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Grenadiers (fish)

life science Maturity 7-9 Next article →

Grenadiers are a large family of deep-sea marine fish belonging to the family Macrouridae. These fish are members of the suborder Macrouroidei and are often called rattails. This common name comes from their unique body shape. They possess large heads with big mouths and large eyes. Their bodies taper significantly into very thin caudal peduncles, which are the narrow parts of the tail. This appearance resembles the tail of a rat.

Rattail
Rattail

These fish inhabit many parts of the world's oceans. They are found at great depths from the Arctic to the Antarctic. Within the deep-sea ecosystem, they are among the most abundant fish. In fact, the Macrouridae family may represent up to 15% of the total deep-sea fish population. Most species are benthic, meaning they live on the ocean floor. However, two genera are known to prefer the midwater regions. They are often attracted to structural oases like hydrothermal vents, cold seeps, and shipwrecks.

Rattail
Rattail

Grenadiers have several specialized physical features to survive in the dark. They possess a well-developed lateral line system to sense their surroundings. This is aided by numerous chemoreceptors on their heads and lips. They also have chemosensory barbels, which are whisker-like organs, located underneath their chins. Some species have photophores, which are light-producing organs, located on their abdomen. These organs sit just before the anus and underneath the skin. Benthic species also have unique muscles attached to their swim bladders. Scientists believe these fish use those muscles to "strum" their bladders to produce sound. This sound may help with courtship or locating mates.

The family is highly diverse and contains 28 recognized extant genera. An extant genus is a group of living species. More than half of all species in this family belong to just three genera: Coelorinchus, Coryphaenoides, and Nezumia. The name for the family is derived from the Greek words "makros," meaning big, and "oura," meaning tail. Different species vary greatly in size. For example, Hymenogadus gracilis is small, while Albatrossia pectoralis is much larger.

Rattail
Rattail

Life histories for these fish are difficult to study because few larvae have been recovered. We do know that they produce a massive number of eggs. A single spawning can produce over 100,000 tiny eggs. These eggs are only a fraction of a millimeter in diameter. They contain lipid droplets, which are tiny drops of oil, to make them buoyant. These eggs are presumed to float up to the thermocline. The thermocline is the layer where warmer surface waters meet colder, deeper waters. The eggs develop there before the juveniles migrate to deeper waters as they age.

Lifespan and reproduction vary between different species. Some species are nonsemelparous, meaning they can live for 56 years or more. However, at least one species, Coryphaenoides armatus, is thought to be semelparous. This means the adults die immediately after they finish spawning. Spawning patterns may be tied to specific seasons, though this depends on the species. Because they grow slowly, these fish may have low resilience to changes in their environment.

Rattail
Rattail

Grenadiers play a vital role in the deep-sea food web. They are often considered apex predators in benthic habitats. This means they are at the top of the local food chain. They are also notable scavengers that eat dead organic matter. Their diet is quite broad, making them generalists. They eat smaller fish and various pelagic crustaceans. These include shrimp, amphipods, and cumaceans. They also occasionally eat cephalopods and lanternfish.

Rattail
Rattail

Despite their abundance, humans have attempted to use them for food. There have been several attempts to establish a commercial fishery for larger species like the giant grenadier. So far, these attempts have been unsuccessful because the fish is considered unpalatable. This means they do not taste good to humans. There is a concern that commercially exploited species could be overfished. If this happens, it could lead to a collapse of their populations in the future.

Rattail
Rattail
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