| Artificial cultivation of Penaeus monodon in a re-circulating with higher density production system is one kind of effective technologies developed in recent years in aquaculture. This technology increases not only water resource use sufficiently, reduces the wasted water discharge, but also enhances the prawn output greatly. The inspection and controlling of water quality during the cultivation is an important work in the raising of Penaeus monodon. Water quality affects the prawn health, growth and survival rate. Therefore, monitoring the changing and variation of water quality and influence factors will provide important information for culture of Penaeus monodon in a recirculating system.The research was conducted based on a higher cultivation density, recirculating aquaculture system and a simulated prawn experiment in aquarium. Water quality variation and influence factors during the culture periods were analyzed and also combined with the simulated trials to testify. The experimental results indicated:1. It was observed that water quality parameters (NH4+, NO2 and COD) initially increased lightly within the 2 hours sampling times after feeding, then a slightly declining after 2 h. after feeding sampling times. It was indicated that feeding has no significant influence on water quality in short time (3h after feeding), and the simulated experiment showed that major influence on the water quality from forage occurred in 6~9h after feeding.2. Under this experimental condition, there is no significant difference among different culture density effects on water quality (NH4+-N, NO2-N and CODMn )3. As the aerator device worked so well during experiment period that DO in kept quite stable in safe range and no dramatic variation of DO in water happened . There is no significant difference of DO among the culture densities. Water temperature in prawn experiment tank increased gradually with the hoisting of outside air temperature. There is daily variation of temperature especially in the morning and at night. Because of the feeding and excrement of shrimp influences, pH of waterdropped gradually, so alkali was added into the experimental water to adjust it. There was also difference and variation observed between the day and night pH values among different treatment of prawn densities.4. The weight and body length of prawn in the tanks with different density treatments were measured and no difference (at LSD0.05) was observed between the treatment means. The maximum prawn output was obtained in highest density tank in this system. The survival rate had significant difference with other three densities treatments tank.5. The water treatment system in our experiment or called an efficient recirculating aquaculture water treatment system comprised sediment subtank, screen filter, foam separation device, bio-filter, ozone for disinfection and heating sub-system for water quality pre- and post- treatment. During a 3 months experimenmtal period, the maximum removal rate of ammonia was 85%, the removal rate of nitrite was not significantly higher, at 44%. The system had a little effect on removal of CCDMn. The maximum removal rate for NH4+-N occurred within 30' after water entering bio-filter, for removal of NO2-N and CODMn, the water should be remained for more than 30 minutes.6. The simulated experiment of prawn at different density indicated that the aerating is an important factor for shrimp culture. The aerating not only provided enough O2 for shrimp growth, but also promoted speeding of the oxygenation of NH4+-N and NO2~-N. Water quality under aerating condition was better than un-aerating, there was a significant difference of water quality between aerating and unaerating treatment.7.The first 9hrs is the important time period for controlling NH4+-N and NO2-N influence on water quality. Water deteriorated rapidly after the 9th hour with feeding and dead shrimp. According to the rule of metabolism of shrimp, shrimp will excrete immediately after feeding. Excretion will pollute the water...
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