AQUACULTURE (farming of fish under controlled conditions) is a growth industry striving to satisfy a growing market for food fish. It currently is one of the fastest growing sectors of agriculture in the India. Farm-reared fresh fish is increasing in popularity and profitability. Catfish, Desi Magur, Tilapia carp and other aquatic species are fast becoming the new “cash crops”. Growing public demand for a healthy tasty and affordable food is stimulating the “boom” in this industry. The decline in wild fish populations as a result of overharvest and water pollution has promoted the culture of farm fresh that are grown in contaminant–free waters in indoor tank systems. Indoor Recirculating Aquaculture System are land-based fish farms, which allows all year round control and delivery of fish. Whether the facility will use fresh water, brackish or marine water, an R.A.S work on the same principles. The system can achieve optimal temperature and optimal stable productions all year around, independent on seasonal variation, location, climate, and environment.
New water is added to the tanks only to make up for splash out and evaporation and for that used to flush out waste materials. In contrast, many raceway system used to grow trout are termed “open” or “flow through” system because all the water makes only one pass through the tank and then is discarded. Fish grown in RAS must be supplied with all the conditions necessary to remain healthy and grow. They need a continuous supply of clean water at a temperature and dissolved oxygen content that is optimum for growth. A filtering (biofilter) system is necessary to purify the water and remove or detoxify harmful waste products and uneaten feed. The fish must be a fed a nutrionally-complete feed on a daily basis to encourage fast growth and high survival. Recirculating aquaculture system are used in home aquaria and for fish production where water exchange is limited and the use of biofiltration is required to reduce ammonia toxicity. Other types of filtration and environmental control are often also necessary to maintain clean water and provide a suitable habitat for fish, the main benefit of RAS is the ability to reduce the need for fresh, clean water while still commercial RAS must have high fish stocking densities if RAS must have high fish stocking, densities, and many researchers are currently conducting studies to determine if RAS is viable from of intensive aquaculture.
Land and built up area required based on one unit of production Capacity/Project size 50 Tons / Yearly Culture unit including culture area, feed storage, office, live fish tanks for sales, switch room etc. Little more open space will be required for toilet, overhead water tanks fish waste Pit an tank, small shed for generator, submersible pump and sidewalks. Total apx. Land area required: 100 x 200sq. ft. Area should be procted by boundary wall and gate.
In intensive fish farming operations using Recirculating aquaculture system, water is mostly re circulated there by reducing water requirement significantly but for cleaning the water a series of treatment processes is utilized to maintain water quality. These steps are often done in order or sometimes in tandem. After leaving the vessel holding fish the water is first treated for solids before entering a biofilter to convert ammonia, next degassing and oxygenation occur, often followed by heating/cooling and sterilization. Each of these processes can be completed by using a variety of different methods and equipment, but regardless all must take place to ensure a healthy environment that maximizes fish growth and health.
Biofiltration is a pollution control technique using a bioreactor containing living material to capture and biologically degrade pollutants. Common uses include processing waste water, capturing harmful chemicals or silt from surface runoff, and microbiotic oxidation of contaminants in air. All RAS relies on biofiltration to convert ammonia excreted by the fish into nitrate. Ammonia is a waste product of fish metabolism and high concentrations are toxic to most finfish. Nitrifying bacteria are chemoautotrophs that convert ammonia into nitrite then nitrate. Water is pumped through the filter, and ammonia is utilized by the bacteria for energy. Nitrate is less toxic than ammonia, and can be removed by a denitrifying biofilter or by water replacement. Stable environmental conditions and regular maintenance are required to ensure the biofilter is operating efficiently.
Removing solids reduces bacteria growth, oxygen demand, and the proliferation of disease. This is done by concentrating and flushing the solids out of the system. The simplest method for removing solids is the creation of settling basin where the relative velocity of the water is slow and particles can settle at the bottom of the tank where they are either flushed out or vacuumed out manually using a siphon. Typical RAS solids removal involves mechanical drum filter where water is run over a rotating drum screen that is periodically cleaned by pressurized spray nozzles, and the resulting slurry is treated or sent down the drain. In order to remove extremely fine particles or colloidal solids a protein fractionator may be used with or without the addition of ozone.
Fish require oxygen to metabolize food and grow, as do bacteria communities in the biofilter. Reoxygenating the system water is a crucial part to obtaining high production densities. Dissolved oxygen levels can be increased through two methods aeration and oxygenation. In aeration air is pumped through an air stone or similar device that creates small bubbles in the water column, this results in a high surface area where oxygen can dissolve into the water. In general due to slow gas dissolution rates and the high air pressure needed to create small bubbles this method is considered inefficient and the water is instead oxygenated by pumping in pure oxygen to ensure that during oxygenation all of the oxygen dissolves into the water column. Careful calculation and consideration must be given to the oxygen demand of a system, and that demand must be met with either oxygenation or aeration equipment.
pH is a measurement of the alkalinity or acidity of a substance & controlled by the addition of alkalinity in the form of lime (CaCO3) or sodium hydroxide (NaOH). The first step of nitrification in the biofilter consumes alkalinity and lowers the pH of the system. Keeping the pH in a suitable range is crucial to maintain the health of both the fish and biofilter. A low pH will lead to high levels of dissolved carbon dioxide (CO2), which can prove toxic to fish. pH can also be controlled by degassing CO2 in a packed column or with an aerator, this is necessary in intensive systems especially where oxygenation instead of aeration is used in tanks to maintain O2 levels.
Temperature is controlled through the use of submerged heaters, heat pumps, chillers, and heat exchangers. All four may be used to keep a system operating at the optimal temperature for maximizing fish production. All fish species have a preferred temperature above and below which that fish will experience negative health effects and eventually death. Warm water species such as Tilapia and Barramundi prefer 24 °C water or warmer, where as cold water species such as trout and salmon prefer water temperature below 16 °C. Temperature also plays an important role in dissolved oxygen (DO) concentrations.
Disease outbreaks occur more readily when dealing with the high fish stocking densities typically employed in intensive RAS. Outbreaks can be reduced by operating multiple independent systems with the same building and isolating water to water contact between systems by cleaning equipment and personnel that move between systems. Also the use of a Ultra Violet (UV) or ozone water treatment system reduces the number of free floating virus and bacteria in the system water. These treatment systems reduce the disease loading that occurs on stressed fish and thus reduce the chance of an outbreak.
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