Effects Of Carbohydrate Sources And Carbohydrate To Protein Ratios On Growth And Carbohydrate Metabolism Of Giant Grouper Epinephelus Lanceolatus Larvae.

This thesis aimed to evaluate effects of dietary carbohydrate sources and carbohydrate to protein ratios on growth, carbohydrate metabolism and mRNA expression levels of some related genes of giant grouper Epinephelus lanceolatus larvae. The main contents and results of this thesis were presented as follows:1. Effects of dietary carbohydrate sources on growth, digestive enzyme activity, gene expression of hepatic GLUTs and key enzymes involved in glycolysis-gluconeogenesis in giant grouper Epinephelus lanceolatus larvae.This study aimed to evaluate effects of dietary carbohydrate sources on growth,digestive enzyme activity, gene expression levels of hepatic GLUTs and key enzymes involved in glycolysis-gluconeogenesis in giant grouper Epinephelus lanceolatus larvae through a 21-day growth trial. Four isonitrogenous (50%) and isolipidic (15.4%)experimental diets including a cellulose control diet and three diets with glucose, maltose or maize starch were formulated. Dietary CHO level was 18%. The 29 DAH (days after hatching) grouper larvae (initial average weight: 0.078 ± 0.0018g) were cultured in flowing-water small cages at a density of 80 fish per cage. Results showed that at 50 DAH,fish fed with maize starch diet had significantly higher weight gain (WG) and specific growth rate (SGR) than fish fed with glucose, maltose or cellulose. Fish fed with glucose had the lowest WG among all experimental treatments. Fish fed with maize starch or cellulose had significant higher mRNA expression levels of hepatic fructose 1,6 bisphosphatase (FBP) gene compared to fish fed with glucose or maltose at 50 DAH. The highest mRNA expression level of hepatic glucose-6-phosphate dehydrogenase (G6PDH)gene was observed in fish fed with glucose at 50 DAH. Fish fed with maize starch had higher mRNA expression levels of hepatic pyruvate kinase (PK) and hexokinase (HK)genes than fish fed with cellulose, glucose and maltose at 50 DAH. The mRNA expression level of hepatic glucose transporter 4 (GLUT4) gene was significantly lower in fish fed with cellulose compared to that in fish fed with digestible CHOs at 50 DAH. There were no significant differences in mRNA expression levels of hepatic glucose transporter 1(GLUT1) gene among all experimental fish at 50 DAH. In terms of digestive enzymes,activities of pancreatic trypsin and intestinal lipase increased during the development of fish larvae, but pancreatic a-amylase specific activity showed an opposite trend of variation as those of trypsin and lipase. During the development of experimental fish larvae from 29 DAH to 50 DAH, pancreatic trypsin specific activity in fish fed with glucose was significantly lower than that in fish fed with cellulose or maltose but did not differ from that in fish fed with maize starch. Intestinal lipase specific activity in fish fed with maize starch or maltose were significantly higher than those in fish fed with cellulose but did not differ from those in fish fed with glucose. In conclusion, giant grouper larvae utilize maize starch better than cellulose, glucose or maltose due to the better growth and higher hepatic glycolytic activity; Fish fed maize starch or cellulose had higher hepatic gluconeogenic activity compared to fish fed glucose or maltose. With the developing of giant grouper larvae,activities of pancreatic trypsin and intestinal lipase increased, but pancreatic a-amylase specific activity decreased.2. Dietary carbohydrate to protein ratio affects growth and metabolism-related gene expression in the liver and muscle of giant grouper Epinephelus lanceolatus larvae.This study aimed to evaluate dietary carbohydrate to protein ratio affects growth and metabolism-related gene expression in the liver and muscle of giant grouper Epinephelus lanceolatus larvae. through a 