Investigation On Integrated Multi-trophic Light-controlled Aquaculture System Of Pelteobagrus Fulvidraco

Yellow catfish（Pelteobagrus fulvidraco）,belonging to the Siluriformes,Bagridae,Pelteobagrus,is a kind of bottom economic fish widely distributed in fresh water in China,which has great development value.In 2020,the national aquaculture production of Pelteobagrus fulvidraco reached 565,500 tons（10th for freshwater aquaculture fish）.Pelteobagrus fulvidraco is fond of shade and afraid of light,feeding on small bottom aquatic animals and compound feed.At present,research on Pelteobagrus fulvidraco mainly focus on the field of thremmatology,lacking systematic research on the biological characteristics and green,efficient aquaculture facility system.In order to build an ecologically efficient aquaculture system suitable for Pelteobagrus fulvidraco,this dissertation had analyzed the optimum light intensity range of Pelteobagrus fulvidraco and its impact on the water environmental.Meanwhile,this dissertation constructed a Pelteobagrus fulvidraco integrated multi-trophic aquaculture system with the functions of light control,water purification and analyzed the ecological,energy characteristics,which provided the basis for green and efficient culture of Pelteobagrus fulvidraco.The main conclusions are as follows:（1）The suitable light intensity range for the growth of Pelteobagrus fulvidraco was analyzed by controlled experiment,finding that Pelteobagrus fulvidraco in 3～6 W/m²had significantly higher weight gain rate,specific growth rate,and lower feed coefficient.Under this light intensity,the activity of pepsin and lipase increased.The direct factors affecting the antioxidant and immune properties were not light intensity,but the accumulation of nitrogen in farming water,which could increase the content of malondialdehyde（MDA）and decrease the activities of superoxide dismutase（SOD）,catalase（CAT）,glutathione peroxidase（GSH-Px）,alkaline phosphatase（AKP）,acid phosphatase（ACP）in body,indicating the inhibition of antioxidant and immune properties.Since the light intensity affected the growth and digestion performance of Pelteobagrus fulvidraco,which in turn caused changes in the water environment,the construction of integrated multi-trophic aquaculture system with the functions of light control and water purification is the direction of green and efficient culture for Pelteobagrus fulvidraco.（2）By maintaining the depth of culture water（1.0～1.2 m）,the Pelteobagrus fulvidraco integrated multi-trophic light-controlled aquaculture system was constructed,which provided a suitable light intensity environment（2.9～5.1 W/m²）for Pelteobagrus fulvidraco.The system consisted of farming area and purification area.The farming area included fry ponds and juvenile pond,where Pelteobagrus fulvidraco fry（2.10ind/m²）and Pelteobagrus fulvidraco juvenile（0.63 ind/m²）were cultured respectively.The purification area included ecological sedimentation pond,biological purification pond,enhanced treatment pond,biomass modular wetland pond,where other trophic organisms such as small fish（Pseudorasbora parva et al,12.55 ind/m²）and macrocrustaceans（Macrobrachium nipponense et al,23.28 ind/m²）were cultured,economic crops（Oryza sativa L et al,10.44 g/m²）and aquatic plants（Hydrocharis dubia（Bl.）Backer et al,305.28 g/m²）were planted.（3）During the experiment,the N/P in the farming area was significantly lower than that in the purification area（P=0.012）,and the total phosphorus was significantly higher than that in the purification area（P=0.036）.Physicochemical factors left（except water temperature）in the farming area were higher than those in purification area（not significant）.The concentrations of total nitrogen（1.72±0.70 mg/L）and total phosphorus（0.12±0.06 mg/L）in system all met the discharge standards for freshwater aquaculture（TN≤3.0 mg/L,TP≤0.5 mg/L）,indicating that the Pelteobagrus fulvidraco integrated multi-trophic light-controlled aquaculture system could provide a suitable water quality environment for culture and reduce water pollution.（4）In Pelteobagrus fulvidraco integrated multi-trophic light-controlled aquaculturesystem,there were 26 species of phytoplankton in 5 phyla,among which Chlorophyta dominated.The phytoplankton biomass in the farming area and purification area were0.45±0.29 mg/L and 0.81±0.53mg/L respectively,with significant difference（P=0.002）.Phytoplankton biomass in farming and purification area decreased in September to November,March to April and increased in May to August,with obvious seasonal fluctuation.Phytoplankton in farming area were mainly affected by water temperature,light,nitrate nitrogen and ammonia nitrogen,while phytoplankton in purification area were mainly affected by water temperature,light,nitrite nitrogen and active phosphorus.There were 13 species of zooplankton,of which Copepoda dominated.The zooplankton biomass in aquaculture area and purification area were 0.80±0.63 mg/L and 0.32±0.16mg/L,respectively,with significant difference（P<0.001）.Zooplankton in the two areas were mainly affected by water temperature,light,ammonia nitrogen and nitrate nitrogen,indicating that zooplankton could be controlled by these factors.（5）In Pelteobagrus fulvidraco integrated multi-trophic light-controlled aquaculture system,primary productivities of farming area and purification area were 1.90±0.77g O₂/m²·d and 3.05±1.43 g O₂/m²·d respectively（P<0.001）with obvious seasonal fluctuation,which decreased in September to November,March to April and increased in May to July.There were different effects of water physicochemical factors on primary productivity in farming area and purification area.Primary productivity of farming area was significantly affected by water temperature,ammonia nitrogen,nitrate nitrogen and phytoplankton biomass（P<0.05）,while the primary productivity of purification area was significantly affected by water temperature,light,nitrate nitrogen,total phosphorus and phytoplankton biomass（P<0.05）.The results showed that the environmental factors affecting the primary productivity of farming area and purification area were different.（6）The results of Ecopath model analysis showed that the scale of the Pelteobagrus fulvidraco integrated multi-trophic light-controlled aquaculture ecosystem was small,leading to the simple nutrient structure,low effective trophic level range（1～2.566）,and concentrated energy flow in trophic levels I（65.39%）.The utilization rate of feed energy flow was high,but the lack of predators of detritus and primary producers（aquatic plants,rice）led to underutilization of detritus and primary production energy flow.The A/TDC and O/TDC were 0.29 and 0.59 respectively,indicating that the elasticity and anti-interference ability of system was outstanding,while its stability needed to be improved.According to the evaluation results of ecological capacity,the maximum individual increase amount of Pelteobagrus fulvidraco fry and juvenile were0.12g/m² and 0.42g/m² respectively,and the maximum joint increase amount of Pelteobagrus fulvidraco fry and juveniles was 0.10 g/m².This dissertation has mastered the optimum light range of Pelteobagrus fulvidraco,constructed a integrated multi-trophic aquaculture system with the functions of light control and pollution purification.The ecological,energy characteristics of the aquaculture system were clarified,which provided a theoretical reference for the cultivation system optimization,improving the development of green and efficient culture of Pelteobagrus fulvidraco.