Aquaculture Research, 2006, 37, 664^670 doi:10.1111/j.1365-2109.2006.01478.x Combined effects of water exchange regimes and calcium carbonate additions on growth and survival of hatchery-reared juvenile spotted babylon (Babylonia areolata Link 1807) in recirculating grow-out system S Kritsanapuntu1, N Chaitanawisuti2,W Santhaweesuk2 & S Y Natsukari3 Faculty of Technology and Management, Prince of Songkla University, Suratani,Thailand Aquatic Resources Research Institute, Chulalongkorn University, Bangkok,Thailand Faculty of Fisheries, Nagasaki University, Nagasaki, Japan Correspondence: N Chaitanawisuti, Aquatic Resources Research Institute, Chulalongkorn University, Bangkok 10330,Thailand E-mail: nilnajc1@hotmail.com Abstract Introduction To determine a suitable culture environment to maximize growth and survival, the hatchery-reared juvenile spotted babylon, Babylonia areolata, were held in plastic rearing tanks at four calcium carbonate additions of 0,100 and 300 g tonne À1, and four water exchange regimes of 0-,15-,30- and 60-day intervals in a recirculating grow-out system for120 days The results clearly showed that growth was greatest between water exchange regimes of 15- and 30-day intervals and all calcium carbonate additions, with water exchange regimes of 0- and 60-day intervals resulting in poor growth Final survival was highest between water exchange regimes of 15- and 30-day intervals, and all calcium carbonate additions, with water exchange regimes of 0-day intervals and all calcium carbonate additions resulting in high mortalities This study showed that water exchange regimes had a stronger in£uence on the growth of juvenile B areolata than calcium carbonate additions It is recommended that B areolata juveniles be maintained within the water exchange regimes range of 15^30-day intervals and at calcium carbonate additions between and 500 g tonne À1, providing optimum conditions for production of this species in a recirculating grow-out system Although large-scale rearing of Babylonia areolata in Thailand was technically feasible using £owthrough systems in concrete/canvass ponds, the disadvantages of these systems that must be solved during grow-out of spotted babylon are: these systems generally require large quantities of water; location of production systems must be near the sea; stock is vulnerable to external water supply and quality problems; and growth rate is signi¢cantly in£uenced by water £ow (Chaitanawisuti, Kritsanapuntu & Nutsukari 2002, 2004) A recirculating grow-out system had been used for growing ¢sh and shell¢sh for more than three decades This system may o¡er an alternative to pond aquaculture technology of this species The interest in recirculating grow-out systems was due to their perceived advantages, including greatly reduced land and water requirements, high degree of environmental control allowing productive cycle growth at optimum rates, feasibility of locating in far proximity from the sea, and a major issue of water conservation and reuse (Lazur & Britt 1997; Losordo, Masser & Rakocy 1998; Masser, Rakocy & Losordo 1999) Research on recirculating grow-out systems can provide major leaps in spotted babylon culture intensi¢cation, technology and the understanding of water quality management for maximium pro¢t by increasing production, lowering costs and conserving water Calcium is a very important element for ¢sh and shell¢sh because it is necessary for a variety Keywords: Babylonia areolata, recirculating growout system, calcium carbonate, water exchange, growth, survival 664 r 2006 The Authors Journal Compilation r 2006 Blackwell Publishing Ltd Aquaculture Research, 2006, 37, 664^670 Combined e¡ects of water exchange regimes S Kritsanapuntu et al of functions such as bone and scale growth, muscle contraction, transmission of nerve impulses, hormone secretion, intracellular signalling, against