Aquaculture, 73 (1988) 323-332 323 Elsevier Science Publishers B.V.. Amsterdam - Printed in The Netherlands

Reproductive Performance of the Tilapia Oreochromis spilurus in Seawater and Brackish Groundwater

THAN1 A. AL-AHMAD, MOHAMMED RIDHA and ABDULKADER A. AL-AHMED

Kuwait institute for Scientific Research, Mariculture and Fisheries Department, P.O. Box 1638,22017 Salmiya (Kuwait)

(Accepted 5 January 1988)

ABSTRACT

Al-Ahmad, T.A., Ridha, M. and Al-Ahmed, A.A., 1988. Reproductive performance of the tilapia Oreochromis spilurus in seawater and brackish groundwater. Aquaculture, 73: 323-332.

The reproductive performance of Oreochromis spilurus was studied in seawater (38-41%0) and compared with that in brackish groundwater (3-4%0). The effect of age of broodstock and delay- ing spawning on fecundity, and the effect of stocking density on fry rearing were determined.

In both seawater and groundwater, the fecundity of yearlings was not significantly different from that of 2- to 3-year-old broodstock during the spawning season from May to October. Delay- ing the spawning by holding males and females separately until August did not improve the fe- cundity in seawater from August to October, and decreased it in groundwater. The mean fecundity in groundwater over the entire season was two to five times as high as in seawater. The hatching rate was twice as high in groundwater (43% ) as in seawater (21% ). Fry performance was best at stocking densities of 2000 and 4000 fry/m” in seawater and at 2000 fry/m” in groundwater.

INTRODUCTION

The mariculture of tilapia was initiated in Kuwait to screen and select spe- cies suitable for intensive commercial production in this arid coastal area that lacks natural supplies of fresh water and has limited brackish groundwater resources. The tilapia Oreochromis spilurus was imported from Kenya in 1982 and preliminary work showed its potential for culture in seawater (Hopkins et al., 1986). Little is known about the tolerance of this species to seawater (Bal- arin and Haller, 1982; Stickney, 1986), and its reproductive performance in relation to salinity has not been evaluated.

In the present study, the reproductive performance of 0. spilurus was deter- mined in seawater (38-41000 ) and brackish groundwater (3-4% ) as part of a program to develop the commercial culture of this species in seawater. The

0 1988 Elsevier Science Publishers B.V.

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reproduction of yearlings was compared with that of older broodstock to take advantage of the possibility of the higher reproductive rate of young brood- stock, and to shorten recruitment time. Delaying the spawning was also stud- ied to extend the period in which fry are available for stocking. The hatching rate and effect of rearing density on fry production were also determined.

MATERIALS AND METHODS

Effect of broodstock age

The fecundity of yearlings (l-year-old) and older broodstock (2- to 3-year- old) was compared from May to October 1984. The fish used were offspring of an original stock of 0. spilurus imported from Kenya in 1982. Males and fe- males were held together before the experiment in 2 m3 capacity fiberglass tanks supplied with groundwater. The fish destined for spawning in seawater were gradually acclimated to this salinity 1 month before the start of the spawning season.

At the start of the experiment each age group was stocked into two 2-m3 (2 x 2 x0.5 m) indoor tanks filled with seawater and two tanks filled with groundwater. The groundwater (3-4%~ ) was piped to the research station through the municipal brackishwater supply network which taps and distrib- utes water from underground aquifers primarily for crop irrigation. The num- ber of fish stocked in each tank was set so as to keep the biomass of the two groups constant while maintaining a sex ratio of 3:l females to males. The number of yearlings stocked in each tank was 30 females and 10 males; for older broodstock, 10 females and 3 males were stocked. Yearling females had a mean body weight of 76 g in seawater and 46 g in groundwater; older females weighed 272 g and 241 g, respectively.

The fish were fed twice daily, 6 days a week, at 2% of their body weight per day on a 40% protein pelleted tilapia feed (President Enterprises Corp., Tai- wan). The tanks were cleaned and water was changed weekly at the time of egg collection. Water temperature ranged from 21 to 31 “C! in seawater and from 20 to 30’ C in groundwater. Photoperiod ranged from 11.5 to 14.0 daylight hours (Fig. 1) .

