This study was conducted to determine the feasibility of using seaweeds as biofilters in a hatchery scale recirculating aquaculture system for juvenile spotted babylons (Babylonia areolata). Two seaweeds Gracilaria salicornia and Caulerpa lentillifera were used with three initial biomass levels of each species (280, 560 and 840 g wet weight m -3 ). Spotted babylon with an average initial shell length of 1.32 ± 0.01 cm and body weight of 0.37 ± 0.01 g was used with a stocking density of 300 snails m -2 . The experiment was carried out in triplicate over a period of 120 days. Results showed that seawater quality (water temperature, conductivity, salinity, pH, dissolved oxygen and total suspended solids) gradually changed with no significant differences between treatments throughout the experimental period, except alkalinity, total ammonia nitrogen, nitritenitrogen, nitrate-nitrogen and phosphate. Growth rates in weight and shell length of the spotted babylon cultured in all seaweed treatments used were not significantly different between seaweeds and density treatments, but significant differences in final survival rate of the spotted babylon were found between seaweed and density treatments. Growth rate and biomass gain of C. lentillifera were significantly higher than those of G. salicornia for all stocking density treatments. This study shows that Gracilaria salicornia and Caulerpa lentillifera can be used as biofilters for regulating water quality in a recirculating culture system for spotted babylons.

A 3 x 4 two-factor factorial experimental design with three replications per treatment was conducted to determine the effects three temperatures viz., room temperature (29˚C ± 1˚C) and elevated temperatures (33˚C and 35˚C ± 0.5˚C) and four salinities (25, 30, 33 and 35 ppt) on survival of postlarvae tiger prawn Penaeus monodon under laboratory conditions. Results showed that temperature had a greater influence on survival of postlarvae P. monodon than salinity and low water temperature (29˚C) gave better larval survival than higher water temperatures (33˚C and 35˚C). In addition, the PL1 had better tolerance to high temperatures than PL15. At the termination of the experiment, the best survival of PL1 was found at 29˚C for all salinities tested with an average of 95.8%, while the best survival of PL15 was also found at 29˚C for all salinities tested with an average of 70.6%. Based on survival at temperatures and salinities tested, the best salinity and temperature combination for the culture of P. monodon PL1 and PL15 were 29˚C at 25, 30, 33 and 35 ppt, and 29˚C at 25 and 30 ppt, respectively.

Growth, survival and shell normality of hatchery reared juvenile Babylonia areolata were examined at four water exchange regimes of 0, 15, 30 and 60 day intervals in a recirculating seawater system over a 120 day experimental period. Higher body weight gains and shell length increments were observed in snails held at water exchange of 15 day intervals, especially when compared with those held at water exchange of 60 and 0 day intervals (P < 0.05). Water exchange affected the final survival of B. areolata. At the end of the experiment, final survival rates were 65.47 ± 0.66%, 87.48 ± 0.67%, 86.34 ± 0.92% and 78.50 ± 3.26% for snails held in the water exchange treatments of 0, 15, 30, and 60 day intervals, respectively, and those of shell abnormality were 97.65 ± 1.04%, 93.09 ± 2.34%, 97.08 ± 1.18% and 96.71 ± 1.84%, respectively. The present study concluded that water exchange regimes of the recirculating system influenced growth, survival, shell normality and water quality of the recirculating culture system for this species.

Growth, production and economic analysis was performed for the polyculture of juveniles spotted babylon, Babylonia areolata, and milkfish, Chanos chanos, to marketable sizes using a large‐scale production of earthen ponds in Thailand. The analysis was based on actual cost and production data from a pilot commercial‐scale farm. A total farm area of 0.8 ha was comprised of 0.3 ha grow‐out earthen ponds, a 0.4 ha seawater reservoir, and a 0.08 ha accommodation and office. Each pond was stocked with spotted babylon juveniles of 0.3 g initial body weight at a density of 200 snails m−2, and they were harvested at a 7‐month period, at an average body weight of 4.6 g for a total yield per production cycle of spotted babylon and milkfish of 9875 and 6875 kg ha−1 respectively. Based on farm data and harvest data used in this study, initial investment requirement was estimated to be $4837. The ownership cost and operating cost per production cycle were $2241 and $18 501 respectively. Total cost per production cycle was $20 742. The cost of producing spotted babylon marketable sizes in this grow‐out farm design was $6.56 kg−1. The enterprise budgets based on the price of spotted babylon at a farm gate in 2003 of $9.00 kg−1 results in gross return, net return, return to capital and management, and return on investment of $31 190, $10 448, $12 689 and 2.62 respectively. Milkfish was not calculated for any returns because they were less than marketable sizes.

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 0 and 500 g tonne À1 , providing optimum conditions for production of this species in a recirculating grow-out system.