In order to evaluate the protein and energy requirement of Persian sturgeon (Acipenser persicus) sub-yearlings, eight experimental diets containing two protein levels (40% and 45%) and four lipid levels (10%, 15%, 20% and 25%) were tested. Sturgeons (W 0 ¼ 136.8 g) were fed the experimental diets to satiation four times daily for 150 days, resulting in a final mean weight of 375.8 g. Growth was significantly affected by lipid content of the diets. At 40% protein level, weight gain and specific growth rate (% per day) were significantly improved (P < 0.05) by increasing the dietary lipid (energy) content. Protein efficiency ratio (PER) was significantly affected by different dietary treatments for each dietary protein level tested, reaching a mean value of 3.58 in fish fed high lipid diets and a PER of 2.77 in low lipid diets. Results obtained in the present study suggest that the optimum dietary protein content for Persian sturgeon is 40%, with an estimated optimum protein-to-energy ratio of 18-20 mg kJ )1 .

A 12‐week feeding trial was conducted to evaluate the optimum dietary inorganic copper (copper sulphate) in juvenile beluga, Huso huso. Eight semi‐purified diets containing 1.1 (Cu1.0), 3.5 (Cu4.0), 7.1 (Cu7.0), 9.7 (Cu10), 13.1 (Cu13), 25.1 (Cu25), 49.9 (Cu50) and 195 (Cu195) mg Cu kg−1 diet in the form of CuSO4.5H2O were fed to fish of initial body weight 8.49 ± 0.32 g and length 11.85 ± 0.66 cm (mean ± SD) in triplicate groups in a flow‐through system. Weight gain (WG) of fish fed Cu10 and Cu13 diets was significantly higher than that of fish fed Cu1.0, Cu4.0, Cu25, Cu50 and Cu195 diets (P < 0.05). Whole‐body and muscle crude protein increased with dietary Cu up to the supplementation level of 13.1 mg kg−1 diet and then decreased. Whole‐body lipid content was negatively correlated, while whole‐body ash was positively correlated with dietary copper concentration. Hepatic copper–zinc superoxide dismutase activity of fish fed Cu10 and Cu13 diets was significantly higher than that of fish fed Cu1.0, Cu4.0 and Cu195 diets. Hepatic thiobarbituric acid‐reactive substances of fish fed Cu13 diet was significantly lower than those of fish fed the other diets except for that of fish fed Cu10 diet. Aspartate aminotransferase, alanine aminotransferase and copper accumulation in tissues increased with dietary copper. Broken‐line analysis of WG suggested that the optimum dietary Cu level was 10.3 mg Cu kg−1 diet. Therefore, these results may indicate that the optimum dietary Cu levels could be greater than 10.3 mg Cu kg−1 diet but less than 13.1 mg Cu kg−1 diet in juvenile beluga, when copper sulphate is used as the dietary source of inorganic copper.

Growth and survival of yearling great sturgeon, Huso huso, were determined at three different feeding rates and three different frequencies. Feeding rates were 2, 3, and 4% body weight day -1 , and these daily rations were offered in 3, 4, and 5 fractions over the day. Sturgeon were offered to 18 tanks with 10 fish each were distributed to each of the 3 feeding rates and 3 frequencies. Thus, a 3x3 experimental design was used with two replicates per treatment involving a total of 18 tanks (stocking density = 10 fish per tank). Initial average body weights of the yearlings were 900 ± 9.2 g. Fish were kept at 23 ± 1.5 ºC in rectangular tanks and fed one commercial diet (40-42 % protein, 12-14% fat, 10-11% moisture and 10% ash). After about 16 weeks of feeding (108 experimental days), final length, weight and feed conversion were determined: all were significantly affected by feeding rate and feeding frequency (P<0.05). The highest feed conversion ratio (FCR) was observed at a ration of 4% body weight (BW) day -1 with the daily ration being given in 5 portions over the day, while maximum length and weight was obtained with a ration of 2% BWday -1 and the daily ration being spread over 3 feeding times. No mortalities occurred during the 16-weeks trial. Results show that the optimum feeding rate and feeding frequency for this size group of great sturgeon yearlings would appear at a feeding rate at 2% BW day -1 with the daily amount being offered in three portions over the day.

The effects of dietary L L-carnitine on growth performance, whole body composition and feed utilization were studied in beluga, Huso huso. Fish were randomly allocated in 15 tanks (30 fish per tank) and triplicate groups were fed to satiety during 84 days one of five isonitrogenous (41% CP) and isoenergetic (20 MJ kg )1 ) diets, each differing in L