H
Species Profile

Haddock

Melanogrammus aeglefinus

Thumbprint of the North Atlantic
NORTHERN IMAGERY/Shutterstock.com

Haddock Distribution

Click a location to explore more animals from that region

This map shows coastal regions where Haddock are found.

Loading map...
A pile of haddock

At a Glance

Wild Species
Also Known As Haddie, Finnan haddie, Scotch haddie, Aiglefin, Eglefino
Diet Carnivore
Activity Cathemeral
Lifespan 8 years
Weight 17 lbs
Status Least Concern
Did You Know?

Key ID: a dark blotch ("thumbprint") just behind the pectoral fin plus a dark lateral line-classic for haddock (FAO; FishBase).

Scientific Classification

The haddock (Melanogrammus aeglefinus) is a commercially important cod-family marine fish of the North Atlantic, recognized by its dark lateral line and a distinctive dark blotch (“thumbprint”) behind the pectoral fin.

Kingdom
Animalia
Phylum
Chordata
Class
Actinopterygii
Order
Gadiformes
Family
Gadidae
Genus
Melanogrammus
Species
Melanogrammus aeglefinus

Distinguishing Features

  • Dark (often black) lateral line contrasting with a pale body
  • Prominent dark blotch above/behind the pectoral fin (“thumbprint” mark)
  • Cod-family body plan with chin barbel (typically small) and three dorsal fins

Physical Measurements

Length
1 ft 12 in (8 in – 3 ft 8 in)
Weight
7 lbs (0 lbs – 37 lbs)

Appearance

Primary Colors
Secondary Colors
Skin Type Thin, mucus-coated skin with small cycloid scales (appearing relatively smooth). Typical gadid body plan with three dorsal fins and two anal fins; no heavy armor or scutes.
Distinctive Features
  • Species: Haddock (Melanogrammus aeglefinus), a North Atlantic gadid (Family Gadidae) associated with demersal shelf and upper-slope habitats.
  • Diagnostic ID marks: dark/black lateral line + distinct dark 'thumbprint' spot behind the pectoral fin (highly characteristic for this species).
  • Body form: laterally compressed/oval-bodied codfish shape; three separate dorsal fins and two anal fins (Gadidae trait).
  • Chin barbel present but small and less pronounced than in Atlantic cod (useful for separating similar gadids in-hand).
  • Typical size: commonly ~50-75 cm total length in many fisheries; maximum reported ~112 cm TL (FishBase/FAO).
  • Maximum reported weight ~16.8 kg (FishBase).
  • Longevity: up to ~20 years reported (FishBase/FAO compilations).
  • Habitat/behavior (appearance-relevant): demersal schooling fish on North Atlantic continental shelf/upper slope; commonly on sand, gravel, or mixed substrates; reported depth range broadly from shallow shelf waters to several hundred meters (FishBase commonly lists ~10-450 m).
  • Relationship to cods: a true cod-family fish (Gadidae) and often co-occurs with Atlantic cod, but reliably separated by the black lateral line + 'thumbprint' blotch combination.

Did You Know?

Key ID: a dark blotch ("thumbprint") just behind the pectoral fin plus a dark lateral line-classic for haddock (FAO; FishBase).

Reported maximum size is 112 cm total length and ~16.8 kg; most adults are much smaller (FishBase).

Longevity is reported up to 14 years (FishBase).

Demersal by habit: typically lives near the seabed on continental shelves and upper slopes, recorded from ~10 to 450 m depth (FishBase).

Spawning produces buoyant, pelagic eggs that drift with currents-helping larvae disperse widely across shelf seas (FAO).

A cod-family fish (Gadidae): like cod, haddock has three dorsal fins and two anal fins-built for efficient cruising near the bottom.

Smoked haddock traditions (e.g., Scotland's "Finnan haddie") helped make this species a culinary icon in the North Atlantic world.

Unique Adaptations

  • Demersal sensory toolkit: a well-developed lateral line system helps detect vibrations and movement along the seabed-useful for finding prey and staying cohesive in groups (general gadid physiology; FishBase notes on sensory/lateral line prominence).
  • Color pattern for recognition/camouflage: the dark lateral line and "thumbprint" spot create a high-contrast field mark that aids species recognition and may disrupt the body outline over mottled bottoms (field-ID literature; FAO identification keys).
  • Gadid fin layout: three dorsal fins and two anal fins provide fine control and stability for near-bottom swimming and maneuvering over uneven substrate (FAO identification keys).
  • Buoyant eggs: pelagic eggs increase dispersal potential, allowing populations to reseed broad shelf regions when currents are favorable (FAO life-history description).

