In general, mouthbrooders have been used more in food fish production, whereas substrate spawners have been used mostly for weed control.
Species selection
Potential tilapia culturists in the U.S.
should first determine which species,
if any, can be legally cultured in
their state. Assuming there are no
restrictions, selection of a species
will depend mostly on growth rate
and cold tolerance. Rankings for
growth rate in ponds are T. nilotica
> T. aurea > T. rendalli > T. mossambica
> T. hornorum. Most of the
hybrids tested grow as fast as their
parent species. Cold tolerance may
become an increasingly important
criterion for selecting a species in
more northerly latitudes. Tilapia
aurea is generally recognized as
being the most cold tolerant.
Pond culture is the most popular
method of growing tilapia. One
advantage is that the fish are able to
utilize natural foods. Management of
tilapia ponds ranges from extensive
systems, using only organic or inorganic
fertilizers, to intensive systems,
using high-protein feed, aeration and
water exchange. The major drawback
of pond culture is the high level
of uncontrolled reproduction that
may occur in growout ponds. Tilapia
recruitment, the production of fry
and fingerlings, may be so great that
offspring compete for food with the
adults. The original stock becomes
stunted, yielding only a small percentage
of marketable fish weighing
1 pound (454 grams) or more. In
mixed-sex populations, the weight of
recruits may constitute up to 70 percent
of the total harvest weight. Two
major strategies for producing tilapia
in ponds, mixed-sex culture and male
monosex culture, revolve around
controlling spawning and recruitment.
There is no restriction on pond size,
but for ease of management and
economical operation, shallow (3 to
6 feet), small (1 to 10 acres) ponds
with drains are recommended.
Draining is necessary to harvest all
of the fish. A harvesting sump is
needed to concentrate the fish in the
final stage of drainage. The pond
bottom should be dried to eradicate
any fry or fingerlings that may interfere
with the next production cycle.
Geographic range for culturing
tilapia in ponds is dependent upon
temperature. The preferred temperature
range for optimum tilapia
growth is 82 to 86 F. Growth
diminishes significantly at temperatures
below 68 F and death will
occur below 50 F. At temperatures
below 54 F, tilapia lose their resistance
to disease and are subject to infections
by bacteria, fungi and
parasites.
In temperate regions, tilapia must be
overwintered in heated water. In the
continental United States, the southernmost
parts of Texas and Florida
are the only areas where tilapia survive
outdoors year-round with the
exception of geothermally-heated
waters, most notably in Idaho. In the
southern region, tilapia can be held
in ponds for 5 to 12 months a year
depending on location.
Mixed-sex culture
Mixed-sex populations of fry are
cultured together and harvested
before or soon after they reach
sexual maturity, thereby eliminating
or minimizing recruitment and overcrowding. A restricted culture
period limits the size of fish that can
be harvested.
In mixed-sex culture, tilapia are
usually stocked at low rates to reduce
competition for food and promote
rapid growth. One month-old,
l-gram fry are stocked at 2,000 to
6,000 per acre into growout ponds
for a 4- to 5-month culture period.
Newly-hatched fry should be used
because older, stunted fish, such as
those held over winter, will reach
sexual maturity at a smaller,
unmarketable size. Supplemental
feeds with 25 to 32 percent protein
are generally used. At harvest,
average weight is approximately
0.5 pound (220 grams), and total
production is near 1,400
pounds/acre for a stocking rate of
4,000/acre. Expected survival is
roughly 70 percent.
Species such as Tilapia zilli, T. hornorum,
or T. mossambica are not
suitable for mixed-sex culture because
they reproduce at an age of 2
to 3 months and at an unmarketable
size of 30 grams or less. Tilapia
suitable for mixed-sex culture are T.
aurea, T. nilotica and their hybrids,
all of which reproduce at an age of 5
to 6 months.
Two to three crops of fish can be
produced annually in the tropics
compared to only one crop in temperate
regions. In temperate regions,
mixed-sex culture is referred to as
young-of-the-year culture because
fry produced in the spring are grown
to marketable size by autumn. Early
spawning is needed to maximize the
growout period. The growout season
is shortened by about 2 months to account
for spawning and rearing of
l-gram fry for stocking growout
ponds.
Male fingerling rearing
With male monosex culture, fry are
usually reared to fingerling size in a
nursery phase, and then male fingerlings
are separated from females for
final growout. All-male fingerlings
can be obtained by three methods:
hybridization, sex-reversal and manual
sexing. None of these methods is
consistently 100 percent effective,
and thus a combination of methods
is suggested. Hybridization maybe
used to produce a high percentage
of male fish. The hybrids may then
be manually sexed or subjected to a
sex-reversal treatment. All three
methods are sometimes used.
