2. Sensory Systems
Fish have relatively small brains and lack some of the features seen in mammalian
brains. Associated with the brain are a similar range of senses as seen in mammals.
A fishes ability to sense and feel pain has been a hotly debated topic over recent
years. However, there is little doubt that fish feel pain and can develop a fear like
response to pain stimuli. It should be remembered that fish have a different brain
structure and it is not known whether they sense pain and stress in the same way
humans do.
The following slides discuss the important senses in fish.
3. Eyes
Fish have eyes that are similar in structure to other vertebrates and most species
have good colour vision, with some species also able to see into the ultra violet
spectrum or are adapted for dark environments. For many species, vision is an
important sense either to avoid capture or for hunting.
Eyes are delicate and easily damaged from:
● Rough handling,
● Overcrowding,
● Feed deficiency, particularly Vitamin C
● Excessive light (UV)
Damage to eyes may impact on feeding and reduce growth and can cause fish to
darken in colour. When aggressive fish often attack the eye area as this one of the
vulnerable organs.
4. Taste and Smell
Most fish also have a keen sense of smell and taste which
are often extremely sensitive and may be located across the
body. This sense can play a major role in behaviour such as
migration when fish can ‘smell’ their home river from
hundreds of kilometres away. Smell is normally more
sensitive than taste in most species. Both senses function
the same as in other vertebrates, and are very sensitive.
Taste and smell are important for feeding of fish, eg.
attractants, can be incorporated in formulated feeds to
stimulate feeding. It also important for behaviour such as
social interaction, crowding, flight/fright, migration, and
imprinting/learning.
5. Hearing, Equilibrium & the Lateral Line
There are several organs involved in hearing and equilibrium and it is too a complex
interaction to discuss in detail. In terms of hearing, fish only have an inner ear which
functions the same as in other vertebrates but is often quite a poor sense. However,
the lateral line (a series of pores along midline of body sides that direst vibrations
directly down the nervous System) is used for detecting low frequency
vibrations/sound, may be used by reef fish to identify their home on the reef. The
swim bladder also plays a role in hearing. Swim bladder acts as an ear drum that
responds to sound waves and relays it straight to the brain.
Equilibrium is sensed via the semicircular canals detect spatial equilibrium and
detects the fishes position in 3 planes. Depth changes are detected by the otolith, a
hard bony substance in the inner ear, often use to identify species and determine the
age of fish.
6. Endocrine System
Bodily functions are generally controlled by hormones, including reproduction,
metabolism, growth, etc. This is known as the endocrine system. A range of organs
produce various hormones including the Hypothalamus, pituitary, thyroid, etc. –
these organs generally have the same function as other vertebrates.
Many hormonal pathways are influenced by environmental factors such as day
length, temperature and food availability. These environmental cues can trigger
migratory and reproductive behaviour in fish.
