Grenadier

Grenadiers, also called rattails, are a large family of deep-sea fishes (Macrouridae) found on continental slopes and abyssal plains throughout the world's oceans. The roundnose grenadier, Coryphaenoides rupestris, is one of the most studied representatives, common in the North Atlantic. Grenadiers are immediately recognizable by their oversized head and body that tapers into a long, thin, whip-like tail with no distinct caudal fin. As one of the most abundant fish groups on the deep seafloor, grenadiers play a significant ecological role in deep benthic communities. Many species are slow-growing and long-lived, and populations of some grenadiers have declined due to deep-water fishing activity in parts of their range.

Grenadiers have a body shape unlike almost any other fish group, making them fairly easy to recognize.

• Large, blunt or conical head tapering abruptly into a long, slender, rat-like tail
• No distinct caudal fin; the body simply narrows to a point
• Large eyes adapted to low-light deep-sea conditions
• Single barbel on the chin in many species
• Silvery-grey to dark brownish-black coloration
• First dorsal fin tall and triangular, set well forward on the body

The dramatic head-to-tail taper and absence of a normal tail fin distinguish grenadiers from virtually all shallow-water relatives such as hake, pollack, and cusk, which retain a conventional tail shape.

Grenadiers are found worldwide on continental slopes, seamounts, and abyssal plains, generally at depths from about 200 meters down to over 6,000 meters, making them one of the most widely distributed deep-sea fish groups. Different species occupy different depth bands, with some restricted to upper slope waters and others adapted to the near-freezing temperatures and crushing pressure of the abyssal zone. They are typically found just above or resting on soft sediment seafloor rather than rocky structure. Because of their broad depth range and abundance, grenadiers are considered a dominant component of deep benthic fish communities across much of the world's deep ocean floor.

Grenadiers are bottom-oriented scavengers and predators, feeding on a mix of small invertebrates, crustaceans, and carrion that sinks to the deep seafloor, often detected using a well-developed sense of smell and lateral line system in the perpetual darkness of the deep sea. Many species are capable of producing sounds using specialized muscles associated with the swim bladder, likely used in communication. Grenadiers are generally slow-growing, late-maturing, and long-lived, life-history traits typical of deep-sea fishes that make populations slow to recover from disturbance. Spawning behavior varies by species but generally involves eggs and larvae that develop in the water column above the deep habitat used by adults.