Flow-through Culture(Raceways)

Production Intensity

Flow-through Culture

Advantages Disadvantages

Continual flow replaces: Oxygen Temperature

While removing: Nitrogen wastes CO2

Can support higher production levels; up to 1,000x greater than pond.

Lower concentrations of solids & nutrients in effluents.

Easier harvesting, feeding, & grading.

Large volumes of water needed.

Difficulties in cleaning.

Difficulties in removing effluents from:

High volume discharge.

Low concentration discharge.

Fish consume more food

Energy for swimming

DO must be maintained at high level.

Construction

Traditional: earthen

More recently: concrete, plastic, metal.

Indoors: temperature may be controlled.

Short-term: depuration & holdover.

Based on

Constant, large volume of H2O

100-1,000 gpm

Topography

Discharge

Site Selection

Water supply

Use large quantities of water (raceways have continual water exchange, often 2 to 10 exchanges/hr).

Gravity springs are most economical

Location

Near water supply

Topography

8-10 percent slope

18-24 inch water drop

Water Treatment

Prescreening

Aeration & removal of unwanted gases

UV sterilization

Filtration & removal of invasives

Head-water pond (settling of suspended solids)

Water Discharge

Raceways should flow into settling pond or wetland.

Regulates temperature, nitrogen, DO, escapees, but must also be managed.

Discharge is regulated for:

Solids (excess feed, waste & carcasses)

Eutrophication (N & P)

Temperature

Pesticides

Pharmaceuticals

Escapes

Solids Capture Systems

• Quiescent zone

• Full-flow settling basin

• Off-line settling basin

Types of Raceways

Single pass

Parallel – flow through one raceway (channel)

Series – flows through multiple raceways (most common)

Recirculating

Floating

Series

Single Pass Raceway

Length: width: height ratio

30:3:1 for adults

6:1:1 for fingerlings

3:1:1 for fry

Water depth not to exceed 3-4 ft.

Units are arranged as tiers with 1-2’ drop, which replaces ~50% of O2 from previous section.

Fish are sorted (youngest to oldest)

Water flows via gravity.

Baffles, quiescent zone, levees, splash boards & screening.

Self-cleaning

For Example: 120 ft x 12 ft x 4 ft

120 ft

12 ft

4 ft

Splash boards

Levee with screening

Quiescent zone

Baffles

Feeding

Multiple demand feeders or automated feeders.

Feed often (8-10 times/day) so waste does not accumulate.

Offer feed over a large area (crowded fish deplete O2; feeding fish deplete O2).

Neutral or sinking feed is best.

Aeration

Oxygen not usually a problem unless using recirculated system. Flow influences aeration:

Laminar flow (fast center, slower edges) Turbulent (lightly mixed) flow

As water flows: DO decreases Ammonia & carbon dioxide increase

Packed column Tubes “packed” with screen where water flows over screening; or

oxygen can be injected. Can be used to reduce nitrogen levels.

Harvest

Grading must be done (grading bars).

Individual growth differs

Hierarchies

Seines and/or nets (crowding to capture)

Floating Raceway System

Floating Raceway Schematic

Single channel view - direction of flow

Air lift intake pipes

Outflow screens

Construction of liner

Feeder locations Avian predator modifications

Year-round operation

High-density culturing

Water ExchangeAdjustable water velocity (m/s)

Growth of Yellow Perch Over Two Years at Cranberry Farm

Weekly Mortality and Water Temperature

Date (2003)

Jul Jul Aug Aug Sep Sep Oct Oct

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55

60

65

70

75

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Mo

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0

1

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5Temperature

Mortality Raceway #1

Mortality Raceway #2

Startup Investment

Capital investment

3-channel raceway $12,000 ($4,000 per raceway)

Barrels & docks $1,500 ($500 per raceway)

Operating expenses

Fish feed $1,250 / 80,000 perch for 6 months

Electricity $800 / year

Labor $7,000 / year

Yellow perch fingerlings $12,350 / 80,000 perch

Paddlewheel

Settling chamber

Algae biofilter

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Partitioned Aquaculture System (PAS)

Partitioned Aquaculture System

Factors in PAS

• Waste treatment reservoir must be shallow (30-60 cm)

• Need green algae in constant growth phase

• Solid waste removal

• Predator exclusion

• Winter / freezing

• Ratio of pond sizes:

– Fish production 5% of water treatment

Split-Pond Culture