osmotic and ionic grains and losses, and against most environmental toxicants (Calta 2000) Calcium is required in rather high levels by aquatic animals in comparison with other mineral elements These requirements are met by dietary resources; however, dissolved calcium is readily taken up by gills of ¢sh/shell¢sh (Robinson, LaBomascus, Brown & Linton 1987) However, little is known about the e¡ects of water exchange regimes and calcium carbonate on growth and survival for growing of juvenile spotted babylon to marketable sizes in recirculating systems in Thailand The aim of this study was to determine the combined e¡ects of calcium carbonate additions and water exchange regimes on the growth and survival of juvenile B areolata in a recirculating grow-out system Materials and methods Experimental recirculating grow-out system Each plastic culture tank of 50 L capacity was an independent recirculating system with an air lift pump and a biological ¢lter tank The bottom area of the culture tank was 0.78 m2 The biological ¢lter tank of 20 L capacity contained shell fragments and gravels as ¢lters Water £owed from the culture tank through the ¢lter via air lift pumps at a £ow rate of 200 L h À1 before it was returned to the culture tank As in the £owthrough system, the tank bottom was covered with a cm layer of coarse sand (0.5^1.0 mean grain size) to serve as a substrate Water depth was 30 cm When water exchange was done for each treatment, the substrate was cleaned by £ushing it with a jet of water and sun dried for h Thereafter, the tanks were re¢lled with new ambient natural seawater Filters were rinsed in seawater to remove particulate matter, sun dried for h, and returned to the ¢lter tanks Temperature was controlled to within room temperature Ỉ 1.5 1C Salinity was monitored daily, as necessary, to keep the variation within Ỉ 2.0 ppt by addition of fresh water to correct for any increased salinity because of water evaporation Each culture tank had no aeration and photoperiod was naturally 12L:12D Water quality of pH, dissolved oxygen, alkalinity, nitrite-nitrogen and ammonia-nitrogen were analysed before water exchanges Experimental animals Juvenile spotted babylons, B areolata, used in growth and survival experiments were produced from a private hatchery, Rayong province, located on the eastern coast of the Gulf of Thailand Individuals from the same cohort were sorted by size to prevent possible growth retardation of small spotted babylons when cultured with larger ones Initial shell length and whole body weight of spotted babylon averaged 1.12 Ỉ 0.13 cm (0.98^1.23 cm) and 0.38 Ỉ 0.16 g (0.26^0.54 g), n 300 respectively Each experiment had mean shell lengths and body weights that were not statistically di¡erent and this allowed for treatments to be compared statistically Juveniles were held in experimental culture tanks as described above at optimal densities of 300 individuals m À or 250 snails tank À1 (Chaitanawisuti & Kritsanapuntu 1999) Experimental design The study was conducted from February to May 2004 at Spotted Babylon Aquaculture Research and Training Unit, Chulalongkorn University, Petchaburi, Thailand This laboratory experiment was designed to test the combined e¡ects of four water exchange regimes (0-, 15-, 30- and 60-day intervals) and four levels of calcium carbonate additions (0, 100, 250 and 500 g tonne À1) on the growth and survival for juveniles of B areolata The experiment was  factorial design, with all 16 water exchange and calcium carbonate combinations test For water exchange regimes, complete seawater was exchanged at each designed time interval, and re¢lled with new ambient seawater For calcium carbonate additions, 90% calcium carbonate powder of designed amounts was dissolved homogeneously in seawater and rinsed in culture tanks Rearing method The snails were fed ad libitum with fresh trash ¢sh, once