Seed (eggs and yolk-sac fry) was collected from each tank weekly by anes- thetizing the fish with 20 mg/l of quinaldine and removing the seed from the mouth of the females. Fecundity is expressed as the number of seed produced per kg female per day.

Effect of delayed spawning

The effect of delaying spawning was studied from May to October 1985. Two groups of broodstock (2- to 3-year-old) were used: a normal group stocked for

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I I I I I I

May Jun. Jul. Aug. Sep. Oct.

Month

Fig. 1. Monthly spawning tank water temperatures and photoperiod. Temperature: seawater 1984(0-O), groundwater 1984(0-O), seawater 1985(w---W) and groundwater 1985( q --- 0). Photoperiod (A-A).

spawning from May to October, and a delayed group in which females and males were held in separate tanks to prevent spawning during May to July, then stocked together for spawning from August to October. Each group was spawned in two 2-m3 seawater tanks and two groundwater tanks. Twelve fe- males and four males were stocked into each tank. The mean body weight of females from the normal group was 311 g in seawater and 273 g in groundwater; females from the delayed group weighed 317 g and 382 g, respectively.

Egg collection, tank management and feeding were similar to the previous experiment. The feed used in this experiment was a 40% protein pelleted sea- bream feed ( Aqualim, France). Water temperature ranged from 24 to 35 “C in seawater and from 23 to 36.5’ C in groundwater (Fig. 1) .

The egg hatching rate and yolk-sac fry recovery rate for harvested seed were determined for both seawater and groundwater from May to October 1985. The eggs and yolk-sac fry were stocked separately, in l-l plastic hatching jars sup-

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plied with running water of the same salinity used for spawning, and were harvested after reaching the swim-up stage.

Effect of density on fry rearing

Swim-up fry (0.01 g mean body weight, 8 mm total length) were stocked into 0.5-m3 tanks and reared for 6 weeks at densities of 2000,400O and 8000/m3 in 38-41% seawater and 3-4% groundwater. Each density was replicated in three tanks at each salinity (except at SOOO/ m3 in seawater in which two tanks were used). The fry were fed daily on powdered 40% protein tilapia feed using au- tomatic belt feeders that delivered feed continuously for 8-10 h during day- time. The fry were fed a daily ration of 20% of body weight during the first 2 weeks, 15% during the next 2 weeks, and 10% during the last 2 weeks. They were sampled and the amount of feed adjusted weekly. Water was changed continuously, starting the second week, at a rate of one to two tank volumes per day. At the end of 6 weeks, total weight and number and total length of 50 fry were determined for each tank. Water temperature ranged from 27 to 33’ C in seawater and from 28 to 32 ‘C in groundwater.

The results of all experiments were analysed using one-way analysis of var- iance and Duncan’s New Multiple Range Test (Steele and Torrie, 1960 ).

RESULTS

The spawning behaviour of 0. spilurus was similar in groundwater and sea- water. Dominant males established and defended territories in each corner and at the middle of the side walls of the tanks. Territorial males can be easily identified because their dorsal fins become black in colour. The females re- mained in a group in the middle of the tank. Individual females would break away from the group and join a territorial male for spawning then return to the middle of the tank. No injury or death of broodstock resulted from this territorial behaviour.

Effect of broodstock age

In seawater, mean fecundity of yearlings over the entire spawning season was not significantly different (P> 0.05) from that of older broodstock (Table 1). The same was true in groundwater. This indicated that seed production per unit weight of females was not influenced by the age of broodstock at either salinity.

