Study On The Oxygen Budgets Of Grass Carp Ponds And Its Critical Impact Factors

Dissolved oxygen is one of the most important indicator for aquaculture. The changein dissolved oxygen is a comprehensive reflection of the physicochemical propertiesand biological processes in water, and also an important parameter which showsproduction of an aquaculture pond. The factors that influence dissolved oxygen balancecan be classified by two categories: The first is the factors affecting dissolved oxygenincome, including photosynthesis, air dissolved and artificial oxygen; Another is aboutdissolved oxygen expenditure factors, including water breathing, breeding animalsbreathing, sediment respiration and escape. Research on the dissolved oxygen balancewas done in the past by a large number of scholars, but with the development ofaquaculture techniques, the breeding density and the feeding have been greatlyimproved, and the pond dissolved oxygen source is increasingly dependent on the use ofthe aerator. But the dissolved oxygen budget in the new situation is short of systemicstudy. In order to studied the balance of dissolved oxygen and its influencing factors, wechoose the pond of different stocking density, and detected the dissolved oxygen underthe condition of different density, weather and breeding molds, the oxygen consumptionrate of sediment and fish breath situation. The results are as follows:1. The weather have an important impact on pond oxygen budgets. The result asfollow: On sunny days, oxygen consumption induced by water respiratory and sedimentrespiration were higher than on cloudy days. Also the oxygen consumption ratio was thesame situation as the oxygen consumption. And the increased oxygen production,oxygen ratio and the total volume induced by photosynthesis under sunny days werehigher than on cloudy days, which was contrary to the artificial oxygen. On sunny days,water breath accounted for the most part of the total oxygen consumption, which was followed by fish breath oxygen consumption （38.2%） and sediment oxygenconsumption （12.7%）. Among the factors that increased oxygen, artificial oxygencontributed the most, which was48.7%of the total. Photosynthesis accounted for46.1%of the augmented oxygen and air dissolved oxygen was the least （5.1%）. Oncloudy days, fish breath consumed the most oxygen, about50.4%, which was followedby water respiration （42.0%） and sediment oxygen consumption （10.3%）. Artificialoxygen is still the most important factor that increased oxygen volume, and59.6%oftotal oxygen content, followed by photosynthesis （34.4%）, and the air dissolved was thelowest, about6.0%. And in contrast to cloudy days, there was higher total oxygenconsumption and total oxygen production under sunny days. The above results showthat the weather have a major impact on the pond dissolved oxygen budget. It is notonly directly affects photosynthesis, but also indirectly affect the water respiration,sediment oxygen consumption, escape consumption and artificial aeration. In addition,the oxygen production of photosynthesis and artificial aeration is very close in thesunny days. In cloudy weather, the oxygen production of aerator is about1times morethan the photosynthesis producing oxygen. The production oxygen of aerator hasreplaced photosynthesis and became the major method to increasing the pond dissolvedoxygen.2. The grass carp ponds’ dissolved oxygen budget of different breeding patterns hasbeen measured. The result showed that: in the low-density raise of the pond, waterrespiration is still the biggest factor of the oxygen consumption. due to the low stockingdensity, dissolved oxygen income was greater than the output, the escape of oxygen wasup to18.0%. Sediment and fish breathing oxygen consumption had little difference.Among the factors that could increase the oxygen volume, the artificial oxygen wasmore than photosynthesis, Artificial oxygen of the total oxygen content was56.3%,photosynthesis accounted for38.4%, and air dissolved accounted for5.3%. In thehigh-density culture of the pond, fish breathe oxygen consumption has become thebiggest factors of oxygen consumption （73.8%）, followed by water breathing （43.6%）.Fish breath and water breath took a high oxygen volume in the high-density culturepond, so for dissolved oxygen, income was insufficient to cover the consumption ofdissolved oxygen, which the oxygen debt was as high as27.4%. For income ofdissolved oxygen, which was similar to low-density pond, artificial oxygen was thehighest proportion of the total oxygen content （52.0%）, followed by photosynthesis oxygen （42.2%） and air dissolved oxygen is5.8%. With the increased breeding density,water and sediment respiration oxygen consumption capacity and the proportiondecreased, and fish breath oxygen consumption and the proportion increased.3. The relationship of sediment oxygen demand（SOD） and physical and chemicalfactors of bottom water and sediment characteristics were studied by measuringsediment oxygen demand in situ. The relationship of sediment oxygen demand（SOD）and physical and chemical factors of bottom water and sediment characteristics in10fish ponds were studied by measuring sediment oxygen demand in situ. The resultsshowed that: The average of SOD rate was0.91g/（m²d） in all ponds and the range ofchanges in different ponds were from0.76¹.09g（/m²d）. Bivariate correlation analysisshowed that the relationship between the SOD rate and the physical and chemicalfactors of the ponds bottom water were all very significant（P<0.01）, the Pearsoncorrelation coefficient with DO was the highest（R=0.779）, followed by temperature （R=0.587）, pH （R=0.557） and ORP（R=-0.421）. The correlation between SOD rate andsediment depth is significant（P <0.05）. The partial correlation analysis results show thatthe correlations of SOD rate and dissolved oxygen and temperature were highlysignificant （P<0.01）, and other factors did not reach significant levels. The mostimportant environmental factor affecting the SOD rate is dissolved oxygen, followed bytemperature. Using BP neural network to analyze the physical and chemical factorsinfluencing the SOD rate, dissolved oxygen, temperature, and sediment depth wereregarded as the input variables to establish the BP neural network model and predict theSOD rate. the BP neural network model’s training and testing correlation coefficientwere0.911and0.879, and the average relative error were11.6%and10.4%,respectively. There were small differences in the predictive value and the true value, andthe model had high accuracy, can effectively predict the SOD rate.4. The oxygen consumption of grass carp had been studied in different temperatureand stocking density and oxygen concentration by closed hydrostatic experimentalmethods. The results showed that: in the range of20-30℃, the oxygen consumptionrate of grass carp increased exponentially with increasing temperature, the regressionequationas as follows: y=0.0146e^0.1025x, R²=0.9351, Q₁₀=2.75. The oxygenconsumption rate of grass carp positively correlated with dissolved oxygenconcentration. The regression equation was: y=0.0734ln （x）+0.1101, R2=0.9509.The impact of stocking density on The oxygen consumption rate of grass carp was not significant.