daily, at 09:00 hours The amount of food consumed was recorded daily and uneaten food was removed immediately after the animals stopped feeding, and air dried for a period of 10 before weighing Size grading of snails in all treatments was not done throughout the grow-out period No chemical and antibiotic agent was used throughout the entire experimental periods The experiment was terminated over a 120-day culture period To determine growth performance, 50% of snails were randomly sampled from each treatment at 15-day intervals, and shell length and whole body weight were r 2006 The Authors Journal Compilation r 2006 Blackwell Publishing Ltd, Aquaculture Research, 37, 664^670 665 Combined e¡ects of water exchange regimes S Kritsanapuntu et al determined Shell length was measured with callipers to the nearest mm from the maximum anterior to posterior distance of shell, and whole weight was measured after air drying for a period of 10 before weighing, and then returned to the tank The number of dead individuals was recorded at 15-day intervals Average shell length increments, body weight gains and growth rates were calculated after the method of Chaitanawisuti and Kritsanapuntu (1999) Body weight gains (BWf^BWi) and monthly growth rates for body weight ((BWf^BWi)/T) were calculated, where BWf is the mean ¢nal body weight, BWi the initial body weight andT the time in months Mortality, expressed as the percentage of the initial stocking density, was calculated from the di¡erence between the number of snails stocked and harvested Statistical analysis Data were analysed with the SPSS statistical package (version 10) Two-way analysis of variance (ANOVA) was used to test the interaction of water exchange regimes and calcium carbonate additions at a 0.05, and di¡erences between means were compared using Tukey’s test at a 0.05 Aquaculture Research, 2006, 37, 664^670 growth of juvenile B areolata than calcium carbonate additions At all calcium carbonate additions, body weight gain was signi¢cantly greater at water exchange regimes of 15- and 30-day intervals than at water exchange regimes of 0- and 60-day intervals, with water exchange of 0- and 60-day intervals resulting in poor growth (Table 1) On the other hand, at all water exchange regimes, body weight gain was signi¢cantly greater at calcium carbonate additions of 0, 100 and 500 g tonne À1 than at calcium carbonate addition of 250 g tonne À1 (Table1) The monthly growth rates in body weight of B areolata in the four water exchange regimes and four calcium carbonate additions are presented in Fig The highest overall growth rates in body weight (0.42^0.52 g month À 2) were achieved for juveniles grown at water exchange regimes of15-day intervals and all calcium carbonate additions The lowest overall growth rates in body weight occurred for juveniles grown at all calcium carbonate additions and water exchange regimes of 0- and 60-day intervals (0.26^0.37 g month À 2) (Tables and 3) Results Growth in body weight The growths, expressed as body weight gains, of B areolata in the four water exchange regimes and four calcium carbonate additions are presented in Fig Two-way ANOVA performed on growth showed that the e¡ect of water exchange regimes was statistically signi¢cant (Po0.05), and interaction between water exchange regime and calcium carbonate addition was found The results clearly showed that water exchange regimes had a stronger in£uence on the Body weight gains (g) 2.5 1.5 days 15 days 30 days 60 days 0.5 0 100 250 500 Calcium carbonate addition (g / ton) Figure Body weight gains of juveniles, Babylonia areolata, in recirculating grow-out system at four water exchange regimes and four calcium carbonate additions Table Average body weight gains (Ỉ SD) of Babylonia areolata juveniles in recirculating grow-out system with four calcium carbonate additions and four water exchange regimes