Background:
Dissolved oxygen is the single most important factor governing the survival and growth of fish in the intensive and semi-intensive culture systems. Feed intake and growth of fish are adversely affected when dissolved oxygen (DO) level becomes low. If DO levels remain low for prolonged periods, fish become susceptible to disease and entire stocks in the pond may be lost due to lack of oxygen.
Technology Details:
Aeration becomes necessary to supplement natural sources of dissolved oxygen in ponds stocked at higher stocking densities. A large number of aeration devices are used. Besides the paddlewheel aerators which are most commonly used in shallow ponds for marine shrimp in the coastal areas, diffused air systems and aspirator pumps, etc. are also used. However, all the existing models of aerators are run with electricity and are stationary. In the countryside, where fish farms are mostly located, the electric supply is either non-existent or highly uncertain. Keeping in mind the erratic power supply, a diesel operated aerator has been developed. Since, it is a mobile aerator, by using an indigenously made bottom racker, it can rack/ disturb the bottom and releases many obnoxious gases deposited in the pond bottom during the culture period. The aerator comprises a 3/3" (air suction and delivery) 990 rpm blower, which is coupled with an 8 HP diesel engine. The water pump of the diesel engine sucks pond water through 4 feet long (4") diameter filter type suction pipe. Water from the pump is thrown towards the rear end of the platform through 6 feet long (3" diameter) rigid PVC pipe. Both the components are mounted on a wooden platform. The wooden planks are screwed tightly to an angle iron frame (12’ x 11’). The entire unit is kept floating using 6 numbers of 250 litre empty HDPE cylindrical barrels (6 on each side). Another barrel is fixed below the water pumps for providing additional support. Air from the blower is taken towards the front side of the platform through 5 feet long 4” diameter cast iron pipe from where it is taken to the pond bottom through 4 numbers flexible pipe (15’ x 1.0" diameter). 4 feet galvanized iron (1.0" diameter) pipe is fitted at right angles at the end of each flexible pipe. Narrow holes at an equidistance of 6” are made in each of the GI pipes. Galvanized iron as well as the flexible pipes can be lowered or raised to any desired level with the help of strong nylon ropes.For bottom racking, a 10 feet angle iron (3/3") with hooks is also attached to the unit. Through clamps on either side of the platform, the bottom racker is hung using two iron wires (12’ each). The racker can be lifted when the racker is not used. A small hull is provided at the rear end for taking the unit to any desired location of the pond.