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Aquaculture and Fisheries Management 1990, 21, 187-194 Production of marketable-size tilapia, Oreochromis spilurus (Giinther), in seawater cages using different production schedules* E. M. CRUZ & M. RIDHA Mariculture and Fisheries Department, Kuwait Institute for Scientific Research, Salmiyah, Kuwait Abstract. In Kuwait, the culture of tilapia, Oreochromis spilurus (Giinther), in sea cages is limited by water temperature for mid-April to niid-November only. Using fry spawned in April, one production cycle is passible, but marketing time is limited to less than 20 days. With a market capacity of 1 tonne/day, the production of 100 tonnes/year planned for a commercial farm requires 100 markeiing days. It is therefore necessary to shorten production time by stocking largerfingerlingsto extend the marketing period. Four (ingerling production schedules were tested, using fry spawned (1) in May, grown normally; (2) in May, stunted; (3) in August; and (4) in December. The fish were initially stocked and overwintered infibregiasstanks. On 19 April, thefishwere transferred to l-m'' net cages at 150fish/cageand grown to marketable size (>300g). Results showed thatfishspawned in May (normal and stunted), August and December were harvested in July, August and October and can be marketed for 125, 100 and 60 days. respectively. It is apparent that the production of 100 tonnes of tilapia to be marketed over a period of 100 days is possible using fry produced in August; the profit, however, is marginal. Fry spawned in December gave the highest profit. Introduction Kuwait, like most arid countries in the Arabian Gulf area, has limited freshwater and brackishwater resources. Thus, aquaculture development is geared towards utilization of the most abundant water resource — sea water. Seed production is usually land-based, whereas grow-out and fattening is sea-based (cage culture). Tilapia, although considered a freshwater fish, was introduced in Kuwait in 1982 because it is very hardy. Some species are euryhaline and can therefore tolerate sea water. Although several species are commercially used, several investigators have indicated the potential of culturing Oreochromis spilurus (Giinther) in sea water (Vine 1980; Hopkins, Ridha, Leclercq & Al-Ahmad 1986; Ai-Amoudi 1987). The growth and production of O. spilurus in brackish water and sea water were comparable to or better than those in fresh water (Al-Ahmad, Hopkins, Ridha, Al-Ahmed & Hopkins 1986; Leclercq & Hopkins 1985; Al-Ahmad, Ridha & Ai-Ahmed 1988a). Hopkins, Adel-Halim, Hopkins, Dan & Mahesh- wari (1985) indicated that the mariculture of tilapia is economically feasible and commer- cially viable only if produced in association with a sea hre-dm, Acanthopagrus cuvieri (Day), farm. • Paper originally presented at the Second Asian Fisheries Forum, 17-22 April 1989, Tokyo, Japan. Correspondence: Dr E.M. Cruz, Mariculture and Fisheries Department, Kuwait Institute for Scientific Research, PO Box 1638, 22017 Salmiyah, Kuwait.
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Production of marketable-size tilapia, Oreochromis spilurus (Günther), in seawater cages using different production schedules

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Page 1: Production of marketable-size tilapia, Oreochromis spilurus (Günther), in seawater cages using different production schedules

Aquaculture and Fisheries Management 1990, 21, 187-194

Production of marketable-size tilapia, Oreochromisspilurus (Giinther), in seawater cages using differentproduction schedules*

E. M. CRUZ & M. RIDHA Mariculture and Fisheries Department, Kuwait Institute forScientific Research, Salmiyah, Kuwait

Abstract. In Kuwait, the culture of tilapia, Oreochromis spilurus (Giinther), in sea cages islimited by water temperature for mid-April to niid-November only. Using fry spawned in April,one production cycle is passible, but marketing time is limited to less than 20 days. With amarket capacity of 1 tonne/day, the production of 100 tonnes/year planned for a commercialfarm requires 100 markeiing days. It is therefore necessary to shorten production time bystocking larger fingerlings to extend the marketing period.

