Effects Of Dietary Carbohydrate Levels And Carbohydrate-to-lipid Ratios On Growth,Feed Utilization And Body Composition Of Hybrid Grouper(Epinephelus Lanceolatus ? × Epinephelus Fuscoguttatus ?) Juveniles

In this study,two growth trials were conducted to investigate effects of dietary carbohydrate levels and carbohydrate-to-lipid ratios on growth,feed utilization and body composition of hybrid grouper juveniles.Results of the study were presented as follows:1.Effects of different corn starch levels on growth,protein input and feed utilization of hybrid grouper(Epinephelus lanceolatus ?× Epinephelus fuscoguttatus?)juveniles.An 8-week growth trial was conducted to study effects of different corn starch levels on growth and feed utilization of hybrid grouper(Epinephelus lanceolatus ? ×Epinephelus fuscoguttatus?)juveniles.Five isonitrogenous(48%crude protein,dry-wt.basis)and isolipidic(10%crude lipid,dry-wt.basis)diets were formulated to contain 0%,7%,14%,21%or 28%corn starch level,respectively.Each dietary treatment had three replicates.Groups of 22 hybrid grouper juveniles(average initial weight of 2.74 g/fish)were stocked into small floating cages(L 120cm × W 70cm ×H 50cm).Triplicate groups of fish were fed each dietary treatment twice daily(0800h and 1600h)to apparent satiation.Water quality was monitored daily.Weight gain(WG)of hybrid grouper displayed no significant difference among all experimental groups.Fish fed 0%corn starch had significantly higher daily protein intake than fish fed 7%,14%,21%and 28%corn starch.Feed conversion ratio(FCR)and daily feed intake(DFI)were significantly higher in fish fed diets with 0%corn starch,but FCR and DFI were not observed to vary among fish fed any of the other experimental diets.Fish fed 0%corn starch had lower protein efficiency ratio(PER)than fish fed other experimental diets,and the differences were significant when compared to fish fed 21%or 28%corn starch.Intraperitoneal fat(IPF)ratios did not show significant variations among all experimental treatments.Hepatosomatic index(HSI)of fish fed 0%corn starch were significantly lower than fish fed 14%,21%and 28%corn starch.Whole-body moisture,protein,lipid,ash contents as well as muscle moisture,protein and lipid contents showed no significant difference among all experimental groups.Hepatic glycogen content increased as dietary corn starch level increased.Fish fed the diet with no corn starch had more protein content in the liver than fish fed 14%,21%or 28%corn starch.Generally,supplementations of 7%-28%dietary corn starch could reduce dietary protein input and improve feed utilization of hybrid grouper without negatively affecting fish growth.2.Effects of dietary carbohydrate-to-lipid ratios on growth,feed utilization and body composition of hybrid grouper(Epinephelus lanceolatus ?× Epinephelus fuscogutttu ?)juvenilesAn 8-week growth trial was conducted to study effects of dietary carbohydrate-to-lipid ratios on growth,feed utilization and body composition of hybrid grouper(Epinephelus lanceolatus ? × Epinephelus fuscoguttatus?)juveniles.Seven isonitrogenous(53.5%crude protein,dry-wt.basis)and isocaloric(3.6kcal/g dry matter)diets were formulated,containing various CHO:L ratios from0.03 to 6.88.Each dietary treatment had three replicates.Groups of 15 hybrid grouper juveniles(average initial weight of 10.16 g/fish)were stocked into small floating cages(L 120cm × W 70cm × H 50cm).Triplicate groups of fish were fed each dietary treatment twice daily(0800h and 1600h)to satiation.Water quality was monitored daily.Maximum weight gain(WG),SGR,PER as well as minimum feed conversion ratio(FCR)were observed in fish fed the diet containing CHO:L ratios of 0.03.VSI and Intraperitoneal fat(IPF)ratios of hybrid grouper decreased as dietary CHO:L ratios increased.CF of fish fed the diet containing CHO:L ratios of 0.03 was higher than fish fed other experimental diets,and the difference was significant when compared to fish fed the diet containing CHO:L ratios of 6.88.HSI and hepatic glycogen content increased as dietary CHO:L ratios increased.Fish fed diets which CHO:L ratio ranged from 0.03 to 0.79 had significantly lower hepatic glycogen content than fish fed the diet containing CHO:L ratios of 6.88.Fish fed the 6.88 CHO:L diet had significantly higher whole-body protein content than fish fed the diets with 0.03-1.4 CHO:L ratios.Whole-body moisture content increased as dietary CHO:L ratios increased,while the lipid content of whole-body decreased as dietary CHO:L ratios increased.Similar trends were observed in muscle lipid content as well as liver protein content.Whole-body ash,muscle moisture,protein as well as liver moisture,lipid contents showed no significant differences among all experimental groups.Plasma total protein(TP)did not show significant variations among all experimental treatments.The lower GLU content of plasma were obtained in fish fed the lower CHO/L ratio diets.Plasma TG of fish fed the 0.03 CHO:L diet was significantly higher than fish fed the 6.88 CHO:L diet.CHOL concentrations of fish fed the 0.03 CHO:L diet were also significantly higher than those of fish fed other CHO:L ratios.In terms of activities of digestive enzymes in intestine tissue,lipase and a-Amylase activities were positively correlated with dietary lipid levels and carbohydrate levels,respectively.Lipase activity decreased as dietary CHO:L ratios increased,while a-Amylase activity increased as dietary CHO:L ratios increased.Histology analyses revealed higher accumulation of fat in the liver of fish fed low CHO/L ratios.Results indicated that hybrid grouper could utilize diets containing 0.03-3.83 CHO:L ratios without negatively affecting fish growth.