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Using of natural plants as immunostimulant in fish is more useful than antibacterial drugs that cause adversely side effects for fish, environment and consumers. Therefore, the present study was to investigate the effects of dietary turmeric (Curcuma longa), rosemary (Rosmarinus officinalis) and thyme (Thymus vulgaris) as feed additives on growth performance, proximate composition and some immuno-hematological parameters on Nile tilapia. Four nitrogenous (31.43-31.56 % crude protein) and isocaloric (17.90-18.04 kJ/g) diets were formulated to contain 0% (control), 1% of turmeric, rosemary or thyme, respectively. The results reveled that, supplementation with medicinal herbs significantly increased (P<0.05) weight gain, specific growth rates and protein efficiency ratio (PER) compared to those in the control group. Moreover, the medicinal herb additives had insignificant effect on carcass composition and some biochemical composition. Hematocrit and leukocrit levels in the fish fed with turmeric, rosemary and thyme added diet were found to be significantly (P <0.05) higher than the control group. However, leukocyte level among the experimental groups was not significantly differed (P >0.05). In neutrophils of experimental fish groups, there were higher numbers of NBT (+) cells fixed on lamellas than those of the control group. So, based on the current findings together with the low cost and the immunostimulative effect of turmeric, rosemary and thyme it can be recommended to be used in fish feed to minimize the mortalities caused by some pathogens.

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The study aimed to compare the growth performance and physiological responses of bester (B) and backcrossed bester ♀ × beluga ♂ (BB) in response to crowding stress under different stocking densities, as well as to establish a threshold stocking density for rearing BB in a recirculating aquaculture system (RAS) without welfare impairment. For this purpose, in the first trial (T1), B (181.15 ± 21.21 g) and BB fingerlings (181.98 ± 28.65 g) were reared in two stocking densities of 2 kg/m2 and 4 kg/m2 in fiberglass tanks (1 m3) for 6 weeks. In a parallel trial (T2), the BB hybrids (335.24 ± 39.30 g) were kept in four initial stocking densities, ranging from 5 kg/m2 to 12 kg/m2. The results of T1 revealed better growth indices (i.e., final mean weight, weight gain, specific growth rate) at lower stocking densities for both hybrids; however, in terms of growth performance, the BB hybrid showed better results when compared with the B hybrid. BB hybrids registered significantly (p < 0.05) lower serum cortisol and MDA and higher lysozyme than B hybrids, showing higher tolerance to crowding stress. Nevertheless, at higher densities, selected serum parameters (i.e., hematological indices, cortisol, glucose, protein, malondialdehyde, lysozyme) and growth performance indices used to evaluate the hybrids indicate that high stocking density could affect the growth and welfare of BB hybrids, and that the selected serum parameters could be used as good indicators for chronic stress caused by overcrowding conditions.

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