Effects of Stocking Density on Fry Survival and Growth of Asian Sea Bass (Lates calcarifer)

JKAU: Mar. Sci., Vol. 18, pp: 53-61 (2007 A.D. / 1428 A.H.) Effects of Stocking Density on Fry Survival and Growth of Asian Sea Bass (Lates calcarifer) Adnan Jameel Salama Faculty of Marine Science, King Abdulaziz University, P.O.Box, 80207, Jeddah, 21589, Saudi Arabia Abstract. Survival rate and growth were determined on Asian sea bass Lates calcarifer larvae using stocking densities of 20, 40, 60, 80 larvae/liter. Temperature, ph and dissolved oxygen values were within the favorable levels for the Asian sea bass larvae, as well as unionized ammonia (NH 3 ) and nitrite (NO 2 ) maximum values in all the larval tanks may have affected the overall larval survival. Fry production after 20 days of rearing showed that survival rate of 28% was significantly higher at a stocking density of 20 larvae/l, which was 2-3 times better than at higher larval densities (P<0.05) however there were no significant differences among survival rates 40, 60 and 80 larvae/l with 14.68%, 8.89% and 8.67%, respectively. Significant exponential correlation of R 2 = 0.8879 between average survival rate and larval density was observed as increasing larval density resulted in decreasing survival rate. Reduction in survival of about 2% with density was highly significant (P < 0.0002), based from the computed relationship of SR = 35.109 e 0.0197D. Significant differences in larval length were only detected on day 5, however, at higher densities larval density started to decline beginning after day 5, particularly when their number became much less after day 15. Growth rates may have increased such that no significant size differences detected at the end of the larval culture period. A very poor linear relationship (R 2 = 0.0806) was obtained between the final larval length at 20 days and larval density. Keywords: Culture, Asian sea bass, larvae, stocking density, survival. 53

54 A.J. Salama Introduction Techniques for the propagation of the Asian sea bass (Lates calcarifer) originally developed in Thailand in the 1970's (Ruangpanit 1986). The considerable research and development efforts exhausted in culturing the species over the past decades have resulted in reliable techniques for its mass propagation (Copland and Grey 1987). At the Fish Farming Center, Jeddah, Saudi Arabia promising results obtained on the preliminary trials conducted on the species from larval rearing to grow-out stages (FFC 1999, 2000, 2001, 2002). The resulting broodstocks produced from these trials made to spawn using the hormone LHRH (FFC 2002, 2003, 2004). Millions of eggs and larvae produced and the available larval rearing tanks were not enough to accommodate the larvae using low stocking rates. Likewise, results from the study on larval stocking showed increasing stocking density can yield increasing number of fry (FFC 2004). According to Tatanon and Tiensongrusmee (1984), Kungvankij et al. (1986) and Parazo et al. (1989), the recommended stocking rates for the species are only 10 to 40 larvae per liter. This study conducted to test higher larval stocking densities to fully utilize the large number of available larvae for rearing and possibly increase Asian sea bass fry production. The present study aimed to improve larviculture techniques and to optimize fry production for Asian sea bass under local conditions and specifically to determine the effects of stocking density on the growth, survival, and production of Asian sea bass fry, and to asses if there are any relationships between stocking density and sea bass fry performance, survival and water quality. Materials and Methods Four larval stocking densities namely (20, 40, 60 and 80) larvae/liter were tested, each treatment being replicated three times. Newly hatched Asian sea bass larvae were randomly stocked in 12 units of 2.5-m 3 tanks in the marine fish hatchery building with each tank randomly assigned to a particular larval stocking density following a complete randomized design (Gomez and Gomez 1984). All data gathered were subjected to analyses of variance (ANOVA) to test if there are any significant differences between treatments. Duncan's multiple range test (DMRT) (Duncan, 1955) was used to compare treatment means if any difference

