dietary ingredients, fish species and size and
feeding frequency. Complex carbohydrates
such as starches are better utilized than
disaccharides and monosaccharides by
tilapias. Hybrid tilapia (O. niloticus x O.
aureus) showed the carbohydrate (44 percent)
digestibility in the following progression:
starch>maltose>sucrose>lactose>glucose.
Nile tilapia can utilize high levels of various
carbohydrates of between 30 to 70 percent of
the diet. It has also been demonstrated that
larger hybrid tilapia (O. niloticus x O. aureus)
utilized carbohydrates better than smaller
sized fish. It’s been reported that the inclusion
of soluble non-starch polysaccharides (NSP) in
the form of cellulose in the diet of Nile tilapia
increased the organic loading of the culture
system, while insoluble NSP (guar gum) placed
less organic load on the system by increasing
nutrient digestibility and improving faeces
recovery.
Vitamin supplementation is not necessary for
tilapia in semi-intensive farming systems, while
vitamins are generally necessary for optimum
growth and health of tilapia in intensive
culture systems where limited natural foods
are available. Several vitamin requirements
of tilapia are known to be affected by other
dietary factors and these must be taken
into consideration in diet formulations.
For example, the vitamin E requirement is
influenced by dietary lipid level with Nile tilapia
requiring 50-100 mg/kg when fed diets with
5 percent lipid and increased to 500 mg/kg
diet for diets with 10-15 percent lipid. Apart
from dietary lipid level, the unsaturation index
of the dietary oil will also affect the amount
of vitamin E required. The presence of other
antioxidants in the diet, such as vitamin C,
has been reported to spare vitamin E in diets
for hybrid tilapia. Choline can be spared to
some extent by betaine. β-carotene can be
bio-converted to vitamin A with a conversion
AgriKultuur |AgriCulture
ratio of about 19:1. Pyridoxine requirement
level has been shown to vary with the level of
protein in the diet: 1.7-9.5 and 15-16.5 mg/
kg diet for fish fed 28 and 36 percent protein
diets, respectively for hybrid tilapia. The
source of dietary carbohydrates influences
niacin requirement for hybrid tilapia which
was reported to be 121 mg/kg for dextrin-
based diets and 26 mg/kg for fish fed glucose-
based diets. Vitamin requirement values
are also dependent on the stability and
bioavailability of the vitamin compound that
was used. For example, the phosphate forms
of ascorbic acid are more available than the
sulphate forms.
There is little information on the mineral
requirements of tilapia. Like other aquatic
animals, tilapias can absorb minerals from the
culture water which makes the quantitative
determination of these elements difficult
to carry out. For example, when Nile tilapia
reared in fertilized ponds were fed with diets
either containing complete mineral mixes or
one deficient in Ca, P, Mg, Na, K, Fe, Zn, Mn
or I and it was found that only the addition of
phosphorous significantly affected weight gain,
food conversion ratio and protein efficiency
ratio. Despite its ability to absorb minerals
from the culture water and the presence
of minerals in feed ingredients, tilapia
feeds should contain supplemental mineral
premixes. This is to ensure that sufficient
levels are available to protect against mineral
deficiencies caused by reduced bioavailability
such as when plant phosphorus sources are
used in tilapia feeds. Like vitamins, the amount
of minerals to be added in the diet will also
depend on the source of the element.
Many of the plant-based feed ingredients have
high phytic acid content which appears to
bind metal ions such as calcium, phosphorus,
magnesium, manganese, zinc and iron
9