Water exchange (day interval) 15 30 60 Average Ỉ SD Calcium carbonate additions (g tonne À 1) 1.40 1.74 1.52 1.48 1.54 100 Ỉ Ỉ Ỉ Ỉ Ỉ 0.04 0.18 0.08 0.03 0.15a 1.19 1.68 1.44 1.38 1.42 250 Ỉ Ỉ Æ Æ Æ 0.04 0.50 0.02 0.02 0.20a 1.05 1.82 1.27 1.12 1.32 Average Ỉ SD 500 Ỉ Ỉ Ỉ Æ Æ 0.04 0.05 0.02 0.04 0.35ab 1.13 1.68 1.49 1.29 1.39 Ỉ Ỉ Ỉ Ỉ Ỉ 0.01 0.04 0.06 0.03 0.24a 1.19 1.73 1.43 1.32 Ỉ Ỉ Ỉ Ỉ 0.15a 0.07b 0.11c 0.15ac Data are means of three replicates Di¡erent subscriptions indicate signi¢cant di¡erences (Po0.05) 666 r 2006 The Authors Journal Compilation r 2006 Blackwell Publishing Ltd, Aquaculture Research, 37, 664^670 Aquaculture Research, 2006, 37, 664^670 Combined e¡ects of water exchange regimes S Kritsanapuntu et al Growth in shell length Shell length increments of B areolata in the four water exchange regimes and four calcium carbonate additions are presented in Fig Two-way ANOVA performed on shell length increments showed that the e¡ect of water exchange regimes was statistically signi¢cant (Po0.05) The results clearly showed the similar trends as body weight gain At all calcium carbonate additions, shell length increment was signi¢cantly greater at water exchange regimes of 15and 30-day intervals than at water exchange regimes of 0- and 60-day intervals (Table 4) On the other hand, at all water exchange regimes, shell length increment was signi¢cantly greater at calcium carbonate additions of 0, 100 and 500 g tonne À1 than at calcium carbonate addition of 250 g tonne À1 (Table 4) The highest overall growth rates in shell length 0.7 Shell length increments (cm) Growth rate (g/mo) 0.6 0.5 0.4 0.3 days 15 days 30 days 60 days 0.2 0.1 0 100 250 500 Calcium carbonate addition (g / ton) Figure Growth rates in body weight of juveniles, Babylonia areolata, in recirculating grow-out system at four water exchange regimes and four calcium carbonate additions 1.8 1.6 1.4 1.2 0.8 0.6 days 15 days 30 days 60 days 0.4 0.2 0 100 250 500 Calcium carbonate addition (g / ton) Figure Shell length increments of juveniles, Babylonia areolata, in recirculating grow-out system at four water exchange regimes and four calcium carbonate additions Table Average growth rates in body weight (Ỉ SD) of Babylonia areolata juveniles in recirculating growout system with four calcium carbonate additions and four water exchange regimes Water exchange (day interval) 15 30 60 Average Ỉ SD Calcium carbonate additions (g tonne À 1) 0.35 0.52 0.47 0.37 0.43 100 Ỉ Ỉ Ỉ Ỉ Ỉ 0.01 0.05 0.02 0.01 0.08a 0.29 0.42 0.36 0.34 0.35 250 Æ Æ Æ Æ Æ 0.01 0.02 0.01 0.01 0.05b 0.26 0.46 0.32 0.28 0.33 Average Ỉ SD 500 Ỉ Æ Æ Æ Æ 0.01 0.01 0.01 0.01 0.09b 0.28 0.42 0.35 0.32 0.34 Ỉ Ỉ Ỉ Ỉ Ỉ 0.01 0.01 0.03 0.01 0.06b 0.29 0.46 0.38 0.33 Ỉ Ỉ Æ Æ 0.04a 0.05b 0.07ac 0.04a Data are means of three replicates Di¡erent subscriptions indicate signi¢cant di¡erences (Po0.05) Table Average shell length increments ( Ỉ SD) of Babylonia areolata juveniles in recirculating growout system with four calcium carbonate additions and four water exchange regimes Water exchange (day interval) 15 30 60 Average Ỉ SD Calcium carbonate additions (g tonne À 1) 0.85 1.22 1.04 0.91 1.01 100 Æ Æ Æ Æ Æ 0.08 0.07 0.08 0.06 0.16a 0.79 1.04 0.90 0.87 0.90 250 Ỉ Ỉ Ỉ Ỉ Æ 0.10 0.02 0.05 0.05 0.10b 0.64 0.94 0.87 0.80 0.81 Average Ỉ SD 500 Ỉ Ỉ Ỉ Ỉ Ỉ 0.05 0.05 0.05 0.11 0.13b 0.90 1.12 1.07 1.10 1.05 Æ Æ Æ Æ Æ 0.08 0.02 0.13 0.09 0.10a 0.79 1.08 0.97 0.92 Ỉ Ỉ Ỉ Ỉ 0.11a 0.12b 0.09c 0.13ac Data are means of three replicates Di¡erent subscriptions indicate signi¢cant di¡erences (Po0.05) r 2006 The Authors Journal Compilation r 2006 Blackwell Publishing Ltd, Aquaculture Research, 37, 664^670 667 Combined e¡ects of water exchange regimes S Kritsanapuntu et al Aquaculture Research, 2006, 37, 664^670 Table Average growth rates in shell length (Ỉ SD) of Babylonia areolata juveniles in recirculating growout system with four calcium