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L-2408SRAC Publication No. 280

July, 1989

SouthernRegionalAquacultureCenter

Pond Culture of Tilapia

James E. Rakocy* and Andrew S. McGinty **

In the U.S., the most appropriatespecies of tilapia for culture are themouthbrooders: Tilapia nilotica, T.

aurea, T. mossambica, T. hornorum,and the substrate spawners: T. ren-dalli and T. zillii. Various hybridsbetween mouthbrooding species mayalso be important; e.g., most of thereddish-orange tilapias are hybrids.In general, mouthbrooders havebeen used more in food fish produc-

tion, whereas substrate spawners

have been used mostly for weedcontrol.

Species selectionPotential tilapia culturists in the U.S.should first determine which species,if any, can be legally cultured in

their state. Assuming there are norestrictions, selection of a specieswill depend mostly on growth rate

and cold tolerance. Rankings forgrowth rate in ponds are T. nilotica> T . aurea > T. rendalli > T. mos-

sambica > T. hornorum. Most of thehybrids tested grow as fast as their

parent species. Cold tolerance may

become an increasingly importantcriterion for selecting a species inmore northerly latitudes. Tilapia

aurea is generally recognized asbeing the most cold tolerant.

* University of the Virgin Islands

** University of Puerto Rico

Pond culture is the most popularmethod of growing tilapia. Oneadvantage is that the fish are able toutilize natural foods. Management oftilapia ponds ranges from extensive

systems, using only organic or inor-ganic fertilizers, to intensive systems,using high-protein feed, aeration andwater exchange. The major draw-

back of pond culture is the high levelof uncontrolled reproduction thatmay occur in growout ponds. Tilapia

recruitment, the production of fryand fingerlings, may be so great thatoffspring compete for food with theadults. The original stock becomes

stunted, yielding only a small per-centage of marketable fish weighing1 pound (454 grams) or more. In

mixed-sex populations, the weight ofrecruits may constitute up to 70 per-

cent of the total harvest weight. Twomajor strategies for producing tilapiain ponds, mixed-sex culture and male

monosex culture, revolve around

controlling spawning and recruit-ment.

There is no restriction on pond size,

but for ease of management andeconomical operation, shallow (3 to6 feet), small (1 to 10 acres) ponds

with drains are recommended.Draining is necessary to harvest allof the fish. A harvesting sump isneeded to concentrate the fish in thefinal stage of drainage. The pond

bottom should be dried to eradicate

any fry or fingerlings that may inter-fere with the next production cycle.

Geographic range for culturingtilapia in ponds is dependent upontemperature. The preferred tempera-ture range for optimum tilapiagrowth is 82 to 86 F. Growth

diminishes significantly at tempera-tures below 68 F and death willoccur below 50 F. At temperatures

below 54 F, tilapia lose their resis-tance to disease and are subject to in-fections by bacteria, fungi and

parasites.

In temperate regions, tilapia must beoverwintered in heated water. In thecontinental United States, the south-ernmost parts of Texas and Floridaare the only areas where tilapia sur-vive outdoors year-round with theexception of geothermally-heatedwaters, most notably in Idaho. In the

southern region, tilapia can be heldin ponds for 5 to 12 months a year

depending on location.

Mixed-sex cultureMixed-sex populations of fry are

cultured together and harvestedbefore or soon after they reachsexual maturity, thereby eliminatingor minimizing recruitment and over-

Texas Agricultural Extension Service qZerle L. Carpenter, Director qThe Texas A&M University System qCollege Station, Texas

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crowding. A restricted cultureperiod limits the size of fish that canbe harvested.

In mixed-sex culture, tilapia are

usually stocked at low rates to reducecompetition for food and promoterapid growth. One month-old,l-gram fry are stocked at 2,000 to6,000 per acre into growout pondsfor a 4- to 5-month culture period.Newly-hatched fry should be used

because older, stunted fish, such asthose held over winter, will reachsexual maturity at a smaller,unmarketable size. Supplementalfeeds with 25 to 32 percent proteinare generally used. At harvest,average weight is approximately0.5 pound (220 grams), and totalproduction is near 1,400pounds/acre for a stocking rate of

4,000/acre. Expected survival isroughly 70 percent.

Species such as Tilapia zilli, T. hor-norum, or T. mossambica are notsuitable for mixed-sex culture be-cause they reproduce at an age of 2to 3 months and at an unmarketablesize of 30 grams or less. Tilapiasuitable for mixed-sex culture are T.aurea, T. nilotica and their hybrids,all of which reproduce at an age of 5to 6 months.