Four (ingerling production schedules were tested, using fry spawned (1) in May, grownnormally; (2) in May, stunted; (3) in August; and (4) in December. The fish were initiallystocked and overwintered in fibregiass tanks. On 19 April, the fish were transferred to l-m'' netcages at 150 fish/cage and grown to marketable size (>300g).

Results showed that fish spawned in May (normal and stunted), August and December wereharvested in July, August and October and can be marketed for 125, 100 and 60 days.respectively. It is apparent that the production of 100 tonnes of tilapia to be marketed over aperiod of 100 days is possible using fry produced in August; the profit, however, is marginal. Fryspawned in December gave the highest profit.

Introduction

Kuwait, like most arid countries in the Arabian Gulf area, has limited freshwater andbrackishwater resources. Thus, aquaculture development is geared towards utilization of themost abundant water resource — sea water. Seed production is usually land-based, whereasgrow-out and fattening is sea-based (cage culture).

Tilapia, although considered a freshwater fish, was introduced in Kuwait in 1982 becauseit is very hardy. Some species are euryhaline and can therefore tolerate sea water. Althoughseveral species are commercially used, several investigators have indicated the potential ofculturing Oreochromis spilurus (Giinther) in sea water (Vine 1980; Hopkins, Ridha,Leclercq & Al-Ahmad 1986; Ai-Amoudi 1987). The growth and production of O. spilurus inbrackish water and sea water were comparable to or better than those in fresh water(Al-Ahmad, Hopkins, Ridha, Al-Ahmed & Hopkins 1986; Leclercq & Hopkins 1985;Al-Ahmad, Ridha & Ai-Ahmed 1988a). Hopkins, Adel-Halim, Hopkins, Dan & Mahesh-wari (1985) indicated that the mariculture of tilapia is economically feasible and commer-cially viable only if produced in association with a sea hre-dm, Acanthopagrus cuvieri (Day),farm.

• Paper originally presented at the Second Asian Fisheries Forum, 17-22 April 1989, Tokyo, Japan.Correspondence: Dr E.M. Cruz, Mariculture and Fisheries Department, Kuwait Institute for Scientific

Research, PO Box 1638, 22017 Salmiyah, Kuwait.

Page 2: Production of marketable-size tilapia, Oreochromis spilurus (Günther), in seawater cages using different production schedules

188 E. M. Cruz & M. Ridha

The culture of O. spilurus in sea cages in Kuwait is limited to the summer months (frommid-April to mid-November) due to low water temperature during winter (Al-Ahmad et al.1986; Cruz & Ridha 1989). Normally, however, the spawning season starts in April and endsin October, with the highest fecundity during May-July, and decreases during August-October (Al-Ahmad et al. 1988b). Using fry spawned in April, one production cycle ispossible within the summer months, although marketing time is limited to less than 20 days.

At present, the market can absorb only 1 tonne/day. With the production of 100tonnes/year planned for a commercial farm, 100 days would be required to market theproduce. This is not possible using fry spawned during the year. Fry should therefore be madeavailable as early as possible so that fish can be produced within one growing season and bemarketed over a longer period. A solution to spreading out the marketing period is to shortenthe production time by stocking large fingerlings in April. This can be done by using fry fromthe previous breeding season as described by Behrends, Burch, Maddox, Nelson & Waddell(1981), Hepher & Pruginin (1981) and Chervinski & Stickney (1982), and/or advancing thebreeding season as described by Rothbard & Pruginin (1975) and Behrends & Smitherman(1983).

This study compares four different schedules for producing marketable-size tilapia in seacages. Information gathered will serve as the basis for formulating a production scheme for alOO-tonnes/year commercial farm.

Materials and methods

Four fingerling production schedules were tested: schedule 1 — fry spawned in May wereallowed to grow normally until April; schedule 2 — fry spawned in May were initially stunteduntil November and allowed to grow normally until April; schedule 3 — fry spawned inAugust were allowed to grow until April; and schedule 4 — fry spawned in Decemberthrough temperature (28-30°C) and light (14:10h light:dark photoperiod) control wereallowed to grow until April. Each production schedule was done in triplicate.

