Effects Of Dietary Carbohydrate Source, Level And Carbohydrate-to-lipid Ratio On Growth Performance And Glycometabolism Of Juvenile Darkbarbel Catfish, Pelteobagrus Vachelli

Feeding trials were conducted to examine the effects of dietary carbohydrate source, level and carbohydrate-to-lipid ratio on growth performance, feed utilization, plasma glucose and glycolytic enzyme activities of juvenile darkbarbel catfish, Pelteobagrus vachelli. The experiments were conducted in an indoor flow-through aquarium system for 8 weeks. Results of the present study are presented as follows:1. An 8-week feeding trial was conducted to evaluate the effects of dietary carbohydrate sources on growth performance, feed utilization, plasma glucose and hepatic glycolytic enzymes of juvenile darkbarbel catfish, Pelteobagrus vachelli. Six semi-purified diets were formulated to contain six carbohydrate sources (glucose, sucrose, dextrin, corn starch, gelatinized corn starch and microcrystalline cellulose). Each diet was randomly assigned to triplicate tanks (50L), and each tank was stocked with 40 fish (Initial mean body weight: 4.20±0.02g). The specific growth rate (SGR), protein efficiency ratio (PER) and feed efficiency (FE) reached highest in the gelatinized corn starch treatment (P<0.05). The apparent digestibility coefficients (ADC) of crude protein and crude lipid in diets reached highest in the gelatinized corn starch treatment (P<0.05). No significant difference was found in plasma glucose or plasma total cholesterol among dietary treatments (P>0.05). The plasma triacylglycerol reached highest in the glucose treatment (P<0.05). No significant difference was observed in the activities of hepatic hexokinase (HK) and pyruvate kinase (PK) among dietary treatments (P>0.05). Activities of glucokinase (GK) and 6-phosphofructo-1-kinase (PFK-1) reached highest in the glucose treatment (P<0.05). Based on these results, complex carbohydrate seemed better for the growth and feed utilization of darkbarbel catfish as carbohydrate source compared to monosaccharide diets.2. An 8-week feeding trial was conducted to evaluate the effects of dietary starch level on growth performance, feed utilization, plasma glucose and glycolytic enzyme activities of darkbarbel catfish, Pelteobagrus vachelli. Six isonitrogenous and isolopidic practical diets were formulated to contain graded levels of starch (3.1, 8.7, 15.7, 22.1, 29.0 and 34.8%). Each diet was randomly assigned to quadruplet tanks (300L), and each tank was stocked with 50 fish (Initial mean body weight: 1.24±0.02g). The specific growth rate (SGR) significantly increased with the increasing dietary starch contents (P<0.05) and reached highest at the starch level of 29.0%, and then leveled off. Feed efficiency (FE) and protein efficiency ratio (PER) increased significantly with the increasing dietary starch contents (P<0.05). The apparent digestibility coefficients (ADC) of dry matter and crude protein in diets reached highest at the starch level of 29.0%, which was significantly higher than that at starch level of 3.1% (P<0.05). No significant difference was observed in plasma glucose among dietary treatments (P>0.05). The liver glycogen increased first and then decreased with the increasing dietary starch, and reached highest at the starch level of 22.1%, which was significantly higher than that at the starch level of 3.1% (P<0.05). The liver lipid at the starch level of 34.8% was significantly higher than that at the starch level of 8.7% (P<0.05). No significant difference was observed in the muscle lipid among dietary treatments (P<0.05). Hexokinase (HK) activities at high starch levels (29.0 and 34.8%) were significantly higher than those at low starch levels (3.1, 8.7 and 15.7%) (P<0.05). Activities of glucokinase (GK) and pyruvate kinase (PK) first increased significantly, and then decreased, with increasing dietary starch (P<0.05). However, no significant difference was observed in 6-phosphofructo-1-kinase activities (PFK-1) among dietary treatments (P>0.05). Results suggested that juvenile darkbarbel catfish exhibited a good tolerance to high dietary starch and appropriate starch supplementation level is 30.2%.3. An 8-week feeding trial was conducted to evaluate the effects of dietary carbohydrate-to-lipid (CHO: L) ratio on growth performance, feed utilization, plasma glucose and glycolytic enzyme activities of juvenile darkbarbel catfish, Pelteobagrus vachelli. Five isonitrogenous and isoenergetic diets were formulated to contain with graded levels of CHO: L ratios (0.75-6.53). Each diet was randomly assigned to triplicate tanks (50L), and each tank was stocked with 40 fish (Initial mean body weight: 4.20±0.02g). The specific growth rate (SGR) increased first and then decreased with the increasing dietary CHO: L, and reached highest in fish fed diets with CHO: L of 3.55, which was significantly higher than those of fish fed the diets with 0.75 and 6.53 ratios (P<0.05). Feed efficiency (FE) and protein efficiency ratio (PER) followed the same general pattern as SGR (P<0.05). No significant difference was observed in the HSI and VSI of the darkbarbel catfish among dietary treatments (P>0.05). The crude protein of fish whole body increased first and then decreased with the increasing dietary CHO: L, and reached highest in fish fed diets with CHO: L of 3.55, which was significantly higher than that at CHO: L of 0.75 (P<0.05). The crude lipid of fish whole body decreased with the increasing dietary CHO: L significantly (P<0.05). There was no significant difference in the plasma glucose and total cholesterol among dietary treatments (P>0.05). Plasma triglycercide concentrations increased significantly with the increasing dietary CHO: L (P<0.05). Hepatic glucokinase (GK) activities increased first and then decreased with the increasing dietary CHO: L, and reached highest at the CHO: L of 3.55, which was significantly higher than those at CHO: L of 0.75 (P<0.05). However, no significant difference was observed in activities of hepatic hexokinase (HK), pyruvate kinase (PK) and 6-phosphofructo-1-kinase activity (PFK-1) among dietary treatments (P>0.05). Based on second-order polynomial regression analysis of SGR against dietary CHO: L ratios, a CHO: L ratio of 4.06 was proved to be optimal for the growth of juvenile darkbarbel catfish.