Interesting Behaviors

  • Seasonal movements: adults commonly migrate between feeding grounds and spawning areas, forming dense spawning aggregations that can be targeted by fisheries (ICES/FAO general gadid spawning behavior; haddock stock assessments).
  • Broadcast spawning with pelagic eggs: males and females release gametes into the water column; fertilized eggs float and drift, then larvae develop as plankton before settling to demersal life (FAO species accounts).
  • Schooling/loose aggregations: haddock often occur in groups over suitable bottom (sand/gravel/mud), especially where benthic prey is abundant (FAO; FishBase habitat notes).
  • Benthic foraging: feeds largely on bottom-dwelling invertebrates (e.g., polychaete worms, crustaceans, mollusks) and small fishes, using smell/taste and the lateral line to locate prey in low light or turbid water (FAO; FishBase diet summaries).
  • Ontogenetic habitat shift: juveniles tend to use shallower nursery areas; older fish occupy deeper shelf and slope habitats within the species' depth range (FAO; regional survey observations summarized in stock reports).

Cultural Significance

Haddock (Melanogrammus aeglefinus) is a key North Atlantic fish important to fisheries and food traditions. In the UK and Ireland it’s a classic fish-and-chips fish; Scotland’s smoked Finnan haddie is used in Cullen skink. It supports coastal markets in northern Europe and Atlantic Canada/New England.

Myths & Legends

St. Peter's thumbprint tale: In northern European Christian folklore, people say the haddock (Melanogrammus aeglefinus) has a dark spot from the Apostle Peter's thumb when he pulled a coin from the fish.

The Finnan haddie origin story says Scottish coastal villagers, often fishwives, smoked haddock (Melanogrammus aeglefinus) over peat and wood fires, making a preserved fish tied to local life and legend.

In some North Atlantic fishing communities, the haddock (Melanogrammus aeglefinus) thumbprint spot is seen as a lucky mark, a small sea superstition sailors link to this well known fish.

Conservation Status

LC Least Concern

Widespread and abundant in the wild.

Population Unknown

Protected Under

  • European Union Common Fisheries Policy (Regulation (EU) No 1380/2013) with TAC/quota management for haddock in relevant ICES areas
  • Magnuson-Stevens Fishery Conservation and Management Act (United States) via NOAA fishery management plans affecting NW Atlantic haddock stocks
  • Canada Fisheries Act and DFO Integrated Fisheries Management Plans applicable to haddock where harvested
  • NEAFC Convention (management framework for portions of the NE Atlantic)
  • NAFO Convention (management framework for portions of the Northwest Atlantic)

Life Cycle

Birth 500000 frys
Lifespan 8 years

Lifespan

In the Wild
0–20 years
In Captivity
0–15 years

Reproduction

Mating System Promiscuity
Social Structure Aggregation Group
Breeding Pattern Transient
Fertilization Broadcast Spawning
Birth Type Broadcast_spawning

Behavior & Ecology

Social School Group: 500
Activity Cathemeral
Diet Carnivore Benthic invertebrates-especially polychaete worms and small crustaceans (dominant prey categories in many North Atlantic stomach-content studies; summarized in FishBase and ICES diet syntheses).
Seasonal Migratory 186 mi

Temperament

Gregarious (strong tendency to aggregate), with schooling/aggregation intensity increasing in juveniles and during migrations and spawning.
Generally non-territorial and non-aggressive; individuals prioritize spacing and alignment within groups rather than direct conflict.
Risk-averse/cautious in the water column: group cohesion tends to increase under perceived predation risk; more dispersed spacing often occurs during benthic foraging when prey is patchy.
Haddock (Melanogrammus aeglefinus) in the North Atlantic switch between demersal, habitat-linked shoals and tighter schools for moving and feeding; group size changes by stock, season, and life stage (juveniles denser; spawning aggregations largest).

Communication

Low-frequency swim-bladder-assisted knocks/grunts/click-like pulses reported in haddock Gadidae), including sound production associated with social/spawning contexts in classic gadid bioacoustics studies (e.g., Hawkins & Rasmussen, 1978; subsequent gadid sound-production literature
Mechanosensory coordination via the lateral line for schooling alignment and spacing Near-neighbor motion and pressure-wave detection
Visual cues for polarization/alignment within schools Notably under higher light levels
Chemical cues likely involved in group cohesion and reproductive synchronization General teleost mechanism; specific haddock pheromonal identification is limited compared with some other fishes
Spawning-ground aggregation mediated by environmental cueing (temperature, depth, bottom type) and conspecific attraction, producing large seasonal concentrations reported by fisheries oceanography/ICES stock descriptions.

