Research On Evolution Rules Of Water Environment In Litopenaeus Vannamei Culturing Ponds

Water quality in 22 ponds of two Litopenaeus vannamei culturing farms in Fengxian District of Shanghai were investigated from 2009 to 2010. Researches including two stages were conducted from April 2009 to September 2010 with every stage consisting of two research cycles. Water quality index were determined during stage 1, which was from April to September in 2009. While from May to September in 2010, which meant stage 2, further researches including Litopenaeus vannamei muscle nutrition analysis were carried out except for water quality investigation, relevance among those water quality parameters and so on.Methods and results were as followed:1. The total hardness of water source 1 and 2 were 3.96 and 4.12 mmol/L respectively, belonging to moderate soft water. While the total hardness in larva prawn pond was 12.82 mmol/L, belonging to extreme hard water. The total alkalinity of water source 1 and 2 were 2.38 and 2.53mmol/L, and that in larva prawn pond was 2.33 mmol/L. Most of the alkalinity was in the form of HCO₃^-. The water types of water source 1, 2 and larva prawn pond were all Cl_III^Na. Changes of major water quality indicators in L. vannamei ponds of 2009 were as followed:1) Change of transparency in both two farms showed similarity. At the beginning of breeding stage, the transparency of the water was low because of water pouring in. Then the transparency started to arise, and later with the passage of the breeding time, transparency fell again.2) The automatic aerators in the farm were operatedvfrequently, so the dissolved oxygen was always at higher level.3) Chlorophyll-a contents were relatively stable, except that water bloom broke out in the pond No.6 of the second farm, which caused a peak of chlorophyll-a content.4) The COD_Mn were in the range of 7.54³1.61mg/L and 6.10³1.24mg/L in farm 1 and farm 2. COD_Mn reached the highest peak at the end of the first culturing period and also showed high content at the end of the second culturing period in 2009.5) The TN were in the range of 0.955¹2.647 mg/L and 0.707¹6.094 mg/L in farm 1 and farm 2. TN climbed to the highest at the end of both the first and the second breeding cycles. On June 4^th in 2009, TN in pond No.5 of farm 2 increased to 16.094 mg/L because of the breakout of water bloom.6) In 2009, PO₄-P were in the range of 0.094⁰.789 mg/L and 0.068¹.316 mg/L respectively in ponds of farm 1 and 2.Changes of major water quality indicators in L. vannamei ponds of 2010 were as followed:1) Chlorophyll-a contents were relatively stable in farm 1. Chlorophyll-a contents increased obviously in farm 2 because no water change was put into practice within the two culturing circle in 2010. Nutrient contents continued to rise, so promoted on phytoplankton growth.2) The COD_Mn were in the range of 6.42³1.21 mg/L and 7.17 44.41 mg/L in farm 1 and 2. Trend of COD_Mn in the farm 1 was similar with 2009, but COD_Mn kept increasing in farm 2 and were higher than that in farm 1.3) The TN was in the range of 1.023⁶.493mg/L and 0.111⁷.471mg/L in farm 1 and 2. TN showed no remarkable change in farm 1 because of the high frequency of water renewal but increased obviously in farm 2.4) The PO₄-P were in the range of 0.030～0.849mg/L and 0.068～1.731mg/L respectively in ponds of farm 1 and 2. The phosphorus change trend is not obvious.2. The COD_Mn and BOD₅ exceeded Water Quality Standard for Fisheries in 2009 and 2010. During the whole breeding period, BOD₅ exceeding rate was 34.7%. COD_Mn exceeding rate reached 14.5% according to the aquaculture discharge standard during the later period of shrimp culture. At the same time, TOC exceeding rate was 19% during the whole research period. All the TNs were higher than the required values for aquaculture while TP exceeding rate was as high as 31.6%. According to the aquaculture discharge standard, exceeding rates of TN and TP reached 10.3% and 15.8 % respectively. Nitrogen and phosphorus pollution was serious in.surrounding water and should be treated before being put