Growth performance, carcass quality, survival and hematological responses of Oncorhynchus mykiss juveniles (initial weight 8.4 ± 0.1 g) fed diets containing thymol-carvacrol powder at the levels of 0, 1.0, 2.0, 3.0 g kg )1 were tested. Thymol-carvacrol powder originated from Origanum vulgare, a Mediterranean plant, added to diets. Each diet was fed to triplicate groups of fish for 45 days. Fish fed diets containing thymol-carvacrol had significantly higher final weight and growth than the control group. Food conversion ratio in fish fed diets containing 2.0 and 3.0 g kg )1 thymol-carvacrol was statistically better than in other treatments. Survival was not different among all treatments. The number of lymphocytes increased when thymol-carvacrol was used at higher levels. Furthermore, whole body lipid content was higher in fish fed 1.0 and 2.0 g kg )1 thymol-carvacrol than the other groups, but body protein in the group fed 3.0 g kg )1 was higher than in other groups. Also, body ash in control and 1.0 g kg )1 was higher than in other groups. Whole body dry matter was not affected by dietary treatments. These results indicated that dietary administration of thymol-carvacrol can influence some growth, hematological parameters and tissue composition in rainbow trout juveniles.

The in£uence of stocking density (1, 2, 4, 6 and 8 kgm À 2 ) was investigated on haematological parameters, growth and ¢n erosion of great sturgeon (Huso huso) juveniles for a period of 8 weeks. The mean weight of ¢sh at the start of trial was 93.13 AE 1.04 g. After 8 weeks of rearing, the mean weight was 362.4, 319.7, 267, 242.1 and 211.1 in densi-ties1^8 kg m À 2 respectively. The results of this study showed that growth parameters, including condition factor, weight, weight gain, feed conversion ratio, speci¢c growth rate and body weight increase, had a statistically signi¢cant di¡erence among treatments (Po0.05). A signi¢cant di¡erence (Po0.05) was observed in haematocrit, but the other haematological parameters, including red blood cells, white blood cells (WBC), haemoglobin concentration, mean corpuscular haemoglobin, mean corpuscular volume, mean corpuscular haemoglobin concentration and di¡erential WBC count, showed no signi¢cant e¡ect with stocking density (P40.05). At the end of the experiment, stocking density had no signi¢cant e¡ect on plasma cortisol and glucose concentration. The ¢n length (dorsal, anal, ventral, pectoral and caudal) of ¢sh was measured to calculate the ¢n index. According to this index, dorsal, anal, ventral and pectoral ¢ns showed no signi¢cant di¡erence among treatments (P40.05), but the erosion of the caudal ¢n was signi¢cantly di¡erent between ¢sh held on 6 and 8 kg m À 2 (Po0.05). These results showed that rearing density has a major e¡ect on the growth indices of H. huso. Unlike many other ¢sh, great sturgeon exhibited lower stress responses to high stocking density. This indicates that they are more tolerable to rearing conditions in high stocking densities.With respect to the various e¡ects that density causes on growth, ¢n erosion and physiological and haematological parameters, better understanding of these phenomena considering di¡erent levels of density could have a bene¢cial impact on many rearing steps of this species.

