Lancetfish

Lancetfishes are large, predatory ray-finned fishes belonging to the genus Alepisaurus. The name Alepisaurus comes from the Greek words for "without scales" and "lizard." These fish are important members of the monogeneric family Alepisauridae. They are found in almost all the world's oceans, though they do not live in polar seas. Specimens have even been recorded as far north as Greenland. Because they are large and inhabit the deep sea, they are vital for studying ocean life.

The physical structure of a lancetfish is specialized for life in the midwater. They have slender bodies that are flattened from side to side. A very high dorsal fin runs along most of their back. This fin has between 41 and 44 rays and can be tucked into a groove. They also possess an adipose fin located behind the dorsal fin. These fish lack scales, and their fins are quite fragile. They also lack swimbladders, which are organs many fish use to control buoyancy.

There are two living species of lancetfish recognized today. The first is Alepisaurus ferox, known as the long-snouted lancetfish. This species was named by R. T. Lowe in 1833. It lives in the tropical and northern subtropical waters of the Pacific Ocean. The second is Alepisaurus brevirostris, the short-snouted lancetfish. This species was named by Gibbs in 1960. It inhabits the Atlantic tropics and the southern subtropics of the Pacific. A third species, Alepisaurus paronai, is known only from fossils found in Italy. These fossils date back to the Middle Miocene epoch.

Lancetfishes are effective ambush predators that use specific behaviors to hunt. They have watery muscle, which means they cannot swim fast for long periods. Instead, they use their narrow bodies and silvery color to hide from prey. They float in the water column and use large eyes to scan for movement. Once they detect prey, they use their deeply forked tails for rapid bursts of speed. Their large mouths and fang-like teeth help them subdue targets quickly. Their distensible stomachs allow them to eat many things at once.

These predators have a very diverse and opportunistic diet. They consume many different animals, including fishes, octopods, squid, tunicates, and crustaceans. Because they digest food very slowly, their stomachs serve as a scientific tool. Actual digestion does not begin in earnest until the food reaches the small intestine. This slow process allows researchers to study the gut contents to map biodiversity. In fact, some deep-sea fish species were first described after being found inside a lancetfish.

Lancetfish play a role in the wider ocean ecosystem and human industries. They are often caught as bycatch by vessels using longlines to catch tuna. In the central and western Pacific, bycatch rates have appeared to increase. Researchers believe this might reflect a faunal regime shift as tuna populations decrease. While they are not a commercial target, they are sometimes considered pests by fishers. They can also host parasites, such as the tetraphyllidean tapeworm Pelichnibothrium speciosum.

Recent studies show how these fish connect different parts of the ocean. Scientists have found plastic refuse in the stomachs of lancetfish in the north Pacific. They also found large amounts of floating macroalgae in the stomachs of adults in the Indian Ocean. This suggests that larger lancetfish may follow prey into shallower surface waters. In 2023, several lancetfish washed up on beaches in Oregon. These events help scientists track the movement of species between the deep sea and the surface.