Fish nocturnal

Blackmouth Catshark

Galeus melastomus

A master of the deep-sea shadows, the Blackmouth Catshark is known for its stunning marbled patterns and its signature midnight-black mouth. Found along the muddy slopes of the Atlantic and Mediterranean, this slender predator is a marvel of deep-water evolution.

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Quick Identification

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Size

Typically 50–79 cm (20–31 inches) in length; Atlantic specimens tend to be larger than those in the Mediterranean.

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Colors

Tan to grayish-brown base with dark brown marbled 'saddles' or blotches outlined in pale white or cream. The most defining feature is the jet-black interior of the mouth.

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Key Features

Distinctive black interior of the mouth
Prominent saw-toothed crest of scales along the upper tail
Elongated, cat-like golden eyes
Complex marbled 'saddle' pattern along the back

When You’ll See Them

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Activity pattern nocturnal

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Peak hours Nighttime and twilight hours in shallower ranges; active throughout the day in deeper, lightless zones.

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Season Year-round

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Diet A versatile generalist predator eating small bony fish, shrimp, crabs, and cephalopods like squid and octopuses.

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Habitat Deep-water continental slopes and muddy seafloors, typically ranging from 150 to 1,400 meters deep.

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Behavior

The Blackmouth Catshark is a resilient and adaptable predator of the dark, cold waters of the continental slope. Unlike many more active pelagic sharks, it spends much of its time cruising just above the seafloor or resting on muddy substrates. It is a highly efficient hunter that uses its keen sense of smell and electroreception to navigate the pitch-black depths where sunlight rarely reaches.

While they are generally solitary, they are often found in high densities where food is abundant. They exhibit a unique 'segregation' behavior based on age; younger sharks tend to stay in shallower waters to avoid being eaten by larger fish, while the fully grown adults dominate the deeper slopes. They are harmless to humans, largely due to the extreme depths at which they live, and are frequently encountered by deep-sea research submersibles.

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Camera Tips

Capturing the Blackmouth Catshark requires specialized equipment, as this is a deep-water species. Instead of a standard backyard camera, you will need a 'lander'—a weighted waterproof housing capable of withstanding high pressure. For the best results, aim for depths between 200 and 500 meters along the continental slope, as this is where the shark is most active and accessible to enthusiast-grade deep-sea equipment.

Lighting is the most critical factor. In the deep sea, many creatures are spooked by bright white lights. Use infrared or red-filtered LEDs if your camera supports them; the Blackmouth Catshark is less likely to see red light, allowing you to capture natural foraging behavior without scaring the animal away. Position your camera about 1-2 feet off the seabed, angled slightly downward to capture the shark as it patrols the muddy bottom.

Bait is essential to bring the shark into the frame. Use a mesh 'scent bag' filled with oily fish like crushed sardines, mackerel, or squid. Secure the bait bag approximately 3 to 5 feet in front of the lens. The shark's powerful sense of smell will lead it directly to the source. Be patient; it can take several hours for the scent plume to travel through the deep-water currents and attract a shark to your location.

Set your camera to record short video clips (15–30 seconds) rather than still photos. These sharks move with a slow, sinuous 'eel-like' motion that is best appreciated in video. Given the cold temperatures of the deep ocean, ensure your battery housing is well-insulated, as extreme cold can cause battery life to drop significantly. If you are using an ROV (Remotely Operated Vehicle), move slowly and avoid stirring up the muddy silt, which can 'white out' your shot for several minutes.

Similar Species

Species that look similar or are commonly confused with Blackmouth Catshark.

Small-spotted Catshark

Found in much shallower water and has small dark spots rather than large marbled saddles.

Sawtail Catshark

Also features a tail crest but lacks the distinct jet-black mouth lining of the Blackmouth Catshark.

Frequently Asked Questions

In their deep-sea habitat, Blackmouth Catshark are active year-round. While they are considered somewhat nocturnal in shallower parts of their range (around 150-200m), in the deeper, lightless zones, they hunt whenever prey is available.

The best way to attract a Blackmouth Catshark is using oily bait like mackerel or sardines placed in a mesh bag. The scent trail is vital in the dark ocean. Use red light instead of white light to keep the shark from fleeing the area.

They are opportunistic feeders with a diet consisting of small fish, shrimp, prawns, and small squid. They forage along the muddy seafloor, using their sensitive snouts to detect vibrations and electrical signals from hidden prey.

No, Blackmouth Catshark are strictly deep-ocean dwellers. You will not find them in coastal shallows or suburban waterways; they prefer the continental slope at depths of at least 150 meters.

Look for the namesake black interior of the mouth and the 'saw-tooth' ridge of scales on the top of the tail. Their marbled 'saddle' markings are also more complex and pale-edged compared to the simpler spots of the Small-spotted Catshark.

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