O. spilurus fry of mixed sexes spawned in brackish water (3-5 ppt) at different times werecultured in 0-5-tonne circular fibreglass tanks. After 6 weeks, the fish were graduallyacclimatized from brackish water to sea water (36 ppt) over a 7-day period. One week afteracclimation, fish weighing 0-5-1-Og were stocked in fibreglass tanks at 500 fish/m^. Water flowwas at 0-20-0-25 I/kg fish/min and was adjusted every 2 weeks. On 19 April, the fish weretransferred to 12 net cages (1 m^ each) at 150 fish/cage at the Salmiyah cage facilities of theMariculture and Fisheries Department, Kuwait Institute for Scientific Research (KISR),Kuwait Bay.

The fish were fed with 2-0-mm crumbles (55% crude protein [CP]) until they reached anaverage weight of lOg. From lOg to 50g, the fish were fed with 2 0-mm pellets (49% CP);from 50g to lOOg, 3-2-mm pellets (46% CP); and those heavier than lOOg, with 4-5-mmpellets (46% CP). The feeds were commercially prepared sinking pellets formulated for seabream by Aqualim of France. The fish were fed initially at the rate of 20% of body weight forfish weighing less than 5 g. gradually decreasing as they grew until the feeding rate levelled offat 2%. During stunting (schedule 2), the fish were fed at the rate of 2-0% of body weight. Thefish were hand-fed three times a day while in tanks and fed continuously for 8h duringdaylight using a belt feeder while in the cages. Feeding was stopped when the sea was rough.The fish were harvested upon reaching market size (>300g).

Page 3: Production of marketable-size tilapia, Oreochromis spilurus (Günther), in seawater cages using different production schedules

Tilapia production in seawater cages 189

The fish were counted and weighed at stocking and at harvest. These data are needed tocalculate the daily weight gain, specific growth rate, total weight gain, survival rate and feedconversion ratio.

The specific growth rate (G) was calculated using the formula of Luczkovich & Olla(1983): where G = 100 [log (final weight) - log (initial weight)]/number of culture days. Feedconversion ratios were calculated as feed given per wet weight gain.

Simple cost and return analysis was conducted to determine the profitability of culturingtilapia using four different production schedules. Prices of input (feeds, labour, water, fry,tanks, cages, etc.) during the last quarter of 1988 were used as the basis for costings. Profitwas calculated as the difference between fish sales (return) and production costs (expensesduring the land-based and sea-based rearings). The basic assumptions used are indicated inthe Appendix.

Tank use, cage use and boat use were considered as fixed costs, whereas fish transport andaeration costs were considered as miscellaneous costs.

Results

After the land-based rearing, fish spawned in May (normal), May (stunted), August andDecember had individual mean weights in April of 175 00, 124-10, 63-01 and 15-24g,respectively (Table 1). Survival rate was highest for schedule 4 and the lowest for schedule 1.

Water temperature during the sea-based rearing ranged from 22-5 to 33-0°C with a meanof 28-16 ± 2-04°C. The dissolved oxygen level (DO) ranged from 4-6 to 6-7 mg/l with a meanof 5-82 ± 0-53 mg/I. A constant level of salinity (about 41 ppt) was observed throughout thetest.

Table 1. Weight, feed consumption and survival rate of O. spilurus during land-based rearing

Parameter

Stocking dataNumberMean weight/fish (g)Toial weight (kg)

Harvesting dataCulture daysNumberMean weight/fish (g)Total weight (kg)

Total weight gain (kg)Daily gain/fish (g)Specific growth (%/day)Feed given (kg)Feed conversionSurvival (%)

1

250M l0-28

301196175-0034 30

34-020-581-68

67-541-98

78-40

2

250M S0-29

301204124-102532

25-030-411-55

38-741-55

81-67

Schedule'

3

2501-210-30

20922063-0113-86

13-560-301-93

21-031-52

88-11

4

2501-370 62

81236

15-243-60

2-980-172-974-291-43

94 53

' Mean of three cages.

