Nutritional Responses to High Carbohydrates in Common Carp (Cyprinus carpio L.) Diet  

Feeding trial was carried out for 70 days to study nutritional effects of three levels of local carbohydrate sources (Standard ration SR 37 %, Medium carbohydrate ration MCR 42 % and high carbohydrate ration HCR 53%) in the diet of juvenile (30g) common carp. Relative weight gain values varied from the highest of 27.1% in SR treatment to 25.9 % in MCR and the lowest of 25.0% in HCR treatment. Although SR ration gave better IGR, but MCR and HCR gave nearly the same instantaneous growth rate values, indicating that the incorporation of carbohydrate up to the level 53% has no significant impact on growth. Feed conversion ratio varied between 4.62 in SR to 4.82 in MCR and 4.87 in HCR treatment. Similar trend was shown in feed conversion efficiency which ranged from 21.73 % in fish fed on SR, 21.00% for MCR and 20.62% for HCR. Fish fed SR ration with the highest level of protein in diet (28.71%) have the lowest protein efficiency ratio (PER). The carbohydrate rich diets which contain lower protein levels (MCR 25.69% and HCR 22.71%) have higher PER values (0.82and 0.91 respectively). Slight decrease in the digestibility of both protein and lipid values are noted in carbohydrate-rich diets. On contrary carbohydrate digestibility increased from 54% to 69% with increasing the dietary carbohydrate levels from 37 to 53 %. Using the x-ray method for studying feed evacuation, it appeared that, the high carbohydrate ration was evacuated faster than MCR and SR ration. After 24 hours of feeding, 91 % of the HCR ration was evacuated compared with 84% and 79 % in both SR and MCR ration. The rate of evacuating HCR ration ranged between 6.7-7.6 %per hour compared with 5.5 -6.3% per hour for MCR and 5.7-7.0 % per hour for SR ration.