Two to three crops of fish can beproduced annually in the tropicscompared to only one crop in temp-erate regions. In temperate regions,mixed-sex culture is referred to asyoung-of-the-year culture becausefry produced in the spring are grownto marketable size by autumn. Earlyspawning is needed to maximize thegrowout period. The growout seasonis shortened by about 2 months to ac-count for spawning and rearing ofl-gram fry for stocking growout

ponds.

Male fingerling rearingWith male monosex culture, fry areusually reared to fingerling size in anursery phase, and then male finger-lings are separated from females forfinal growout. All-male fingerlings

can be obtained by three methods:hybridization, sex-reversal and man-ual sexing. None of these methods is

consistently 100 percent effective,and thus a combination of methodsis suggested. Hybridization maybeused to produce a high percentageof male fish. The hybrids may thenbe manually sexed or subjected to asex-reversal treatment. All three

methods are sometimes used.Hybridization and sex-reversalreduce the number of female finger-

lings that must be discarded duringmanual sexing. This saves time,space and feed. Problems neverthe-less still exist with hybridization andsex-reversal. Producing sufficientnumbers of hybrid fry maybe

difficult because of spawning incom-patibilities between the parentspecies. Sex-reversal is more techni-cally complicated and requires obtain-ing recently hatched fry and rearing

them in tanks with high qualitywater. Both hybridization and sex-reversal may produce less than 100

percent males.

Manual sexing is commonly used byproducers. Manual sexing (handsexing) is the process of separatingmales from females by visual inspec-tion of the external urogenital pores,often with the aid of dye applied tothe papillae. Secondary sex charac-teristics may also be used to help dis-tinguish sex. Reliability of sexingdepends on the skill of the workers,the species to be sorted and its size.Experienced workers can reliablysex 15-gram fingerling T. hornorum

and T. mossambica, 30-gram T.nilotica, and 50-gram T. aurea.

In the tropics, fingerlings maybeproduced year-round. In temperateregions, fingerlings are producedduring summer and stored in over-wintering facilities for the next grow-ing season. If manual sexing is used,it is done prior to overwintering. The

best fingerling size for overwinteringdepends on the number of finger-lings that will be needed and theavailable storage capacity. Fry of 1gram or less are stocked in nurseryponds and fed high-quality feeds.Ponds stocked at 20,000 fry/acre willproduce 100-gram fingerlings in 18weeks, while 40,000 fry/acre will pro-duce 50-gram fingerlings in 12weeks, and 72,000 fry/acre will pro-

duce 27-gram fingerlings in 9 weeks.

Fingerlings that weigh less than 20grams should not be overwinteredbecause their survival rate will below.

Overwintering facilities consist ofgeothermal springs, greenhouses

and heated buildings. Fingerlingscan be held in cages located ingeothermal springs or in small pondsor tanks through which warm springwater is diverted. In greenhousesand heated buildings, recirculatingsystems are used to hold largequantities of fingerlings. Fingerlingscan be overwintered in long, narrowponds that are covered with clearplastic if the winter is mild.

Male monosex cultureMales are used for monosex culture

because male tilapia grow fasterthan females. Females use consider-able energy in egg production anddo not eat when they are incubatingeggs. Male monosex culture permitsthe use of longer culture periods,higher stocking rates and fingerlingsof any age. High stocking densitiesreduce individual growth rates, butyields per unit area are greater. Ifthe growing season can be extended,it should be possible to produce fishweighing one pound (454 grams) ormore. Expected survival for all-male

culture is 90 percent or greater. Adisadvantage of male monosex cul-ture is that female fingerlings are dis-carded.

The percentage of females mistaken-ly included in a population of mostlymale tilapia affects the maximum at-tainable size of the original stock ingrowout. For example, manuallysexed T. nilotica fingerlings (90 per-cent males) stocked at 3,848/acrewill cease growing after 5 months

when they average about 0.8 pounds

(365 grams) because of competitionfrom recruits. If larger fish are

desired, females should comprise 4percent or less of the original stockand predator fish should be in-cluded.

The stocking rate for male monosexculture varies from 4,000 to 20,000/acre or more. At proper feedingrates, densities around 4,000/acre

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allow the fish to grow rapidly with-out the need for supplemental aera-tion. About 6 months are required toproduce 500-gram fish from 50-gramfingerlings, with a growth rate of 2.5

grams/day. Total production ap-proaches 2.2 tons/acre.

