Fitzsimmons from University of Arizona
One of the great advantages of tilapia for
aquaculture is that they feed on a low trophic level. The members of the genus Oreochromis are all omnivores, feeding on
algae, aquatic plants, small invertebrates, detrital material and the associated
bacterial films. The individual
species may have preferences between these materials and are more or less
efficient depending on species and life stages in grazing on these foods.
They are all somewhat opportunistic
and will utilize any and all of these feeds when they are available. This provides an advantage to
farmers because the fish can be reared in extensive situations that depend upon
the natural productivity of a water body or in intensive systems that can be
operated with lower cost feeds.
In extensive aquaculture, the fish will be
able to grow by eating algae and detrital matter and the farmer can grow more
fish in a given area because the fish are depending directly on the primary
productivity of the body of water, primary consumers. Fish which feed on a higher trophic
level, eating larger invertebrates or small fish, are secondary consumers and a
system can only support a fraction of the biomass of secondary consumers
compared to primary consumers.
In intensive systems, tilapia have the
advantage that they can be fed a prepared feed that includes a high percentage
of plant proteins. Carnivorous
fish require fish meal or other animal proteins in their diets, which in general
are more expensive than plant proteins. Nutritional studies which substitute
plant proteins supplemented with specific amino acid supplements may lower
costs, but still not to the level that can be achieved with tilapia
Complete diets are used in systems that
cannot provide any dependable nutrition. This would include intensive
recirculating systems, cages placed in water with low productivity and even
heavily stocked ponds that do not provide enough nutrition for all the fish in
the system. Supplemental diets
will provide only portions of the nutritional demands of the fish, with the
assumption that they will get most of the nutrients from the growing
system. Supplemental diets are
usually much less expensive than complete diets and usually high in
carbohydrates. Some simple
supplemental diets serve a dual purpose of fertilizing the pond as well
Considerable research has been conducted on complete diets and on
fertilization programs for natural and man-made water bodies. Development of supplemental diets
directed to specifically provide limiting nutrients is a growing area of
Tilapia exhibit their best growth rates when
they are fed a balanced diet that provides a proper mix of protein,
carbohydrates, lipids, vitamins, mineral and fiber. Jauncey and Ross (1982), El-Sayed
and Teshima (1991) and Stickney (1996) provide excellent reviews that examine
the details of tilapia nutrition.
The nutritional requirements are slightly different for each species and
more importantly vary with life stage. Fry and fingerling fish require a
diet higher in protein, lipids, vitamins and minerals and lower in carbohydrates
as they are developing muscle, internal organs and bone with rapid growth.
Sub-adult fish need more calories
from fat and carbohydrates for basal metabolism and a smaller percentage of
protein for growth (Table 1).
Of course the absolute amount the fish is eating will still be increasing
as the fish is much larger.
Adult fish need even less protein, however the amino acids that make up
that protein need to be available in certain ratios (Table 2). Feed formulators
will adjust protein sources to fit the desired pattern of amino acids through
the growth cycle. Broodfish
may require elevated protein and fat levels to increase reproductive efficiency
(Santiago et al. 1985; Chang et al 1988).
Table 1. Typical protein requirements for
First feeding fry 45 - 50 %
2. 0.02 - 2.0 g
2.0 - 35 g
- harvest 30 -
Table 2. Essential Amino Acids in
experimental tilapia diets at the University of Arizona.
Essential Amino Acids
5 (74% of Cysteine)
In general, the lipid requirements for fish
under two grams represent 10% of the diet. This decreases to 6-8% from two grams
to harvest. The lipids should
contain both omega 3 and omega 6 fatty acids. Each fatty acid should represent 1%
of the diet, although some reports suggest that fish grow better with a higher
proportion of omega 6 to omega 3.
The fiber component is usually the reciprocal of the lipid content.
That is starting at 6-8% in small
fish up to 35g and increasing to 10% above 35g. Carbohydrates usually represent less
than 25% of the diet for fish under a gram and increases to 25 - 30% for fish
greater than a gram up to harvest.
Carbohydrates are often supplied by the least
expensive ingredients in the diet. Corn, wheat, rice and a number of
agricultural byproducts are typical carbohydrate sources. The ratio of energy supplied by
lipids and carbohydrates to the proteins available in the diet is often a
critical measure. Shiau (1997)
provides a comprehensive review of carbohydrate and fiber utilization in
tilapia. Vitamins and minerals
are critical to proper nutrition in tilapia and considerable research has been
conducted to determine these requirements (Watanabe et al. 1997; El-Sayed and
Teshima 1991; Roem, et al. 1990; Jauncey and Ross 1982). Commercial premixes are available
which allow feed makers to purchase a whole group of micronutrients rather than
attempting to determine how much is available from the productivity of the
system and the other ingredients (Table 3). Table 3.
Vitamin and mineral mix used in University
of Arizona tilapia diet.
(recommended amounts before
11 Folic acid
5 Riboflavin 20
B12 0.01 Pyridoxine
88 Ascorbic acid (C) 375 Vitamin K
0.20 (Note: Should not be above 0.3
Feed manufacturers will adjust the mix of
ingredients to create what are called “Least Cost Feed Formulations”. These are formulations that use
spreadsheet and database programs to examine the nutritional characteristics of
many ingredients at the same time.
The program can then select the mix of ingredients that meet all the
nutritional requirements at the lowest manufacturing cost. These feeds will then meet the
“Guaranteed Analysis” on the manufactures label, which tells any purchaser of
the feed what they can expect from the feed. This is meant to be
only a short introduction to tilapia nutrition. Specific nutritional needs vary by
species, age of fish, production system, and salinity. A wealth of information is available
and feed manufacturers have developed considerable expertise. Tilapia nutrition is critical to
further increases in efficiency and profitability for the small producer growing
for personal consumption and the large producer in international