How Fish Sense Their World: Sight, Smell, Hearing and More

By Dr Duncan Houston

A fish can notice movement beside the aquarium, find food it cannot see and respond to another fish before their bodies touch. Water carries light, dissolved chemicals, sound and local movement, so the same aquarium offers several overlapping kinds of information.

Understanding those senses helps you make better choices about lighting, shelter, equipment and daily interactions. The important starting point is the species: a daylight-feeding fish, a bottom-searching catfish and a weakly electric elephantnose fish do not experience their surroundings in the same way.

Quick Answer

Fish use sight, smell, taste, hearing and touch, while their lateral-line system detects nearby water movement. Some groups also sense electric fields, and particular species have specialised visual abilities such as ultraviolet sensitivity. Give aquarium fish conditions suited to their species, a predictable light cycle and places to retreat, rather than trying to stimulate every sense.

How do fish see underwater?

Many fish have rounded lenses that focus light in water. Vision helps them locate food, recognise shapes and movements, and respond to other animals. However, the colours and fine details a fish can detect depend on its visual system and the light available in its habitat.

Colour vision is not identical in every fish

Research on larval zebrafish has measured four types of cone photoreceptor sensitive to different parts of the spectrum, including ultraviolet. This is a specific example of a visual system, not proof that every aquarium fish sees the same colours. The research on zebrafish colour processing also shows why a fish's view cannot simply be equated with a human view of a brightly lit tank.

Polarised light is another specialised feature. A study of young sockeye salmon found sensitivity to polarisation under particular experimental conditions. That finding does not establish the same ability in all fish, or a need to buy special aquarium lighting. Choose lighting for the species and its environment, not an assumed universal fish superpower.

Make light predictable

Use a consistent daytime lighting routine and a dark period at night. Keep the aquarium away from direct sun, and provide shade or cover appropriate to its inhabitants. A brighter display is not automatically a better home. Check the needs of both the fish and any live plants before changing the lighting arrangement.

How do fish smell and taste?

Smell detects chemicals dissolved in water. Water passes over sensory tissue associated with the nasal openings, called nares, and the resulting signals travel to the brain. Smell can therefore provide information even when an object is out of view.

Taste involves a different set of receptors. Depending on the species, taste receptors may occur inside the mouth and on external areas of the head or body. Some fish can sample food-related chemicals before taking an item fully into the mouth. It is inaccurate to describe every fish as having taste buds spread over its whole body.

New York Sea Grant's introduction to fish senses describes these differences. For an owner, the useful distinction is that smelling something and deciding to eat it are separate steps. A response to food scent does not tell you that a food is nutritionally suitable.

What does a fish's lateral line detect?

The lateral line is a system of small sensory organs, called neuromasts, arranged over the head and body. Their sensory hair cells respond to movement of water. Some neuromasts lie on the surface and others sit within canals, depending on the species and developmental stage.

This gives a fish information about local flow and nearby disturbances. A moving neighbour, an object that changes the flow or the fish's own swimming can all affect the water around these sensors. The system contributes to orientation and interactions with the surroundings, especially when visual information is limited.

Research in zebrafish shows that neuromast position and hair-cell orientation help organise directional information. This is more precise than describing the lateral line as a single row of pressure-detecting pores. See the original study of lateral-line water-motion detection.

The practical lesson is to match flow to the fish. There is no single gentle-current setting that protects every species' sensory organs. A fish adapted to moving water may need a different environment from one associated with sheltered water. Review the whole tank layout, including resting areas, rather than assuming the filter's strongest outlet must suit every inhabitant.

Can fish hear without visible ears?

Yes. Fish have inner-ear structures even though they do not have the external ear flaps seen in mammals. In bony fish, dense structures called otoliths move differently from surrounding tissues as sound-related motion reaches the body. This movement stimulates sensory hair cells.

Underwater sound includes both particle motion and pressure changes. The inner ear detects motion; in some species, gas-filled structures such as the swim bladder improve the transmission of pressure-related information to the ear. Research comparing goldfish, bigeye and triplefin found differences associated with their hearing specialisations. Fish hearing cannot be reduced to one sensitivity shared by every species.

