4 Key Differences Between Cod and Flounder

Cod and flounder differ in size, appearance, hunting methods, and reproduction strategies. Cod are larger, streamlined, active hunters, and spawn in groups, while flounders are flat, camouflaged, stealth hunters that mate individually and have unique larval development.

what is the difference between a cod and a flounder

The ocean is home to a wide variety of marine life, including cod and flounder. Despite sharing the same habitat, they have distinct differences in appearance, hunting habits, and reproduction. Cod, part of the Gadidae family, is popular for its mild-flavored flesh and is heavily fished. Flounder, a type of flatfish, is also widely consumed and important to the fishing industry.

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1. Size

Gadus morhua, pacific Cod, Portrait,close up. Ocean deepwater fish.

Cod and flounder vary in size due to their species and habitats. Factors like environment, diet, and genetics can influence a fish’s size. Generally, cod are larger than flounder. Atlantic cod average about 51 inches in length and can weigh up to 77 pounds, although some exceed these measurements. Pacific cod are slightly smaller, with adults measuring around 30 inches and weighing close to 22 pounds.

Flounders, being flatfish, are measured by width instead of length. On average, a flounder can grow up to 25 inches wide, while varieties like halibut can reach 8 feet wide and weigh over 600 pounds.

2. Appearance

Photo of pair of Summer Flounder caught off the coast of Ocean City Maryland on a headboat.  The summer flounder is a popular mid-atlantic gamefish and very good eating.

Cod and flounder have contrasting appearances. Cod have a streamlined body for fast swimming, with a prominent barbel on their lower jaw to detect food on the ocean floor. They typically have three dorsal fins and two anal fins. In contrast, flounders have flat bodies that rest on the seafloor. One unique feature of flounders is their migrating eyes. Initially, they have an eye on each side of their head, but as they mature, one eye moves to the other side, resulting in both eyes being on one side of the body.

Cod exhibit various colors, usually a mix of brown and green, with a white underbelly. Their elongated bodies have a distinct lateral line, which detects water vibrations. Flounders’ coloration is an adaptation to their bottom-dwelling lifestyle. They often have speckled brown, black, and beige upper bodies, providing effective camouflage against the seafloor. Their underbelly is typically white, serving as countershading camouflage, blending with the surface light when viewed from below.

3. Hunting Methods

Cod fishes swimming underwater, Norway.

Cod and flounder have different hunting strategies. Cods are active hunters, using their barbels to search the seafloor for smaller fish, crustaceans, and mollusks. They can also catch squid and other fish in the water. In contrast, flounder use stealth and deception. They blend with the ocean floor and wait patiently for prey. Their flat bodies allow them to hide effectively, and their eyes are positioned to see a wide range of potential meals.

Both cod and flounder primarily dwell near the seafloor, but they utilize the environment differently. Cods actively search for food, using their strong fins to swim, while flounder prefer to remain still and let the food come to them. Their camouflage techniques also vary. Cods rely on mottled coloration to blend into sandy or rocky bottoms. Flounder, on the other hand, takes camouflage to a higher level. They match the seafloor colors and can adjust their pigmentation to become nearly invisible to both prey and predators.

4. Reproduction Strategy

flounder swimming underwater in ocean

Cod and flounder have different reproduction strategies. Cod practice broadcast spawning, where females release eggs into the water to be fertilized by males. This results in a large number of offspring, but survival rates are low. Flounder, on the other hand, has a different process. Male flounders fertilize eggs after the female lays them on the seafloor.

The eggs stick to the substrate and stay there until they hatch, providing protection. Cod spawn in groups during specific seasons, while flounder mates individually. Flounder larvae start off swimming upright but undergo a metamorphosis where one eye moves to the other side of the body, and they begin swimming sideways and living on the ocean floor.

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