Stomiiformes

Some fish live in the deep, dark ocean.

These fish have very big mouths. They also have many sharp teeth. Most of them can make their own light.

This light comes from small spots on their bodies. They use the light to help them hunt. Many of these fish swim up to find food at night. They go back down deep when the sun rises.

These strange fish are very interesting to see.

Stomiiformes are a large group of deep-sea fish.

They live in many parts of the world's oceans. This group includes dragonfishes and hatchetfishes. Some species are very small. The bristlemouth is only 1.5 cm long. Other species are much bigger. The barbeled dragonfish can grow quite large.

These fish often look very strange. Most have large mouths and many teeth. Their teeth are often clear. This helps them hide from prey. Most stomiiforms have photophores. These are tiny organs that make light. The light can be white, red, or yellow.

The light comes from a change in tiny parts of their bodies. Many fish have rows of these lights on their bellies.

Many of these fish follow a daily plan. During the day, they stay in deep water. At night, they swim up to find food. They go back down when the sun rises. This helps them find small animals to eat. Some fish even change their sex as they grow. They start as males and then become females.

Stomiiformes are a large group of deep-sea fish.

They are very diverse in how they look. This group includes dragonfishes, lightfishes, and marine hatchetfishes. There are at least 410 different species in this order. They live in many parts of the world's oceans. They can be found in warm waters or cold Antarctic waters. The name comes from the Greek word for mouth. This is because many of these fish have huge mouths.

Most of these fish use light to live in the dark. They have special organs called photophores. These organs produce light through a chemical reaction. This reaction uses a substance called coelenterazine and calcium ions. The light can be white, red, yellow, or violet. Most fish have rows of these lights on their bellies. The light helps them in the deep, dark ocean. Some fish even have these lights on a chin barbel.

Many stomiiforms follow a special daily schedule. During the day, they stay in very deep water. When the sun sets, they swim up toward the surface. This area has more food like small fish and plankton. They hunt at night and swim back down at sunrise. They can sense how much sunlight is reaching them. This helps them stay in a zone where light is very low. Some larger predators stay deep and eat the migrating fish.

These fish have many interesting physical traits. Their teeth are often clear and do not reflect light. This helps hide them from prey in the dark. Some species are very tiny, like the 1.5 cm bristlemouth. Other species, like the barbeled dragonfish, are much larger. Many of these fish also change their sex as they grow. They start their lives as males. Later, they transform into females when they are mature.

Scientists have studied these fish for a long time. The earliest known stomiiform lived during the Cretaceous period. It was found in fossils from Morocco and Italy. Researchers use different names to group these fish families. Recent studies in 2025 changed how we classify them. We now know there are several different families. These include the dragonfishes and the marine hatchetfishes. Scientists are still studying how all these fish are related.

Stomiiformes is an order of ray-finned fishes that live in the deep ocean.

This group is famous for its diverse body shapes and unusual appearances. It includes many well-known deep-sea animals like dragonfishes, lightfishes, and marine hatchetfishes. Scientists estimate there are at least 410 species within this order. The name Stomiiformes comes from the Greek word "stoma," meaning mouth. This refers to the massive mouth openings found in many of these species.

They are found in almost every ocean around the world. Their range extends from warm subtropical waters to the freezing Antarctic.

The biology of these fish is specialized for life in the dark. Most stomiiforms possess photophores, which are organs that produce light. This light is created by an enzymatic reaction. Specifically, calcium ions catalyze the substance coelenterazine to produce light. The light can appear in colors like white, yellow, violet, or red.

Many species arrange these photophores in one or two rows along their bellies. These rows often run from the head down to the tail. Some fish, like those in the family Stomiidae, even have lights on their chin barbels. The light production can be simple or involve complex lenses and refractors.

To hunt effectively, many stomiiforms have evolved unique dental features. Their teeth are often transparent and do not reflect light. This helps hide their presence from prey during bioluminescent encounters. Research shows that the transparency of species like Aristostomias scintillans comes from nanoscale structures. These structures are made of collagen and hydroxyapatite. Interestingly, the teeth of Chauliodus sloani are also transparent but contain dentin tubules. Scientists are still investigating why these two species in the same family differ in this way. Most species also have teeth on both the maxilla and the premaxilla.

Many members of this order follow a pattern called daily migration. During the daylight hours, they stay in the deep, dark waters. When the sun sets, they swim upward toward the surface. This area is much richer in food, such as planktonic invertebrates and small fish. They hunt throughout the night and return to the depths at sunrise. They appear able to measure the intensity of sunlight to find their way. They stay in a zone where light is very low but not completely dark. However, some large predators stay deep all the time to eat the migrating fish.

The life cycles of stomiiforms involve fascinating changes. While they spawn in the deep sea, their eggs are light and float upward. These eggs eventually hatch in the surface waters. After the larvae finish metamorphosis and look like adults, they descend back to the deep. Some genera, such as Cyclothone and Gonostoma, exhibit sequential hermaphroditism. This means they change their sex during their lifetime. They typically begin life as males and transform into females when they reach sexual maturity.

History and classification of these fish are constantly evolving. The earliest known stomiiform, Paravinciguerria, lived during the Cenomanian period. Fossils of this genus have been found in Morocco and Italy.

For a long time, scientists debated how to group these fishes into families. In 2025, new research revealed that previous classifications were paraphyletic. This means the old groups did not include all the descendants of a common ancestor. This discovery led to the revival of several new families. The current classification includes families like Vinciguerriidae, Diplophidae, and Ichthyococcidae.

Different species within the order vary greatly in size. The bristlemouth, Cyclothone pygmaea, is the smallest species. It lives in the Mediterranean Sea and reaches only 1.5 cm as an adult. In contrast, the barbeled dragonfish, Opostomias micripnus, is much larger. This large predator is found in the Atlantic, Indian, and Pacific Oceans. Because they are so diverse, they are often studied to understand deep-sea evolution. Their unique traits help scientists learn how life adapts to extreme environments.