2.1.Aquaculture
Today, 40% more fish, shellfish, aquatic plant, and algae species       
are grown in a range of marine, brackish, and freshwater systems across the world (Metian et al.,2020).
    Aquaculture, which accounts for more than half of worldwide fish output, is the fastest-growing food-producing business.
About 424 aquatic species are farmed worldwide, providing nutrition, food security, sustainable livelihoods, and reducing poverty for millions of people (Galappaththi et al.,2020).
   The greatest aquaculture producers outside of Asia are Norway and Chile, which mostly produce Atlantic salmon (Salmo salar), and Egypt, which produces Nile tilapia.
Egypt's aquaculture sector has seen tremendous growth during the last two decades expanded at a dizzying rate. Aquaculture accounted for around 30% of overall fish output in the late 1990s, with fisheries responsible for the remaining 70%% (Kleih et al., 2013; El-Sayed et al., 2015 and Shaalan et al., 2018).
2.2. Aquaculture system types in Egypt
Egypt possesses several aquaculture systems. The most popular form of aquaculture ponds for fresh water are semi-intensive earthen ponds (El-Gayar., 2003 and Kleih et al., 2013). 
Furthermore, widespread, and intense farming fish and other aquatic organism’s existent and developing. Extensive and Clay ponds are typically used for semi-intensive aquaculture. whilst intense aquaculture is typically carried out in concrete tanks (El-Gayar., 2003 and Kleih et al., 2013).
Furthermore, float cage aquaculture is considerable, with yearly fish output topping 249,390 tonnes (GAFRD, 2012). Since the 90s, Nile tilapia aquaculture cages have been in use and silver carp have been erected in the Nile River branches (Cardia and Lovatelli, 2007). More than 37,000 cages are in operation in the Nile's tributaries, mostly at Damietta and Rashid in northern Egypt. (Cardia and Lovatelli, 2007; El-Sayed, 2007 and GAFRD, 2012).
Legislation is among the most important challenges Aquaculture in Floating Cages faces. Environmental concerns prompted the regulation and prohibition of cages in various locations (Bostock et al., 2010; Goulding and Kamel, 2013 and Shaalan et al., 2017). It was also determined that cages have a limited influence on the environment, with a 5 metre radius around each cage. (Brigolin et al., 2016).
2.3. Basa ( pangasianodon hypophthalmus )
           Pangasius catfish considered in many countries as one of the most successful aquaculture species due to its relative ease in culture, high-market demand, and suitability to local climate conditions (Rahman, 2005; Rahman and Ali, 2012).
           Pangasius are cultured both intensively with commercial feeds, semi-intensively (with limited feed), and in extensive (no feed) polyculture with it ability for both tilapia and carp (Ahmed et al., 2010).
           High disease resistance, along with high stocking density with greater production rates (up to 120 fish/m2 , average 40 tons/ha; (FAO, 2010), led to the suggestion that Pangasius is an ideal cultivar for increasing aquaculture production in Egypt, particularly in regions unfamiliar with farming other species, as well as reducing the burden of population growth.
           Introducing Pangasius aquaculture to the Egyptian coastal regions, in which water resources are largely underutilized, may significantly enhance the dietary consumption of protein for low-income families, as well as provide new sources of income and employment. 
          Temperature plays an important role in the life of most ectotherms with their body temperature essentially following temperature of surrounding environment (Wootton, 2011) .
           Some studies found out Pangasius sp. May be tolerant to salinity (David, 1962).
           Recently, juveniles of Pangasius catfish are reported to tolerate salinities up to 13 ppt without significant mortality (Castaneda et al., 2010).
           The pH of water affects the normal physiological functions of aquatic organisms, including the exchange of ions with the water and respiration (Alabaster and Lloyd, 1980).
            Better understanding of growth performance, feed utilization, and survival rate, can benefit Pangasius catfish culture dissemination. The aim of this study is to focus on determining the effect of introducing Para probiotics to Pangasius and the optimal level of such introduction .
                    Pangasius hypophthalmus (Sauvage, 1878) is an omnivorous fresh water fish originating from the Mekong River in Vietnam (Rodríguez et al., 2018).
           Panga has several names as sutchi catfish, striped catfish, iridescent shark-catfish, or tra fish, it has high acceptability by consumers due to its low price, good taste and white meat that can replace cod or other expensive white fishes (Little et al., 2012 ; Guimarães et al., 2016).
            Recently, Pangasius become one of the best aquaculture candidates in several countries as it can be cultured easily in ponds, concrete tanks or fish cages, it has the ability to survive at high stocking density, poor water quality, low oxygen levels and can easily accept external feeding.
            Moreover, it considered as a fast growing fish with high yield production and disease resistant that meet up the farmer‟s demand. (Hill and Hill, 1994; Ali and Haque, 2011; Vaishnav et al., 2017).