optimum dietary carbohydrate/lipid ratio can spare protein in growing beluga, Huso huso

A 4 × 4 factorial design was used to examine the possible protein sparing effects of the optimum carbohydrate/lipid ratio to minimize the dietary protein level in growing Beluga, Huso huso. Three replicate groups of fish averaging 891.9 ± 33.4 g (mean ± SD) were fed one of the 16 experimental diets that were prepared containing four different dietary carbohydrate/lipid ratios of 0.8, 1.1, 1.4, and 1.7 at each of four different levels of protein 35, 40, 45 and 50%. At the end of 16 weeks of the experimental period, there were significant dietary protein effects on feed efficiency (FE) and protein efficiency ratio (PER) (P < 0.05). There were also interactive effects of protein and carbohydrate/lipid ratio on % weight gain (WG), specific growth rate (SGR), FE and PER. Fish fed 35%:1.4 had a significantly higher WG and SGR than did fish fed 40%:0.8, 50%:0.8 or 50%:1.7 (P < 0.05). Best performance of fish in terms of FE was recorded with diet 35%:1.4 (P < 0.05). At carbohydrate/lipid level of 1.7, SGR, FE, and PER of fish fed 50% protein were significantly lower than those of fish fed the other diets (P < 0.05). Beluga seems to utilize both lipid and carbohydrate as energy sources effectively within the range of 0.8-1.7 dietary carbohydrate/lipid ratio. The fish fed 35%:1.4 did show the best protein sparing effect.