Differences in spawning of 0. spilurus in seawater and groundwater were also evident from these data. For both yearlings and older broodstock, the mean seasonal fecundity was twice as high in groundwater as in seawater (Table 1). The progress of spawning throughout the season was also different at each

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TABLE 1

Spawning results of two Oreochromis spiluru.~ age groups in seawater and groundwater

Age group Month Mean female weight Mean seed produced per Mean fecundity’ (seed/

(kg/tank) tank kg female day- ’ )

Seawater Groundwater Seawater Groundwater Seawater Groundwater

Yearling May 2.432 1.532

broodstock June 2.730 1.861

July 3.130 2.252

August 3.490 2.634

September 3.844 2.998

October 4.214 3.389

Mean

(*SE)

Older May 2.756 2.475

broodstock June 2.832 2.620

July 2.938 2.794

August 3.029 2.964

September 3.118 3.124

October 3.213 3.298

Mean

(*SE)

7504 8818

13290 20065

9570 17782

7523 8016

9052 6464

6092 9611

4515 17344

11625 20342

13337 32446

11824 14022

10490 13329

8017 12912

148 289”

161 362”

96 266”h

69 10lb’

78 70’

47 9obr

99.7 196.1

( -t 14.6) (536.0)

75 350

143 260””

151 373”

128 154b’

113 148b’

81 128”

114.8 235.2

(IL 13.4) ( k30.1)

‘Values for each age group followed by different letters are significantly different at the 5% level using

Duncan’s New Multiple Range Test.

salinity. In seawater, no significant differences among monthly fecundities were detected in either age group. For example, the fecundity of yearlings ranged from 47 to 161 seed/kg female day-‘, but these differences were not statisti- cally significant (P> 0.05). The same was true for the older broodstock in seawater. In groundwater, however, fecundity of both age groups was higher from May to July than from August to October.

Effect of delayed spawning

In seawater, the mean fecundity of the normal spawners from August to October was not significantly different (P> 0.05) from that of the delayed group during the same period (Table 2). This indicated that delaying the spawning until August did not result in a change in fecundity at this salinity. In groundwater, however, the fecundity of the normal spawners during August to October was higher (P < 0.01) than that of the delayed group (Table 2)) indicating that delaying the spawning had a negative effect on fecundity at this salinity.

The mean fecundity of the normal group from May to October was five times

TABLE 2

Effect of normal and delayed spawning on fecundity of Oreochromis spilurus in seawater and groundwater

Spawning Month

group

Mean female weight Mean seed produced per Mean fecundity (seed/

(kg/tank) tank kg female day-‘)

Seawater Groundwater Seawater Groundwater Seawater Groundwater

Normal May 3.728 3.276 6607 33308 64 338

spawning June 3.660 3.462 5316 20431 53 228

July 3.564 3.284 3806 14054 38 153

Mean 52 240

(*SE) (k6.6) (k26.0)

August 3.594 3.368 1716 12326 18 131

September 3.677 3.477 22242 10096 24 103

October 3.677 3.477 2034 14512 20 148

Mean 21 127

(&SE) (k7.1) (k10.6)

Delayed August 3.085 4.579 1794 4192 16 33

spawning September 3.610 4.610 3980 8018 40 64

October 3.931 4.762 1268 4699 12 35

Mean 23 44

(*SE) (k5.9) (k7.8)

as high in groundwater as in seawater (183 compared with 36 seed/kg female day-l ) . Also, the mean fecundity of the delayed group from August to October was twice as high in groundwater as in seawater. The fecundity of the normal spawners from May to October ranged from 18 to 64 seed/kg female day-l in seawater (Table 2), but these differences among the months were not signifi- cant (P> 0.05). In groundwater, it ranged from 103 to 338 seed/kg female day-‘, and was significantly higher (PC 0.01) during May and June than dur- ing the remaining months.

The egg hatching rate was twice as high (P~0.01) in groundwater as in seawater (Table 3 ). The recovery rate of yolk-sac fry (the percentage of yolk- sac fry reaching the swim-up stage ) in groundwater was also higher (P < 0.01) than in seawater, indicating that fewer yolk-sac fry survived to the swim-up stage in seawater.

Effect of density on fry rearing

In seawater, the fry grew to a larger body weight and total length (P < 0.01) at stocking densities of 2000 and 4000/m3 than at a density of 8000/m3, but the survival rate was not different among these densities (Table 4). This in- dicated that swim-up fry could be stocked in seawater at a density up to 4000/

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TABLE 3

Percent hatch and yolk-sac fry recovery rate for seawater and groundwater

Egg hatching rate (% f SE) N’ Sac fry recovery rate (% f. SE) N

Seawater Groundwater

21f4.9 43 + 4.2 39 62 66 * 6.6 92 + 1.7 23 55

‘Number of replicates.

