| Five experiments were conducted to examine the effects of dietary protein, lipid and energy on weight gain, body composition of channel catfish, Ictalurus punctatus. And the effects of dietary supplemental GA on weight gain, body composition, plasma index and LPL mRNA in channel catfish (a worldwide freshwater fish with higher sensitivity to lipid).Experiment1, a60-day feeding trial of three dietary protein levels (28%,32%and36%) and three dietary lipid levels (5.0%,7.5%and10.0%) designed with four replications was conducted to determine the effects of dietary protein and lipid levels on growth, digestive enzyme activities and muscle composition of juvenile channel catfish (1.5±0.02g initial weight). Fish were fed respectively to apparent satiation by nine experimental diets named as P28L10, P32L10, P36L10, P28L7.5, P32L7.5, P36L7.5, P28L5.0, P32L5.0and P36L5.0. The results indicated that specific growth rate (SGR)(20-40d,40-60d and1-60d), weight growth rate (WGR) and feed coefficient rate (FCR) were significantly affected by dietary protein and lipid levels or a dietary protein×lipid interaction (P<0.05). SGR, WGR and FCR of fish fed the P28L10diet were the lowest among all the treatments (P<0.05). Growth performance of fish fed diets with28%protein were worse than that of fish fed by other protein levels (P<0.05); the worst growth performance was observed in fish fed the P28L10diet. The highest WGR was obtained in fish fed the P36L7.5diet; and no obvious differences of WGR were found in fish fed the P36L7.5, P36L10and P32L7.5diets (P>0.05).Activities of liver-lipase and stomach-protease changed significantly as dietary lipid levels increased (P<0.05). Muscle lipid levels decreased significantly with dietary lipid levels (P<0.05), and muscle protein levels could be influenced by dietary protein and lipid levels. Viscera/body ratio (VBR), mesenteric lipid-somatic Index (MSI) and condition factor (CF) together may show that muscle protein and lipid levels could be affected by dietary protein×lipid interaction. In conclusion, this study suggests that growth performance of juvenile channel catfish is improved at a suitable protein/lipid ratio in diet. It also indicates that lipid economizes protein in diet without influencing muscle quality in the fish.Experiment2, a60-day feeding trial including diets with two protein levels (22%,28%), two lipid levels (10.0%,14.0%) and two digestible energy levels (3.4kcal·g-1,3.0kcal-g-1) designed with three replications was conducted to investigate the growth, nutrient utilization and body composition of Juvenile Channel Catfish. Four hundred and eighty fish (initial weight,141.5±1.0g) were randomly distributed into24tanks (3mx0.8mx0.8m) at a rate of20fish per tank and fed three times daily. Fish were fed respectively to apparent satiation by experimental diets named as P28L10E3.4, P28L14E3.4, P22L10E3.4, P22L14E3.4, P28L10E3.0, P28L14E3.0, P22L10E3.0and P22L14E3.0. Final weight, weight gain, specific growth rates (SGR) and feed conversion ratio (FCR) were not significantly affected by dietary protein or dietary lipid or dietary digestible energy (P>0.05), but were significantly affected by a dietary protein x lipid interaction (P<0.05), and extremely significantly affected by a dietary protein x lipid x digestible energy interaction (P<0.01). With the protein/energy radio increasing, it took an increasing trend to final weight, weight gain and SGR (P<0.05), except that fish fed diet P28L10E3.0. The digestibility of dietary protein, lipid, energy and dry matter is increasing by dietary digestible energy decreased (P<0.05) and dietary lipid increasing (P<0.05). With the dietary protein decreasing, it took a decreasing trend to the digestibility of dietary protein, energy and dry matter (P<0.05). The digestibility of dietary protein, lipid, energy and dry matter is increasing by dietary lipid levels (P<0.05). Nitrogen retention was significantly increased as dietary protein levels decreased (P<0.05), lipid retention decreased significantly with dietary digestible energy and lipid levels decreasing (P<0.05), protein efficiency radio (PER) was significantly increased as dietary digestible energy decreased (P<0.05). Carcass protein and lipid were not significantly affected by dietary digestible energy concentrations (P>0.05); however, carcass lipid tended to improve (P=0.066) as dietary