Effects of Stocking Density on Fry Survival and Growth of Asian 55 exists. Regression analyses were also used to determine if any relationships exist between the stocking density and growth, survival rate, fry production, and water quality attained. Larval rearing protocol was used in all the experimental tanks. From Day 2 to Day 15 larvae were fed with S-type rotifer maintained at 10 rotifers (Brachionus plicatilis)/ml density. From Day 10 to Day 15 newly-hatched Artemia nauplii were fed to the larvae twice daily at a density 1 nauplii/ml, while from Day 16 to Day 19 Superselco-enriched one day old nauplii were fed to the larvae four times daily at a density of 2 nauplii/ml. A density of 2 10 5 cells of the green microalgae Nannochloropsis were maintained in all the rearing tanks for 15 days. Seawater flow-through started on day 6 at a daily water exchange rate of 25% up to day 10, and 50% from day 11 up to day 20. Tank s bottom was siphoned daily from day 10. All the experimental tanks were provided with moderate aeration. Growths in terms of length (mm) were measured every 5 days in all the treatments while survival and production were determined by counting the remaining larvae after 20 days. Survival rate computed as the percentage of the remaining larvae from the original stock. Water temperature, ph, and salinity and dissolved oxygen were measured every 3-4 days, while ammonia and nitrite were analyzed every five days using the Hach DREL/2400 Basic Water Quality Laboratory. Results and Discussion As shown in Table 1 and Fig. 1, survival rate of 28% was significantly higher at a stocking density of 20 larvae/l, which was 2-3 times better than at higher larval densities (P < 0.05) however there were no significant differences among survival rates 40, 60 and 80 larvae/l with 14.67%, 8.89% and 8.67% respectively. Significant exponential correlation of R 2 = 0.8879 between average survival rate and larval density was observed as increasing larval density resulted in decreasing survival rate. The reduction in survival of about 2% with density was highly significant (P < 0.0002) based from the computed relationship of SR = 35.109 e 0.0197D where SR is the survival rate in percentage and D is larval density per liter. Low survival rates obtained in densities of 60 and 80 larvae per liter may be attributed to cannibalistic behavior and the

56 A.J. Salama insufficient amount of rotifer fed to the larvae during early rearing from day 2 to day 15, which is 10/ml, where Rimmer et al. (1994) made use of 15 to 20 rotifers per ml in their intensive larval rearing. Also, as shown in Table 2, temperature, ph and dissolved oxygen values were within the favorable levels for the Asian sea bass larvae, however unionized ammonia (NH 3 ) and nitrite (NO 2 ) maximum values in all the larval tanks exceeded the allowable tolerable levels for the larvae (Rimmer and Russel, 1998) which may have affected the overall larval survival. Table 1. Growth (mm) and survival rate (%) of Asian sea bass larvae reared at stocking densities of 20/l, 40/l, 60/l and 80/l. Stocking Initial density larvae/tank Intial length (mm) Length (Dat 5) (mm) Means without a common are significantly different (P < 0.05). Length (Day 20) Final numbers Survival rates (%) 20 50.000 2.38 2.62 a 7.63 14.000 28.00 a 40 100.000 2.38 2.57 a 7.57 14.677 14.67 b 60 150.000 2.38 2.41 b 7.50 13.333 08.89 b 80 200.000 2.38 2.23 c 7.27 17.333 08.67 b Larval Length and Survival at Various Densities 8.0 50.0 40.0 Length, mm 6.0 4.0 L 20 = -0.0058D + 7.7833 R 2 = 0.0806 %SR = 35.109e -0.0197D R 2 = 0.7556 30.0 20.0 Survival Rate, % 2.0 10.0 Length at 20 days % Survival Rate 0.0 0.0 0 20 40 60 80 100 Density, larvae/l Stocking Larvae / L Fig. 1. Relationship between larval stocking density, survival rate and growth in terms of length, in Asian sea bass.

Effects of Stocking Density on Fry Survival and Growth of Asian 57 Table 2. Ranges and means of water quality parameters in the Asian sea bass larval tanks. Stocking density (larvae/l) 20 26.7-29.8 40 26.8-29.8 60 26.4-29.8 80 26.7-29.8 Temperature (ºC) Dissolved oxygen (ppm) Stocking densities of 20 and 40 larvae per liter tested in the present study were in agreement with recommended range in the previous studies on the intensive larval rearing of Asian sea bass of 10 to 40 (Tatanon and Tiensongrusmee 1984, Kungvankij et al. 1986, NICA, 1986 and Parazo et al. 1998). According to NICA (1986) the overall survival for intensively reared Asian sea bass larvae from hatching to about 10 mm total length usually ranges between 15 to 40% considering the larval stocking range of 10 to 40 per liter. As shown in Table 1 and Fig. 2, significant differences in larval length were only detected on day 5 in favoer of SD of 20 and 40 larvae/l. The large variation in length of larvae measured during each sampling period contributed to the difficulty in detecting statistical differences. However, larvae generally grew faster at a density of 20 larvae/l compared to other densities as shown by the relatively bigger larval size throughout the culture period. When larvae density started to decline at higher densities beginning after day 5, and particularly when their number became much less after day 15, growth rates may have increased such that no significant size differences were detected at the end of the larval culture period. A very poor linear (no significant) relationship (R 2 = 0.0806) was obtained between the final larval length at 20 days and larval density. The estimated reduction in length with density of about 0.006 mm at 5% level is not significant. Compared to the growth obtained by Mannewongsa and Ruangpanit, 1984 (in Tookwinas, 1989), growth after five days of 2.91 mm even at a high stocking density of 80 l/l the lower growth values in the study clearly showed inadequate ph Unionized ammonia (ppm) Nitrite (ppm) Range Mean Range Mean Range Mean Range Mean Range Mean 28.2 4.2-5.7 28.2 3.5-5.7 28.2 4.0-5.3 28.2 4.2-5.7 5.0 7.31-7.77 4.7 7.27-7.74 4.8 7.31-7.75 4.9 7.31-7.71 7.57 0-0.41 0.14 0.11-0.23 7.52 0-0.25 0.08 0.07-0.23 7.53 0-0.36 0.16 0.12-0.25-7.51 0-0.41 0.10 0.07-0.28 0.19 0.15 0.19 0.23

