Aquafeed Vol 13 Issue 4 2021

Page 28


Novel strains of Bacillus subtilis for improving water quality and controlling pathogens in shrimp aquaculture Karthik Masagounder, Michelle Dargatz, Evonik Operations GmbH, Germany, Sarah He, Evonik (China) Co., Ltd., China

Whiteleg shrimp production has doubled in the past decade, growing from 2.6 million metric tons (mMT) to 4.97 mMT between 2010 and 2018. It had the largest share (53%) of total crustacean production (FAO, 2020) over this period too. This significant increase in production is partly because of the intensification of shrimp farming, which is gradually shifting from semi-intensive to intensive and superintensive farming. As farming practices intensify, stocking density has gone up from 50 shrimp/m2 to 200-400 shrimp/m2. Unfortunately, the rapid growth and intensification of shrimp farming create tremendous pressure on the water quality and nutrient load of the surrounding environment. Clean water is an essential resource for the sustainable growth of shrimp farming. With stocking density continuing to increase, there is an escalating challenge to maintain the ideal water quality parameters needed for healthy shrimp. Shrimp feed contains 35-45% crude protein, of which only about 35% is retained in the body. The rest is largely catabolized, contributing to nitrogen waste. One way to improve feed protein utilization is to formulate feed following the ideal protein concept. This means meeting the exact amino acid requirements of shrimp with no deficiency and no, or little, excess. In practical diets – formulated using ingredients such as fishmeal, soybean meal and wheat products – except for the first limiting amino acid, methionine (Met), the other amino acids are provided in excess

and are inevitably catabolized, contributing to nitrogen excretion. With the use of supplemental amino acids such as AQUAVI® Met-Met (DL-Methionyl DL-Methionine), Biolys® (Lysine Sulfate) and ThreAMINO® (L-Threonine) in diet formulation, we can reduce the inclusion of protein-rich ingredients, and minimize the excess levels of dietary protein or amino acid levels – still meet the requirements for all the limiting amino acids. This will increase the protein utilization to 40-45% (Nunes et al., 2019; Masagounder et al., 2021). However, while this approach can reduce the nitrogen load, there is still a lot going into the culture water which needs to be removed. Ammonia is the principal nitrogen waste product excreted by shrimp. Ammonia from the hemolymph (blood) of shrimp is largely excreted into the water across the gills via diffusion process in the form of un-ionized ammonia. Assuming 35-45% protein retention, this means, for 10 g shrimp stocked at 100/m2 in a 1 hectare (ha) pond (water depth 1 m) and fed at 3% body weight per day with a feed containing 35% crude protein, about 11,000-13,000 g ammonia per ha or 1.1-1.3 parts per million (ppm) NH3 is added into the pond every day. In other words, for every 100 kg feed, about 0.4 ppm of NH3 is added into the pond water. If this is not removed, this will quickly increase the ammonia concentration in water. As the concentration of ammonia in the water increases, the diffusion gradient

Aquafeed: Advances in Processing & Formulation Vol 13 Issue 4 2021

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