Lecture 6 – Sensory Systems in Fish

ICHPTHYOLOGY

Why is sight limited underwater?

Water absorbs light quickly; visibility is limited to ~10 meters, with red wavelengths absorbed first.

How far can various senses reach in fish?

Hearing: kms, Smell: 100s of meters, Lateral Line: 100m, Sight: 10m, Electroreception/Taste: cms.

What light adaptations exist in deep-sea fish

They see only blue light; eyes are adapted to detect bioluminescence and short wavelengths.

How do fish eyes focus light?

The spherical lens moves back and forth using retractor lentis muscle and suspensory ligaments.

How do fish control light entering the eye?

Some have slow irises; others use pigments, operculum, or nictitating membranes to block light.

What is the difference between rod and cone cells?

Rods detect low light; cones detect color. Deep-sea fish have more rods.

What structure provides oxygen to the retina?

The choroid, sometimes with a choroid gland and rete mirabile to maintain high oxygen levels.

What is the Tapetum lucidum?

reflective layer behind the retina in some fish that enhances light sensitivity.

What are the three light zones of the ocean?

: Euphotic (light, color, photosynthesis), Dysphotic (dim, silhouette detection), Aphotic (no light).

What are tubular eyes and their advantage?

Vertical, cylindrical eyes with large lenses for capturing faint light from above; good for silhouette detection.

What is the disadvantage of tubular eyes

Narrow field of vision; poor peripheral vision.

How do fish like the barreleye and spookfish expand their visual field?

By rotating tubular eyes and using accessory retinas and diverticula to reflect light from other angles.

Why do some deep-sea fish warm their eyes?

To improve temporal resolution and visual acuity in cold, dark environments.

How do fish generate eye heat

Via specialized extraocular muscles that warm the brain and eyes.

What is the main function of fish nostrils?

Smell (olfaction), not respiration.

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How is the olfactory system structured?

aired nostrils, rosettes with folded epithelium, incurrent and excurrent openings; water flow generated passively or actively.

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What are functions of olfaction in fish?

Food detection, migration, predator detection, mate recognition, and courtship stimulation.

How is taste different from smell in fish?

A: Taste requires physical contact; receptors are in mouth (elasmobranchs) or across the body (teleosts).

What do taste buds detect?

Bitter, sweet, amino acids, CO₂, salt, sour – often used to follow food trails.

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What is the lateral line system?

A mechanosensory system that detects water movements and vibrations using neuromasts.

What are neuromasts?

Organs with hair cells embedded in a gelatinous cupula that respond to water displacement.

How are hair cells stimulated?

Stereocilia bend toward kinocilium = excitation; away = inhibition.

What is the function of the lateral line?

Predator-prey detection, schooling, current awareness, self-motion detection.

: How do deep-water fish enhance lateral line sensitivity?

By placing neuromasts on the skin instead of in canals.

What do mackerel have for increased water motion detection?

Free neuromasts and head pores for directional detection.

What are the functions of the fish inner ear?

Hearing, spatial orientation, and equilibrium.

How does the inner ear detect movement?

via endolymph movement through 3 semicircular canals; ampullae with hair cells detect movement.

What are otoliths?

dense calcium carbonate stones in the inner ear that detect sound and gravity.

How do otoliths detect orientation?

They rest on macula hair cells; shift with movement to detect head posture and acceleration.

How do otoliths aid hearing?

Their density makes them vibrate differently than tissue in response to sound waves.

What are Weberian ossicles?

Bones connecting the swim bladder to the inner ear, enhancing sound detection in some fish.

How are fish aged using otoliths?

By counting alternating growth rings – hyaline (winter) and opaque (summer).

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What types of sound do fish produce?

incidental (swimming, feeding), stridulation (rubbing body parts), and active swim bladder vibration.

How do fish produce sound actively?

By contracting intrinsic or extrinsic muscles on the swim bladder or expelling gas.

What is electroreception?

the ability to detect electric fields; used for navigation, prey detection, communication.

What are ampullary receptors?

Receptors detecting low-frequency electric fields; e.g., ampullae of Lorenzini in elasmobranchs.

Where are ampullae of Lorenzini located?

Clustered around the head and filled with conductive gel; detect electrical stimuli.

What are phasic receptors?

Rapid, high-frequency receptors used in electrogenic species for generating and detecting electrical signals.

Which fish produce electricity?

: Electric eels, catfish, and some rays; they use modified muscle stacks.

What is the function of electricity in fish?

Hunting, defense, communication, navigation, and electrolocation in murky waters.