MECHANISM OF RECIRCULATING AQUACULTURE SYSTEM (RAS)

Mechanism or Working of Recirculating Aquaculture System (RAS)

In a Recirculation Aquaculture System  the water is treated continuously to remove the waste products excreted by the fish, and oxygen is added to keep the fish alive and well. From the outlet of the fish tanks the water flows to a mechanical filter and further on to a biological filter before it is aerated and stripped of carbon dioxide and returned to the fish tanks. This is the basic principle of Recirculation Aquaculture System.

Several other facilities can be added, such as oxygenation with pure oxygen, ultraviolet light or ozone disinfection, automatic pH regulation, heat exchanging, denitrification, etc. depending on the exact requirements. Fish in a fish farm require feeding several times a day. The feed is eaten and digested by the fish and is used in the fish metabolism supplying energy and nourishment for growth and other physiological processes. Oxygen enters through the gills, and is needed to produce energy and to break down protein, whereby carbon dioxide and ammonia are produced as waste products. Undigested feed is excreted into the water as faeces, termed suspended solids (SS) and organic matter. Carbon dioxide and ammonia are excreted from the gills into the water. Thus fish consume oxygen and feed, and as a result the

Water in the system is polluted with faeces, carbon dioxide and ammonia. Only dry feed can be recommended for use in a recirculation system. The use of trash fish in any form must be avoided as it will pollute the system heavily and infection with diseases is very likely. Dry feed is delivered in different pellet sizes suitable for any fish stage, brood stock, grow-out, etc.

In a Recirculation System, a high utilization rate of the feed is beneficial as this will minimize the amount of excretion products thus lowering the impact on the water treatment system. In a professionally managed system, all the feed added will be eaten keeping the amount of uneaten feed to a minimum. Uneaten feed is a waste of money and results in an unnecessary load on the filter system.  The composition of such feeds aims at maximizing the uptake of protein in the fish thus minimizing the excretion of ammonia into the water.

flow diagram of RAS

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