carbonate additions and four water exchange regimes Calcium carbonate additions (g tonne À 1) Water exchange (day interval) 0 15 30 60 Average Æ SD 0.21 0.30 0.26 0.22 0.25 100 Æ Æ Æ Æ Æ 0.02 0.02 0.02 0.03 0.04a 0.22 0.26 0.22 0.21 0.23 250 Ỉ Ỉ Ỉ Ỉ Ỉ 0.03 0.05 0.03 0.03 0.02a 0.15 0.24 0.19 0.20 0.19 Average Æ SD 500 Æ Æ Æ Æ Æ 0.02 0.02 0.04 0.03 0.04b 0.23 0.28 0.27 0.27 0.26 Ỉ Ỉ Æ Æ Æ 0.03 0.01 0.06 0.01 0.02a 0.20 0.27 0.24 0.23 Ỉ Ỉ Ỉ Ỉ 0.04a 0.03b 0.04c 0.03ac Data are means of three replicates Di¡erent subscriptions indicate signi¢cant di¡erences (Po0.05) 0.4 Growth rate (cm/mo) 0.35 0.3 0.25 0.2 0.15 days 15 days 30 days 60 days 0.1 0.05 0 100 250 500 Calcium carbonate addition (g/ ton) Figure Growth rates in shell length of juveniles, Babylonia areolata, in recirculating grow-out system at four water exchange regimes and four calcium carbonate additions (0.19^0.30 cm month À 2) were achieved for juveniles grown at water exchange regimes of 15- and 30-day intervals and all calcium carbonate additions (Fig 4) The lowest overall growth rates in shell length occurred for juveniles grown at all calcium carbonate additions and water exchange regimes of 0- and 60-day intervals (0.15^0.27 cm month À 2) (Table 5) Final survival The ¢nal survivals of B areolata in the four water exchange regimes and four calcium carbonate additions are presented in Fig Two-way ANOVA performed on ¢nal survival showed that the e¡ect of water exchange regimes was statistically signi¢cant (Po0.05), and interaction between water exchange regime and calcium carbonate addition was found (Table 5) Tukey’s test showed that at all calcium carbonate additions, ¢nal survival was greater at lower water exchange of 15- and 30-day intervals than those at water exchange regimes of 0- and 60-day 668 intervals, and at all water exchange regimes, ¢nal survival was greater at lower calcium carbonate additions of 0, 100 and 250 g tonne À1 than at calcium carbonate addition of 500 g tonne À1 (Table 5) The highest overall ¢nal survivals (65.55^93.52%) were achieved for juveniles grown at water exchanges of 15- and 30-day intervals and all calcium carbonate additions The lowest overall ¢nal survival occurred for juveniles grown at all calcium carbonate additions and water exchanges of 0-day intervals (47.55^ 80.00%) (Table 5) Discussion The results of the present study clearly showed that growth was greatest between water exchange regimes of 15- and 30-day intervals and all calcium carbonate additions, with water exchange regimes of 0- and 60-day intervals resulting in poor growth Final survival was highest between water exchange regimes of 15- and 30-day intervals, and all calcium carbonate additions, with water exchange of 0-day intervals and all calcium carbonate additions resulting in high mortalities The results showed that water exchange regimes had a stronger in£uence on the growth of juveniles of B areolata than calcium carbonate additions It is recommended that B areolata juveniles be maintained within the water exchange regimes range of 15^30-day intervals and at calcium carbonate additions between and 500 g tonne À1 provided optimum conditions for production of this species in a recirculating grow-out system Chaitanawisuti and Kritsanapuntu (1999) reported that the average monthly growth rate of spotted babylon in a £ow-through culture system in concrete/canvass tanks was 1.4 g month À1 Food conversion ratio and ¢nal survival were 1.6% and 95.8% respectively Chaitanawisuti, Kritsanapuntu r 2006 The Authors Journal Compilation r 2006 Blackwell Publishing Ltd, Aquaculture Research, 37, 664^670 Aquaculture Research, 2006, 37, 664^670 Combined e¡ects of water exchange regimes S Kritsanapuntu et al Table Average ¢nal survivals (Ỉ SD) of Babylonia areolata juveniles in recirculating growout system with four calcium carbonate additions and four water exchange