Utilization Of Pure Oxygen In Japanese Flounder Paralichthys Olivaceus Culture: Exploring The Mechanisms Of Growth And Physiological Adaptation

The aim of this study was to investigate the feasibility of pure oxygen in Japanese flounderParalichthys olivaceus culture. Two important environmental factors, ammonia and stockingdensity combined with oxygen were studied. Furthermore, the visual software package and anexpert system were developed based on the data from the present study. The results of thisstudy provided basic data for updating aquaculture techniques, and the best design ofintensive culture. The main contents are the following:1. Acute ammonia toxicity and gill morphological change of Japanese flounderParalichthys olivaceus in normal versus supersaturated oxygenAmmonia toxicity and morphological changes in gills of juvenile Japanese flounderParalichthys olivaceus (5.76±0.12g) were investigated when fish were separately exposedto normal dissolved oxygen (DO) at6.5±0.5mg/L and supersaturated oxygen at16.0±2.0mg/L at different ammonia concentrations. Under normal oxygen, ammonia concentrationswere tested from0.04(control) to93.3mg/L total ammonia nitrogen (TAN), whereas underoxygen supersaturation, ammonia concentrations ranged from0.04(control) to226.7mg/LTAN in the trial. After exposure to ammonia for96h, the ammonia LC50for fish was62.48mg/L TAN (0.50mg/L NH3-N) at normal oxygen and160.71mg/L TAN (0.65mg/L NH3-N)at oxygen supersaturation. Light microscopic observations confirmed that gill damage innormal oxygen was more profound than in oxygen supersaturation when fish were exposed tothe same level of TAN (93.3mg/L). Compared to the ammonia control, lamellar thicknessincreased significantly at93.3mg/L TAN. Likewise, gill lamellae became thicker in normaloxygen than in oxygen supersaturation. Furthermore, electronic microscopic scanning alsoshowed more crimple, retraction and fibrosis on the secondary lamella surface in fish exposedto normal oxygen than those in fish exposed to supersaturated oxygen at the same TAN (93.3mg/L). This study suggests that supersaturated oxygen can increase ammonia tolerance inJapanese flounder through reducing gill damage by ammonia, which partially explains themerit of using pure oxygen injection in intensive fish farming. 2. Effects of ammonia and dissolved oxygen on growth, body composition and energy budget of juvenile Japanese flounder Paralichthys olivaceusA2x2factorial experiment was conducted for40days to determine the effects of dissolved oxygen (DO) concentration combined with sublethal doses of ammonia on growth and body composition in juvenile Japanese flounder. Fish with a mean (S.D.) initial weight of10.38±0.13g were reared in12aquaria (triple replicates;12fish per aquarium) at normoxic (6.5±0.5mg/L) and hyperoxic (14.0±2.0mg/L) conditions, and also under both normoxia and hyperoxia with an additional sublethal concentration of unionized ammonia (0.17mg NH3) added, at15℃. The results showed both DO and ammonia significantly influenced body weight, specific growth rates (SGR), food intake (FI) and moisture content. Results of energy budget revealed that fish had energy strategy to adopt different environments as shown the response of FRe (J·g-1d-1) and Ge (J·g-1d-1). Hyperoxic without ammonia added (T3) had the highest SGR for its highest FRe (J·g-1d-1) and Ge (J·g-1d-1) while normoxic/NH3(T2) had the lowest. DO affected lipid significantly and the lipid content had positive relation to the body weight. Hyperoxic conditions can increase the tolerance to unionized ammonia in Japanese flounder, as growth rate was significantly higher in the hyperoxic/NH3(T4) treatment compared to the normoxic/NH3(T2) treatment. The results of present study provided useful information to intensive fish culture.3. Effects of dissolved oxygen and stocking density on growth and physiological parameters of small size juvenile Japanese flounder, Paralichthys olivaceusThe effects of dissolved oxygen (DO) and stocking density on growth and physiological parameters were investigated in juvenile Japanese flounder, Paralichthys olivaceus (1.26±0.13g) at20±0.4℃. DO levels and stocking densities were arranged in two modes:5.5±0.5mg/L (charged by air) and14±2mg/L (charged by pure O2) with density of200,400,600,800,1000ind/m2respectively. The experiment was lasted40days and the lowest survival rate was94%during the experiment period.①There were significant differences of average body weight after10d when fish were cultured under the air charged conduction while no significant differences were found under the pure oxygen charged condition.