Effect of Dietary Carbohydrate-Lipid Ratio on Growth, Body Composition and Digestive Enzyme Activities of Juvenile Goldfish (Carassius auratus)

The effect of dietary carbohydrate: lipid (CHO: L) ratios on growth performance, body composition and digestive enzyme activities of juvenile goldfish, Carassius auratus (1.69±0.01 g) were investigated for 8 weeks. Juvenile gold fish (n=225) were randomly allocated to five treatments groups (T1 to T5) with 3 replicates of 15 fish in each. Diets were iso-nitrogenous (40% crude protein) and iso-energetic (18.52 MJ/g) with varying CHO: L ratios (1.04 to 38.4). Weight gain, specific growth rate (SGR), feed conversion ratio (FCR) and protein efficiency ratio (PER) improved significantly (P<0.05) as dietary CHO: L ratio increased, however, this trend was not maintained above CHO: L ratio of 4.33. Hepatosomatic index (HSI) increased significantly (P<0.05) as dietary CHO: L ratio increased, whereas viscerosomatic index (VSI) followed an opposite trend (P<0.05). Opposite to moisture content, whole body lipid content increased significantly (P<0.05) as dietary CHO: L ratios decreased, while whole body protein showed little difference among the treatments. Protease activity of intestine and liver of fish fed varying CHO: L diets did not show any discernible changes among the dietary treatments. However, intestinal and liver lipase activity decreased, while intestinal α-amylase activity increased significantly (P<0.05) with increasing dietary carbohydrate levels. Based on second-order polynomial regression analysis of SGR, the optimal dietary carbohydrate and lipid levels for young ones of C. auratus were 325 g/kg and 84 g/kg respectively, corresponding to dietary CHO: L ratio of 3.86.