World Aquaculture Magazine - June 2020

62 JUNE 2020 • WORLD AQUACULTURE • WWW.WA S.ORG Effect of Nutrient Additions on the Nutritional Value of Biofloc Urea (45 percent N) and super phosphate (20 percent P) were used as sources of macronutrients; chicken manure was used as an organic fertilizer; and corn starch, corn meal, rice meal and rice bran were used as sources of organic carbon. These nutrients were combined in different ratios with the goal to obtain the best nutritional value of microbial protein from biofloc. Each experiment was carried out for two weeks. Seawater with 30 g/L salinity collected from the Beach Club, Ismailia, Egypt was used in all experiments. In the laboratory, polyethylene bags were filled with 10 L of seawater. Water inside the bags was mixed by diffused air. Productivity of biofloc was assessed in terms of dry weight biomass produced. At the end of each experiment, settled biofloc was poured into plastic bottles and placed in a refrigerator for 24 h. Excess seawater was decanted away and concentrated biofloc was poured into Petri dishes that were placed in a drying oven at 70 C for 12 h. Dried biofloc was weighed and stored frozen (-4 C) for further analysis. The proximate composition of biofloc was determined using standard analytical methods of the AOAC (2000) to determine the best level of nutrients in terms of biofloc productivity and nutritional value. Effect ofN:PRatio Four nitrogen to phosphorus (N:P) ratios were evaluated, 1:1, 2:1, 4:1 and 8:1. Ratios were effected by fixing P addition at 2.5 mg/L super phosphate and then adjusting urea addition between 2 and 15 B iofloc technology (BFT) is a technique of enhancing water quality through the addition of organic carbon to the aquaculture system from a supplemental carbon source or increased carbon to nitrogen ratio (i.e. lower protein level) of feed. Nitrogen uptake by heterotrophic microbial growth decreases the total ammonia concentration more rapidly than nitrification (Hargreaves 2006). Immobilization of ammonia by heterotrophic bacteria occurs much more rapidly because the growth rate and microbial biomass productivity per unit substrate of heterotrophic bacteria are 10 times greater than those of nitrifying bacteria (Crab et al . 2012). Biofloc is composed of a variety of microorganisms, uneaten feed, feces and detritus, and flocs are kept in suspension with water propulsion and aeration. Biofloc offers numerous ecological advantages for microbes, including protection from grazers, direct access to nutrients and necessary substrate for attachment (De Schryver et al . 2008). Biofloc technology (BFT) can be considered a culture technique in which water quality is maintained and in situ feed is simultaneously produced in the form of biofloc particles (Crab et al . 2007). This study evaluated the effect of nutrient additions on the productivity and nutritional value of biofloc produced in indoor bioreactors. It also aimed to determine the best combination of nutrients that should be added to seawater to produce biofloc that can be used in studies for feeding fish or shrimp. Experiments took place in the Mariculture Laboratory of the Department of Marine Science, Suez Canal University, Ismailia, Egypt. Manipulating the Nutritional Value and Production of Bioflocs Aya S. Hussain, Deyaaedin A. Mohammad, Wafaa S. Sallam and Elham M. Ali FIGURE 1. Polyethylene tube bags containing 10 L of seawater used to produce bioflocs. TABLE 1. Amino acid profile, expressed as mg /100 mg dry weight, of biofloc obtained from the different carbon sources. Essential amino acid Nonessential amino acid Carbon source Leucine Lysine Argnine Valine Histidine Threonine Isoleucine Phenylalanine Glutamic Aspartic Proline Alanine Glycine Tyrosine Serine Corn meal 2.5 1.4 1.3 2.0 0.6 1.4 1.5 1.1 4.0 2.6 1.7 1.9 1.5 0.9 1.4 Rice bran 1.3 0.8 0.9 1.4 0.3 0.8 0.7 0.6 1.9 1.5 0.8 1.0 0.9 0.4 0.8 Rice meal 1.7 1.6 1.2 1.2 0.3 1.0 0.9 0.8 3.6 2.4 1.1 1.4 1.3 0.2 1.3