digestible energy levels increased. The results of this study indicated that the diet containing28%protein with14%lipid and3.0kcal-g-1digestible energy is optimal for growth of Juvenile Channel Catfish (150to300g weight). However, group P28L10E3.4and P22L10E3.0got second best weight, highest nutrient utilization and best body composition of Juvenile Channel Catfish. It also indicates that lipid saved protein in diet of Juvenile Channel Catfish. Experiment3, Glycyrrhetinic acid, the main active constituents of Glycyrrhiza glabra roots, is extensively used as food additives and herbal medicines. This study was carried out to evaluate the effects of different dietary levels of GA on growth and body composition of channel catfish (average weight,1.10±0.02g). Eight diets were formulated to contain two levels of lipid (6.0%and8.0%), and four levels of GA (0,0.3,0.6, and0.9g/kg). The experiments lasted for60days. Results showed that weight gain tended to decrease as dietary GA levels increased (P>0.05) with the lowest found in fish fed0.9g/kg dietary GA (P<0.05). Feed intake increased significantly as dietary GA concentrations increased up to0.6g/kg (P<0.05) and viscera/body ratio, condition factor, hepatosomatic index and intraperitoneal fat ratio decreased significantly as GA concentration increased (P<0.05).Lipid content of whole-body, viscera and liver decreased significantly (P<0.01) as dietary GA increased, whereas moisture content showed an opposite trend. The cortisol in fish fed0.3and0.6g/kg GA were not significantly higher than that of fish without GA supplementation, but glucose in the former two groups was higher (P<0.05). Results of this study indicate0.3and0.6g/kg GA had a positive influence in reducing body lipid and IFR deposition in channel catfish without significant side effects on growth. The beneficial effect may be due to extending endogenous cortisol half-life and increasing the duration of action.Experiment4, Glycyrrhetinic acid (GA), the main active constituents of Glycyrrhiza glabra roots, is extensively used as food additives and herbal medicines. This study was carried out to evaluate the effects of different dietary levels of GA on growth, body composition and plasma biochemical index of channel catfish (average weight,159.0±5.0g). Five diets were formulated to contain five levels of GA (0,0.075,0.15,0.3and0.9g/kg). Fish were randomly distributed into30tanks and fed three times daily (08:30,12:00and16:30h) for8weeks. Dietary GA levels have little significantly effect on weight gain (WG) and feed conversion ratio (FCR). Intraperitoneal fat ratio (IFR)(P<0.05) and viscera/body ratio (VBR)(P<0.01) decreased significantly as GA levels increased, and hepatosomatic index (HSI) tended to decrease as dietary GA levels increased (P<0.1). Lipid content of liver decreased significantly as GA concentrations increased (P<0.01), and lipid content of muscle tended to decrease as dietary GA concentrations increased (P<0.1). Plasma triglycerides (TG) and total cholesterol (CHO) was decreased as dietary GA concentrations increased (P<0.05); whereas, plasma cortisol and glucose (GLU) showed an opposite tendency (P<0.05). Results of this study indicate0.3g/kg GA had a positive influence in improving lipid deposition in channel catfish without negative effect on growth; the beneficial effect may be due to extending promoting lipolysis.Experiment5, this study was carried out to evaluate the effects of different dietary levels of GA on plasma biochemical index and LPL mRNA of intraperitioneal fat, liver and muscle of channel catfish (average weight,159.0±5.0g). Five diets were formulated to contain five levels of GA (0,0.075,0.15,0.3and0.9g/kg). Fish were randomly distributed into30tanks and fed three times daily (08:30,12:00and16:30h) for8weeks. Plasma triglyeride and plasma cholesterol increased significantly as GA levels increased within4h (P<0.05), and decreased significantly as GA levels increased within24h (P<0.05). LPL mRNA of intraperitioneal fat, liver and muscle of channel catfish decreased significantly as GA levels increased (P<0.05). Results of this study indicate diatery supplement GA had a positive influence in improving lipid deposition in channel catfish; the beneficial effect may be due to LPL mRNA of intraperitioneal fat, liver and muscle. |
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