Hybridization and sex-reversal
reduce the number of female fingerlings
that must be discarded during
manual sexing. This saves time,
space and feed. Problems nevertheless
still exist with hybridization and
sex-reversal. Producing sufficient
numbers of hybrid fry maybe
difficult because of spawning incompatibilities
between the parent
species. Sex-reversal is more technically
complicated and requires obtaining
recently hatched fry and rearing
them in tanks with high quality
water. Both hybridization and sexreversal
may produce less than 100
percent males.
Manual sexing is commonly used by
producers. Manual sexing (hand
sexing) is the process of separating
males from females by visual inspection
of the external urogenital pores,
often with the aid of dye applied to
the papillae. Secondary sex characteristics
may also be used to help distinguish
sex. Reliability of sexing
depends on the skill of the workers,
the species to be sorted and its size.
Experienced workers can reliably
sex 15-gram fingerling T. hornorum
and T. mossambica, 30-gram T.
nilotica, and 50-gram T. aurea.
In the tropics, fingerlings maybe
produced year-round. In temperate
regions, fingerlings are produced
during summer and stored in overwintering
facilities for the next growing
season. If manual sexing is used,
it is done prior to overwintering. The
best fingerling size for overwintering
depends on the number of fingerlings
that will be needed and the
available storage capacity. Fry of 1
gram or less are stocked in nursery
ponds and fed high-quality feeds.
Ponds stocked at 20,000 fry/acre will
produce 100-gram fingerlings in 18
weeks, while 40,000 fry/acre will produce
50-gram fingerlings in 12
weeks, and 72,000 fry/acre will produce
27-gram fingerlings in 9 weeks.
Fingerlings that weigh less than 20
grams should not be overwintered
because their survival rate will be
low.
Overwintering facilities consist of
geothermal springs, greenhouses
and heated buildings. Fingerlings
can be held in cages located in
geothermal springs or in small ponds
or tanks through which warm spring
water is diverted. In greenhouses
and heated buildings, recirculating
systems are used to hold large
quantities of fingerlings. Fingerlings
can be overwintered in long, narrow
ponds that are covered with clear
plastic if the winter is mild.
Male monosex culture
Males are used for monosex culture
because male tilapia grow faster
than females. Females use considerable
energy in egg production and
do not eat when they are incubating
eggs. Male monosex culture permits
the use of longer culture periods,
higher stocking rates and fingerlings
of any age. High stocking densities
reduce individual growth rates, but
yields per unit area are greater. If
the growing season can be extended,
it should be possible to produce fish
weighing one pound (454 grams) or
more. Expected survival for all-male
culture is 90 percent or greater. A
disadvantage of male monosex culture
is that female fingerlings are discarded.
The percentage of females mistakenly
included in a population of mostly
male tilapia affects the maximum attainable
size of the original stock in
growout. For example, manually
sexed T. nilotica fingerlings (90 percent
males) stocked at 3,848/acre
will cease growing after 5 months
when they average about 0.8 pounds
(365 grams) because of competition
from recruits. If larger fish are
desired, females should comprise 4
percent or less of the original stock
and predator fish should be included.
The stocking rate for male monosex
culture varies from 4,000 to 20,000/
acre or more. At proper feeding
rates, densities around 4,000/acre
allow the fish to grow rapidly without
the need for supplemental aeration.
About 6 months are required to
produce 500-gram fish from 50-gram
fingerlings, with a growth rate of 2.5
grams/day. Total production approaches
2.2 tons/acre.
A stocking rate of 8,000/acre is frequently
used to achieve yields as
high as 4.4 tons/acre. At this stocking
rate the daily weight gain will
range from 1.5 to 2.0 grams. Culture
periods of 200 days or more are
needed to produce large fish that
weigh close to 500 grams. To produce
a 500-gram fish in temperate
regions, overwintered fingerlings
should weigh roughly 70 to 100
grams and be started as early as possible
in the growing season. A stocking
rate of 8,000/acre does require
nighttime emergency aeration when
the standing crop is high.
Stocking rates of 12,000 to 20,000/
acre have been used in 1.2 to 2.5-
acre ponds, but this requires the continuous
use of two to four, one-horse
power paddlewheel aerators per
pond. Yields for a single crop range
from 6 to 10 tons/acre.
With optimal temperatures, feeding
rates depend on fish size and density.
