Effects Of Flow Rate And Temperature On Feed Intake Of Turbot (Scophthatmus Maximus L) And The Establishment Of Dynamic Feeding Model

Based on the view of Eco-nutrition and Water environmental control, the studyaims to explore the effects of flow rate and temperature on the feed intake, growth,water quality, digestive enzyme activity and immunity of turbot (Scophthatmusmaximus L) in a closed recirculation aquaculture system, looking for the optimumflow rate and temperature for feeding, growth, water ecology of turbot. According tothe features of flow rate and temperature on the feeding of turbot, combining withlaboratory research, we established multi-parameter dynamic model on the base ofkey factors such as body weight, temperature, density and flow rate. We also build theeffect model of ammonia excretion rate of turbot on the base of body weight,temperature and density .1 Effects of flow rate on feed intake, growth and water quality of turbot wereinvestigated in closed recirculation aquaculture system. Fish with a mean initialweight of 200.3±7.6g were reared at four different flow rates (200L/h, 400 L/h,600L/h, 800L/h), equaling 0.5, 1.0, 1.5, 2.0 tank volumes/h in 400L tanks during 42days. Six hundred and sixty fish were randomly allotted in four treatments with threereplicates for each treatment in a stocking density of 14.1±0.51kg/m².The resultsindicated:(1) Feed intake, specific growth rate and weight gain rate were increasing rapidlyfirst and then slowly with increased flow rate, while food conversion rate showed areverse pattern. The specific growth rate of group B,C,D are significantly higher thangroup A by 30.77%～52.31%, while feed conversion rate is lower than group A by13.83%～22.34%.(2) Concentrationsoftotalammonianitrogen(TAN),unionizedammonianitrogen(UIA-N) and nitrite (NO₂^--N) in water decreased rapidly first and then slowly withincreased flow rate. The ammonia nitrogen of group B,C,D are significantly higherthan group A by 53.70%～79.07%. (3) The optimal growth and ecological flow rate was calculated as 625L/h (1.56tank volumes/h), combining the specific growth rate with total ammonia nitrogen inwater. Another optimal growth and ecological economical flow rate was calculated as480L/h (1.20 tank volumes/h), combining specific growth rate with powerconsumption and TAN in water.(4) TheflowrateshavesignificantinfluenceonthebloodNa⁺,K⁺,CI^-,GPT,SOD,LZM, GOT of turbot: the GPT and SOD first increased and then decreased withincreased flow rate, while GOT showed a reverse tendency and LZM showedtendency of growing. Compared with group A, the SOD activity significantly (P<0.05) increased by 14.25% 21.25%; LZM activity by 22.16% 57.53%; ALPactivity by17.88% 73.74%; GPT activity by 35.68% 71.65% in groups B,C, D.There were no significant difference (P> 0.05) in serum sodium, potassium, chloridecontent of blood among these four groups.2 Effects of water temperature on feed intake, growth, water quality, digestiveenzyme activity and immunity of turbot were investigated in closed recirculationaquaculture system. Fish with a mean initial weight of 371.68±43.15g were reared atfour different temperature (14℃, 16℃, 18℃, 21℃, represented by A～D) in 400Ltanks during 56 days. Three hundred and sixty fish were randomly allotted in fourtreatments with three replicates for each treatment in a stocking density of14.20±0.48kg/m². The results indicated:(1) At the range of 14 18℃, the feed intake of turbot increased withtemperature, but when the temperature was 21℃, the group's total feed intake,average daily feed intake decreased significantly compared with the other threegroups. The total feed intake, average daily feed intake, daily feeding rate of groups A,B, C are significantly different with D group (P <0.05), average daily feed intake ofthe three groups increased by 25.65%, 32.26% and 45.08%. Under the propertemperature(16～18℃), the daily feeding rate of high-density culture turbot was0.52%～0.55%.