Aquaculture Production System (j.colt, 1991)

Aquacultural production systems J. Colt J Anim Sci 1991. 69:4183-4192.

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AQUACULTURAL PRODUCTION SYSTEMS’ John Colt James M. Montgomery, Consulting Engineers, Bellevug, WA 98005 ABSTRACT

The wide range of species reared, species requirements, water resources, and regional preferences create the need for a wide variety of aquaculture production systems. Factors such as the interaction between water temperature and water quality and the feeding, growth, and survival of aquatic species cause the design of aquatic production systems to be much more location-specific and site-specific than the designs of systems for terrestrial animal agriculture. Economic and regulatory pressures are continuing to change the characteristics of aquatic production systems. Key Words: Aquaculture, Systems, Design, Environmental Control, Aquatic Environment J. Anim. Sci. 1991. 69:41834192

Classification.The simplest type of system is the static pond (Figure la), and it is Current aquatic animal culture in North commonly used for channel catfish. Under America is estimated at 500,000 t (Nash and normal operating conditions, water is added to Kensler, 1990). Major groups are channel make up evaporation and Sitration losses. catfish, trout and salmon, crayfish, and oysters. Trout and salmon are typically reared in flowMinor species include such diverse groups as through systems at high density (Figure lb) frogs, turtles, alligators, sea-squirts, abalone, using large water flows to remove metabolic sturgeon, striped bass, and redfish. A wide wastes. Commonly, pretreatment is required to variety of production systems are used in remove suspended solids, iron or manganese, aquaculture. This paper presents basic informa- nitrogen and carbon dioxide gases, or to add tion on the characteristics of impor&ant produc- oxygen (Figure IC). Environmental regulations tion systems, their limitations, and future typically require some type of posttreatment trends in system development. Emphasis is before discharge cl;“igure IC). In areas of placed on commercial systems used in the limited water, the water may be treated to United States. remove metabolic wastes and reused (Figure Id). This type of system is called a reuse, recycle or closed system. Hybrid pond systems Aquatic Productlon Systems (Figure le) using ponds and algae or aquatic Aquatic production systems are typically macrophytes (water hyacinths, cattails, Ulva, classified according to type, biomass density, etc.) are being developed for warm-water and feeding practices. Division based on water aquaculture. A cage system can be considered flow provides a fundamentally more useful a flow-through system (Figure lf), although in way of describing water quality processes that areas with restricted flushing, the system may control production (Krom et al., 1989). function as a reuse system with minimal treatment of the water. Using the nomenclature developed by chemical engineers, the hydraulic mixing charl~cscnteci at a symposium titled “Aqwwulture in acteristics of the different types of culture Animal Science” at the ASAS 82nd h u . Mtg., Ames. systems can be classified into three groups: IA. plug-flow reactor (PFR), continuous-flow 22375 130th Avenue NE, Suite 200. stirred tank reactor (CFSTR), or arbitrary flow Received August 27, 1990. Accepted April IS, 1991. reactor (AFR). Introduction

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To Atmosphere

(4

4

v

m

I

4

4 0

Bilogical Filtration

*

Solids Removal

I

figure 1. Water flow in aquatic culture systems: (a) static system, @) flow-through system, (c) flw-through witb pretreatment and posttnamcnt, (d) reuse system, (e) reuse system wing natural p m m , and (0 cagc system.

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Length from Head of Raceway

Dischange Influent water

I, I - *

Length Across Circular Tank

Distance from Water Surface Figure 2. Hydyraulic miXing characteristics of aquatic culture systems: (a) raceway, @) circular tank, and (c) pond.

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In an ideal PFR, the water moves through the rearing unit as a plug of water with no longitudinal mixing. As a result, the concentration of metabolic wastes such as ammonia increases linearly along the longitudinal direction (Figure 2a). The common raceway used to rear salmon and trout approximates a PFR. In an ideal CFSTR, the contents of the rearing unit are well-mixed and the effluent concentration of a metabolic waste such as ammonia is equal to the bulk concentration in the rearing unit (Figure 2b). The circular tank approximates a CFSTR. The lack of a gradient in a CFSTR has important advantages in highintensity systems (Colt and Watten, 1988). In ponds, thermal heating, photosynthesis, chemical reactions in the sediment, and wind action produce an AFR that is either a PFR or a CFSTR. Many of these processes tend to result in thermal and chemical stratification in the vertical direction (Figure 2c). Wind action will tend to mix the pond but may result in significant horizontal gradients. Although it is necessary to use some type of classification as a basis for discussion, it is important to note that many graduations and combinations exist. Few simple flow-through systems exist, and some type of pretreatment and posttreatment is typically needed. Based on fundamental water treatment processes, a pond system should be classified as a reuse system. Pelfonnance Criteria. Compared to other types of animal agriculture, aquaculture systems are described in different terms. Some of the more common terms are listed below: D, =

E A

D, = V L = M -

Exc =

Q

.o64

e,=-

V V

1.444

where Da = areal density of culture animal (kg/ m2 of rearing area), M = mass of culture animal (kg), A = area of rearing unit (m2), D = volumetric density of culture animal (kg/mil of rearing volume), V = volume of rearing unit (m3), L = loading (kgfliters per min), Q = flow to rearing unit (litershin), Exc = water

1000 g Feed

\

\

250 g 0 1 340 g CO?