The lateral line and inner ear both respond to mechanical information, but they are distinct systems. One should not be described as a replacement for the other. The study of pressure and particle-motion detection explains the distinction.

As a practical precaution, observe fish without tapping the glass or deliberately startling them to obtain a reaction. Do not switch off essential filtration simply to make the tank seem quieter to you. Investigate rattling equipment using its maintenance instructions while keeping the aquarium's life-support needs in mind.

Which fish can sense electricity?

Electroreception is the ability to detect electric fields. Sharks, skates and rays have specialised organs called the ampullae of Lorenzini, which include gel-filled canals connected to pores. These help detect weak electric signals, including those associated with prey. The Florida Museum explains this system in its overview of fish adaptations.

Some bony fish also have an electric sense, but their receptors should not all be called ampullae of Lorenzini. Weakly electric mormyrids, including elephantnose fish, generate electric signals and use specialised skin receptors. Mormyromasts contribute to detecting objects through changes in the fish's own field; other receptors, called knollenorgans, are involved in electric communication.

This separates passive sensing, detecting an outside electric field, from active electrolocation, producing a field and detecting how objects alter it. The University of Regensburg's reference on electroreception and communication describes these different systems. None of this means that all fish produce useful electric fields, or that owners should add electrical stimulation to an aquarium.

How should this change everyday aquarium care?

Use the science to reduce avoidable disturbance and improve the match between the fish and its home. A sensible review has three stages:

1. Before changing equipment: confirm the species, its preferred habitat and the purpose of the change. Separate a viewing preference, such as brighter lighting, from an actual care need.
2. During ordinary daily care: watch where each fish rests, feeds and spends time. Note the light phase and whether behaviour differs near the outlet, open water or cover. Observe without repeatedly provoking a response.
3. When the setup does not seem to fit: review lighting, shelter, current, water testing and compatibility with a knowledgeable aquatics professional. Persistent unfamiliar behaviour is not enough to identify a sensory problem; seek veterinary advice for health concerns.

These are husbandry observations, not a home test for blindness, hearing loss or disease. A photo or short video and the tank's care records can help you explain what you have noticed without repeatedly chasing, netting or rearranging the fish.

Common mistakes to avoid

• Assuming all fish see ultraviolet or polarised light, or all have an electric sense.
• Choosing decorations solely for appearance without leaving usable swimming space and suitable shelter.
• Changing several parts of an established setup at once, making it harder to describe what changed.
• Adding more food simply because fish respond to feeding cues. Sensory interest is not a feeding allowance.
• Tapping the glass, flashing lights or moving objects repeatedly to see whether a fish reacts.

Frequently asked questions

Can fish smell food underwater?

Yes. Their smell receptors detect dissolved chemicals carried by water. Which cues matter most varies between species.

Is the lateral line the same as hearing?

No. The lateral line detects local water movement, while hearing involves the inner ear. Both provide mechanical information about the environment.

Can every fish see ultraviolet light?

No universal claim is justified. Ultraviolet sensitivity has been demonstrated in particular fish, including zebrafish, but their visual abilities should not be assigned to every species.

Do fish need the aquarium light on overnight?

Provide a regular day and night cycle appropriate to the species. Keeping the display illuminated for continuous viewing is not a substitute for that routine.

Should I test my fish's senses by making it react?

No. Quiet observation of its usual behaviour is more useful for daily care. Leave assessment of a suspected sensory or health problem to a veterinarian familiar with fish.

The practical takeaway

A fish's world contains much more than the view through the glass. Good sensory-aware care means respecting species differences, allowing retreat and keeping routine interactions predictable. Start with the needs of the fish you actually keep, then use careful observation to improve its surroundings.

Further husbandry reading

• RSPCA guidance on aquarium environment, filtration and lighting
• RSPCA guidance on fish behaviour, shelter and species-specific needs
• Original research abstract on visual sensitivity in young sockeye salmon

Keep this ASK A VET™ guide alongside your species-specific aquarium care notes.