Optimal daily feeding rates for
fish of 30,50, 100, 175 and 450 grams
are 3.5, 3.0, 2.5, 2.0 and 1.5 percent
of body weight, respectively. If densities
are high, sub-optimal feeding
rates may have to be used to maintain
suitable water quality, thereby
increasing culture duration.
Polyculture
Tilapia are frequently cultured with
other species to take advantage of
many natural foods available in
ponds and to produce a secondary
crop, or to control tilapia recruitment.
Polyculture uses a combination
of species that have different
feeding niches to increase overall
production without a corresponding
increase in the quantity of supplemental
feed. Polyculture can improve
water quality by creating a
better balance among the microbial
communities of the pond, resulting
in enhanced production. The disadvantage
of polyculture is the special
equipment (sorting devices, conveyors,
etc.) and extra labor needed to
sort the different species at harvest.
The role of natural pond foods is
less important in the intensive culture
of all male populations and may
not justify the expense of sorting the
various species at harvest.
Tilapia can be cultured with channel
catfish (Ictalurus punctatus) with
only a minor reduction in catfish
yields. Male tilapia stocked at a rate
of 800/acre yield nearly 770
pounds/acre when channel catfish
are stocked at 3,000/acre. At this
stocking rate, net production of catfish
declines by roughly 170 pounds/
acre, but for every reduction of
1 pound in catfish production, 4.5
pounds of tilapia are produced.
Catfish production does not decline
when cultured in combination with
tilapia, silver carp (Hypophthalmichthys
molitrix) and grass carp
(Ctenopharyngodon idellus) at densities
of 800, 1,000 and 20/acre,
respectively. With no additional
feed, total net production can reach
nearly 4,120 pounds/acre compared
to 2,370 pounds/acre for catfish cultured
alone. The incidence of offflavor
catfish may be less in
catfish/tilapia polyculture than catfish
monoculture.
Another promising polyculture system
consists of tilapia and prawns
(Macrobrachium rosenbergii). In
polyculture, survival and growth of
tilapia and prawns are independent.
Feed is given to meet the requirements
of the fish. Prawns, which are
unable to compete for the feed,
utilize wasted feed and natural foods
that result from the breakdown of
fish waste. Stocking rates for 1 to 2
gram prawns vary from 4,000 to
36,000/acre, but a rate of 8,000/ acre
is often used to obtain a high percentage
of market-size prawns
(<25 grams) and a yield of about
445 pounds/acre. Tilapia can be
stocked in the range of 2,000 to
4,000/acre.
Another type of poylculture involves
the use of a predatory fish, such as
largemouth bass (Micropterus salmoides),
to reduce tilapia recruitment.
Stocking predators with mixedsex
tilapia populations controls
recruitment and allows the original
stock to attain a larger market size.
Predators must be stocked at a small
size to prevent them from eating the
original stock. Predators may be
stocked when tilapia begin breeding.
The number of predators required
to control tilapia recruitment in culture
ponds depends primarily on the
maximum attainable size of the predator
species, the ability of the predator
to reproduce, and the number
of mature female tilapia. In general,
as predators grow they eat larger
sized tilapia recruits. Eventually this
may result in an increasing biomass
of small tilapia that are not consumed.
However, this problem should not
develop in ponds that are completely
harvested one or more times a year.
More predators are required to control
recruitment when there are
larger numbers of mature female
tilapia. For tilapia populations ranging
from 2,000 to 4,000/acre and containing
50 percent females, the
recommended predator/prey ratio is
one largemouth bass to 15 tilapia.
With 10 percent females, the recommended
ratio is one largemouth bass
to 65 tilapia.
Use of predators has been effective
on an experimental scale, but they
have not been used widely in commercial
operations because of the
difficulty in finding reliable sources
of fingerlings. Some of the best
predators, such as guapote tigre
(Cichlasoma managuense) and
peacock bass (Cichla ocellaris), are
exotic species and may be illegal to
use.
Fertilization and manuring
The most appropriate mouthbrooding
tilapia for culture can feed low
on the food chain, on a diet of plankton
and detritus. If the natural
productivity of a pond is increased
through fertilization or manuring,
significant production of tilapia can
be obtained without supplemental
feeds. Although yields are not as
high as those obtained with feed, fertilizers
and animal manures can be
used to reduce the quantity and expense
of supplemental feeds. An increase
in natural food has a much
greater effect on tilapia production
at densities less than 4,000/acre.
Inorganic fertilizers are used less
often because of their expense, but a
single large application of an inorganic
fertilizer high in phosphorus is
frequently made prior to stocking
fish to create an algal bloom. Tilapia
productivity is stimulated mainly by
an increase in phosphorus and to a
lesser extent by an increase in
nitrogen. Phosphorus is effectively
increased through the application of
liquid polyphosphate (13-38-0) at a
rate of 20 pounds/acre (2.4 galions/
acre).
