THE FUNCTIONAL ANATOMY OF FEEDING
AND DIGESTION IN FISHES.
By Jim E. Quarles
While my primary interest is in discus fish the understanding of this
subject applies to most fishes and their required feeding habits. The
digestive system of a fish is quite simple when compared to that of higher
vertebrates. However there is great variations between species. This
involves the anatomy of the mouth parts which are frequently modified for
unique food habits.
The predators have developed mouths that allows them to capture and
swallow fairly large prey. This is generally done by swallowing the prey
whole, and most often head first.
Some fish are cannibalistic. One such fish we know and love is the
Oscar. It will eat anything it can catch and swallow. And in some cases
die trying to ingest food far to large for its mouth to handle.
Some species have teeth others do not. Some use a slash and cut method
such as the piranha. On the other hand the pacu which is closely related
have developed teeth used to crush nuts and fruit. Regardless of how they
capture and ingest food the process of digestion is the same only the
finer details very from species to species. As I will explain some species
have rather large guts that can contain large amounts of food for
digestion, others, such as the discus and angel fish have very small gut
areas and this in turn requires feeding far more often in small amounts at
any given time. Ingested food passes from the stomach into the intestine,
where it is processed further and nutrients are absorbed into the body.
Bile salts produced by the liver are stored by the gallbladder and
neutralize stomach acids and emulsify dietary fat. Certain dietary acids
must be present in order for vitamins to be absorbed. So feeding extra
vitamins without these acids should be avoided, as they can cause liver
damage. The pancreas secretes enzymes that digest carbohydrates into the
FOOD NUTRIENTS AND THEIR
Protein and Energy: Protein is the major nutrient required for growth
of fish and on a dry weight basis, makes up most of the body structure.
The proper protein nutrition cannot be overemphasized in making up a diet
for fish of all types.
Proteins contain essential components such as amino acids which are
used by fish to synthesize new body tissues and enzymes. Not all protein
is of equal value in the body building process. Proteins vary in their
ability to support growth, depending upon their source and processing. It
has been found that seafood and fish meals provides the best combination
of digestible amino acids. Remember feeds that have been dried at high
temperature lose nutritional value, because the essential amino acids bind
to other components and become unavailable to the fish.
Fish are super efficient at converting food to body tissues, so they
need less food to grow than almost any other animal. Over feeding is not
only a waste but leads to reduction in water quality as well. This seems
to be one of the major problems with those that keep tropcial fish, that
and over use of chemicals and drugs which are totally unnecessary in most
PROTEIN FOR FRY
Fish fry and larvae grow rapidly and require a very rich diet for
maximum growth and survival. In the wild protein makes up at least 50
percent or more of their diets on a dry weight bases. High protein foods
are important in the hatchery as well. The protein requirements of fish
decreases as they gain in size. Young adults can be reared on foods
containing 35 to 40 percent protein.
FATS AND ESSENTIAL FATTY ACIDS
Fats can supply energy for normal body needs, sparing proteins for
growth. Carbohydrates can also serve this function. If a feed is well
designed it will supply just enough energy for maximum growth without
producing fatty fish. Tank reared fish are especially prone to fatness
because they expend little energy searching for food.
Fat-soluble carotenoid pigments ( carotenes and xanthophylis ) are
responsible for the yellow, orange, red and green colors of the skin,
flesh, or eggs of many fish. I have read mounting evidence that some of
these pigments are important nutrients.
Survival of fertilized eggs to hatching has been shown to be related to
the concentration of pigments in the embryonic yolk. And in the
pre-spawning diet of the female fish. Carotenoid pigments may serve a
protective function for delicate membranes and other sensitive tissues.
Also bear in mind that a higher amount of vitamin E and other antioxidants
are needed in the diet when carotenoid pigments are included.
One problem to keep in mind in any feeding of fish is that ocular
cataracts, that can cause blindness in fish occurs when foods contain
inappropriate levels of certain minerals, vitamins and amino acids. The
discus hobbyist of today often complains of a white cloudy eye appearance
occurs on their fish. In most cases they mistake this for a parasitic
problem, and foolishly treat with chemicals or anti-biotics when such
treatments are not required.
A well balanced diet using different substances such as brine shrimp,
fresh-chopped fish, algae, beef heart well cleaned of fat and gristle or
veins. Lots of vegetables added to prepared foods is always a good idea.
PROPER FOOD IS JUST AS IMPORTANT AS PROPER WATER CONDITIONS IN
MAINTAINING HEALTH FISH.