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BIOLOGY OF TILAPIA
Tilapia
is a member of the family Cichlidae. Three genera are
well-known namely Oreochromis, Tilapia and Sarotherodon,
of which nile tilapia belongs to genus Oreochromis. This species
is naturally distributed in Palestine, the Nile River as well
as most part of African river and lakes. It was introduced in
the Philippines in 1972. It's rising popularity is due to their
hardness, resistance to diseases, ease in breeding, reasonable
growth rate, good taste, and tolerance to a wide range of environmental
conditions including temperature and salinities.
Taxomic
Positions of Tilapia
Most
tilapia species of the tribe Tilapiani now being used in aquaculture
were grouped initially into one genus, Tilapia. The species within
this genus were later classified according to differences in
their mode of reproduction (Low McConnel; 1959 Trewawas, 1973,
1978, 1982). Species which evolved as substrate spawner but guard
their eggs were retained in the genus tilapia while those which
orally rear their clutches were grouped into a new species Sarotherodon.
Classification of the three genera Tilapia, Sarotherodon and
Oreochromis was based largely on the differences on their reproduction
and feeding habits.
Classification of Tilapia
Species used in Aquaculture
Genus Tilapia (Substrate spawners)
Both parents guard, protect, aerate the
breed, and help move clutch to different nest sites. Fry at first
feeding are 4-5 mm and show feeble swimming ability. Fry survival
relatively low.
Genus Sarotherodon (Paternal/biparental)
Both parents stay close to each other.
Eggs and fry brooded in oral cavity up until they are ready for
release. Brood may not be collected once released. Fry are between
7-9 mm at first breeding, well developed fins for swimming. Fry
survival high.
Genus Oreochromis (Maternal)
Female solely involve in brood care.
After spawning, female leaves nest to rear her clutch in safety.
Fry brooded up until free swimming. There is an extended period
of care during which fry seek shelter in buccal cavity for safety.
First feeders have well-developed fins for swimming. Fry survival
high.
Sex
Identification
Sex
identification of tilapia is relatively simple. The male has
two openings just in front of the anal fin. The large opening
is the anus and the smaller opening at the tip is the urogenital
pore. The female has three openings: the anus, the genital pore,
and the urinary pore. The genital papilla is usually smaller
in the female. Tilapia can be sexed when it has attained the
weight of 15 grams. Application of ink or dark dyes to the papillae
may increase the accuracy of sexing and may allow sexing of smaller
fish. By rubbing ink along the papillae of the tilapia, sexes
can be readily distinguished.
Spawning
The
Nile tilapia is a mouth-brooder. The male establishes a territory
and builds a round nest in the pond bottom. (Usually the diameter
of a nest is 30 to 60 centimeters. The size of the nest is correlated
to the size of the male). The female enters the nest and lays
the eggs. The eggs are fertilized by the male. The female then
collects and incubates the eggs in her mouth. The eggs are yellow
in color. Eggs hatch in about five to seven days. After hatching
the fry remain in the mouth of the female for another four to
seven days. The fry begin to swim freely in schools, but may
return to the mouth of the mother when threatened. Females do
not feed during incubation or the brooding period.
Females spawn every four to six
weeks, but may spawn sooner if the eggs are removed. The number
of eggs per spawning is related to the size of the female. A
female of about 100 grams may produce approximately 100 eggs
per spawning while a female of about 100 to 600 grams can produce
approximately 1,000 to 1,500 or more eggs per spawning.
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