Freshwater

Within the human eye, the shape of the lens is constantly changing in an
effort to achieve proper focus. The lens in a fish’s eye remains the same
shape, but focuses with help from special ocular ligaments that actually
move the eye forward and backward in its socket.
Hearing
Fish do not have complex ears like we do because sound travels in water
much faster than in air, so by evolution standards this was not needed. Fish
ears are composed of a simple inner chamber. Vibrations picked up from the
environment are passed over sensory components, which generate sound.
Most ichthyologists (fish experts) believe that a fish’s swim bladder works
together with the components of the inner ear to distinguish specific sound
patterns.
Smell
Smell plays an important role in detecting food and prey, and in locating a
suitable mate. Fish take in smells through their nostrils, which are connected
to their olfactory system. This olfactory system is not completely joined with
the respiratory system and acts as a separate unit.
Taste
Fish have taste buds on their mouths, lips, and, in special cases, on their fins.
The complete range of taste for fish is very short, so they must constantly
forage through their environment in hopes that they can “stumble across” the
food they need to survive. Catfish have evolved barbels (whiskerlike appendages)
that contain taste buds for locating food in cloudy or dark water.
Feeling
Chapter 7: Fish Anatomy
The old argument as to whether fish can feel pain or not has been at issue for
many years. We would really hate to find out that our fish could feel pain if
we did something that caused them harm. The safest bet is to assume always
that your fish can feel pain and treat them with respect and great care just
like you would any other pet.
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