to use for shrimp culture. And Discharge water from shrimp ponds should also be treated to remove organics, nitrogen and phosphorus.3. Organic contents in pond of a Litopenaeus vannamei culturing farm were investigated during two aquaculture cycles from April to September in 2009. Total organic carbon (TOC), Chemical oxygen demand (COD_Mn), and Biological oxygen demand (BOD₅) were analyzed respectively. The results showed that BOD₅ changed in the range of 4.40～19.00mg/L and 3.90～17.00mg/L in the two cycles of April to July and July to September respectively, and COD_Mn were in the range of 7.54～25.81mg/L and 7.26～28.07mg/L, while TOC were from 10.05 to 42.60mg/L and 9.92～34.52mg/L. The rates of TOC to COD_Mn (TOC/COD_Mn) were from 1.01 to 2.07 and 0.84～2.06 with an average of 1.35 and 1.32, and TOC/BOD₅ in the range of 1.29～3.11 and 1.18～3.88 with an average of 2.10 and 2.08, while BOD₅/COD_Mn of 0.35～0.88 and 0.47～0.91 with an average of 0.66 and 0.65。Significant relationships lied among the three water quality parameters. Linear regression equations and related coefficients were as follows. In cycle 1: BOD₅=0.4174TOC+1.2777, r=0.8022. COD_Mn=0.5616TOC+3.2091, r=0.8342. BOD₅=0.6264COD_Mn+0.4209, r=0.8106. In cycle 2: BOD₅=0.4764TOC+0.7902, r=0.7480. COD_Mn=0.7941TOC+0.0237, r=0.7962.BOD₅=0.568COD_Mn+1.2912, r=0.8920. Then 106 sets of data were used to inspect the equation and the fitted values deviated when the contents of organics were higher . Concentrations of organics in 2010 were higher than that in 2009 according to the investigation, so the equation established in lower concentration didn't fit the situation in 2010 so well. Which meant equations were fit within certain ranges and should be revised if the concentration changed.4. Water quality parameters in 22 ponds of the L. vannamei culture farm were investigated from April to September in 2009. Fifteen parameters including chlorophyll-a (Chl.a), temperature, pH, dissolved oxygen (DO), transparency, suspended substance (SS), total organic carbon (TOC), biological oxygen demand (BOD₅), chemical oxygen demand (COD_Mn), nitrite nitrogen (NO₂^--N), nitrate nitrogen (NO₃^--N), total ammonia nitrogen (TAN), total nitrogen (TN), active phosphorus (PO₄3--P) and total phosphate (TP) were determined. Descriptive statistics was conducted and the correlation between Chl.a and the other parameters was analyzed. The statistical analysis results showed that Chl.a had extremely significantly linear positive correlation with SS, TOC, BOD₅, COD_Mn, TN and TP. Significantly linear positive correlation existed between Chl.a and DO. Extremely significantly linear negative correlation was confirmed between Chl.a and transparency while Chl.a had significantly linear negative correlation with PO₄-P. Chl.a had no significant correlation with water temperature, pH, NO₂^--N, NO₃^--N and TAN. According to the principles of selecting independent variables in the multiple linear regression analysis, four water quality parameters including COD_Mn, TN, PO₄- P and TP were used for establishing the stepwise regression model which was Chl.a=- 0.03457 +0.0217 TN+0.0007 COD_Mn - 0.49 PO₄-P+0.338 TP, (r=0.6896)The effects of these four factors to Chl.a were tested using the partial regression coefficient. The most influenced water quality parameter to Chl.a was TN and then TP, PO₄-P, COD_Mn in turn. Explain that through regression equation of chlorophyll a calculated value that is acceptable.The results would help further study on ecological rules and water environmental protection in aquaculture ponds.5. Contents of moisture, protein, lipid and the composition of amino acids in the muscle of L. vannamei were analyzed in 2010. The result showed that crude protein contents were 16.30% and 18.30% in samples from farm 1 and 2, while lipid contents were 1.42% and 1.61%. The total amino acids were 23.27% and 27.52% in shrimps from farm 1 and 2. The rates of essential amino acids to total amino acids accounted for 9.09% and 10.74% respectively in shrimps from farm 1 and 2 while the flavor amino acids were 8.52% and 10.16%.