A stocking rate of 8,000/acre is fre-quently used to achieve yields ashigh as 4.4 tons/acre. At this stock-ing rate the daily weight gain willrange from 1.5 to 2.0 grams. Culture

periods of 200 days or more areneeded to produce large fish thatweigh close to 500 grams. To pro-

duce a 500-gram fish in temperateregions, overwintered fingerlings

should weigh roughly 70 to 100grams and be started as early as pos-

sible in the growing season. A stock-ing rate of 8,000/acre does require

nighttime emergency aeration whenthe 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 con-tinuous use of two to four, one-horse

power paddlewheel aerators perpond. Yields for a single crop rangefrom 6 to 10 tons/acre.

With optimal temperatures, feedingrates depend on fish size and den-sity. Optimal daily feeding rates for

fish of 30,50, 100, 175 and 450 gramsare 3.5, 3.0, 2.5, 2.0 and 1.5 percentof body weight, respectively. If den-sities are high, sub-optimal feedingrates may have to be used to main-

tain suitable water quality, therebyincreasing culture duration.

PolycultureTilapia are frequently cultured withother species to take advantage ofmany natural foods available inponds and to produce a secondarycrop, or to control tilapia recruit-

ment. Polyculture uses a combina-tion of species that have differentfeeding niches to increase overall

production without a correspondingincrease in the quantity of supple-mental feed. Polyculture can im-

prove water quality by creating abetter balance among the microbialcommunities of the pond, resultingin enhanced production. The disad-

vantage of polyculture is the specialequipment (sorting devices, convey-ors, etc.) and extra labor needed tosort the different species at harvest.The role of natural pond foods isless important in the intensive cul-ture of all male populations and maynot justify the expense of sorting thevarious species at harvest.

Tilapia can be cultured with channelcatfish (Ictalurus punctatus) withonly a minor reduction in catfishyields. Male tilapia stocked at a rateof 800/acre yield nearly 770pounds/acre when channel catfishare stocked at 3,000/acre. At this

stocking rate, net production of cat-fish declines by roughly 170 pounds/acre, but for every reduction of1 pound in catfish production, 4.5pounds of tilapia are produced.

Catfish production does not declinewhen cultured in combination withtilapia, silver carp (Hypophthalmich-thys molitrix) and grass carp(Ctenopharyngodon idellus) at den-sities of 800, 1,000 and 20/acre,respectively. With no additionalfeed, total net production can reachnearly 4,120 pounds/acre comparedto 2,370 pounds/acre for catfish cul-tured alone. The incidence of off-flavor catfish may be less incatfish/tilapia polyculture than cat-fish monoculture.

Another promising polyculture sys-

tem consists of tilapia and prawns(Macrobrachium rosenbergii). Inpolyculture, survival and growth of

tilapia and prawns are independent.Feed is given to meet the require-ments of the fish. Prawns, which are

unable to compete for the feed,utilize wasted feed and natural foodsthat result from the breakdown offish waste. Stocking rates for 1 to 2gram prawns vary from 4,000 to

36,000/acre, but a rate of 8,000/ acre

is often used to obtain a high per-centage of market-size prawns(

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used to reduce the quantity and ex-pense of supplemental feeds. An in-crease in natural food has a muchgreater effect on tilapia production

at densities less than 4,000/acre.

Inorganic fertilizers are used lessoften because of their expense, but a

single large application of an inor-ganic fertilizer high in phosphorus isfrequently made prior to stockingfish to create an algal bloom. Tilapiaproductivity is stimulated mainly by

an increase in phosphorus and to alesser extent by an increase innitrogen. Phosphorus is effectivelyincreased through the application ofliquid polyphosphate (13-38-0) at arate of 20 pounds/acre (2.4 gal-ions/acre).

Manuring, which is widely used for

food fish production overseas, hasnot been practiced in the U.S. be-cause of public perception. Manur-ing may have application in theproduction of tilapia as a source offish meal for animal feeds. The qual-ity of manure as a fertilizer dependson several factors. Pig, chicken andduck manures increase fish produc-tion more than cow and sheepmanure. Animals fed high qualityfeeds (grains) produce manure thatis better as a fertilizer than those feddiets high in crude fiber. Fresh

manure is better than dry manure.Finely-divided manures providemore surface area for the growth ofmicroorganisms and produce better

results than large clumps of manure.