②FCE declined along with the increase of density, especially under the air charged condition.③The activity of protease in intestine tissue declined along with the increase of density under two dissolved oxygen levels, but more profound influence was found under the air charged condition.④Under the pure oxygen charged condition, hemoglobin concentration (Hb) and respiratory frequency were significantly lower than that of fish held under the air charged condition. The results indicated that oxygen supersaturated condition can alleviate the stress caused by high stocking density effectively.4. Effects of dissolved oxygen concentration and stocking density on the growth, energy budget and body composition of large size juvenile Japanese flounder, Paralichthys olivaceusAn energetic method is used to investigate the effects of stocking density and dissolved oxygen (DO) concentration on the growth of juvenile Paralichthys olivaceus. Fish, with initial weights of14±2.1g, are exposed to normal and high DO of5.5±0.5and14±2mg/L, as well as four stocking densities per DO concentration (100,200,300, and400ind/m2for normal DO and200,400,600, and800ind/m2for high DO). The feed efficiency (FEW) decreases significantly with increasing stocking density and increases significantly with increasing DO concentration. Maximum weight is achieved at400ind/m2under high DO depending on our rearing conditions. The stocking density and DO concentration change energy ingestion and its allocation for respiration, growth and excretion lost in nitrogen excretion, but do not affect the energy loss through feces. The results on the body composition of fish indicate that stocking density and DO concentration have no significant effects on the moisture, lipid content and gross energy, however, are affected by the same. Energetic analysis demonstrates that high DO concentrations could alleviate the growth depression caused by high stocking densities, decrease energy loss in respiration and nitrogen excretion, and increase the energy proportion allocated to growth.5. Effects of dissolved oxygen concentration and stocking density on physiological parameters of large size juvenile Japanese flounder, Paralichthys olivaceusAn extended work on blood and digestive physiology was done in this chapter.①There were no significant difference of red blood cell (RBC) count, white blood cell (WBC) count and Hb under the air charged condition. Under the pure oxygen charged condition, there were no significant differences in RBC and WBC account, except for Hb (P<0.05). At the density of200ind/m2, there were no significant differences in RBC and WBC account under the two dissolved oxygen levels except for Hb. While RBC, WBC account and Hb were significantly lower in the pure O2charged condition compared with the air charged condition at density of400ind/m2.②No significant differences were found in activity of protease in stomach tissue at the two dissolved levels while there were significant differences in activity of protease in intestine tissue. At the same density, the activity of protease in intestine tissue under the pure oxygen charged condition was significant higher than that of under the air charged condition.③No significant differences were found in activity of SOD at the two dissolved oxygen levels.④The density had no significant effect on the respiratory frequency while the DO had significant effect on the respiratory frequency. Overall, the results support the crowding stress of high stocking density can be effectively alleviated by high dissolved oxygen.6. Explore the intelligent system in Japanese flounder Paralichthys olivaceus cultureBased on the data from chapter4and chapter5, a linearly mathematic model was established and a visual software package that can be used as a decision-making tool for farmers written in.NET was designed. The relation between the stocking density and stoking specs was conducted by mathematical method as bellow: y=-1.2857x2-0.7143x+391.8R2=0.99y=0.7143x2-20.714x+668R2=0.94A visual software package written in.NET was designed for aquaculture plant to determine the optimal stocking density in different stocking modes. In this chapter, an expert system was also designed based on Windows system. A data base including facility module, water quality module, fish physiological module, and culture technique module combined with the expert module were the main structure of the intelligent system. Decision support function for an expert system was achieved.