regimes Calcium carbonate additions (g tonne À 1) Water exchange (day interval) 0 15 30 60 Average Ỉ SD 60.89 91.58 93.52 92.88 84.72 100 Ỉ Ỉ Ỉ Æ Æ 0.28 0.22 0.18 0.36 15.91a 80.00 90.44 90.44 82.67 85.89 250 Ỉ Ỉ Ỉ Ỉ Ỉ 0.17 0.23 0.19 0.10 5.37a 73.55 94.44 91.55 66.44 81.49 Average Ỉ SD 500 Ỉ Ỉ Ỉ Ỉ Ỉ 0.31 0.15 0.18 0.25 13.64a 47.55 73.11 65.55 57.11 60.83 Ỉ Ỉ Ỉ Æ Æ 0.28 0.21 0.26 0.38 11.00b 65.49 87.39 85.27 74.78 Ỉ Ỉ Ỉ Ỉ 14.35a 9.67b 13.21b 16.04ab Data are means of three replicates Di¡erent subscriptions indicate signi¢cant di¡erences (Po0.05) 140 Final survival (%) 120 100 80 60 days 15 days 30 days 60 days 40 20 0 100 250 500 Calcium carbonate addition (g/ton) Figure Final survival of juveniles, Babylonia areolata, in recirculating grow-out system at four water exchange regimes and four calcium carbonate additions and Santhaweesuk (2004) reported that the average growth rate of juvenile spotted babylons was 3.86 mm month À1 in length and 1.47 g month À1 in weight after months when cultured at a density of 300 snails m À in a £ow-through system and 3.21mm month À1 and 1.10 g month À1 when held in a recirculating system In recirculating systems, good water quality must be maintained for maximum growth and for optimum e¡ectiveness of bacteria in the bio¢lter A key to successful recirculating production systems is the use of cost-e¡ective water treatment systems components All recirculating production systems remove waste solids, oxidize ammonia and nitrite-nitrogen, remove carbon dioxide, and aerate or oxygenate the water before returning it to the culture tank Calcium is a very important element for ¢sh and shell¢sh because it is necessary for a variety of functions such as bone and scale growth, muscle contraction, transmission of nerve impulses, hormone secretion, intracellular signalling, against osmotic and ionic grains and losses, and against most environmental toxicants Calcium enters the ¢sh through the gills, intestines and skin The gills are a particularly important calcium uptake site (Calta 2000) Calcium is required in rather high levels by aquatic animals in comparison with other mineral elements These requirements are met by dietary resources; however, dissolved calcium is readily taken up by gills of ¢sh/shell¢sh and some species can acquire 65^80% of their metabolic needs from the water (Robinson et al 1987) Masser et al (1999) reported that most recirculating systems are designed to replace 5^10% of the system volume each day with new water This amount of exchange prevents the build-up of nitrates and soluble organic matter that would eventually cause problems In some situations, su⁄cient water may not be available for these high exchange rates A complete water exchange should be done after each production cycle to reduce the build-up of nitrate and dissolved organics For emergency situations, the recirculating system has an auxiliary water reservoir equal to one complete water exchange and the reservoir should be maintained at the proper temperature and water quality Hincks and Mackie (1997) reported that maximum growth of zebra mussel (Dreissena polymorpha) occurred at calcium levels of 32 mg Ca L À 1, an alkalinity of 65 mg CaCO3 L À and a total hardness of 100 mg CaCO3 L À1 There was negative growth at calcium levels less than 31mg CaCO3 L À1, and positive growth of juveniles zebra mussel only occurred at pH greater than 8.3 Rakocy (1989) reported that recirculating systems for ¢sh culture generally recycle 90^99% of the culture water daily and the rearing tank is aerated as in £ow-through systems with low exchange rates The recirculating rate (amount of water exchange per unit of time) can be determined by dividing the volume of water in the tank by the capacity of the pump Increasing the number of turnovers per day would provide increased bio¢ltration, greater nitri¢cation and reduced ammonia r 2006 The