Oarfish

The oarfish is a large and unusual pelagic fish. Pelagic means it lives in the open ocean. It belongs to a small family called Regalecidae. This name comes from the Latin word regalis, which means royal.

The giant oarfish, or Regalecus glesne, is the longest bony fish alive today. These fish live in the ocean layers called the epipelagic and mesopelagic zones. This means they stay between 250 and 1,000 meters deep. Because they live so deep, humans rarely see them alive. They are often found in tropical, subtropical, and warm temperate waters around the world.

Oarfish have a very unique body structure. They have a long dorsal fin that starts above their eyes. This fin runs the entire length of their body. It has about 400 rays. The first 10 to 13 rays are very long and form a crest. This crest has reddish spots and skin flaps at the tips. They also have long pelvic fins on their bellies.

Unlike many other fish, oarfish lack a swim bladder. A swim bladder is an organ used to stay at certain depths. Because they lack this, they must use frequent tail movements to regulate their depth. They also have hyperossified bones. These are very hard bony rays that run along their backs. These rays provide support and prevent fractures during movement.

Oarfish move through the water using a method called amiiform swimming. This means they rhythmically undulate their dorsal fin. This motion allows them to swim while keeping their long bodies straight. They can also swim in a vertical orientation. In this position, they face upward toward the light. This helps them silhouette their prey against the sunlight.

They primarily feed on zooplankton. They use suction to pull in tiny crustaceans like euphausiids and shrimp. They also eat small fish, jellyfish, and squid. While they are mostly deep-sea dwellers, larvae and juveniles drift near the surface. The larvae look very different from the adults. They have long fins and extensible mouths.

There are three known species within the oarfish family. The first is the giant oarfish, Regalecus glesne. It is the largest member of the group. The second is the streamer fish, or Agrostichthys parkeri. This species has skin covered in hard tubercles, which are small bumps. The third is Russell's oarfish, or Regalecus russelii. This species has tubercles along its belly midline.

All species are silver with small dark spots. They do not have scales on their skin. Scientists first described these fish in 1772.

To protect themselves, oarfish use a process called autotomy. This is when a fish self-amputates its own tail. They do this as an anti-predator adaptation to escape danger. The break can happen near the tip or involve several vertebrae. In extreme cases, the entire tail is lost. The wound will heal, but the tail does not regenerate.

This survival tactic is common in Russell's oarfish. All captured specimens of that species over 1.5 meters long have used autotomy.

Oarfish have a long history in human folklore. Because they are so long and rare, people often mistook them for sea serpents.

In Japan, they are called the Messenger from the Sea God's Palace. Some people believe they are harbingers of doom. This is because they often beach themselves before natural disasters. For example, many oarfish washed up in Japan before the 2011 Tōhoku earthquake and tsunami. However, a 2019 study suggests this is an illusory correlation. This means the link between the fish and earthquakes is not actually real.

Understanding oarfish helps scientists learn about the deep ocean. They are part of the order Lampriformes. Scientists use mitochondrial genome analysis to study their evolution. This helps them see how oarfish are related to other fish like Trachipterus trachypterus. Studying their reproduction also provides new data. In 2019, researchers successfully used artificial insemination on Russell's oarfish. This was the first time this was done for the species. These discoveries help us understand how life thrives in the deep, dark parts of our oceans.