In a general sense, recirculating aquaculture system are designed tp approximate the fundamental aspects of natural system in order to support aquatic life. They may involve tank, pund, and other culture system where water is reused. In fish culture, the waste load mainly results from excreta and wasted feed, shich obviously cause water quality deterioration if unchecked. System management requires major attention to water quality, mainly dissolved oxygen, total ammonia nitrogen, nitrite, biochemical oxygen demand, and suspended solids. The processes required and options for water treatment in recirculating systems have been clearly recognized. Among the critical processes are gas exchange (aeration and degasification), solids removal, and biological filtration or biofiltration. Solids removal is a solid-liquid separation process, and may onvolve garavity separation, filtration (screen, granual media, porous media), and flotation for finr organics and other solids (foam fractionation, protein skimming, froth flotation, and air stripping are other terms used). Biofiltration involves the use of living organisms to treat the wate. In tank recirculating system, it refers primarily to nitrification, which is the conversion of toxic ammonia and intermediate form nitrite to relatively harmless nitrate. In pund system and integrated system, biofiltration also includes the utilizationof aquatic plants and animals other than the culture species. Other treatment processes include pH and alkalinity control, denitrification, and ultraviolet (UV) sterilization. Heaters and/ or chillersmay be proviede for trmperature control. While the processes and equipment are provided for specific purposes, thet are complementary, and a complex interrelationship exists in recirculating system. System design, components, and sizing criteria vary widely, and are mainly provided to comply with specific production needs, Recirculating systems for fish production are generally meant to be intensive. The paramount objectives is to design reliabel and cost-effective system.

Growth, molting, food ingestion, and absorption in juvenile Macrobrachium rosenbergii were evaluated at 2.5, 3.5, 5.0, and 7.7ppm dissolved oxygen (DO), 29°C, and 0.5°/oo salinity. DO levels were maintained by bubbling nitrogen gas against water flowing down through PVC gas-exchange columns. Prawns (0.58 to 0.60g dry weight) were grown individually in 4 l glass chambers for 40 days and fed in excess twice daily. In a separate experiment, food ingestion and absorption in prawns (0.66 to 1.36g dry weight acclimated to the tour DO levels were determined gravimetrically. Growth rate was significantly reduced only at 2.5ppm DO. The mean growth rates, as percentage dry weight increase per day, were 0.76, 1.56, 1.81, and 1.76% at 2.5, 3.5, 5.0, and 7.7ppm DO, respectively. Molting was not inhibited at the tour DO levels tested. Intermolt periods of all prawns ranged trom 8 to 18 days with a mean of 13.6 days. Food ingestion was reduced at 2.5ppm DO, but apparent absorption of dry matter was independent of oxygen at the tour levels tested. Mean ingestion rates, as percentage of dry body weight were 5.51, 8.85, 8.05, and 10.35%. The mean apparent absorption efficiency of all prawns was 87.95%. This study showed that juvenile M. rosenbergii requires about 3.5ppm DO to grow optimally in the laboratory. Reduction in growth of M. rosenbergii at DO levels below 3.5ppm is due in part to a reduction in food intake and not to changes in absorption efficiency and molting frequency.

The experimental system put up at SEAFDEC [Southeast Asian Fisheries Development Center; Philippines] consisted of six rectangular (96 x 196 x 42 cm) fiberglass-coated tanks made of marine plywood. It can depurate about 230 to 310 kg bivalves in two days. Initial findings showed that under normal seawater conditions (salinity 29-32 ppt, temperature 27-30 degrees Celsius; oxygen content 3-6.2 mg/L; and pH 7.4-8.3) and moderate rate of flow (7-10 L/min), highly contaminated oysters (MPN 1.0 x 10 to the fifth power to 2.0 x 10 to the sixth power/100 g meat) can be depurated within 48 hr or less. A short flume type of tank with a volume of about 250 L was designed, tested and showed to cleanse oysters under normal conditions in only 24 hr with a flow rate of 7L/min and with very little resulting mortality. More important, the tank can be lifted and moved by only two men of average body built.

To be self-sufficient in spawner/larval supply, a small-scale Penaeus monodon hatchery should have the following: 1) broodstock tanks or pens depending on location and other factors; 2) pond sources of broodstock of appropriate size and age; and 3) maturation by ablation (optional for P. indicus and P. merguensis).

