الفهرس 
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Abstract
1. INTRODUCTION
Sector of aquaculture production should be enhanced in order to increase the human population, especially food-fish contribution from capture fisheries is levelled off (FAO, 2018). The growing demand of aquatic animal leads to the intensification of the culture practices, overdrawing stressors for fish and thus magnifying the risk of diseases (Hassaan et al., 2019). Feed additives have been an increasingly a well-known management technique in aquaculture production systems, where abundant supplements have established an efficiency to enhance the fish immune response or controlling the severity of infections under intensification (Menanteau-Ledouble et al., 2015; Hassaan et al., 2019). The perfect feed ingredients used in fish feed should ensure growth, immunity and health promoting factors to achieve a great effect on the farm net gain. Various studies have been cleared over the years to extend solutions to these negative effects such as the use of antibiotics, hormones or other chemotherapy (Fawole et al., 2016).
Periphyton refers to the entire complex of attached aquatic biota on submerged substrates comprise phytoplankton, zooplankton, benthic organisms and detritus (Azim et al., 2005; Van Dam et al., 2002) and forms an additional food in aquatic production systems. Many trials in fish culture ponds have demonstrated the utility of submerged substrate in enhancing the fish production (Asaduzzaman et al., 2008; Azim et al., 2005). Immunostimulants are used in aquafeed to improve the fish health through the induction of non-specific immune system (Hassaan et al., 2018; Hassaan et al., 2019). Dietary immunostimulants affect the physiological status of aquatic organisms (Akhtar et al., 2010). The metabolic enzymes like aspartate aminotransferase (AST), alanine aminotransferase (ALT), malate dehydrogenase (MDH) and lactate dehydrogenase (LDH) are valuable indicators of physiological and health status of aquatic organisms (Pan et al., 2003). The enzymes like superoxide dismutase (SOD) and catalase help to control the reactive oxygen radicals (Campa-C_ordova, et al., 2002). It has been reported that periphyton developed over the submerged substrate improves non-specific immune response in Litopenaeus vannamei (Zhang et al., 2010). The biofilm developed over substrate are capable to elicit immune response in fish and shrimps (Verdegem, et al., 2005). Numerus reports are offered about beneficial effects of algae products as a dietary ingredient in Aquatic animal (Ju et al., 2009; Kuhn et al., 2010). However, there is a dearth of information about the role of periphyton as a dietary immunostimulants and its role on physiological status of Tilapia, and no information is available to support the dietary effect of periphyton. Thus, this study investigates the effects of dried periphyton supplementation with graded levels on growth, survival and digestive enzyme, hematology, blood biochemicals, immune responses, oxidative stress, intestinal-liver histomorphometry and chemical composition of Nile tilapia.
2. REVIEW OF LITER