Fishes have all the senses that terrestrial vertebrates have: water permits additional senses
1. Chemoreception-Smell and Taste
2. Auditory- hearing
3. Pressure sensitivity in muscles, skin-Touch
4. Vision
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5. Lateralis system - water displacement
6. Electroreception - electrical fields, magnetic field of the earth
I. Chemoreception
A. Olfaction - oldest "sense" in evolutionary terms
a. sensitivity: gonadotropin = 1 X 10-15
bile acids = 1 X 10-9
sex steriods= 1 X 10 -12
b. Size of olfactory bulb proportional to sensitivity-many sharks have large olfactory bulbs, greatly reduced in pufferfishes (Tetraondontidae, Diodontidae)
c. Folding of olfactory epithelium: eels - 90 folds, perch 18-20 folds
d. sexual dimorphism in development of olfaction:
deep sea angler-fishes: males: highly developed olfaction
females: poorly developed olfaction
e. homing in salmonids depends on imprinting smells to identify natal spawning grounds - perhaps smell of conspecifics
Hatchery raised fish?
f. concentration gradient searching
B. Taste (Gustation)
1. taste buds - Bulbous epithelial structures that protrude through
epidermis; sensory neurons synapse with receptor cells, activation results from binding of receptor sites to stimulus molecules
located in and on :
a. mouth, gill rakers, pharynx (most Teleosts)
b. barbels, and other body parts (catfishes),
c. pelvic fins: cod (Gadidae) gouramis (Belontiidae)
d. not elaborated in Elasmobranchs
e. enlarged vagal lobe in brain usually indicates reliance on taste
II. Acoustico-lateralis system
Functions: auditory
Maintence of balance
Near-field water pressure differentials
A. Mechanoreception
1. Nature of sound in water
a. Sound propagation 4.8 X faster in water than air; also travels
further
b. Near-field - water particle displacement
c. Far-field - pressure waves
2. Hearing - pars inferior
a. pars superior - labyrinth organ, maintains positional
equilibrium (detects yaw, pitch, and roll)
b. pars inferior - sacculi and lagunae, each with otoliths
sound detection
1. most fish tissues are transparent to sound, similar
density as water. Otoliths (ear bones) are more dense, displacement by sound wave lags
c. hair (receptor) cells - mechanical deformation stimulates
action potential - present in labyrinth, sacculus and neuromast cells
d. accessory amplification structures
1. extensions of swim bladder ending close to ear
EX: squirrelfishes (Holocentridae), tarpons (Megalopidae), deepsea cods, sea bream (Sparidae)
2. Weberian ossicles - otophysans - Characiformes,
Cypriniformes, Siluriformes
3. macula neglecta connects inner ear to
"tympanum" on some Elasmobranchs
--sensitive only to low frequency sounds, but
show evidence of locating objects in far-field (250 m)
3. Equilibrium and Balance - pars superior
1. semicircular canals filled with endolymph, sensory hair
cells in ampullae, change in orientation deforms cupula
2. utricle with otolith - verticle orientation
4. Lateral line-near field pressure detection (Teleosts and
Elasmobranchs)
1. canals on head - supra-, infra-orbital, preopercular
2. line down the lateral surface of fish
3. particularly well developed in stream fishes
4. Receptor cells, neuromasts (hair cells with cupula)
can be in canal or on the surface.
5. disruption of waves produced by swimming detected by lateral line system
III. Vision - eye very similar to other vertebrates
A. Eye structure
1. thin cornea
2. iris - elasmobranchs can change pupil diameter, teleosts can not
3. lens - spherical in teleosts, focus by moving lens relative to retina
4. retina: 5-layers, pigment epithelium, photoreceptor layer, bipolar
layer and ganglion layer, nerve fiber layer
5. choriod may contain tapetum lucidum; photomechanical movement
6. choriod gland - rete mirable
B. Photoreceptors
1. Rods-sensitive to low light levels, motion detection
2. Cones- bright light, color and detail discrimination
vary in sensitivity to different wavelengths - some can see UV!
3. Relative numbers of rods and cones correlate well to light environment
4. Spectral tuning of pigments through mutation of Rhodopsin
C. Unusual Eye morphologies
1. Deep sea fishes-elongate tubular eyes with dense retina
2. Four-eye fishes-Anableps (Anablepidae) have two pupils,oblong
lens and divided retina (dorsal and ventral). Light from surface
focused on ventral retina, light from water focused on dorsal retina.
IV. Electroreception - prey detection, signalling to conspecifics
Electric fields result from ion concentration differences, muscular activity
A. Receptor Cells - probably phylogenetically related to neuromast
cells; but lack cilia. Ca+ ion cascade in response to changes in electrical field induce neurotransmitters
1. Ampullary receptors - ampullae of Lorinzini (elasmobranchs) detect
weak electric fields of prey: Skin conductivity low, tissues high,
differences between freshwater and saltwater fishes
2. Tuberous receptors - found in fishes that generate electric fields, not
sensitive to weak fields
B. Electric communication - Gymnotid knifefishes
C. Magnetic reception
1. Elasmobranchs - conductor swimming through the earth's magnetic field induces field in the conductor; east - west generates opposite magnetic fields, north-south no signal
2. Magnetite found in yellow fin tuna (Scombridae), chinook salmon (Salmonidae)