Habitat

Seabed/Benthic Coastal Open Ocean
Biomes:
Terrain:
Coastal Sandy Muddy Rocky
Elevation: 32 ft 10 in – 1476 ft 5 in

Ecological Role

Demersal mesopredator linking benthic production to higher trophic levels on North Atlantic shelves.

Regulates benthic invertebrate communities (polychaetes/crustaceans/bivalves) through predation Transfers energy from benthos to pelagic predators (e.g., larger gadoids, halibut, seals) that consume haddock Supports commercial fisheries and associated food webs by converting benthic secondary production into fish biomass

Diet Details

Main Prey:
Polychaete worms Benthic crustaceans Decapods Bivalve and gastropod mollusks Echinoderms Small fish

Human Interaction

Domestication Status

Wild

Haddock (Melanogrammus aeglefinus) is a wild marine gadid harvested primarily from natural North Atlantic stocks. There is no established domesticated form comparable to long-domesticated terrestrial livestock. Hatchery production and grow-out have been researched intermittently (cold-water marine aquaculture trials), but commercial supply remains overwhelmingly wild-caught (FAO species fact sheets; ICES stock assessments; FishBase summaries report wild capture dominance).

Danger Level

Low
  • Handling injuries: punctures/cuts from fins, gill covers, or knives during processing (occupational hazard rather than inherent aggression)
  • Food safety: potential parasites typical of marine fishes (risk primarily if eaten raw/undercooked; mitigated by proper cooking or freezing standards used in seafood safety guidance)
  • Allergy: fish allergy reactions in sensitive individuals
  • Fishing/boating risk: indirect injury risk from commercial/recreational capture operations (hooks, gear entanglement, slips)

As a Pet

Not Suitable as Pet

Legality: Haddock (Melanogrammus aeglefinus): Not usually kept as a pet. Local laws may limit catching, size, seasons, gear, require permits, and restrict moving live fish. Live haddock are usually kept in public aquariums.

Care Level: Expert Only

Purchase Cost: Up to $200
Lifetime Cost: $5,000 - $30,000

Economic Value

Uses:
Major commercial capture-fishery species (human food) Seafood processing and trade (fresh, frozen, smoked products) Fisheries-dependent employment and coastal economies Recreational angling (regional, smaller contribution than commercial) Scientific research and stock assessment inputs for management HUBS (Gadidae/codfishes): wide human interaction range including intensive industrial trawl/longline fisheries, strong quota/stock-management regimes (e.g., ICES/NOAA), extensive processing (filleting, salting, smoking), global cold-chain trade, bycatch issues, and limited/experimental marine aquaculture and enhancement research
Products:
  • Fresh/chilled fillets
  • Frozen fillets/blocks
  • Smoked haddock (e.g., "finnan haddie")
  • Salted/cured products
  • Prepared foods (e.g., fish cakes; fish-and-chips market supply)
  • Byproducts (frames/trimmings for fish stock, fishmeal/oil in some supply chains)

Relationships

Ecological Equivalents 5

Animals that fill a similar ecological role in their ecosystem

Haddock is an immensely popular food around the world, perhaps nowhere more so than the United Kingdom, where it’s practically a staple in some local dishes. This fish is closely related to cod, another popular dish. With a firm and slightly sweet taste, it is commonly fried, baked, and smoked.

3 Incredible Haddock Facts

  • It is adapted to life in deep, cold waters at around 35 to 50 degrees Fahrenheit.
  • Haddock swim together in large schools for protection.
  • Despite being a deep-sea fish, this fish spends the early part of its life near the surface. Its diet and behavioral habits change with age.
Just-caught Haddock in someone's hand

Just-caught Haddock in someone’s hand.

Haddock Classification and Scientific Name

The scientific name of the haddock is Melanogrammus aeglefinus. Melanogrammus basically means black line in Greek. Aeglefinus comes from the French word for the haddock, églefin. As a type of ray-finned fish, it is a member of the true cod family and the only living member of its genus.

Haddock Appearance

The haddock is a medium-sized fish, measuring anywhere between 1 and 3 feet in length and about 7 pounds (though the largest one ever caught was an immense 40 pounds). It is most easily identified by the black or purplish line running along the back and the distinctive marking on each side of the body. This marking is sometimes referred to as the “Devil’s thumbprint,” and it’s quite conspicuous against the white or silvery body. The haddock is also characterized by three dorsal fins along the back, two anal fins along the bottom, and a small barbel on the chin, the purpose of which is probably to sense its surrounding environment.

