Giant oarfish

The giant oarfish (Regalecus glesne) is a very special kind of fish known for being one of the longest ray-finned fish in the world. It swims in oceans all around the globe, except in the very cold polar regions. People call it many names, like Pacific oarfish, king of herrings, and ribbonfish.

This amazing fish looks like a long, thin ribbon. It has a back fin that runs almost the whole length of its body, small side fins, and very long, paddle-shaped belly fins that give it its name. The giant oarfish shines with a silver and blue color, dotted with dark spots, and its fins are a striking deep red.

Because of its unusual shape and the way it glides through the water, many people over the years have thought giant oarfish might be the reason some people reported seeing huge "sea serpents" in the ocean. In 2016, a TV show called River Monsters looked into this idea and decided that the giant oarfish is the most likely explanation for those old sea serpent stories. The show's host, Jeremy Wade, even went swimming with two healthy giant oarfish in the Mediterranean Sea!

Taxonomy

The giant oarfish was first described by Peter Ascanius in 1772. Its genus name, Regalecus, means "belonging to a king" in Latin. The specific name glesne comes from a farm called Glesnaes near Bergen, Norway, where the original specimen was found.

This fish is sometimes called the "king of herrings" because of its crown-like features and because it has been seen near groups of herring. The name "oarfish" probably refers to the shape of its pelvic fins or its long, slender body.

Distribution

The giant oarfish can be found all over the world, except in the polar regions. It lives mostly in warm and temperate areas, from tropics to middle latitudes. You can spot them in both the Atlantic and Pacific Oceans, but they are more common in the Atlantic. These fish usually stay in the upper layers of the ocean where there is light, called the epipelagic zone, and sometimes go into dimmer areas below, known as the mesopelagic zones. The deepest place they have been seen is in the Gulf of Mexico, during a research project called the Gulf SERPENT.

Description

The giant oarfish is one of the longest bony fish in the world, reaching lengths of about 7–8 metres (23–26 ft), and maybe even up to 11 metres (36 ft). It is often around 3 metres (9.8 ft) long. Young fish have a see-through body with dark spots, but adults have a pale silver, ribbon-like body that is very long and thin. They have a red crest on their heads and long, oar-shaped fins. The giant oarfish can be told apart from a similar fish called Russell's Oarfish by counting the rays in their fins and measuring certain body parts.

Life cycle

Scientists have found eggs from these fish in the western Pacific Ocean. They used special tests to identify them. They also found a very young fish, just 13.7 millimetres long, showing early development. The eggs are round and have many tiny spines covering their outer layer.

Behavior

Scientists still do not know much about how oarfish behave. These fish can swim by moving their long dorsal fin from side to side. They can also swim upright, moving their whole body and fin together.

In 2010, scientists captured the first footage of a giant oarfish in its natural home — the deep water of the Gulf of Mexico. They used a special underwater vehicle called an ROV near a place called Thunder Horse PDQ. The video showed the fish swimming straight up and down, with its tail pointing downward.

A TV show called River Monsters filmed two oarfish in the deep waters of the Mediterranean Sea near France. The host, Jeremy Wade, saw the fish near a buoy anchored to the sea floor. These rare fish swam up and down the buoy’s chain, sometimes coming very close to the surface. Wade got close enough to gently touch one, and both fish seemed calm and curious. Scientists are unsure why they were there — maybe to find food or because they were a pair. The oarfish moved gracefully and quickly, preferring to rest upright with their tails down before swimming away.

Feeding

Scientists don't know much about what giant oarfish eat. Often, when they have been studied, their stomachs and guts were empty or had only colored liquid inside. One time, a giant oarfish was found with thousands of tiny shrimp-like animals called krill in its gut. Another time, two adult giant oarfish had 43 heads and 7 whole krill in their stomachs.

Growth

The giant oarfish gets bigger and changes as it grows. Young fish start with just one dorsal fin ray. When the fish grows to about 50 mm (which is about 2 inches), more rays grow behind the first one, becoming more special and longer.

Parasites

There are not many known parasites that live on giant oarfish. Scientists once found an adult female giant oarfish that had at least 63 special larvae inside it. These larvae are a type of tapeworm called plerocercoids.

Self-amputation

The giant oarfish, Regalecus glesne, can sometimes lose parts of its body. This happens behind the area where waste leaves the body. The fish might lose just its tail fin or even a large part of its body. Because the fish’s important organs are all in the front part, losing these parts does not hurt the fish.

Scientists are not sure why this happens. The fish does not have any known natural enemies, so it is not to protect itself. There are stories that sharks might attack them, but no such attacks have been proven. Once, a group of pilot whales attacked an oarfish, but they did not eat it.

Population size

No one has tried to count how many giant oarfish, Regalecus glesne, exist. We know there is at least one group in the Northern Atlantic and another group that can have babies in the Mediterranean Sea. Very young oarfish have been seen near the Gulf Coast of Florida and off the coast of Canada. Eggs from these fish have been found in the waters of New Zealand and near the West Mariana ridge in the western North Pacific. This species is considered "Least Concern" on the IUCN Red List, meaning it is not in danger of disappearing.

Fossil record

Scientists have found only one fossil of the giant oarfish. This fossil was discovered near Macerata in Marche, Italy. The fossil shows a piece of the fish's body that is about 355 mm long, or 14 inches, along with parts of its pelvic fins.

Relationship with humans

The giant oarfish is not caught for food, but sometimes gets caught in nets by accident. People who have tried eating it say the taste is like paper and the meat is very soft and not pleasant.

Because of their long bodies and special way of swimming, giant oarfish are thought to be behind some stories of sea serpents. A TV show once suggested that the oarfish might be the real reason for these old tales. Even though they were once thought to be rare, we now believe they might actually be more common, but seeing them in their natural home is still unusual.