Recirculating aquaculture system (RAS) is a highly promising system for intensive aquaculture. This system along with hydroponics is pertinently adopted by fish farmers today as there is a scarcity of land and water. The major issue in maintaining RAS is the feed and faecal waste, which give rise to generate dissolved and undissolved organic and inorganic load in RAS. Nitrogen (N) and phosphorous (P) in metabolic waste produced by fish are the significant dissolved waste. The suspended solids from the feed and fecal matter are the second most culprit. Both wastes are removed using different filters. Mechanical filtration combined with subsequent biological filtration is the typical strategy for managing wastes in this enclosed system. The feed used in RAS is the primary source for the release of dissolved wastes such as ammonia, nitrite, phosphate, etc. Thus, the feed should be formulated in such a way that it produces low nitrogenous and phosphorus wastes. The use of technological interventions in feed technology and the incorporation of additives to enhance feed digestibility, physical structure and protein-energy ratio should be considered while developing feed intended to use in RAS.
Recirculating aquaculture system (RAS) is an enclosed fish farming system where water is replaced only to the extent of loss caused due to evaporation and cleaning. This aquaculture system supports intensive practices with the benefits of a controlled environment, least space, and water requirement for sustained production. High production of 60 MT fish from 1/6 th ha from RAS has been reported, which is much better than the conventional aquaculture of 3-10 MT per ha (DAHDF, 2017). Feed accounts for 40-60% of the production costs in aquaculture systems, with protein sources accounting for a significant proportion of this cost (Fotedar, 2004). Usually, 80% or more of the feed is consumed, but 10 to 20% of the feed goes unconsumed and released to the culture system (Boyd and Tucker, 2014).
Almost 40% of consumed feed remains undigested and released as fecal matter. With new commercial fish feeds, fish retain only ~40 percent of the phosphorous content. In RAS, nitrogen (N) and phosphorous (P) in metabolic waste produced by fish are the origins of dissolved waste. Ribeiro (2006) demonstrated that commercial feed composition of 28% crude protein had nitrogen and phosphorus content of about 5.24% and 1.14% respectively of dry weight matter.
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Kumar Ph.D., Sikendra & Varghese, Tincy & Patel, Anusha. (2021). Agriculture Observer Dissolved Wastes in Recirculating Aquaculture System (RAS): Management through the Dietary Modifications. 2. 30-34.