Manuring, which is widely used for
food fish production overseas, has
not been practiced in the U.S. because
of public perception. Manuring
may have application in the
production of tilapia as a source of
fish meal for animal feeds. The quality
of manure as a fertilizer depends
on several factors. Pig, chicken and
duck manures increase fish production
more than cow and sheep
manure. Animals fed high quality
feeds (grains) produce manure that
is better as a fertilizer than those fed
diets high in crude fiber. Fresh
manure is better than dry manure.
Finely-divided manures provide
more surface area for the growth of
microorganisms and produce better
results than large clumps of manure.
Manure should be distributed evenly
over the pond surface area. Large accumulations
of manure on the pond
bottom produce low oxygen conditions
in the sediment that reduce
microbial activity and sometimes
result in the sudden release of toxic
chemicals into the water column.
To maximize fish production, manure
should be added daily to the
pond in amounts that do not reduce
dissolved oxygen (DO) to harmful
levels as it decays. The maximum application
rate varies from 90 to 180
pounds/acre/ day for dry manure.
The maximum rate depends on the
quality of the manure, the oxygen
supply in the pond and water
temperature. If early morning DO is
less than 2 ppm, manuring should be
reduced or stopped until DO increases.
If it is not possible to
measure DO, the maximum rate
should be limited to 90
pounds/acre/day to ensure a margin
of safety. When water temperatures
are less than 64 F, manuring should
be discontinued. At low temperatures
the rate of decomposition decreases
and manure may accumulate
on the pond bottom. A subsequent
increase in temperature could then
result in an oxygen depletion.
The rate of manuring should be increased
gradually as the fish grow.
The recommended manuring rate as
dry matter is 2 to 4 percent of the
standing fish biomass per day.
Yields of male monosex populations
in manured ponds have been
modest, but production costs are
very low if the manure is free. For example,
all-male hybrids (T. nilotica
x T. hornorum, 29 grams) stocked
at 4,000/acre will produce a net yield
of 1,470 pounds/acre of 200-gram
fish in 103 days when given fresh cattle
manure at an average rate (dry
weight) of 46 pounds/acre/day. In
comparison, fish receiving a commercial
high-protein feed will give a net
yield of 2,370 pounds/acre. Feeding
costs per pound of production are
two to twenty times higher for fish
fed the commercial diet compared
to fish receiving manure.
Integrated systems
Collection, transport, storage and distribution of manure involve considerable expense and are major obstacles to manured systems. These problems can be overcome by locating the animal production unit adjacent to or over the fish pond so that fresh manure can easily be delivered to the pond on a continuous basis. Effective and safe manure loading rates are maintained by having the correct number of animals per pond surface area.
Chicken/fish farming
Maximum tilapia yields are obtained from the manure output of 2,000 to 2,200 chickens/acre, which deliver 90 to 100 pounds (dry weight) of manure/ acre/day. Broiler flocks should be composed of three size groups to stabilize manure output. Several crops of chickens can be produced during a fish production cycle.
Pig/fish farming
Approximately 24 to 28 pigs/acre are required to produce a suitable quantity of manure (90 to 100 pounds of dry matter/acre/day) for tilapia production. The pigs are usually grown from 44 to 220 pounds over a 6-month period.
Duck/fish farming
Ducks are grown on ponds at a density of 300 to 600/acre. The ducks are generally raised in confinement, fed intensively, and allowed access to only a portion of the pond where they forage for natural foods and deposit their manure. Ducks that arc raised on ponds remain healthier than land-raised ducks. Also by raising ducks on ponds, feed wasted by the ducks is consumed directly by the fish. Since ducks reach marketable size in 10 to 11 weeks, staggered production cycles are needed to stabilize manure output.
Harvesting
Tilapia are best harvested by seining and draining the pond. A complete harvest is not possible by seining alone. Tilapia are adept at escaping a seine by jumping over or burrowing under it. Only 25 to 40 percent of a T. nilotica population can be captured per seine haul in small ponds. Other tilapia species, such as T. aurea, are even more difficult to capture. A l-inch mesh seine (with bag) of proper length and width is suitable for harvest.
Further Articles
Tilapia: Life History and Biology
Cage Culture of Tilapia
Tank Culture Of Tilapia
Source: Southern Regional Agricultural Center and the Texas Aquaculture Extension Service - Taken from site - December 2005