With the growing interest among fishfarmars in the culture of sugpo or Penaeus monodon, some attention is being focused on the lesser known prawns and shrimps such as putian, Hipong puti (Tagalog), putian (Cebuano, Ilongo), lunhan (Cebuano) and udang putih (Indonesia) are collective names given to two closely related species -- Penaeus indicus, so named bacause it is the Indian prawn and P. merguiensis or the banana prawn which gets its specific name from the Mergui Archipelago in Thailand, its type locality. Both are also called white prawn referring to their light color and almost transparent shell. Aside from the Philippines and Indonesia, the distribution of these Indo-West Pacific species extends from Southest Africa for P. indicus and the Persian Gulf for P. merguiensis to India, South China, Southeast Asia, North Australia and New Guinea. Very similar in apperance, the two species can be differentiated by means of a straight rostrum and high traingular rostral crest for P. merguiensis and curved rostrum amd low rostral crest for P. indicus. More convenient for a laymen is to associate yellowish to greenish antennae with P. indicus and a brown or raddish antennae with P. merguiensis. The maximum recorded body weight is 50 g and 35 g, respectively, for P. merguiensis and P. indicus.

The paper discusses the food and feeding habits of Penaeus monodon , present knowledge of nutrient requirements and available formulation in the market including those developed at the Aquaculture Department, Southeast Asian Fisheries Development Center. Economics of feeding is also presented. Further research on the use of indigenous feed ingredients and nutritional requirement studies should be carried out to lower cost of feed and increase profits for the farmers.

Production of farmed shrimp has grown at the phenomenal rate of 20-30% per year in the last two decades. The leading shrimp producers are in the Asia-Pacific region while the major markets are in Japan, the U.S.A. and Europe. The dramatic failures of shrimp farms in Taiwan, Thailand, Indonesia and China within the last five years have raised concerns about the sustainability of shrimp aquaculture, in particular intensive farming. After a brief background on shrimp farming, this paper reviews its environmental impacts and recommends measures that can be undertaken on the farm, country and regional levels to promote long-term sustainability of the industry. Among the environmental effects of shrimp culture are the loss of mangrove goods and services as a result of conversion, salinization of soil and water, discharge of effluents resulting in pollution of the pond system itself and receiving waters, and overuse or misuse of chemicals. Recommendations include the protection and restoration of mangrove habitats and wild shrimp stocks, management of pond effluents, regulation of chemical use and species introductions, and an integrated coastal area management approach. Regional cooperation is needed in research and information sharing, and trade in supplies and equipment. The contribution of farming to global shrimp production has dramatically risen from a mere 6% in 1970 to 26% in 1990 (FAO, 1993). In terms of value, this has meant a 16-fold increase from US$300 million in 1980 to $7 billion worth of cultured shrimp by 1993 (Rosenberry, 1993). Annual growth rate of farmed shrimp has been 20-30% in the last 20 years (Table 1). In contrast, increases in commercial landings of shrimp have stabilized at 2-3% yearly due to the full or close to full exploitation of most wild stocks and high fuel costs. However, the recent failures of shrimp crops in Taiwan followed by China and Indonesia have raised concerns about the sustainability of shrimp aquaculture. This paper will a) give a background of the shrimp farming industry, b) review the different shrimp culture systems, c) evaluate the environmental impacts of shrimp farming, and d) recommend actions to promote long-term sustainability in the industry including suggestions for regional cooperation.

In the course of routine microscopic analysis of hatchery-reared Penaeus monodon postlarvae, several batches were found with hindgut abnormalities not previously described in shrimp postlarvae. The abnormality was named swollen hindgut syndrome (SHG) because it affected mainly the hindgut. Postlarvae with SHG showed enlargement and distention of the hindgut folds and its junction with the midgut, although in some cases swelling also occurred in the midgut of the sixth abdominal segment. Over a five-year period, the yearly prevalence of SHG ranged from 6 to 13% of all batches examined. No seasonal pattern was observed as SHG occurred year-round. Despite the numerous samples obtained, SHG has not been associated with specific predisposing factors in the hatchery. The abnormality caused cessation of the rhythmic movements of the hindgut-midgut junction resulting to failure of affected postlarvae to excrete fecal pellets. Swollen hindgut syndrome, although reversible to some extent, caused mortality and significant size variation within batches of postlarvae resulting in their unsuitability for stocking in grow-out farms.