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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.

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Use of prebiotics, nondigestible dietary ingredients that beneficially affect the host by selectively stimulating the growth of and/or activating the metabolism of health‐promoting bacteria in the intestinal tract, is a novel concept in aquaculture. An 8‐week feeding experiment was conducted to investigate the effects of dietary prebiotic inulin on growth performance, intestinal microflora, body composition and hematological parameters of juvenile beluga, Huso huso. Three replicate groups of fish (initially averaging weight as group 16.14 ± 0.38 g) were fed diets containing prebiotic inulin levels ranging from 1 to 3%. The basal diet contained 3% cellulose. Fish were fed to apparent satiation and growth performance was monitored. The results of linear regression showed that there was a negative relationship between some performance indices including weight gain (WG), specific growth rate (SGR), protein efficiency ratio (PER), energy retention (ER), feed efficiency (FE), protein retention (PR), and supplementation level of inulin, which indicated that inulin is not appropriate for supplementation in the diet of beluga. At the end of trial, in both basal and inulin groups, the total count of intestinal bacteria decreased within the second 4 weeks, but the intestinal lactic acid bacteria (LAB) increased in the 1% inulin group. These changes were not, however, reflected in the survival rate of the fish, although survival was higher compared to other groups.

The effect of dietary mannan oligosaccharide (MOS; activeMOS®) on growth, survival, and body composition in giant sturgeon juvenile (Huso huso) with initially average weight 46.89 ± 2.57 was investigated for a period of 46 days. Basal diet were supplemented with 0 (control), 2, and 4 g kg(-1) MOS in a totally randomized design trial in triplicate groups. The results showed no significant differences in growth and feeding parameters between control and treatment groups (MOS supplementation diets) (P > 0.05). There was a statistically significant decrease (P < 0.05) in feed per fish level in only group treated with 4 g kg(-1) MOS. The highest and the lowest growth performances were observed in 2 and 4 g kg(-1) MOS, respectively. There were no significant differences in survival rate among all treatment groups (P > 0.05). In group treated with 2 g kg(-1) MOS was a significant difference in lipid carcass (P < 0.05), whereas protein, ash, and moisture remained unaffected (P > 0.05). However, no significant difference was observed in intestinal lactic acid bacteria between all treatment groups (P > 0.05). There were no significant differences in hematological parameters between control and MOS treatment groups (P > 0.05). These results suggested that the prebiotic mannan oligosaccharide did not influence the growth performance in giant sturgeon juvenile, and it is not appropriate for supplementation in the diet of cultured juvenile giant sturgeon.