In fish culture, raceways are enclosed channel systems with relatively high rates of moving or flowing water. This high rate of water movement gives raceway systems distinct advantages over the other culture systems. Stocking densities for raceways are usually higher than other available culture systems. Densities of 10 to 15 fish per cubic foot are not unusual for raceway systems. The Pond Raceways consists of rectangular boxes that can be constructed in various sizes and from several types of materials depending on the intended use. It is a system just like the cage construction that could be adopted to almost any body of water but with the advantage of controlled water movement to improve the water quality and allow for increased stocking density thereby increasing total production per unit area.
The most important factor to be considered in site selection is the source of water supply.For running water system, water supply must be sufficient throughout the year. Another important thing that must be taken care of is that the supplied water have to be free from pollution either of agricultural wastes (pesticides) or industrial wastes.
The best area for a running water fishpond is a ground with slight slope or flat. The optimal slope between 0.5 and 1 percent is preferred for raceways so that water flowing from one end can be removed from the other. The site must be near the source of water. A suitable site should be free from the occurrence of flood water, landslides and typhoons.
A raceway is most often a rectangular canal or tank with a water current flowing from a supply end to an exit end. The length to width ratio is important in raceways and a ratio of 6:1 (minimum) or 10:1 (maximum) is recommended.This prevents the fish stock from swimming in circular movements, which would cause debris to build up in the centre. If the width is too large this could result in a feeble (slow) current speed which is not desirable. Each segment of a raceway is of about 30m long (Length); 2.5 – 3m wide (Width) and 1-1.2m deep (Depth). These are rectangular, triangular, oval or hexagonal in shape.
Fish stocking density of 30 to 50 kg/m3 are normal in raceways, while for marine species, such as sea bass and sea bream, it is between 15 and 20 kg/m3.
In raceway culture, fishes are dependent on a prepared diet for all of their nutritional needs. Therefore, feeds for intensive fish culture should be totally balanced with higher protein content and with complete vitamin and mineral supplements. Since raceways are flowing water systems, feeds not directly used by the fish are lost from the system. Installation of feeding rings or temporarily stopping water exchange may be considered to avoid food quickly flushing out from the system.
Three sizes of different raceway ponds are available. They are used for fry culture, brood stock maintenance and for production of marketable fish. The raceways for fry production have a culture depth of 30cm with a bottom slope of 1/100 or more, while those for production of marketable fish have a depth of 60cm with a similar bottom slope. The raceways for brood stocks are about 90 cm in depth. The outlets of the raceways are screened to avoid escape of fish.
Harvesting is easy with minimum labour and effort and with minimal damage to the fish. Accomplished by pulling a seine from one end of the raceway to the other, crowding the fish into a small area where they can be netted. Automated harvesting screens or grader bars are also used which allow smaller fish to escape from the crowing area and are left to grow further.
Jorhat, PIN - 785013 Assam