EFFECTS OF DIETARY CARBOHYDRATE TO LIPID RATIO ON GROWTH, FEED UTILIZATION, PLASMA GLUCOSE AND GLYCOLYTIC ENZYME ACTIVITIES OF JUVENILE DARKBARBEL CATFISH, PELTEOBAGRUS VACHELLI

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 key glycolytic enzyme activities of juvenile darkbarbel catfish (Pelteobagrus vachelli). Five isonitrogenous (crude protein 40%) and isoenergetic (19 MJ/g) diets were formulated to contain with graded levels of CHO:L ratios (0.75—6.53). Each diet was randomly assigned to triplicate tanks (50 L), and each tank was stocked with 40 fish with initial body weight of (4.20±0.02) g. The specific growth rate (SGR) increased first and then decreased with the increasing dietary CHO:L, and reached to the 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 (PFE) and protein efficiency ratio (PER) showed no significant difference among treatments with CHO:L of 1.30—3.55, but FE and PER significantly decreased at CHO:L of 0.75 and 6.53 respectively (PP>0.05). The crude protein of fish whole body increased first and then decreased with the increasing dietary CHO:L, and reached to the highest in fish fed diets with CHO:L of 3.55, which was significantly higher than that at CHO:L of 0.75 (PPP>0.05). Plasma triglycercide concentrations increased significantly with the increasing dietary CHO:L (PPP>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.