Page 4: Production of marketable-size tilapia, Oreochromis spilurus (Günther), in seawater cages using different production schedules

190 E. M. Cruz (ft M. Ridha

After the sea-based rearing, the fish had individual mean weights of 373-21, 315-16,313-91 and 324-91g for schedules 1, 2, 3 and 4, respectively (Table 2). The survival rates forschedules 1 and 2 (72-0 and 78-7%, respectively) were lower than those for schedules 3 and 4(87-3 and 93-3%, respectively), hence the yields were also lower. High mortality occurredimmediately after stocking.

Stunting of the fish in schedule 2 had an adverse effect on fish growth. The stunted fishwere unable to attain the same weight as the fish of the same batch (schedule 1).

Fish spawned in May (schedules 1 and 2) reached market size in cages in less than 100culture days and can therefore be marketed for more than 125 days, exceeding the 100 daysrequired for marketing 100 tonnes of fish. August (schedule 3) and December (schedule 4)spawns were harvested in mid-August and October and can therefore be marketed for 100and 60 days, respectively.

Fish spawned in May (schedules 1 and 2) were very expensive to produce and hence gavenegative profits (Table 3). Land-based rearing costs more than 75% of the total productioncost. Water constituted the biggest cost item during the land-based rearing for schedules 1and 2 (Kuwaiti dinars [KD] 29.230 and 18.010, respectively). Stunting the fish initially(schedule 2) decreased water costs by about KD 11.220.

Although production of marketable-size tilapia to be marketed over a period of 100 daysis possible using fry produced in August, profit was marginal (KD 0.390). Fry spawned inDecember gave the highest profit (KD 12.210).

For fry spawned in December, feed cost seems to be where the biggest reduction in costcan be made since it constitutes 52-95% of the production cost (Fig. 1, schedule 4). Atpresent, the sea bream feeds used in this study are imported from France. By producing thefeed formulated particularly for tilapia locally, it would be possible to decrease productioncost and increase the profit by KD 9.660, 7.600, 7.420 and 8.960 for schedules 1, 2, 3 and 4,respectively (Table 4).

Furthermore, since tilapia production is part of the sea bream farm, water cost can bereduced or eliminated by using effluent water from sea bream broodstock tanks forland-based rearing of tilapia. When water cost is not considered, profit is increased by KD29.230, 18.010, 4.690 and 0.520 for schedules 1, 2, 3 and 4, respectively. When water cost isnot considered and low cost feed is used, the increase in profit is KD 38.890, 25.610, 12.890and 9.480 for schedules 1, 2, 3 and 4, respectively.

Discussion and conclusion

The growth rate of O. spilurus during the cage rearing was comparable with those reported byAI-Ahmad et al. (1988a), who cultured O. spilurus tTom 118g to 323g in 101 days (2-03 g/fishper day), and was higher than those obtained by Campbell (1985) and Coche (1977) for O.niloticus (L.) in fresh water (l-6g and 1-8 g/fish/day, respectively). The production ratesobtained in this study were likewise comparable to those obtained by Al-Ahmad etal. (1988a)for O. spilurus in sea cages (13kg m~^/month).

High mortality immediately after stocking fish into the cages can be attributed to handlingstress. Ai-Ahmad et al. (1988) indicated that growing O. spilurus in sea water were moreprone to stress caused by handling. In this study, higher mortality was observed in cagesstocked with bigger fish (schedules 1 and 2) than smaller fish (schedules 3 and 4). It is

Page 5: Production of marketable-size tilapia, Oreochromis spilurus (Günther), in seawater cages using different production schedules

Tilapia production in seawater cages 191

Table 2. Weight gain, feed conversion, yield and survival rate of O. spilurus during sea-based rearing

Parameter

Stocking dataNumberMean weight/fish (g)Total weight (kg)

Harvesting dataCulture daysNumberMean weight/fish (g)

Total weight gain (kg)Daily gain/fish (g)Specific growth (%/day)Feed given (kg)Feed conversionSurvival (%)Production/cage (kg)Possible market days

1

150175-2126-28

90108373-21

14-032-200-84

29-082-07

72-0040-31

125

2

150124-9718-74

91118315-16

18-452-091-01

37-15201

78-6737-19

125

Schedule'

3

15063-11

9-47

120131313-91

31-652-091-34

67-102-12

87-334 M 2

100

4

15015-90238

160125324-91

43-091-931-89

85-321-98

93-3345-4760

' Mean of three cages.

