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.
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.
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.
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).
The raceway ponds set together for the trout culture.
The concrete silos normally used for the seed production/fry
culture of trouts.
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:
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).
Aeration by pumping of the culture water in the trout
Aeration by water agitators in the trout raceways.
(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.
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
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.
Aeration by compressors in the trout aquaculture raceways.
Raceway bottoms are regularly cleaned by total water
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.