In intensive culture system, improving fish performance and disease resistance are major challenges facing fish culturists. Moreover, bacterial diseases are one of the limiting factors for fish intensive culture (Rahman et al., 1997, 2001; Li et al., 2006). Also, the intensive use of antibiotics to prevent and control bacterial diseases in aquaculture has led to an increase in antibiotic-resistant bacteria (Alderman and Hastings, 1998; Teuber, 2001). The use of antibiotics has become limited because certain pathogens have developed resistance to the drugs. Increasing on knowledge is focused on control or elimination of the use of antibiotic in culture conditions.

As per Yousefian and Amiri (2009), last few decades, antibiotics were used to control bacterial diseases but this type of chemical substance is advisable to avoid in aquaculture. In recent years in the aquaculture industry, alternative strategies have been developed for disease control as well as reduction in the widespread use of antibiotics. Prebiotic is a well-known group of these strategies which enhances non-specific immune response. According to Bailey et al, 40 prebiotic can modify microbes of GI tract by increasing immune responses.

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Prebiotics are non-digestible food ingredient which enhance growth performance as well as microbial activities of digestive tract, also boost immune system and improve stress resistance thus improves host health (Guerreiro et al., 2016; Das et al., 2017). Gibson et al. (2004) reported that a food ingredient which acts as prebiotic must possess the following criteria such as showing resistance to gastric acidity, hydrolysis by digestive enzyme, fermentation by gastrointestinal microflora and increase the abundance of intestinal bacteria related to health.

Numerous studies have investigated the different aspect of prebiotic application (e.g. inulin, oligofructose, xylooligosaccharide, fructooligosaccharide, galactooligosaccharide) in cultured finfish and shellfish, and the results revealed that prebiotics are promising and have beneficial effects on growth performance, gut microbiota, immunity and disease resistance (Ringø et al. 2010a, 2014; Ganguly et al. 2013; Daniels & Hoseinifar 2014; Song et al. 2014; Torrecillas et al. 2014).

Different Prebiotic substances in aquaculture have been used to increase aquatic animal growth, survival, health, and disease prevention (Samrongpan et al., 2008; Grisdale-Helland et al., 2008; Sang and Fotedar, 2010; Zhou et al., 2010; Ibrahem et al., 2010; Ahmdifar et al., 2011; Ye et al., 2011; Torrecillas et al., 2011; Zhang et al., 2012; Geralylou et al., 2012; Mpurino et al., 2012; Akrami et al., 2013).

Sterlet (Acipenser ruthenus) is a bottom feeding sturgeon species that exclusively inhabits freshwater habitats. It represents a species of significant economic importance in the Danube River, and it is also the only sturgeon species in this river basin that is still an object of commercial fishery (Jari? et al., 2010).

In the present study the Biomin PEP dietary supplement contains two sets of combination that combined in an isotonic method including essential oils (oregano essential oil, which contains caracrol material that has potent anti-microbial and antioxidative effects. Anise essential oil, which contains anethole with anti-viral and anti-fungal effects and is an appetite stimulant. And citrus essential oils, containing Limonene material that enhances the flavor of food. Prebiotic (which contains fructo oligo saccharide and also have prebiotic and bifidogenic effects).