galéos” at the fishmonger’s can mean either.
  • Pacific figures belong to another species. Since 2010, according to FishBase, the spiny dogfish of the North Pacific count as a separate species, *Squalus suckleyi*. Older figures on size, age or migrations of “the spiny dogfish” from Alaska or Japan therefore often do not describe the animal you catch in the North Sea or the Mediterranean.

That leaves the question every article in this series starts with: when. Habitat, prey and habits are above, and they are fixed. What changes every day is everything else — light, air pressure, wind, water temperature, current — and whether a day over the drop-off is worth it is decided right there. That is what StrikeAhead calculates: it takes the conditions on your water and tells you when the trip is worth it. And because you don’t know unfamiliar water, its edges and its rules from day one, StrikeAhead Pathfinder tells you who to head out with: curated guides and skippers, personally vetted before listing — licence and insurance —, with verified catches instead of advertising photos, no paid ranking and no booking fee for you as an angler. The app tells you when, Pathfinder tells you with whom.