(2) The growth and survival rate of turbot increased first and then decreased withincreasing temperature. The weight gain ratio of groups A, B, C increased 75.23%91.05% and 121.18% than the D group, while the specific growth rate increased by34.29%, 80%, 102.86%. Under the proper temperature(16～18℃), the specificgrowth rate of high-density culture turbot was 0.63%/d～0.71%/d. (3) Water temperature has significant effects on the total ammonia nitrogen,nitrite concentrations. The ammonia peaks appeared in the range of 16～18℃and thiswas consistent with tendency of feeding, growth and digestion. The nitrite peaksappeared in the middle temperature range even though that the maximum value of twowere different. The mechanism relationed between bacteria and biological filter needsto be discussied in future research. Through 24 hours of continuous monitoring,ammonia excretion of turbot cyclical changed during day and night and the peaksappeared 6 to 9 hours after feeding. The TAN of group C was significantly (P <0.05)higher than that of A, D group by 32.34%, 25.57% (the first water qualitymeasurement) and 82.14%, 34.21% (the first water quality measurement).(4) At 14 18℃, the pepsin activity, SOD activity, LZM activity and serumcortisol concentration of turbot increased with temperature, but when the temperaturewas 21℃, the four indicators decreased significantly. Serum GOT, GPT showed atrend of first increased and then decreased. The cortisol levels, SOD, LZM, pepsinactivities were higher than the other three groups by 11.46% 13.54% , 6.69% ¹5.38%, 9.17% 70.22% and 39.63% 202.64%. Serum GOT, GPT increased firstwith temperature and then decreased. The Intestinal amylase activity increased withincreasing temperature and the group D was higher than the C group by 10.81%,significantly (P<0.05) higher than group B by 59.74% and significantly (P<0.01)higher than the group A by 115.79%. Four groups of intestinal lipase activity and gillNa ⁺, K⁺- ATPase activity showed no significantly different.(5) In this experiment, combining different indicators, the study identified thespecific growth rate of turbot (300-400g body weight) was 0.63% / d 0.71% / d,while the average daily feeding rate was 0.52 % 0.55% and the ammonia excretionrate was 0.12～0.13 mg N·kg^-1·W·h^-1 in high-density closed recirculation aquaculturesystem when the suitable temperature range was 16 18℃.(6) Combining the feed intake and ammonia excretion, the research identified theproportion of ammonia excretion in feed and feed nitrogen was 2.7% and 33.7%. Itmeanes fish can excrete 0.027kg and 0.337kg TAN when intake 1kg feed and feednitrogen.3 Ontheanalysisof experimentaldata,weestablishedtheinitialmodeloffeeding,ammonia excretion and specific growth rate of turbot in a closed recirculationaquaculture system. (1) Feedingmodel:F_I=W ^0.769 D ^-0.087 e^{-3.211-0.032T+0.125F_r}F_I represents daily feed intake(g/fish/d),W represents body weight(g),D representsstocking density(kg/m²), T represents temperature(℃),Fr represents flow rate(tankvolumes/h).(2) Ammoniaexcretionmodel:A =W ^{-3 .409} D ^2.298 e^{0.037 T-12.370}Specific growth rate model:G =W ^{-0 .423} D ^-0.024 e^{1.496+0.257 F_r+0.087(18 -T)}A represents ammonia excretion rate(mg N /kgW/ h), W represents bodyweight(g),D represents stocking density(kg/m²), T represents temperature(℃), Frrepresents flow rate(tank volumes/h), G represents specific growth rate(%/d).(3) Purpose and significance of the model:â‘ the model can make the actualfeeding ration achieve the quantitative, clean and dynamic.â‘¡Combing the satiationfeeding model, the specific growth rate model and the ammonia excretion model, wecan get ecological feeding of faster growth, lower water pollution, which is beneficialfor the accurate feeding and water environmental regulation.â‘¢The associated modelin the production is very convenient and practical, basing on any three variables toestimate the fourth variables. For example: we can predict water ammoniaconcentration according to forecast of ammonia excretion rate by temperature, fishweight and fish stocking density. This offers a lot for the actual farming.â‘£Theestablishment and improvement of the model can initially achieve the aim of optimalgrowth, least feed waste, provide of a stable metabolite of feeding for the bio-filter,and it can also make the feeding and water environmental control achieve the level ofdynamics in closed recirculating aquaculture system.