Raceway culture for Freshwater Species  

Raceway is based on the continuous water flowing through the culture tanks. The culture density is directly dependent on the culture water flowing through the system. Because the water sources supporting the system normally come from streams or springs water which are colder than lakes or rivers, the system targets cold water fishes, mostly rainbow trouts in Korea. One of the most important parameters is a diet. The diet should be totally balanced.

Raceway Structures

The basic structure of raceways should be designed in a way where none of the parts of culture waters are stagnant in the tanks, otherwise debris or feces are accumulated in locations, deteriorating water quality or further causing outbreaks of disease in the system. The raceways operated in Korea are most made of concrete, but a few are of other materials such as stone, earth, and fiberglass. The primary factor affecting raceway construction is water sources available. When water sources available are much enough to support all the system, the raceways can be located in a way across the water current. However, the raceways are to locate along the water current in case that water sources are to be a limiting factor to the system operation.

Two different types raceway are operated for rainbow trouts in Korea; raceway ponds and concrete silos.

Raceway pond

Three size-different raceway ponds are available, one for fry culture and the other for production of marketable trouts. 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 trout have a depth of 60cm with a similar bottom slope. The raceways for broodstocks is about 90cm in depth. The outlets of the raceways are screened to avoid of trout escape. The screen with larger mesh sizes are preferred within the size permits. The widths of the raceways are 1.5m for fry and 3m or less for growing trouts. The lengths of the raceway are 10 to 30m. A number of pond units may be constructed together in which volumes of water flow via gravity through a series of raceways and are discharged into a receiving stream with little or no wastewater treatment. Aeration occurs between raceways as the water flows over a screened outfall and pours into the head of the raceway below.

Concrete silo

The concrete silos used for trout vary from 2 to 10 m in diameter, depending on the trout sizes cultured. The concrete silos are constructed with bottom slopes of 5∼10% to remove solid waste before water is discharged. The water from inlets is designed to be a driving force to circulate the water in the silo, allowing the solid wastes removed through the outlet located in the center of the silo. The silos for seed production of trouts are small-sized (less than 1m in diameter) are often of FRP (fiberglass reinforced plastics).

System operation for trout aquaculture

In the raceway system, the fish need more oxygen concentrations and produce more waste products as they grow. Therefore, the fish need bigger ponds as they grow. Water is also exchanged at higher rates to maintain optimal quality and oxygen level the fish need. Followings are required for the operation of the system for trout aquaculture:

(1) Aerations

In any case water qualities are never better than those of the incoming water, but dissolved oxygen may be increased by aeration using some aerating machines, including pumps, agitators, and blowers).

(2) Removal of solid waste matters

Accumulation of waste matters in the raceway bottom spoils water quality, therefore successful removal of the waster matters is essential. Removal of the waste matters is achieved by sucking the matters directly with the aid of pumping machine or it can be performed by increasing water flow in the raceways. Normally, water velocities over 7∼8cm/sec are found to be effective for the waste removal in our system. Lowered water level down to 30 cm in depth makes the removal more effective. The waste matters accumulated in the raceway bottom should  be pumped out.

(3) Productivity

Productivity of fish is strongly related with exchanging rate of the culture water. For rainbow trout, it amounts 1㎏/year under water flowing rate of  1ℓ/min. However, the productivity increases up to 5kg/year under same water flowing rate in case that best management is offered.

(4) Waste water treatment

Waste water treatment is one of the crucial factors in the raceway operation. Because only 20∼30% of total phosphorus supplied to the culture system are absorbed by the culture fish, appropriate treatment of the waste water is required. Bad treatment of the waste water often results in outbreaks of red tide in the reservoirs or rivers, causing a significant social problems.

The government enforced a new regulation dealing with waste waters coming from raceways in 1999. According to the new regulation, all the farms should prepare a facility for waste water treatment, covering 20% of total farming areas. More strict regulation will be enforced on the waste water treatment in the near future in terms of BOD and SS. This regulation is to keep the freshwater environment from being polluted.