Manure should be distributed evenlyover the pond surface area. Large ac-

cumulations of manure on the pondbottom produce low oxygen condi-tions in the sediment that reducemicrobial activity and sometimesresult in the sudden release of toxic

chemicals into the water column.

To maximize fish production, ma-nure should be added daily to thepond in amounts that do not reducedissolved oxygen (DO) to harmfullevels as it decays. The maximum ap-plication rate varies from 90 to 180

pounds/acre/ day for dry manure.The maximum rate depends on the

quality of the manure, the oxygensupply in the pond and watertemperature. If early morning DO isless than 2 ppm, manuring should bereduced or stopped until DO in-creases. If it is not possible to

measure DO, the maximum rateshould be limited to 90

pounds/acre/day to ensure a marginof safety. When water temperaturesare less than 64 F, manuring shouldbe discontinued. At low tempera-tures the rate of decomposition de-creases and manure may accumulateon the pond bottom. A subsequentincrease in temperature could thenresult in an oxygen depletion.

The rate of manuring should be in-creased gradually as the fish grow.

The recommended manuring rate asdry matter is 2 to 4 percent of thestanding fish biomass per day.

Yields of male monosex populationsin manured ponds have beenmodest, but production costs arevery low if the manure is free. For ex-

ample, all-male hybrids (T. niloticax T. hornorum, 29 grams) stockedat 4,000/acre will produce a net yieldof 1,470 pounds/acre of 200-gramfish in 103 days when given fresh cat-tle manure at an average rate (dry

weight) of 46 pounds/acre/day. Incomparison, fish receiving a commer-cial high-protein feed will give a netyield of 2,370 pounds/acre. Feedingcosts per pound of production aretwo to twenty times higher for fishfed the commercial diet comparedto fish receiving manure.

Integrated systemsCollection, transport, storage anddistribution of manure involve con-siderable expense and are major

obstacles to manured systems. Theseproblems can be overcome by locat-ing the animal production unit ad-

jacent to or over the fish pond sothat fresh manure can easily bedelivered to the pond on a contin-uous basis. Effective and safe

manure loading rates are maintained

by having the correct number ofanimals per pond surface area.

Chicken/fish farmingMaximum tilapia yields are obtainedfrom the manure output of 2,000 to

2,200 chickens/acre, which deliver 90to 100 pounds (dry weight) of ma-

nure/acre/day. Broiler flocks shouldbe composed of three size groups tostabilize manure output. Severalcrops of chickens can be producedduring a fish production cycle.

Pig/fish farmingApproximately 24 to 28 pigs/acre arerequired to produce a suitable quan-tity of manure (90 to 100 pounds ofdry matter/acre/day) for tilapiaproduction. The pigs are usually

grown from 44 to 220 pounds over a6-month period.

Duck/fish farmingDucks are grown on ponds at a den-

sity of 300 to 600/acre. The ducks aregenerally raised in confinement, fedintensively, and allowed access toonly a portion of the pond where

they forage for natural foods anddeposit their manure. Ducks that arcraised on ponds remain healthierthan land-raised ducks. Also by rais-ing ducks on ponds, feed wasted by

the ducks is consumed directly bythe fish. Since ducks reach market-

able size in 10 to 11 weeks, staggeredproduction cycles are needed to sta-

bilize manure output.

HarvestingTilapia are best harvested by seiningand draining the pond. A completeharvest is not possible by seining

alone. Tilapia are adept at escapinga seine by jumping over or burrow-ing under it. Only 25 to 40 percent of

a T. nilotica population can be cap-tured per seine haul in small ponds.Other tilapia species, such as T.aurea, are even more difficult to cap-ture. A l-inch mesh seine (with bag)of proper length and width issuitable for harvest.

This publication was supported in part by a grant from the Unitcd States Department of Agriculture, Number 87-CRSR-2-3218, sponsored jointly by theCooperative State Research Service and the Extension Service.

Educational programs conducted by the Texas Agricultural Extension Service serve people of all ages regardless of socioeconomic Ievel, race, color, sex, religion, handicap or

national origin.

Issued in furtherance of Cooperative Extension Work in Agriculture and Home Economics, Acts of Congress of May 8, 1914, as amended, and June 30, 1914, in cooperation with theUnited States Department of Agriculture. Zerle L. Carpenter, Director, Texas Agricultural Extension Service, The Texas A&M University System.

2M 4-90, Reprint FISH