Opisthoproctus facts for kids
Quick facts for kids Opisthoproctus |
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| Illustration of a specimen taken to the surface. In a live specimen, the membrane over the top of the head forms a transparent dome. | |
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Opisthoproctus soleatus is a fascinating deep-sea fish. It belongs to a family of fish called Opisthoproctidae. This fish was first discovered in 1888 by Léon Vaillant.
You can find O. soleatus in warm, tropical parts of the ocean. It's often seen in the eastern Atlantic Ocean, near places like Ireland and Angola. It also lives in the South China Sea. This small fish usually grows to about 10.5 centimetres (4.1 in) long. It typically lives very deep, often between 500 to 700 metres (1,600 to 2,300 ft) below the surface.
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Meet the Barreleye Fish
Opisthoproctus soleatus is a small fish, usually no longer than 10.5 centimetres (4.1 in). Its body is deep and flattened from side to side. It has large, thin scales. The bottom part of its body is flat and oval-shaped. This flat part extends forward, even under its head. It is covered in scales that get darker towards the edges. The back and sides of the fish are dark. Its snout, or nose area, is see-through.
How It Glows: The Light Organ
This fish has a special part of its body near its bottom, called the rectal bulb. This bulb contains tiny glowing bacteria. These bacteria produce light, making the fish bioluminescent.
There's another special organ in the flat part of its body. This organ acts like a mirror for the light from the rectal bulb. The light from the bacteria shines into this reflector organ. The bottom wall of this organ is shiny and reflects the light downwards. The fish can control how much light passes through its scales. This allows it to turn its glow on or off.
Unique Eyes and Head
The head of Opisthoproctus soleatus is also flattened. Its snout is about three-eighths the length of its head. The mouth is small and opens halfway along the snout. The top of its snout and the area above its brain are semi-transparent, meaning you can see through them a little. It has small teeth on its lower jaw.
The eyes of this fish are very unusual. They are shaped like tubes and point straight upwards. This helps the fish look for food above it. The eyes are large, about the same length as its snout. A bone covers the side of its eye.
Fins and Tail
The tail fin is large and forked, like a "V" shape. It has 33 rays, which are like the bones that support the fin. The top fin, called the dorsal fin, is small. It starts behind the middle of the body and has 11 soft rays. The anal fin is at the back of the body and has 6 rays. The side fins, called pectoral fins, have 13 to 15 rays. Some of these rays are long and extend past the dorsal fin. The pelvic fins have 9 to 10 rays. It also has a small, fleshy fin called an adipose fin.
Where It Lives: Ocean Habitat
O. soleatus can be found in tropical and mild parts of all the world's oceans. It has been seen in the Atlantic, Pacific, and Indian Oceans.
In the eastern Atlantic, it is often found between western Ireland and Mauritania. It also lives between Sierra Leone and Angola. Its range in the Atlantic Ocean stretches from 20° North to 10–12° South.
This fish lives very deep, usually between 300 to 800 metres (980 to 2,620 ft) down. It is most common at depths of 500 to 700 metres (1,600 to 2,300 ft). This depth range is called the mesopelagic region. This area gets only dim light from the surface. Many animals live here all the time, while others move up and down depending on the light.
What It Eats: Diet
Opisthoproctus soleatus mostly eats glowing creatures called siphonophores. These siphonophores also produce light, which helps them hide in the dim ocean light. However, the special eyes of O. soleatus help it see through this camouflage. Its eyes are designed to improve vision and help it spot these hidden prey.
Staying Safe: Avoiding Predators
Opisthoproctus soleatus has been found in the stomachs of whales, like Sowerby's beaked whales. Other fish from the same family have also been found in the stomachs of pygmy sperm whales and some seabirds.
Scientists think that the light this fish produces from its glowing organ points downwards. This might help it hide from predators that look upwards. By shining light downwards, it can blend in with the dim light coming from above.
How It Behaves
Like other deep-sea fish, Opisthoproctus soleatus needs to find food in a very dark place. It also needs to avoid being eaten by bigger fish. Fish with large, upward-pointing eyes likely hunt by seeing the outlines of prey above them. They spot their prey against the faint light coming from the surface.
At the depths where this fish lives, light still comes from a certain direction. Many fish species have special light-producing organs on their undersides. These organs help them hide by matching the faint light from above. O. soleatus does not have these organs. Instead, it has its glowing organ inside its bottom. The light it produces shines onto a reflector. This reflector then bounces the light downwards through its scales. This creates a similar hiding effect to other fish.
The exact reason for this unique glowing system is not fully known. However, it is thought that O. soleatus uses it for camouflage. It might also use it to communicate with other fish of its kind.
Opisthoproctus soleatus likely lives alone. This is similar to another fish in its family, Macropinna microstoma.
Life Cycle and Reproduction
The baby Opisthoproctus soleatus, called larvae, look similar to the adult fish. They have similar body shapes. However, the larvae have more color, especially near their tail fin. The bottom part of the larvae is silver. It has two lines of black color that get bigger towards the bottom.
Opisthoproctus soleatus lays eggs. All fish in the Argentinidae family, which includes this fish, lay eggs.
Conservation Status
This fish lives in the deep ocean. People rarely see it. This makes it hard to know if its population is growing or shrinking. It's also difficult to tell if it faces any special dangers.
However, it is found across a large part of the ocean. In 2012, there were many records of this fish. O. soleatus is not caught by fishing boats. It also rarely gets caught by accident in fishing nets. Because of these reasons, the International Union for Conservation of Nature says that its conservation status is of least concern. This means it is not currently at risk of disappearing.