Table 3. Cost and return analysis of culturing O. spilurus using four production schedules in Kuwaiti dinars per cubicmetre'

Parameter

Production costs:(I) Land-based rearingWaterFeedFish stockLabourAerationTank useSubtotalPer cent of total

(2) Sea-based rearingFeedLabourFish transportCage useBoat useSubtotalPer cent of total

TotalFish salesProfit"Production cost/kg

I

29-23022-59012-50013-7202-9406-960

87-94084-840

9-6002-7200-5304-0500-530

17-42015-160

105-36060-470

-44-8902-610

Schedule

2

18-01012-88012-0008-5802-9404-860

59-27077-820

12-2602>2S0pm4-0500-530

19-51022-180

78-78055-790

-22-9902-120

3

5-4707-300

U-25026001-6802-470

30-77054-350

22-1402-8700-1905-4000-700

31-30045-650

62-07061-6800-3901-510

4

0-5201-500

11-5501-2400-7500-630

16-19033-500

28-1603-4700-0507-2000-940

39-81066-500

56-00068-21012-2101-230

' 1 Kuwaiti dinar = 3-60 USS (December 1988)*' Profit = Fish sales minus production costs.

Page 6: Production of marketable-size tilapia, Oreochromis spilurus (Günther), in seawater cages using different production schedules

192 E. M. Cruz & M. Ridha

Fry12 69%Labour9-72%

Feed32-68%

Miscellaneous3-52%

Water29-67%

Miscellaneous•43%

Schedule Schedule 4

Miscellaneous4-20%

Feed31-92%

Fry15-23%Labaur13-80%

Fixed9 8 %

Water22-86%

Fixed13-81% Fry

18-12%

Feed47 4 3 %

Miscellaneous3 0 1 %Water8 8 1 %

Labour8-81%

Schedule 2 Schedule 3

Figure I. Production costs of the different production schedules.

apparent that bigger fish are more susceptible to transport and handling stress than smallerfish. Thus, stocking of big fish (>100g) is not advisable. The size of about ^60g at stocking isrecommended. Balarin, Haller & Araiitage (1986) recommended a similar starting size ofbetween 40 and 60g for optimal production.

Stunting of fish resulted in slower rate of growth than non-stunted fish. With milkfish,Chanos chanos Forsskal, stunting had no adverse effect on growth (Lijauco, Grino, Gerochi& Rodriguez 1978; Bombeo-Tuburan 1988).

Table 4- Profit of the four production schedules with or without water cost and using high and low cost feeds

Parameter

With water cost-high cost feed

No water cost-high cost feed

With water cost-low cost feed

No water cost-low cost feed

1

-44-890

-15-660(29-230)

-35-230(9-660)

-6-000(38-890)

Schedule

I-22 990

-4-980(18-010)

-15-390(7-600)2-620

(25-610)

3

0-390

5-080(4-690)7-810

(7420)13-280

(12-890)

4

12-210

12-730(0-520)21-170(8-960)21-690(9-480)

Figures enclosed in parentheses arc increase in profit from schedules with water cost and high cost feeds.

Page 7: Production of marketable-size tilapia, Oreochromis spilurus (Günther), in seawater cages using different production schedules

Tilapia production in seawater cages 193

Based on the results of this study, using fry spawned in previous spawning season,overwintered and grown in sea cages during the second season is technically feasible.However, its profitability depends on the duration and size of fish during land-based rearing.Profit is less with fry spawned in May compared to those spawned in August since it costsmore to culture fish for a longer period of time. For fish cultured for the same period of time(in May), profit is higher with stunted fish compared with non-stunted fish since less space,water, feeds, etc. are needed to rear smaller fish than bigger fish. Hence, using fry spawned inMay grown normally is not economically feasible due to the high cost of producing thefingerlings.

