Anoplogaster cornuta, commonly known as the fangtooth fish, is a pelagic fish that grows to a maximum of 16 centimeters in length. Pelagic refers to aquatic organisms that can be found anywhere between 500 and 2,000 meters below sea level (see Figure 1).
With a name including ‘fangtooth,’ these organisms can be visualized as vicious predators within the deep ocean. Their elongated teeth bring about a fearsome visage. Certainly, to an unaware deep sea visitor, this fish may seem key to avoid. Despite its formidable name, the common fangtooth fish is hardly an eager, frightening hunter–in part to its small size, but also through its feeding behavior.
Habitat and General Description
A. cornuta can be identified through its large caudal (or head) region and two milky eyes. These organisms have incredibly poor vision, which would be expected to pose a disadvantage, considering they dwell at incredible, poorly-lit depths. To combat this visual disadvantage, fangtooth fish possesses a highly developed lateral line system (see Figure 2). A lateral line is a sensory organ that runs laterally (horizontally) along the body and is highly sensitive to changes in the surrounding environment. This organ senses vibrations in the water driven by nearby movement, as well as changes in pressure.
Highly developed lateral line systems, or those with high levels of efficient detection are useful for avoiding predation. In tandem with this form of defense, the common fangtooth has another useful mechanism to protect their lineage. These organisms have ultra-black skin, meaning their skin contains high concentrations of pigment that allow them to absorb nearly 100% of all available light! This allows the fish to hide in plain sight by blending in with its dark, deep surroundings (see Figure 3).
Feeding Behavior and Morphology (Anatomy)
The most notable feature of the fangtooth fish’s morphology by far is its set of long, sharp teeth and cavernous jaw. In fact, the fangtooth has the largest teeth-to-body-size ratio of any known fish in the ocean. With record-setting lengths, how does this little fish close its mouth without puncturing its brain? The answer is with specialized pouches! These pouches are in the roof of the fish’s mouth and extend into deep sockets, allowing the teeth of its lower jaw to safely slide inside without doing harm to its noggin. Interestingly, juvenile fangtooth fish have much smaller teeth, and only a single row. As a result, juveniles filter feed zooplankton with gill rakes (bony or cartilaginous structures extending from the gill arch, see Figure 4) until they develop their name-worthy fangs.
As adults, fangtooth fish are opportunistic feeders, meaning a large portion of their hunting pattern involves consuming what happens to get close enough to capture. Indivudals of A. cornuta engage in diel migration, where they remain in the ocean depths during the day and migrate to shallower waters at night for feeding. Here, these organisms can enjoy a diverse diet of small prey that happen to get within range. Examples of prey include juvenile squid and juvenile or small adult fishes. Whereas these fish often consume prey at or beneath body size, these organisms have been known to consume prey much larger. Regardless of size, the fangtooth fish does indeed have poor visual acuity, and as a result relies on specialized chemoreceptors (or chemical sensing organs) to smell the organism underwater. Once a prey is obtained, it is unlikely to escape, making this fish an effective hunter should the opportunity arise.
If you would like to learn more about this incredible species, you can view the BBC Studies Blue Planet video below titled: “Fangtooth in the Abyss.”