30 g Ammonia

500 g Fecal Solids

’”

Figure 3. Waste outpat of fish consuming 1 kg of feed

arad 250 g of oxygea.

exchange rate (rearing unit volumes/h), = mean hydraulic detention time (d), COC = cumulative oxygen consumption (mgfliter), DOi, = influent dissolved oxygen (mg/liter), and DOout = effluent dissolved oxygen ( m u liter). System Characteristics. Based on m n t commercial production in the United States, the system characteristics of typical production systems are presented in Table 1. Ponds and flow-through systems account for the majority of commexial facilities. Although there are a number of more complex reuse systems built in the past years, their contribution to commercial production is very limited at this time. Environmental Quallty Management

In Aquatlc Systems

The c u l m of aquatic animals is fundamentally different from most conventional forms of animal agriculture. First, the animals are temperature conformers and, as a result, temperature has a major effect on metabolic processes such as feeding, growth, and reproduction. Second, environmental quality is more important because feed, dissolved oxygen, and metabolic wastes are all contained or transmitted through the liquid phase. As a result, culture practices and metabolic activities are tightly interrelated. For example, overfeedjng in ponds and the resulting oxygen demand can decrease the dissolved oxygen to lethal levels. Zmpact of Culture Animals on Water Quality. The metabolic activities of culture animals result in significant changes in water quality. For fed fish, some of the most important metabolic processes are shown in Figure 3. The ammonia excretion, oxygen consumption, and carbon dioxide excretion rate show a significant daily fluctuation, depending primarily on the time of feeding.

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AQUACULTURAL PRODUCTION SYSTEMS

TABLE 1. CHARACTERISTICS OF COMMON AQUATIC PRODUCTION SYSTEMS USED IN THE UNITED STATES Hydraulic detentiontime, d

system type

~~

Unfed, monoculture Fertihed, polyculture

Fed.no aeration Fed, aeration

Density,

m3

Loading.

Annual production,

k@literspermin

Lgma

Common species

~

100-300 100-300 100-300 100-200

.03-.05 s.7 .2-.3

-

3-1.0

-

300-500 5,000-7,000 2,000-3.000 3.000-10,OOO

-

-

Channel catfish Chinese carps channel catfish Channel catfsh

Cages Freshwater Marine

.02-.04 .00&.010

100-200 50-100

No aeration Aeration Pure oxygen

.oW-.014

014-.020 .mo-.040

15-30 20-40 30-50

Aeration

.014-.020

30-50

Pure Oxygen

.020-.040

40-80

-

2.000-3,000 2,000.000 Flow-through (cold water) "5-2 1-3 2-6 Flow-through (warm water) 2-4

3-8

Channel catfish

Salmon

-

Salmon and trout Salmon and trout Salmon and irout

-

Channel catfish striped bass hybrids

-

Tilapia

Reuse

Mechanical

-

Ecoloaical

014-.030 .~ . ~ .Mo-.040

.

20-50 10-20

With the exception of pond systems, the water quality changes due to the culture animals can be computed from the application of mass balance principles using the metabolic characteristics of the culture animals. In ponds, the water quality is driven by the metabolic activity of microalgae and bacteria. Water Quality Requirements. Water quality criteria for typical cold and warmwater fish are presented in Table 2. The concentrations of calcium, heavy metals (copper, zinc, lead,

2-4 4-8

Salmon and trout

mercury, etc.), toxic compounds. and biocides may be important under some conditions. Physical Requirements. Some species and life stages may have special requirements such as substrate, hiding places, or specific light levels. These requirements are typically more critical during broodstock maturation, egg development, and early fry rearhg. Density and Density-Loading Interactions. Criteria for volumetric and areal densities are influenced by the animals' response to crowd-

TABLE 2. CRITICAL WATER QUALITY CRITERLA FOR AQUATIC SYSTEMS Cold water

W m

Trait

Ammonia N, pg/liter as NH3 Nitrite N, mglliter Nitrate N, mg/liter Dissolved oxygen, mgAiter Dissolved oxygen,mm Hg Gas supersaturation,mm Hg Hydrogen sulfide, peter Carbon dioxide, m t e r Residual chlorine, pghter PH Temperature, 'C Iron,mgllitex Manganese, mg/liter

loto 15 .1 > 100 6to7 300 10 to 20 1 10 to 20 2 6.5 to 8.5 Depends on species and age < 1 (Incubation) < l(kubation)

20 to 30 1.0 > 1,Ooo 3 to 4 300 30 to 40 2 20 to 40 10 6.0 to 10.0 Depends on species and age