Nelson, Behrends, Waddell & Burch (1981) attributed the high production cost to theestablishment of overwintering facilities and high operating costs. Therefore, economicalmethods should be explored to mass produce and overwinter fingerlings. In this study, watercost is one of the major cost items during overwintering (schedules 1, 2 and 3). Integratingtilapia fingerling production with sea bream broodstock and hatchery can drastically reduce ifnot totally eliminate water cost. The effluent with water temperature ranging from 18 to 27*Cis considered of good quality (El-Zahr, unpublished data) and therefore suitable for tilapiafingerling production. When water cost was not considered, an overall improvement in theprofitability was observed. However, profits remained negative for fish spawned in May(normal and stunted).

Advancing the spawning through temperature and light control gave better economicreturns compared to using overwintered fingerlings. This practice will eliminate theestablishment of huge overwintering facilities and reduce operating costs as indicated byRothbard & Pruginin (1975) and Behrends & Smitherman (1983). Because ofthe high profit,this practice should be used to produce marketable-size tilapia that should be marketed overa period of 60 days.

Feed cost, likewise, is one of the major cost components of the production costs for allproduction schedules. Sea bream feeds were the only feed available during the conducting ofthe study. For commercial production, the use of tilapia feeds, which are about 100 fils kg~^cheaper, will reduce production cost by about 9-16%.

Since fry spawned in December can be marketed in 60 days, it may be possible to use fryspawned 40 days earlier (around October) rather than in August. The economic retums forfry produced in October would be better than those produced in August since the costs duringthe land-based rearing would be lower. Further experiments, though, should be conducted totest this approach.

It is apparent from the preliminary results ofthe experiment that production of 100 tonnesof marketable-size tilapia to be marketed over a period of 100 days is possible using fryproduced in August. However, a production scheme using fry spawned from August onwardsas a means of spreading out the market period for 100 days is more technically andeconomically attractive than using only August spawns.

Acknowledgments

The authors are grateful to Mr Wuan Thong Onn and the staff of the Cage Culture Project fortheir support during the experiment. Special appreciation is due to Dr Ziad H. Shehadeh forhis constructive criticism during study and for editing this paper.

Page 8: Production of marketable-size tilapia, Oreochromis spilurus (Günther), in seawater cages using different production schedules

194 £. M. Cruz & M. Ridha

References

Al-Ahmad T.A., Hopkins K.D., Ridha M., Al-Ahmed A.A. & Hopkins M.C. (1986) Tilapia Culture in Kuwait.Kuwait Institute for Scientific Research/International Center for Living Aquatic Resources Management.KISR Report No. KISR2122, Kuwait.

Al-Ahmad T.A., Ridha M. & Al-Ahmed A. A. (1988a) Tilapia culture in Kuwait: production of and feeding rates ofthe tilapia Oreochromis spirulus in seawater. Aquaculture 73, 111-118.

Al-Ahmad T.A., Ridha M. & Al-Ahmed A.A. (1988b) Reproductive performance of the tilapia Oreochromisspilurus in seawater and brackish groundwater. Aquaculture 73, 323-332.

AI-AmoudiM.M. (1987) Acclimation of commercially cultured Oreoc/iromis species to seawater — an experimentalstudy. Aquaculture 65, 333-342.

Baiarin J.D., Haller R.D. & Armitage A.T.C. (1986) Research on intensive culture of tilapia in tanks. Proceedingsof the African Seminar on Aquaculture Research in the African Region, pp. 206-216. Pudoc, Wageningen.