15-day growth trial. Seven isoenergetic (396.2 kcal/g) and isolipidic (15.4%) experimental diets were formulated to contain different dietary carbohydrate to protein ratios (CHO26.4/P38, CHO22.4/P42, CHO18.4/P46,CHO14.4/P50, CHO10.4/P54, CHO6.4/P58, CHO2.4/P62). Experimental fish larvae(initial body weight: 0.298 g) were randomly distrubuted into 21 glass tanks (L 60 cm × W 45 cm× H 50 cm) with a density of 50 larvae each tank. Results showed that at 44 DAH, SGR of fish fed the CH026.4/P38 diet was significantly lower than that of fish fed other experimental diets. Fish fed the CH022.4/P42 diet had significantly lower SGR compared to fish fed with CHO10.4/P54, CHO6.4/P58, CHO2.4/P62 diets, but there had no significant differences when compared the SGR of fish fed CHO22.4/P42 with that of fish fed CHO18.4/P46 and CHO14.4/P50. There were no significant differences in SGR values between fish fed CHO18.4/P46, CHO14.4/P50, CHO10.4/P54, CHO6.4/P58 and CH02.4/P62. Water ammonia production of experimental fish showed an increased trend with the decreasing of dietary CHO/P ratio. The survival rates of fish fed CHO/P ratio diets were significantly lower than those of fish fed low CHO/P ratio diets.For CHO metabolism, fish fed diets with CHO14.4/P50, CHO10.4/P54, CHO6.4/P58,CH02.4/P62 had significantly lower mRNA expression levels of hepatic key enzyme genes (Pyruvate kinase / PK,Glucokinase / HK) involved in glycolysis than fish fed diets with CH026.4/P38, CH022.4/P42, CH018.4/P46. The mRNA expression levels of hepatic CS, PFK, ICDH and a-KGDH displayed no remarkable variations among the experimental treatments. The mRNA expression levels of PK gene in muscle tissue showed a decreased trend with the decreasing of dietary CHO/P ratio. With the decreasing of dietary CHO/P ratio, the mRNA expression levels of enzymes (Pyruvate carboxylase / PC, Fructose 1,6 bisphosphatase / FBP ) genes involved in hepatic gluconeogenesis were increased, but dietary CHO/P ratios had no significant influences on the mRNA expression level of hepatic G6P2.For protein metabolism, the mRNA expression levels of hepatic ribosomal protein(RPS6) gene related to protein synthesis in fish fed CHO26.4/P38, CHO22.4/P42,CHO18.4/P46, CHO14.4/P50 were significantly lower than those of fish fed CHO10.4/P54,CHO6.4/P5, CHO2.4/P62. Fish fed high dietary CHO/P ratios had significantly higher mRNA expression levels of genes (Target of rapamycin / TOR, Growth hormone / GH,Ribosomal protein S6 kinase beta-1 / S6K1) related to protein synthesis in muscle than fish fed low dietary CHO/P ratios, and a similar trend was also shown in the muscle proteolysis genes (Muscle RING finger 1 / MURF1, Unc-51 like autophagy activating kinase 1 / ULK1,UV radiation resistance-associated gene protein / UVRAG, Branched-chain -keto acid dehydrogenase E2 subunit / BCKDE2, Mitochondrial E3 ubiquitin protein ligase 1 / MUL1,?-type proteasome C2 subunits / C2, ?-type proteasome C3 subunits / C3).For lipid metabolism, fish fed CHO26.4/P38,CHO22.4/P42,CHO18.4/P46 had significantly lower mRNA expression levels of hepatic enzyme genes (Fatty acid synthase /FAS,ATP citrate lyase / ACLY) related to lipogenesis than fish fed CHO14.4/P50,CHO10.4/P54, CHO6.4/P58, CHO2.4/P62. The ACC gene related to lipogenesis in muscle shown an opposite trend with CHO/P ratios. The gene mRNA expression of hepatic carnitine palmitoyl transferase 1 (CPT1A) involved in lipid oxidation displayed an increased trend with the decreaseing of dietary CHO/P ratio both in liver and muscle.In conclusion,results of this study indicated that high dietary CHO/P ratios(CHO26.4/P38, CHO22.4/P42) negatively affected growth performance and survival ratios of giant grouper larvae. Water ammonia production was increased as dietary CHO/P ratios decreased. Dietary CHO/P ratios had a significant role in protein, lipid as well as carbohydrate metabolism both in liver and in muscle tissues of giant grouper larvae.