| The present paper dealt with the ecological environmental characteristics of prawn culture in higher-place ponds and biomanipulation technology and quantitative analyses of suspended organic matters in farming water of the prawn green-farming experimental ponds at Zhanjiang city, Guangdong province.1 Ecological environmental characteristics in higher-place ponds of Penaeus vannameiThe water diaphaneity ranged from 0.2 to 1.5 m (averaged 0.68 m) ; pH value altered in the range of 7.89 to 9.02 (mean=8.37); the amount of suspended matters in the ponds fluctuated froml8.5 to 162.3 mg/L (mean=98.5 mg/L) ; COD of the suspended matters altered in the range of 0.34 to 4.18 mg/L, averaging 1.94 mg/L; COD of the pond water altered in the range of the 3.52 to 14.58 mg/L, averaging 9.65 mg/L; COD and the amount of suspended matters increased steadily with the cultural tune.The amount of ammonia-nitrogen altered in the range of 0.023-1.210 mg/L, averaging 0.434 mg/L; the amount of nitrite altered in the range of 0.108-0.623 mg/L, averaging 0.353 mg/L; the amount of the phosphate altered in the range of the 0.009-0.067 mg/L, averaging 0.028 mg/L. The amount of nitrogen increased gradually while the amount of phosphate decreased gradually and resulted in a considerable high ratio of N/P (range: 22.1-189.3, mean=62.7). Taken all aspects into accounted, the water quality was in the state of supereutrophication. However, work could still go along by means of scientific measurements such as water-exchanging and used aerator, etc.The average wet weight of the sediment was 8.69 kg/m2, dry weight was 2.29 kg/m2, and moisture was 73.2% during the four months' cultural period. The sediment concentration distributed uniformly at the beginning of culture; and unevenly in the later period with high concentrate in the center of the pond. The amount of the sediment increased monthly. The pH value of the sediment altered in the range of 6.21 to 7.67, averaging 6.55. The organism content in the sediment ranged from 6.9% to 28.1%, averaging 17.6%. Oxygen demand of the sediment altered in the range of 0.58-3.56g O2/m2-d, averaging 1.81 g-O2/m2-d. The organism content in the sediment was positively related to the oxygen demand. The sediment was rich in nutrients, including nitrogen, phosphate and potassium.The phytoplankton identified from the four experimental prawn-farming ponds belonged to 32 gena (species), 7 phyla. The phytoplankton biomass altered in the range of 2.15-83.24 mg/L, averaging 30.41 mg/L. The diversity index of the phytoplankton was relatively low, which altered in the range of 0.075-0.414, averaging 0.202. The zooplanktons from the prawn ponds were identified to 23 species and the zooplankton biomass altered in the range of 0.45-6.34 mg/L, averaging 3.38mg/L. The average biomass of the phytoplankton and of the zooplankton differed much between months. There was a significant positive relationship between phytoplankton biomass and the body length of the prawn (r=0.764,P<0.01) .The primary productivity of the water column of the prawn ponds altered in the range of 2.03-12.54 g (V m2.d, averaging 6.58 g O2/ m2.d; The respiratory capacity altered in the range of 1.24-12.05 g O2/ m2.d, averaging 5.89 g O2/ m2.d. The ratio of P/R of the pond altered in the range of 0.9-2.21, averaging 1.27.The total bacterial amount in the prawn pond water layers altered in the range of 2.31 l06-87.2xl06 cell/mL, averaging 29.72xl06 cell/mL. The amount of heterotrophic bacteria altered in the range of 0.48x104-61.2x104 cell/mL, averaging 12.18xl04 cell/mL. The level of bacteria amount did not differ remarkably in different water layers, but had a notable diurnal dymnamic. The total bacteria content in the sediment altered in the range of 136.1 xl07-782.3x107 cell/g, averaging 352.9x107. The heterotrophic bacteria altered in the range of 0.75xl07-15.78xl07 cell/g, averaging 6.36xl07 cell/g. The total bacterial amount in the water layers had remarkably positive relationship with COD and water temperature, but had not sig... |
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