Why do some deep-sea animals glow?
Far below the surface, sunlight disappears. Some ocean creatures make their own light.
The short answer
Some deep-sea animals make their own light through chemical reactions. Depending on the species, it attracts prey, helps communication or conceals the body. Making light differs from reflecting sunlight.
Equal-sized Puschel and Flauschi examine a museum model of a female deep-sea anglerfish with a glowing lure. An enlarged artistic model, not a precise species identification. External lighting makes its body visible; a real deep-sea fish does not live in a museum box. AI-created illustration, not a photograph of nature.
What the diagram shows
The diagram simplifies the process. First compare its shapes and arrows. You can read its labels in larger text below.
Read the picture labels
These are the words and sentences from the diagram above. The full explanation follows below.
- A glowing lure
- Female deep-sea anglerfish
- Possible prey
- Bacteria in the light organ → chemical reaction → light The lure is part of the fish. Bacteria are tiny living organisms. Model: enlarged and simplified; attracting prey is not guaranteed.
An imagined Wusel scene
Puschel and Flauschi investigate
In the dark museum scene, Flauschi finds a bright point. Puschel first searches for a Sun in the picture. The label explains the animal's own light. They sort examples by purpose and find that not every glow has the same explanation.
Look closely
Find the small bright point in front of the fish’s head. The museum model represents a female deep-sea anglerfish. The diagram separates light source, lure and possible prey.
An example to help you understand
With an adult, hold a small battery-powered torch behind a cardboard fish shape with a hole where its lure would be. In a dim room the bright point stands out. This shows how light can attract attention. But a torch works electrically, while living light comes from chemical reactions. You are modelling visibility, not making bioluminescence.
Try explaining it
What can some deep-sea animals produce themselves?
Choose a), b) or c), then explain your choice.
- a)Heat that we see as light in the dark water.
- b)Light through processes in their bodies.
- c)Light that they reflect from the sea surface.
Show the explanation
Correct: b): Light through processes in their bodies.
Some deep-sea animals make their own light through chemical reactions. Depending on the species, it attracts prey, helps communication or conceals the body. Making light differs from reflecting sunlight.
Word help
- nutrient
- A substance a living thing needs to live and grow.
Explore in more detail
Here you will find longer explanations and further details. You can explore them together.
1. Less sunlight reaches deeper water
Near the sea surface it is bright during the day. Deeper down, less sunlight reaches the water. Below about two hundred metres, little usually remains. Below roughly a thousand metres, sunlight normally does not reach the water. It is dark, but not necessarily without any light: some living things glow. Water clarity also affects how much light gets through.
Checked against: [1]
2. A chemical reaction produces light
A chemical reaction changes substances into other substances. Some reactions release energy as light. Living things that produce light in this way are bioluminescent. Bioluminescence means light made by living organisms. They do not need a light bulb, and they do not simply glow because they were previously in sunlight.
Checked against: [2]
3. A glowing lure
Some female deep-sea anglerfish have a special lure in front of their heads. It is part of the fish. Tiny bacteria, very small living organisms, live in its light organ and produce the light. The fish provides protection and nutrients. The glowing lure can attract prey. Not all anglerfish live in the deep sea, and not every lure glows.
Checked against: [3]
4. Different animals use light differently
Light does not have the same job in every animal. Some species attract prey; others communicate with members of their species or use light for defence and escape. Researchers do not yet know the exact purpose of every organism’s glow. It would be wrong to say all glowing animals only want to attract food.
Checked against: [2]
An optional question for further exploration
You can use the longer explanation above. This is extra, not needed for the first quiz.
An extra question
How is the torch comparison helpful, and where does it stop being accurate?
Discover the answer
Both can produce light that stands out in darkness. But a torch uses electric current. Bioluminescence comes from chemical reactions; bacteria create the light in the lures of some deep-sea anglerfish.
Pictures and sources for adults
Sources for further reading
Facts checked against the specialist sources below on 12 October 2026. The Wusel scene is fictional; comparisons and simplified models are explicitly explained. Sources are in English.