The effects of acute stressors on physiological responses of juvenile great sturgeon or beluga Huso huso L. were investigated in two experiments. In the first experiment, fish were handled by placing them in containers at either low density (LD, one fish l(-1)) or high density (HD, four fish l(-1)) for 60 s. Concentrations of plasma cortisol, glucose and lactate were determined from blood collected at 0, 1, 3, 6 and 12 h after application of the stressor. Plasma cortisol concentrations increased after the disturbance in H. huso from both handling treatments, but changes were not significant. Plasma glucose rose significantly by 22.9 and 31.6% in LD and HD handling treatments, respectively, after 3 h. Significant increases in plasma lactate occurred within 1 h in both treatment groups, but that of the HD group was much higher. In the second experiment, fish were held at two different densities, LD (2 kg m(-2) tank bottom surface area) and HD (7 kg m(-2)), for 8 weeks and then subjected to an aerial emersion handling stressor in a net for 60 s; blood samples were taken before handling (resting, 0 h) and at 1, 3, 6 and 9 h after handling. Plasma cortisol increased significantly in fish from the HD treatment from 8.8 +/- 0.3 to 19.2 +/- 2.4 ng ml(-1) (mean +/-s.e.) by 1 h after stress, but post-handling changes in the LD group were not significant. Significant increases in both plasma glucose and lactate were observed by 1 h in both treatment groups, with peak levels of plasma glucose evident at 3 h [69.4 +/- 2.9 and 60.9 +/- 1.7 mg dl(-1) (mean +/-s.e.) in LD and HD groups, respectively]. Plasma glucose levels were significantly higher in the LD group than in the HD group at 3 and 6 h. Post-handling haemoglobin content increased by 1 h and white blood cell numbers were reduced by 3 and 6 h in the HD treatment group compared with resting values, but changes in these blood features in the LD group were not significant. Acute handling did not affect haematocrit in either treatment. The results suggest that H. huso is relatively resistant to handling and confinement, and could tolerate normal hatchery practices associated with aquaculture. Because changes in cortisol concentrations were relatively low compared with those in most teleosts, glucose and lactate concentrations may be more useful as stress indicators in juvenile H. huso. This study also demonstrated that prior exposure to a chronic stressor, specifically high stocking density, could alter the physiological response to subsequent acute handling in H. huso.

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Rainbow trout (initial body weight 4.16 ± 0.25 g) were fed diets [crude protein 420 g kg )1 ; gross energy 18.7 MJ kg )1 dry matter (DM); crude fat 110 g kg )1 ] containing graded levels of either a canola meal (crude protein 350 g kg )1 DM) supplemented with DL-methionine as partial fish meal protein. A growth trial was conducted over 16 weeks at a water temperature of 12 ± 1°C. At the end of the growth trial, in addition to body composition analyses, plasma tri-iodothyronine (T 3 ) and thyroxine (T 4 ), cholesterol and liver fatty acid composition were measured. Replacement of fish meal with canola meal (100-570 g kg )1 replacement) did not affect on growth performance. At 16th week, plasma cholesterol levels were reduced in fish fed all diets in comparison with 8th week. Plasma T 4 levels were significantly higher in the canola meal-fed fish sampled after 16 weeks, but no significant differences in T 3 levels were obtained (P > 0.05). Proximate compositions were affected by dietary treatments. The liver fatty acid composition reflected that of the diet with a higher level of polyunsaturated (n-6) fatty acids in fish fed diet canola meal and a higher content in n-3/n-6 ratio in fish fed diet without canola meal. These studies show that canola meal has potential to replace substantial levels of fish meal in diets for carnivorous fish without compromising performance. KEY WORDS

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.

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The e¡ects of constant light (24L:00D), no light (00L:24D) and two light^dark periods (18L:06D; 12L:12D) on the growth, stress and haematological variables were assessed in juvenile great sturgeon, Huso huso. During the 8-week experimental period, juveniles (22.5 AE 0.6 g) were kept under a 150 lx light intensity in ¢breglass tanks (0.8 m 2 , 500 L). Di¡erences in growth were insigni¢cant during the experiment, but lactate levels were higher in the 00L:24D and 24L:00D photoperiods compared with 12L:12D and 18L:06D photoperiods. Cortisol levels did not show di¡erences among the various photoperiods. At the end of the experimental period, ¢sh reared under a 12L:12D photoperiod had higher haemoglobin values and erythrocyte numbers than in the other photoperiods, while no di¡erences were found between groups with regard to haematocrit values or leucocyte numbers. The highest survival rate (89%) was observed in the 12L:12D period in which the levels of lactate and cortisol as stress indicators were minimal. The results indicate that various photoperiods cause di¡erent stress levels in juvenile great sturgeon and have no signi¢cant e¡ects on growth, at least in short time periods.