58 A.J. Salama amount of food available using a rotifer density of 10/ml in the early larval rearing. 9.0 Larval Growth Curves Length, mm 8.0 7.0 6.0 5.0 4.0 3.0 20 Larvae/L 40 Larvae/L 60 Larvae/L 80 Larvae/L 2.0 1.0 0.0 0 5 10 15 20 Day Fig. 2. Growth in terms of length in Asian sea bass larvae at four different stocking densities. From the present study, it is recommended that the growth and survival of the Asian sea bass larvae could be improved by increasing the amount of rotifers and better water quality to raise the growth and survival rates. References Copland, J.W. and Grey, D.L. (1987) Management of Wild and Culture Sea bass/barramundi (Lates calcarifer). Proceedings of an International Workshop, 24-30 September (1986), Darwin, NT, Australia, ACIAR Proc. No. 20. Duncan, D.B. (1955) Multiple range and multiple F tests, Biometrics, 11: 1-42. FFC. (1999-2003) Fish Farming Center Project Progress Report, Ministry of Agriculture, Fish Farming Center, Jeddah, North Obhur. Gomez, K.A. and Gomez, A.A. (1984) Statistical Procedures for Agricultural Research, John Wiley and Sons, Inc. New York U.S.A. 680 p. Kungvankij, P., Tiro, L.B., Pudadera, B.J. and Potestas, I.O. (1986) Biology and Culture of Sea bass (Lates calcarifer), Network of Aquaculture Centers in Asia Training Manual Series No. 3, Food and Agriculture Organization of the United Nation and Southeast Asian Fisheries Development Center. Nica (1986) Technical Manual for Seed Production of Sea bass, National Institute of Coastal Aquaculture, Songkhl, Thailand.

Effects of Stocking Density on Fry Survival and Growth of Asian 59 Parazo, M.M., Garcia, L.Ma. B., Ayson, F.G., Fermin, A.C., Almendras, J.M.E. and Reyes, D.M. (1998) Sea bass Hatchery Operations, Aquaculture Extension Manual No. 18. Rimmer, M.A. and Russell, D.J. (1998) Aspects of the Biology and Culture of Lates calcarifer, In: De Silva S. (ed.), Tropical Mariculture, pp: 449-476. Rimmer, M.A., Reed, A.W., Levitt, M.S. and Lisle, A.T. (1994) Effects of nutritional enhancement of live food organisms on growth and survival of barramundi, Lates calcarifer (Bloch), larvae, Aquaculture and Fisheries, Management, 25: 143-156. Ruangpanit, N. (1986) Developing hatchery techniques for Sea bass (Lates calcarifer): a review. In: Management of Wild and Cultured Sea bass/barramundi, Lates calcarifer, Proc. of an International Workshop, Darwin, N.T. Australia, 24-30 (Sept.), pp: 132-135. Tattanon, T. and Tiensongrusmee, B. (1984) Manual for Spawning of Sea bass, Lates calcarifer, in Captivity, Food and Agriculture Organization of the United Nations, Rome. Tookwinas, S. (1989) Larviculture of Sea bass and Grouper in Thailand, In: Advances in Tropical Aquaculture, Workshop at Tahiti, French Polynesia (20 February 4 March), pp: 645-660.

60 A.J. Salama تا ثير آثافة التخزين على حيوية وأداء نمو يرقات القاروص الا سيوي calcarifer) (Lates عدنان جميل سلامة آلية علوم البحار- جامعة الملك عبدالعزيز- جدة ص ب ٨٠٢٠٧ جدة ٢١٥٨٩- المملكة العربية السعودية ajsalama@kaau.edu.sa. (Lates calcarifer). / ( ) (Lates calcarifer). - /.(P<0.05) /.,,, (0.8879 =R 2 ). (P<0.0002).35.109e -0.197D = ( ) (Lates calcarifer)

Effects of Stocking Density on Fry Survival and Growth of Asian 61 ( ).( ). 0.0806=R 2. ( )