A Preliminary Study Of Pistia Stratiotes L. On Effeccts Of Environment And Fish Of Net Pens

Cage culture is a kind of highly intensive aquaculture way，but large amounts ofnutrients enter the water through various channels in the breeding process，whichproduces enormous pressure to water environment and hindered the sustainabledevelopment of cage culture. Absorbing nutrients by using of aquatic plants and takeaway nutrients from water by harvesting aquatic plants is a simple，efficient and lowcost method of remedy the eutrophic water，which is widely used in recent years. Thefloating aquatic plants of Pistia stratiotes L. is cultivated in the cage culture andabsorbing nutrients, and take away nutrients from water by harvesting Pistia stratiotesL.，which can alleviate the pollution problem of traditional cage culture and produce amore environmentally ecological cage.Based on the situation of the removalefficiency of Pistia stratiotes L.，the growth of Pistia stratiotes L. under different lightintensity and initial planting density and the effect of Pistia stratiotes L. on growthand nitrogen and phosphorus waste output of Leiocassis longirostris，reared in netpens，this paper has done some research on how to achieve nitrogen and phosphorusbalance of ecological cage including the followings：A)Preliminary research on Pistia stratiotes L. removal effect on nitrogen andphosphorus in waterStimulated experiments were carried out to study nitrogen and phosphorusuptake and removal ability of Pistia stratiotes L. from varying degrees of eutrophicwaters. The results showed that Pistia stratiotes L. grew normally in different degreesof eutrophic waters with initial concentrations of2.45～9.41mg/L TN and0.44～1.53mg/L TP. Accumulated Pistia stratiotes L. wet weight and dry weight increasedto164.33～193.40g and8.57～10.53g for the period of study.Total nitrogen and phosphorus uptaken by Pistia stratiotes L. were35.20～208.21mg and8.99～48.37mg，respectively. Meanwhile，accumulated assimilation of nitrogen andphosphorus increased with increasing initial nitrogen and phosphorus concentration ineutrophic waters. In three different degrees of eutrophic waters，contribution of Pistiastratiotes L. uptaking nitrogen and phosphorus removal were53.26%、64.23%、65.24%and59.58%、68.84%、74.19%，respectively. Therefore，Pistia stratiotes L.had good removal efficiency，and planting Pistia stratiotes L. in eutrophic waterscould improve water quality.B)Effect of light intensity managing and initial planting density on the growth ofPistia stratiotes L.Cultivated Pistia stratiotes L. in the cage, the effects of different light intensity（55535lx、13328lx、2220lx）and initial planting density（0.5kg/m~2、1.0kg/m~2、1.5kg/m~2、2.0kg/m~2）on the plant length，root length，leaf number，leaf area，rametrate and biomass of Pistia stratiotes L. were researched. Results showed that（1）lightintensity of55535lx was more conducive to the growth of Pistia stratiotes L. and theplant length，root length，leaf area，ramet rate and biomass of Pistia stratiotes L. underthis light intensity significantly higher than that of the other two kinds of lightintensity. Order of the size of the plant length，root length，leaf number，leaf area，ramet rate and biomass of Pistia stratiotes L. under different light intensity was lightintensity of55535lx＞13328lx＞2220lx.(2) Pistia stratiotes L. grew the fastest at thedensity of2.3kg/m~2，when the density reached5.6kg/m~2，the biomass of Pistiastratiotes L. almost no longer continue to increase. Experiments showed that thesuitable lighting of Pistia stratiotes L. was light intensity of55535lx，the suitableplanting density of Pistia stratiotes L.was2.3kg/m~2and5.6kg/m~2was probably thegrowth of upper density of Pistia stratiotes L.C)Effect of Pistia stratiotes L. on growth and nitrogen and phosphorus wasteoutput of Leiocassis longirostris, reared in net pensIn order to reduce the cage culture on water pollution and explore ecologicalenvironment protection type cage，studyed on the input and recycle of nitrogen，phosphorus of Leiocassis longirostris cultured in ecological cage and traditional cage were compared.The results showed that the rate of recycle of nitrogen of ecologicalcage and traditional cage were47.80%and44.36%，respectively. There had noremarkable change （P＞0.05）between the two kinds of cages. The rate of recycle ofphosphorus of ecological cage and traditional cage were25.37%and15.55%，respectively. There had remarkable change（P＜0.05）between the two kinds of cages.The utilization efficiency of nitrogen and phosphorus of ecological cage andtraditional cage were26.87%、15.82%and25.37%、15.55%， respectively. Theecological cage slightly higher than the traditional cage，but there had no remarkablechange（P＞0.05）between the two kinds of cages. Pistia stratiotes L. in ecologicalcage was harvested three times in the experiment，the total weight of harvested Pistiastratiotes L. was189.0kg，the net gain of Pistia stratiotes L. was154.25kg and thenet recycle volume from water by Pistia stratiotes L. was257.32g and67.08g，respectively. Through calculating the amounts of nitrogen and phosphorus removaland the amounts of total input and output，we can obtain that when the area of netpens: the area of planting Pistia stratiotes L. was1:32～35，the cage culture ofLeiocassis longirostris can achieve nitrogen and phosphorus balance.