en Genetics Genetics پژوهشي Orginal research papers The effect of feed supplemented with L-camitine at four levels of 0, 300, 600 and 900mg kg^-1 on growth performance and body composition of beluga, <em>H. huso</em>, juveniles was evaluate din two separate trials. In the first trial, 180 juveniles (525&plusmn;9gw) were fed with the test diet for a period of 71 days, and the trial extended to another 126 days in the second phase by randomly selecting 120 juveniles (870.7&plusmn;32g) and rearing them with similar diets. All trials, in triplicates, were conducted in circular fiberglass tanks (200cm diameter, 40cm height).The fish were fed 4 times daily to apparent satiation.<br> In the first phase, L-carnitine did not significantly affect mean final weight, feed conversion ratio (FCR) or specific growth rate (SGR) of the fish, however, the fish receiving 900mg kg^-1 L-carnation showed better growth increment, SGR and feed efficiency (FE) than those in control group (p&sup3;0.05); neither did it significantly affect protein, lipid, moisture or ash as well as leptosomatic index (HSI) (p&sup3;0.05). The protein efficiency ratio (PER) was significantly affected by L-carnitine supplemented diet, particularly at 900mg kg^-1(p&pound;0.05). In the second phase, fish fed L-carnitine-supplemented diets produced significantly higher W2, SGR and PER than the control group (p&pound;0.05), but HSI decreased significantly (P&pound;0.05).At the end of the trial, the whole body composition of fish did not differ significantly among experimental treatments, but slightly reduced lipid content were observed at 600 and 900mg kg^-1 L-carnitine (p&pound;0.05).The results of this study indicated that supplementation of diets with 300-600mg carnitine kg^-1 improved growth rate, feed utilization and stimulated protein-sparing effect in this species. L-carnitine, Growth rate, Body composition, Beluga, Huso huso 157 170 http://jifro.ir/browse.php?a_code=A-10-1050-2&slc_lang=en&sid=1 M. Mohseni mahmoudmohseni@yahoo.com 100319475328460024213 100319475328460024213 Yes J. Seyfabadi 100319475328460024214 100319475328460024214 No H. Pourali 100319475328460024215 100319475328460024215 No M. Pourkazemi 100319475328460024216 100319475328460024216 No M. Bahmani 100319475328460024217 100319475328460024217 No