Studies On Nutritional Physiology Of Vitamin C For Tonguefish (Cynoglossus Semilaevis) And Choline For Flounder (Paralichthys Olivaceus) And Turbot (Scophthalmus Maximus)

Ten-week feeding trials were conducted to investigate the nutritional physiology of vitamin C for tonguefish (Cynoglossus semilaevis) and choline for flounder (Paralichthys olivaceus) and turbot (Scophthalmus maximus). The feeding trials were conducted in indoor floating water culture system. The dietary requirements of vitamin C for tonguefish and choline for flounder and turbot were estimated using different indicators. Results of these studies are presented as follows:1. Six practical diets were designed with 0, 10, 50, 150, 450 and 1500 mg ascorbic acid equivalent kg-1 supplemented respectively to the basic diet, as L-ascorbyl-2-polyphosphate (LAPP). Two 10-week feeding experiments were carried out by using different size of fish (average body weight: (4.21±0.02) g in ExperimentⅠand (116.93±0.91) g in ExperimentⅡ). Each diet was fed to triplicate groups of fish to apparent satiation (experimentⅠ: three times a day, 6:00, 14:00 and 22:00; experimentⅡ: twice a day, 07:30 and 18:30), stocked with 60 (ExperimentⅠ) and 18 fish (ExperimentⅡ) respectively. During the experimentⅠ, water temperature ranges from 20 to 10℃, salinity from 24 to 26‰, pH from 7.8 to 8.0 and dissolved oxygen content was approximately 6mg/L. During the experimentⅡ, water temperature ranges from 24.1 to 18.8℃, salinity from 24 to 26‰, pH from 7.8 to 8.0 and dissolved oxygen content was approximately 6mg/L. The results showed that: ExperimentⅠ: Survival rate, specific growth rate and feed efficiency ratio showed an increasing tendency with increasing dietary vitamin C, but without significant (P>0.05) difference. Liver, kidney and muscle ascorbic acid concentration significantly increased with increasing dietary vitamin C (P<0.05). ExperimentⅡ: Survival rate and feed efficiency ratio increased with increasing dietary vitamin C, but not significantly (P>0.05). Specific growth rate wasn't influenced significantly by dietary vitamin C. When supplemented more than 50mg/kg, liver, kidney, and muscle ascorbic acid concentrations significantly increased with increasing dietary vitamin C, all significantly higher than 0mg/kg diet group (P<0.05). We may conclude that, though dietary vitamin C benefits to survival to some extent, it is not nessesary to supply extra vitamin C in the basic diet of tonguefish (Cynoglossus semilaevis) under the experimental conditions.2. Six semi-purified diets were designed with 0, 100, 300, 900, 1800 and 3600 mg/kg choline chloride supplemented respectively to the basic diet to get six experimental diets with 260.2, 350.4, 531.5, 1020.9, 1914.3 and 3457.6mg/kg choline. A 10-week feeding experiment was carried out with flounder weighing (3.73±0.04) g. Each diet was fed to triplicate groups of fish to apparent satiation twice a day, 07:30 and 18:30), stocked with 20 fish each group. During the experiment, water temperature ranges from 16 to20℃, pH from 7.5 to 7.8, dissolved oxygen content was approximately 6mg/L and salinity was about 27‰. The results showed that: flounder fed the basal diet exhibited deficiency such as retarded growth, lower feed efficiency ratio and pale intestinal tract. Weight gain (WG) and feed efficiency ratio (FER) increased significantly (P<0.05) with increasing dietary choline, and survival rate (SR) showed increasing tendency without significant difference (P>0.05). WG levels off when dietary choline is more than 1914.3mg/kg. Hepatosomatic index (HSI) and visceral somatic index (VSI) of flounder decreased significantly with increasing dietary choline. (P<0.05). Moisture of flounder significantly decreased (P<0.05), whereas crude lipid increased (P<0.05). No significant differences were detected in liver lipid and muscle lipid, just showing increasing tendency, but cholesterol and triglyceride in plasma significantly increased as dietary choline increased. On the basis of WG (using broken-line modle), the optimum dietary choline requirement of juvenile flounder was estimated to be 1707.3mg/kg.3. Six semi-purified diets were designed with 0, 100, 300, 900, 1800 and 3600 mg/kg choline chloride supplemented respectively to the basic diet to get six experimental diets with 260.2, 350.4, 531.5, 1020.9, 1914.3 and 3457.6mg/kg choline. A 10-week feeding experiment was carried out with turbot weighing (6.25±0.04) g. Each diet was fed to triplicate groups of fish to apparent satiation twice a day, 07:30 and 18:30), stocked with 30fish each group. During the experiment, water temperature ranges from 16 to19℃, pH from 7.5 to 7.8, dissolved oxygen content was approximately 7mg/L and salinity was about 27‰. The results showed that: turbot fed the basal diet exhibited deficiency such as high death, retarded growth, lower feed efficiency ratio and pale intestinal tract. Weight gain (WG) and survival rate (SR) increased significantly (P<0.05) with increasing dietary choline, and feed efficiency ratio (FER) showed increasing tendency without significant difference (P>0.05). WG levels off when dietary choline was more than 1914.3mg/kg. Hepatosomatic index (HSI) wasn't significantly affected, but visceral somatic index (VSI) of flounder decreased significantly with increasing dietary choline (P<0.05). Moisture and ash of flounder significantly decreased (P<0.05), whereas crude protein and crude lipid increased (P<0.05), crude lipid leveled off when dietary choline was more than 1914.3mg/kg. No significant difference was detected in muscle lipid, but liver lipid was (P<0.05), showing increasing then decreasing tendency. Cholesterol and triglyceride in plasma significantly increased as dietary choline increased. When dietary choline was above 1020.9mg/kg, triglyceride leveled off. On the basis of WG, crude lipid and triglyceride (using broken-line modle), the optimum dietary choline requirements of juvenile flounder were estimated to be 2089.8, 1800 and 951.6mg/kg. Practically considering, 2089.8mg/kg is recommend in turbot diet.