Behrends L.L. & Smitherman R.O, (1983) Use of warm water effluents to induce winter spawning of tilapia in atemperate climate. In: Proceedings of the International Symposium on Tilapia in Aquaculture (ed. by L.Fishelson & Z. Yaron), pp. 446-454. Tel Aviv University Press,

Behrends L.L., Burch D.W,, Maddox J.J,, Nelson R.G. & Waddell Jr, E.L. (1981) TUapia culture in heatedeffJueats; potential for commercialization in temperate climates. In: Third Waste Heat Manual and UtilizationConference (ed. by S. Sengupta & S.S. Lee), pp, 429-436. Hemisphere Publishing Company, New York.

Bombeo-Tuburan I, (1988) The effect of stunting on growth, survival, and net production of milkfish (Chanoschanos Forsskal). Aquaculture 75, 97-103.

Campbell D, (1985) Large scale cage farming of Sarotherodon niloticus. Aquaculture 48, 57-69.Chervinski J. & Stickney R.R. (1981) Overwintering facilities for tilapia in Texas. Progressive Fish-CuUurist 43,

20-21.Coche A.G. (1977) Preliminary results of cage rearing TUapia nilotica (L.) in Lake Kossou, Ivory Coast.

Aquaculture \Q, 109-140.Cruz E.M. SL Ridha M. (1989) Preliminary study on the production of the tilapia, Oreochromis spilurus (Gunther),

cultured in seawater cages. Aquaculture and Fisheries Management 20, 381-388.Hepher B- & Pruginin Y. (1981) Commercial Fish Farming with Special Reference to Fish Culture in Israel. John

Wiley and Sons, New York.Hopkins K.D,. Ridha M.. Leclercq D.I. & Al-Ahmad T.A. (1986) Tilapia Culture in Kuwait: Screening Tilapia for

Seawater Culture. Kuwait Institute for Scientific Research, Report No. KISR2070. Kuwait.Hopkins K.D., Adel-Halim M.M., Hopkins M.L., Dan N. & Maheshwad G. (1985) Tilapia Culture in Kuwait: A

Feasibility Study. Kuwait Institute for Scientific Research Report No, KISR1637, Kuwait.Leciercq D.I. & Hopkins K.D. (1985) Preliminary tests of an aerated tank system for tilapia culture. Aquaculture

Engineering 4, 299-304.LijaucoM.M.. GrinoE.G., Gerochi D. & Rodriguez E.M. (1978) Preliminary study on the growth and survival of

stunted and non-stunted milkfish fingerlings. SEAFDEC Quarterly Research Report 2, 35-36.Luczkovich J,J, & 011a B.L. (1983) Feeding behavior, prey consumption, and growth of juvenile hake. Transactions

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aspects. In: Third Waste Heat Manual and Utilization Conference (ed. by S. Sengupta & S.S. Lee), pp. 397-404.Hemisphere Publishing Company, New York.

Rothbard S, & Pruginin Y. (1975) Induced spawning and artificial incubation of tilapia. Aquaculture 5, 142-148-Vine P, J. (1980) Cultivation of fishes in the family Cichlidae in the Red Sea. In: Proceedings ofthe Symposium on the

Coastal and Marine Environment of the Red Sea, Gulf of Aden and Tropical Western Indian Ocean, pp.389-399. The Red Sea and Gulf of Aden Environmental Programme, Jeddah (ALECSO).

Appendix: Basic assumption used

(1) Cost per fry is 50 fils for May and August (6) Cost of tank use is 10 fils/1 tank volume,spawning and 55 fils for December spawning. (7) Cost of cage use is 7,5 KD/m-*.

(2) Prices of feed are 330, 350 and 370 fils/kg for 46, (8) Aeration expense is 10 fils/day.49 and 55% crude protein pellets, respectively. (9) Boat rental is 6.5 fils/m^ cage/day.

(3) Water cost is 100 fils/40001. (10) Fish sale is KD 1,500/kg regardless of size.(4) Labour cost is lKD/h. (11) Water flow is 11/5 kg fish.(5) Fish transport cost is 20 fils/kg fish. (12) Maximum loading rate is 50kg fish/m^.

Page 9: Production of marketable-size tilapia, Oreochromis spilurus (Günther), in seawater cages using different production schedules