Comparative Study On Variation Of Main Water Quality Parameters And Culture Benefits Between Litopenaeus Vannamei Cultured In Plastic Greenhouse Ponds And High-Intensive Ponds

Litopenaeus vannamei cultured in plastic greenhouse ponds and high-intensive ponds are the two popular culture models in our country. This experiment studied onvariation of main water quality parameters and culture benefits in the two models. Culture benefits include the economy benefits and using effects of organic carbon, nitrogen and phosphorus. In seven months, thirteen culture ponds in four density levels of LuYuan Mariculture Factory were monitored. Effects of Litopenaeus vannamei cultured in different density and two models are compared in this paper. The main results are as follows.1. The variation of main water quality parameters in plastic greenhouse pondsThe variation of main water quality parameters were observed in this experiment. The results showed that temperature and salinity of water in plastic greenhouse ponds fluctuate with season character and the total dissolved solids (TDS) has the same fluctuant trend with salinity. The levels of dissolved oxygen (DO) and pH fall down as the culture days prolonged and this decline has no relationship with stocking density. The turbidity level rises in the former culture phase and maintains in some level in the following phase. The variation of oxidation-reduction potential (ORP), total ammonia nitrogen (NH₄-N), inorganic phosphorus (PO4-P) and Chlorophyll-a (CHL-a) are erratic. The variation of nitrite (NO₂-N), nitrate (NO₃-N) and chemical oxygen demand (COD) has an obvious trend. All these three factors increase as the culture days prolonged, and the variation has some relationship with the stocking density. The variation of DO, pH, NO₂-N, NO₃-N, and COD has a distinct regularity.2. The effect of stocking density on culture benefits in the plastic greenhouse culture model The culture results of 13 plastic greenhouse ponds showed that both culture density and culture technology had serious effects on the culture output, shrimp growth, bait coefficient and water quality. The appropriate stocking density for the experiment ponds is 240 shrimp per m³. The average length and bait coefficient of groups with 150 and 240 shrimp per m³ are better than the group with 300 shrimp per m³. There were no significant differences in water quality factors among three groups. Both average length and water quality factors of group with 180 shrimp per m³ in XuWang Mariculture Factory are not better than the group with 240 shrimp per m³ in LuYuan Mariculture Factory. This phenomenon implies that culture technology would significantly affect the culture benefits.3. Input and output of total organic carbon (TOC), nitrogen (N) and phosphorus (P) in the plastic greenhouse pondsIn this study, 10 plastic greenhouse ponds in 3 stocking densities were monitored. The results of input and output of TOC, N and P nutrient elements showed that 93.21%～95.36% TOC, 95.26%～96.77% N and 7 8.45%～87.85% P were from feed. Nutrient budget showed that only 20.53±2.58%～23.4±1.05% TOC, 29.22±3.49%～34.85±1.82% N and 19.20±3.55%～36.43±2.77% P of the total input were transformed into harvested shrimp finally. The major output of TOC, N and P (76.38±1.06%～79.23±2.57%, 64.99±1.82%～70.63±3.49% and 62.67±2.73%～79.85±3.57%) were from discharge water in the present study. The using proportion of three nutrient elements is best in the group of 240 shrimp per m³, from transformed into harvested shrimp to discharge water's output. But in this field, the group of 300 shrimp per m³ is worst.4. The variation of main water quality parameters in high-intensive pondsThe variation of main water quality parameters were observed in this experiment. The results showed that temperature and salinity of water in high-intensive ponds fluctuate with season character and TDS has the same fluctuant trend with salinity. The levels of DO and pH fall down as the culture days prolonged and this decline has no relationship with stocking density. The turbidity level rises in the former culture phase and maintains in some level in the following phase. The variation of ORP, NH4-N, and CHL-a are erratic. The variation of NO₂-N, NO₃-N, PO₄-P and COD has an obvious trend. All the four factors increase as the culture days prolonged, and the variation has some relationship with the stocking density. The variation of DO, pH, NO₂-N, NO₃-N, PO₄-P and COD has a distinct regularity.5. The effect of stocking density on culture benefits in high-intensive pondsThe culture results of 2 density gradients in high-intensive ponds showed that the stocking density had serious effects on the culture output, shrimp growth and bait coefficient. The appropriate stocking density for the experiment ponds is 80 shrimp per m3. The comparative results between 2 ponds of 80 and 120 shrimp per m3 in the fields of culture produce, harvested shrimp average length and bait coefficient are 1101.9<1259.5(kg), 9.64±0.70>8.81±0.67(cm) and 1.42<1.86.6. Input and output of TOC, N and P nutrient elements in high-intensive pondsIn this study, 6 high-intensive ponds in 2 stocking densities were monitored. The results of input and output of TOC, N and P nutrient elements showed that 82.95%～87.94% TOC, 86.44%～90.52% N and 82.90%～87.87% P were from feed. Nutrient budget showed that only 13.36%～16.45% TOC, 19.84%～25.33% N and 14.30%～17.11% P of the total input were transformed into harvested shrimp finally. The major output of TOC, N and P were from sediment (39.18%～45.03%, 30.62%～40.22% and 53.60%～56.09%) and discharge water(37.32%～46.60%, 34.89%～36.96% and 17.52%～20.56%) in the present study. The using proportion of three nutrient elements is better in the group of 80 shrimp per m3, from transformed into harvested shrimp to nutrient elements output. But in this field, the group of 120 shrimp per m3 is worse.7. Comparative analysis on effects of Litopenaeus vannamei cultured in both models of plastic greenhouse ponds and high-intensive pondsThis experiment compared the differences in water quality factors, culture results, and using rates of three elements between models of plastic greenhouse ponds and high-intensive ponds. The water quality factors in high-intensive ponds are better than plastic greenhouse ponds'in the mass. But culture model of plastic greenhouse ponds are better in the parts of shrimp growth, bait coefficient, culture output and using rates of TOC, N, P elements. Both models do not have a high using rate level about the three elements, and it implies that people should enhance the economic and ecological benefits of shrimp culture.