Similar to the cod, haddock is often caught for culinary purposes.

Cod vs. Haddock

There are actually several species of cod, versus only one species of haddock. The most closely related species to the haddock is probably the Atlantic cod. Both of them have a similar body shape, a similar arrangement of fins, and the same chin barbel. But the main difference is that the cod tends to be much larger, sometimes more than twice as large, and lacks the same markings.

Distribution, Population, and Habitat

This fish can be found on either side of the North Atlantic, usually swimming at depths of 300 to 700 feet, though sometimes as deep as 1,500 feet. The largest stocks in United States waters are located in the Gulf of Maine and Georges Bank (off the coast of New England). They are currently classified by the IUCN Red List as a vulnerable species, but this assessment may be out of date because their status hasn’t been properly evaluated since 1996.

NOAA (National Oceanic and Atmospheric Administration) monitors haddock populations in the Atlantic and reports that stocks in the Gulf of Maine and Georges Bank are not overfished and are being managed sustainably. This represents an improvement from population levels in the latter half of the 20th century, when the haddock stocks were stressed. The United States has also put in place regulations designed to minimize accidental bycatch.

Predators and Prey

This fish is a carnivorous predator. It spends much of its time searching around on the ocean floor for slow-moving invertebrates and smaller fish. It can move relatively quickly to evade potential predators.

What eats the haddock?

Juveniles are preyed upon by skates, spiny dogfish, cod, halibut, and other groundfish. Adults are also preyed upon by grey seals.

What does the haddock eat?

The haddock feeds on worms, sea stars, sea urchins, sand dollars, mollusks, crustaceans, and occasionally smaller fish and eggs.

haddock swimming near rocks in aquarium

Female haddock can produce up to 3 million eggs per breeding season.

Reproduction and Lifespan

Haddocks typically spawn between January and June, at least in American waters, when the schools come together to breed. Egg production depends on the size of the female. Every breeding season, the average female produces about 850,000 eggs, and the larger females can produce around three million. The female releases her eggs in large clutches near the ocean floor, where the male will then fertilize them. The eggs then rise to the surface along the water column and drift along the ocean currents for about 15 days.

Newly hatched haddocks spend the first few months of their lives near the coast, feeding on small crustaceans called copepods. After reaching about 3 inches in length, the haddock travels back down to the depths and transitions to an adult diet. By the end of the first year, the haddock has reached about a foot in size, but it may take anywhere up to four years to achieve full sexual maturity and begin reproducing. The typical lifespan of the haddock is 10 or more years. Many of the fish are caught between the ages of three and seven after they’ve had an adequate opportunity to reproduce. Obviously, given the number of eggs produced, haddock suffer massive attrition before most of them ever reach adulthood.

Fishing and Cooking

fish and chips with french fries - unhealthy food

Haddock is one of the most popular fish to eat.

The haddock is one of the most popular saltwater marine fishes in the United States and northern Europe. They are harvested all year round using long lines, gill nets, and rod and reel lines to minimize the impact on the surrounding habitats. Trawls are also used with some restrictions. In 2019 alone, commercial fishing yielded more than 19 million pounds of haddock, valued at nearly $19 million. Recreational fishers caught an additional 1.8 million pounds.

The flesh of the haddock is very similar to cod: white, firm, and moist. The flesh is so similar, in fact, that they’re sometimes used interchangeably with each other, although the haddock has a slightly sweeter taste. In the United Kingdom, both haddock and cod are popular components of fish and chips recipes, in which the fish is battered and fried in oil. Finnan Haddie is the name of cold-smoked haddock originating from the northeast of Scotland. Other popular recipes include baked haddock covered in bread crumbs.

View all 287 animals that start with H

Sources

  1. NOAA Fisheries / Accessed August 2, 2021
  2. Commonwealth of Massachusetts / Accessed August 2, 2021
A-Z Animals Staff

About the Author

A-Z Animals Staff

AZ Animals is a growing team of animals experts, researchers, farmers, conservationists, writers, editors, and -- of course -- pet owners who have come together to help you better understand the animal kingdom and how we interact.
Connect:

Thank you for reading! Have some feedback for us?


Haddock FAQs (Frequently Asked Questions)

The haddock is a medium-sized saltwater ray-fin fish. It is a member of the true cod family. As a carnivore, most of its prey consists of slow-moving invertebrates along the ocean floor.