TABLE 4

Mean size and survival of Oreochromis spilurus fry reared at three densities for 6 weeks after reaching the swim-up stage

Stocking density

(fry/ma)

Mean body weight

(g)

Mean total length

(mm)

Mean survival

(%)

Seawater 2000 0.79 33.9 31 4000 0.82 33.5 25 8000 0.29 24.0 38

Groundwater 2000 0.63 29.2 68 4000 0.31 22.4 66 8000 0.35 23.6 46

m3 without adversely affecting growth and survival rates. In groundwater, fry growth was higher (P-C 0.01) at a density of 2000/m3 than at 4000 and 8000/ m3. Survival rate was higher (P < 0.01) at 2000 and 4000/m3 than at 8000/m3.

There were differences in growth and survival of fry in seawater and ground- water at low densities. At 2000/m3, growth in seawater and groundwater, in terms of body weight and total length, were not significantly different (P> 0.05), but survival rate in groundwater was twice as high (PC 0.05) as in seawater. At 4000/m3, body weight and total length of fry were higher (P-C 0.05) in seawater than in groundwater, but the survival rate in groundwater was still twice as high (P-C 0.05) as in seawater. No differences in growth or survival rates were detected between fry reared in seawater and groundwater at a den- sity of 8000/m3.

DISCUSSION

The reproductive performance of two age groups of 0. spilurus broodstock was compared to improve the efficiency of fry production of this tilapia species.

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The results showed that in both slightly brackish groundwater and in seawater, the fecundity of yearlings was not different from that of older broodstock. The lack of details in the literature on spawning of 0. spilurus necessitates com- paring it with other tilapia species. Several researchers reported that yearling 0. niloticus had a higher reproductive rate than older broodstock (Hughes and Behrends, 1983; Payne and Collison, 1983; Peters, 1983; Siraj et al., 1983; Wa- tanabe and Kuo, 1985); therefore, more efficient fingerling production might be obtained by using younger broodstock.

The differences between our results for 0. spilurus and those reported for 0. niloticus may be caused by inherent species differences. Nevertheless, we can also recommend the use of younger broodstock for fry production because they can be recruited earlier for spawning, thus reducing the cost and the period of maintaining broodstock.

Improvement in fry production of 0. spilurus was also attempted by delaying the start of spawning to the middle of the season. This was based on earlier preliminary observations that the fecundity of this tilapia in groundwater was highest from May to July then decreased during August to October. We sus- pected that this might have been caused by exhaustion of the broodstock; therefore, improvements might be made by delaying the spawning until August.

In this experiment, delaying the spawning did not affect fecundity in sea- water, but decreased it in groundwater. This clearly indicates that there is no advantage to this approach for improving fry production. One reason for the failure to increase the fecundity may be that the females, held separate during the early part of the season, were producing and resorbing their eggs during that period. Thus, when mixed with the males in August, they were either exhausted by egg production or they required a longer period to develop a batch of spawnable eggs. Peters (1983) reported a marked tendency for tilapia to resorb ripe eggs. The differences in response to delayed spawning in seawater and groundwater cannot be explained by our data and warrant further investigation.

In both spawning seasons, the fecundity in groundwater was highest during the first 2-3 months and then decreased. This decrease in fecundity does not seem to be related to temperature, which remained above 27°C until Septem- ber. The slight decrease in photoperiod starting from August (Fig. 1) may have contributed to the decrease in fecundity, but this cannot be confirmed on the basis of available data. Manipulation of the photoperiod may provide suitable explanations for these results.

The results of the fry rearing experiment indicated that higher rearing den- sities decreased the growth rate. This led to recommending that stocking den- sities of swim-up fry should not exceed 4000 fry/m3 in seawater and 2000 fry/ m3 in groundwater under local conditions. In freshwater, Macintosh and De Silva (1984) found no significant density effect on growth and survival rates of 0. niloticus x 0. aureus hybrid fry during the first 50 days after yolk sac

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absorption. Rothbard et al. (1983)) however, reported that high stocking den- sities inhibited the growth rate of 0. niloticus x 0. aureus hybrids. Snow et al. ( 1983 ) also indicated that lower stocking densities resulted in larger 0. aureus fry.