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water

-

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permits include the following types: county building permits and zoning regulations, regional management agencies, state fish and game agencies, water rights, waste discharge, navigation, dredging or filling in wetlands, and lease for the use of public land. Design Basis. Before the start of detailed design, it is necessary to define the process criteria for both the species and system components or culture steps. This includes such items as data on growth rate, fecundity, and survival and water quality criteria. Even for widely cultured animals, much of this information is not readily available in conSystem Design venient form. Additional information on Because of the impact of temperature on detailed design of aquatic systems can be animal growth, the available locations for the found in the publications by Huguenin and culture of a particular species are more limited Colt (1989) and Wheaton (1977). In flow-through and reuse systems, the than for terrestrial animal agriculture. In addition, water quality problems such as low computation of required water flow can be dissolved oxygen, high concentrations of nitro- computed from a mass balance approach. gen gas or carbon dioxide, or dissolved Commonly, it is assumed that dissolved compounds may require pretreatment at a oxygen is the most limiting factor in these systems. In high-intensity systems, the limiting given site. Sire Selection. Ideally, the site should be water quality factor can also be ammonia, selected by means of a thorough site recon- carbon dioxide, or pH. The degree of intensity naissance and selection process (Webber, in these types of systems is more accurately 1971). Important factors in site selection measured by the cumulative oxygen consumpinclude physical, climatic, and biological com- tion (COC) through the system (Meade, 1988). ponents, as well as social, legal, and economic The effect of excreted carbon dioxide on pH aspects. In many private and public projects and ammonia cannot be ignored (Colt and the site selection process is very abbreviated Orwicz, 1991). For a flow-through system because the site options are either few or the without aeration, the most limiting factor is pH site is already determined at the start. Trying to at low pHs, dissolved oxygen at intermediate design a culture system for a site chosen for pHs, and un-ionized ammonia at high pHs reasons independent of technical considera- (Figure 4a). In systems using pure oxygen, tions may prove to be very expensive or even carbon dioxide can become limiting at interimpossible. One reason for the construction of mediate pHs (Figure 4b). In an open system in several commercial-sized reuse systems has which oxygen and carbon dioxide can be been the realization after the completion of the exchanged across the air-water interface, unsite selection process that water was very ionized ammonia is the most limiting factor (Figure 4c). The use of power plant effluent to limited or of unusable quality. Permits. The time and expense of obtaining accelerate the growth of warmwater fish has all the necessary permits for a given project attracted significant research and pilot-scale may have a significant impact on the feasibil- money fliews, 1981). This type of culture ity of the whole project, especially in the system has proven to be largely unsuccessful, marine area or in “wetlands.” The actual cost primarily because of operational and manage of the permits themselves is typically low. The ment problems. With a few notable exceptions, major costs associated with the permitting the use of geothermal waters has also been process are indirect costs (Bowden, 1981), unsuccessful. such as costs associated with time delays and Although ponds seem to be a simple increased financial uncertainty. The total cost production system, the complex interactions of obtaining permits for marine aquaculture in between the culture animals, algae, zooplankCalifornia may constitute up to 5.7% of the ton, bacteria, and physical and chemical total project costs (Bowden, 1981). Common processes are not fully understood. As a result, ing and water quality. When water quality is not limiting, some of the most commonly reared animals can be cultured at densities in the range of 100 to 200 kg/m3. The effects of density and loading are confounded in many “density” studies. When water flow remains constant, increasing density increases both density and loading. The two parameters are related by L = .06Dv/Exc. Densities as high as 540 kg/m3 have been achieved in experimental salmonid culture (Buss et al., 1970) by increasing the exchanges to 50h.

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AQUACULTURAL PRODUCTION SYSTEMS 16

. (a)

14

-

12

-

10

-

PH

8-

6-

Limited Region

I I I I I I I I I I I I I I I I I I

I I I I I

Oxygen Limited Region

I I I I

I I

I I I I I I I I I

I I I I

4-

-

Ammonia Limited Kegion

I

6

7

8

9

PH

Figure 4. Overall cumulative oxygen consumption as a function of equilibrium p H (a) closed system with no gas transfer, (b) closed system with pure oxygen addition, and (c) open system with no loss of ammonia (water temperature = 15'C. barometric pressure = 760 mm Hg,intluent dissolved oxygen = 90% of saturation, influent carbon dioxide = 100% of saturation, an-ionized ammonia criteria = 12.5 @iter NH3. dissolved oxygen criteria = 6.5 mg/liter, pH &tax = 6.0, and carbon dioxide criteria = 20 @ter).

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the design and operation of ponds are based largely on empirical information. Depletion of dissolved oxygen is a serious problem in many pond systems and may be caused by a) daily fluctuations in dissolved oxygen due to photosynthesis and respiration or b) the sudden dieoff of algae. In channel catfish ponds in the southern United States, mechanical aeration is typically required when the daily feed input exceeds 40 to 50 kgha (Tucker et al., 1979). Operational problems with ponds also include high pHs and off-flavor. Cages and netpens depend on natural flushing to remove metabolic waste products and to supply dissolved oxygen. An ideal location for marine cages is an area with good flushing that is protected from extreme wind and wave action. A number of rugged offshore cages and netpens have recently been developed and may allow sitting away from pollution and developed shorelines. