Re-circulating Aquaculture Systems (RAS): Bio-security for Fish Rearing

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Dr ASHFAUQ FAROOQ AGA

Man, while he ‘domesticated’ many animals and plants, left the fish out – the carps and the trout are relatively very recent attempts. The neglect of fish perhaps mainly owed to man’s unfamiliarity with the water environment; what is under water is not easily seen. Man could commune with his terrestrial cohabitants and make them his pets and beasts of burden. He could watch his land live-stock and easily recognize a sick cow or chicken. Even when an attempt is made to learn how the fish performed, he could not comprehend it easily. The air he breathes is so thin, same as that for the cow and the chicken, whereas the water used for breathing by fish is so heavy and contains so little of oxygen, that man could not feel the “pain” of the fish to extract the life giving gas, which looms as it were as the perennial risk of the denizens of water.
Add to it the loose though expansive membrane with many holes and slots, spread on the breathing apparatus of the fish. Fish have to fight continuously against loss and gain of some of their body contents through their gill surfaces, at times pitiably difficult. The major task for the aqua-culturist is to breach this gap in knowledge to know his animal before he really succeeds in rearing it to his advantage. He has to know the biological characteristics and potentials of the aquatic organism he wants to grow and also the nature of its environment, that is, the physics, chemistry and biology of its ambient medium.
Look at the fish in the wild – try to capture them; it is difficult, but much easier than to rear them to adult size and make them reproduce, under controlled conditions. A fish pond, a race way, a cage or pen is only an extension of this concept but the problem becomes more complex. Freshwater fisheries are often far from the public gaze and are therefore overlooked. The challenge of providing answers to how water resources for fisheries might be managed most efficiently is complicated because it is not just the quantity of water available over the course of a year that is important, but the timing of peak and minimum flows, and also water quality. Fish breeding and feeding depend on flows, and flow velocity can also be crucial to survival. Instead, we usually observe in culture tanks that there is Effluent High concentrations of suspended and dissolved solids ,high ammonia levels, high concentration of CO2 ,low levels of dissolved oxygen.
Re-circulating Aquaculture is a technique for raising water borne animals in a closed (usually indoor) system which minimizes water consumption, provides maximum control of the livestock’s environment, and reduces the risk of exposure to parasites, disease, and predators High Density Re-circulating Aquaculture System (HDRAS) is a system in which aquatic organisms are cultured in water which is serially reconditioned and reused. Closed-system aquaculture presents a new and expanding commercial opportunity. Re-circulating aquaculture systems (RAS) are tank-based systems in which fish can be grown at high density under controlled environmental conditions. They are closed-loop facilities that retain and treat the water within the system.
In RAS, water flows from a fish tank through a treatment process and is then returned to the tank, hence the term re-circulating aquaculture systems. RAS can be designed to be very environmentally sustainable, using 90-99 percent less water than other aquaculture systems. RAS can reduce the discharge of waste, the need for antibiotics or chemicals used to combat disease, and fish and parasite escapes. In aquaculture, RAS is refining techniques and methods to increase production, profit and environmental sustainability.
Bio-security Hatcheries with RAS facility are often fully closed and entirely controlled, making them mostly bio-secure – diseases and parasites cannot often get in. Bio-security means RAS can continuously operate without any chemicals, drugs or antibiotics. Water supply is a regular route of pathogen entry, so RAS water is often first disinfected or the water is obtained from a source that does not contain fish or invertebrates that could be pathogen carriers.
Why Re-circulate?
We conserve water, permit high density culture in locations where space and or water are limiting. It minimizes volume of effluent, facilitating waste recovery, allows for increased control over the culture environment, especially indoors, improved bio-security and environmentally sustainable
Re-circulating System Applications
Brood stock maturation, Larval rearing systems, Nursery systems, Nutrition and health, research systems, Short-term holding systems, Ornamental and display tanks, High density grow out of food fish and most frequently used for breeding purposes
The fish cannot wink, but can watch you with its un-shut eye and lead you to a world of its own; man can benefit by it. This is aquaculture.

—The author can be reached at: [email protected]

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