Authors Journal Compilation r 2006 Blackwell Publishing Ltd, Aquaculture Research, 37, 664^670 669 Combined e¡ects of water exchange regimes S Kritsanapuntu et al levels Most ¢sh production recirculating systems are designed to provide at least on complete turnover per hour (24 cycles per day) On the basis of the results of this study, B areolata juveniles should be held at water exchange regimes between 15- and 30-day intervals and calcium carbonate additions between and 500 g tonne À1 in recirculating grow-out systems Within these culture parameters, juvenile growth and survival will be optimal, and the e⁄cient utilization of water and reduction in operation costs will be maximized Acknowledgments We thank the National Research Council of Thailand (NRCT), who provided funds for this research in ¢scal year 1996^2005 We are specially grateful to Associated Professor Dr Padermsak Jarayabhand, Director of Aquatic Resources Research Institute, Chulalongkorn University, for his encouragement and facilities References Chaitanawisuti N & Kritsanapuntu A (1999) Growth and production of hatchery-reared juvenile spotted babylon, Babylonia areolata Link1807, cultured to marketable sizes in intensive £ow-through and semi-closed recirculating water system Journal Aquaculture Research 31, 415^419 Chaitanawisuti N., Kritsanapuntu A & Natsukari Y (2002) Economic analysis of a pilot commercial hatchery-based operation for spotted babylon, Babylonia areolata Link 670 Aquaculture Research, 2006, 37, 664^670 1807, juveniles in Thailand Journal of Shell¢sh Research 21,781^785 Chaitanawisuti N., Kritsanapuntu A & Natsukari Y (2004) Research and development on commercial land-based aquaculture of spotted Babylon, Babylon areolata, in Thailand: pilot hatchery-based seedling operation Aquaculture Asia 9, 16^20 Calta M (2000) The e¡ect of calcium concentration of water on chloride cell density in gill of brown trout (Salmo trutta L.) larvae TurkishJournal of Biology 24, 331^336 Hincks S.S & Mackie G.L (1997) E¡ects of pH, calcium, alkalinity, hardness and chlorophyll on the survival, growth, and reproductive success of zebra mussel (Dreissna polymorpha) in Ontari Lakes Canadian Journal of Fisheries and Aquatic Sciences 54, 2049^2057 Lazur A.M & Britt D.C (1997) Pond recirculating production systems Southern Regional Aquaculture Center, Mississippi State University, USA, SRAC Publication No 455,7pp Losordo T., Masser M & Rakocy J (1998) Recirculating aquaculture tank production systems: an overview of critical considerations Southern Regional Aquaculture Center, Mississippi State University, USA, SRAC Publication No 451, 6pp Masser M., Rakocy J & Losordo T (1999) Recirculating aquaculture tank production systems: management of recirculating systems Southern Regional Aquaculture Center, Mississippi State University, USA, SRAC Publication No 452,11pp Rakocy J.E (1989) Tank culture of Tilapia Southern Regional Aquaculture Center, Mississippi State University, USA, SRAC Publication No 282, 4pp Robinson E.H., LaBomascus D., Brown P.B & Linton T (1987) Dietary calcium and hosphorus requirements of Orechromis aureus reared in calcium ^ free water Aquaculture 64, 267^276 r 2006 The Authors Journal Compilation r 2006 Blackwell Publishing Ltd, Aquaculture Research, 37, 664^670 ... signi¢cantly greater at water exchange regimes of 1 5and 30-day intervals than at water exchange regimes of 0- and 60-day intervals (Table 4) On the other hand, at all water exchange regimes, shell length... than at water exchange regimes of 0- and 60-day intervals, with water exchange of 0- and 60-day intervals resulting in poor growth (Table 1) On the other hand, at all water exchange regimes, ... survival was greater at lower water exchange of 15- and 30-day intervals than those at water exchange regimes of 0- and 60-day 668 intervals, and at all water exchange regimes, ¢nal survival was