The reproductive performance of 0. spilurus was superior in brackish groundwater than in seawater. In groundwater, fecundity was two to five times higher than in seawater; hatching rates of eggs and survival rate of swim-up fry were also twice as high in groundwater. Therefore, in arid coastal countries such as Kuwait, in which the use of seawater for fish culture is imperative due to the limited supply of freshwater, it is more efficient to operate the hatchery of this tilapia species using groundwater. Grow-out of fingerlings to market size, which requires relatively larger quantities of water, should be attempted in seawater.

REFERENCES

Balarin, J.D. and Haller, R.D., 1982. The intensive culture of tilapia in tanks, raceways and cages. In: J.F. Muir and R.J. Roberts (Editors), Recent Advances in Aquaculture. Croom Helm. London, pp. 266-355.

Hopkins, K.D., Ridha, M., Leclercq, D. and Al-Ahmad, T.A., 1986. Tilapia culure in Kuwait: screening tilapia for seawater culture. Kuwait Institute for Scientific Research, Report KISR2070, Kuwait, 28 pp. (unpubl.).

Hughes, D. and Behrends, L., 1983. Mass production of Tilapia nilotica. In: L. Fishelson and Z. Yaron (Compilers), Proceedings, International Symposium on Tilapia in Aquaculture, 8-13 May 1983, Nazareth, Israel. Tel Aviv University, Israel, pp. 394-401.

Macintosh, D.J. and De Silva, S.S., 1984. The influence of stocking density and food ration on fry survival and growth of Oreochromis mossambicus and 0. niloticus fernalex 0. aureus male hybrids reared in a closed circulated system. Aquaculture, 41: 345-358.

Payne, A.I. and Collison, R.I., 1983. A comparison of the biological characteristics of Sarothero- don niloticus (L.) with those of S. aureus (Steindachner) and other tilapia of the delta and lower Nile. Aquaculture, 30: 335-351.

Peters, H.M., 1983. Fecundity, egg weight and oocyte development in tilapias (Cichlidae, Teleos- tei). ICLARM Translations, 2. International Center for Living Aquatic Resources Manage- ment, Manila, The Philippines, 28 pp.

Rothbard, S., Solnik, E., Shabbath, S., Amado, R. and Grabie, I., 1983. The technology of mass production of hormonally sex-inversed all male tilapias. In: L. Fishelson and Z. Yaron (Com- pilers), Proceedings, International Symposium on Tilapia in Aquaculture, 8-13 May 1983, Nazareth, Israel. Tel Aviv University, Israel, pp. 425-434.

Siraj, S.S., Smitherman, R.O., Castillo-Gallusser, S. and Dunham, R.A., 1983. Reproductive traits for three year classes of Tilapia nilotica and maternal effects on their progeny. In: L. Fishelson and Z. Yaron (Compilers), Proceedings, International Symposium on Tilapia in Aquaculture, 8-13 May 1983, Nazareth, Israel. Tel Aviv University, Israel, pp. 201-218.

Snow, J.R., Berrios-Hernandez, J.M. and Ye, H.Y., 1983. A modular system for producing tilapia seed using simple facilities. In: L. Fishelson and Z. Yaron (Compilers), Proceedings, Interna- tional Symposium on Tilapia in Aquaculture, 8-13 May 1983, Nazareth, Israel. Tel Aviv Uni- versity, Israel, pp. 402-413.

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Steele, R.G.D. and Torrie, J.H., 1960. Principles and Procedures of Statistics. McGraw-Hill, New York, NY, 481 pp.

Stickney, R.R., 1986. Tilapia tolerance of saline waters: a review. Prog. Fish-Cult., 48(3): 161- 167.

Watanable, W.O. and Kuo, C-M., 1985. Observations on the reproductive performance of Nile tilapia (Oreochromis niloticus) in laboratory aquaria at various salinities. Aquaculture, 49: 314-323.