The haddock (Melanogrammus aeglefinus) is a commercially important fish belonging to the cod family, Gadidae. It is widely distributed across the cold waters of the North Atlantic Ocean. The haddock is easily recognized by its dark lateral line and a distinct dark blotch above its pectoral fin, often called the “St. Peter’s thumbmark.” Its feeding habits are strongly linked to the ocean floor, which dictates its diet throughout its adult life.
Primary Food Sources of Adult Haddock
The adult haddock is classified as a demersal species, meaning it spends its life near the seabed. Its diet reflects this bottom-dwelling existence, as haddock primarily consume a wide array of slow-moving benthic invertebrates. This feeding behavior makes them highly dependent on creatures residing within soft, sandy, or muddy substrates.
A large portion of the adult haddock’s menu consists of small crustaceans, such as crabs, shrimp, and tiny amphipods and copepods. They also actively target various marine worms, specifically polychaetes, which they are adept at extracting from their burrows. Mollusks, including small clams and snails, form another regular component of their consumption as they forage across the bottom terrain.
Echinoderms are also a common food source for the haddock, including brittle stars, sea urchins, and sand dollars. While they are opportunistic feeders, targeting whatever is most readily available, larger haddock will occasionally prey on small fin fish. These include sand lance, herring, or capelin, but such mobile species rarely constitute the bulk of the haddock’s total food intake.
Developmental Shifts in Haddock Diet
The feeding habits of haddock change significantly as they grow, transitioning from a life in the open water to a life on the seabed. Haddock eggs are buoyant, floating to the surface where they drift with ocean currents after being spawned. Newly hatched larvae, measuring only a few millimeters in length, initially rely on their attached yolk sac for nourishment for about ten days.
Once the yolk sac is absorbed, the larvae begin their first active feeding phase in the pelagic (open water) zone, consuming minute zooplankton. Small crustaceans like copepods are a primary food item for these young fish while they remain near the surface for several months. This pelagic phase ensures they have access to a rich supply of planktonic organisms necessary for rapid early growth.
The transition to a demersal lifestyle occurs as the juvenile haddock grow to a length of approximately 3 to 10 centimeters, typically between three and five months of age. At this point, the fish gradually descend to the ocean floor, where they begin to adopt the adult diet. This involves shifting from small, drifting zooplankton to larger, bottom-dwelling invertebrate prey.
Feeding Mechanics and Preferred Habitat
Haddock are specialized bottom feeders, possessing physical adaptations that allow them to efficiently locate and consume prey buried in the sediment. Their mouth is relatively small and positioned on the underside of their head, giving it a downward-facing orientation perfectly suited for grazing on the seafloor. This structure enables the fish to effectively root out organisms living within the substrate.
A small barbel, a sensory whisker-like organ, is located on the haddock’s chin, which they drag along the bottom to detect hidden prey. This chemosensory tool allows them to find worms and mollusks that are completely concealed beneath the sand or mud. When food is located, the haddock uses its muscular lips and mouth structure to create a strong suction, pulling the prey directly from the ocean floor.
These fish are found across a wide depth range, from 40 to 450 meters, though they are most common between 80 and 200 meters. The preferred habitat for haddock is soft, smooth bottoms made of mud, sand, or gravel. These substrates are home to the densest populations of benthic invertebrates, and their feeding strategy is integrated with these soft-bottom environments.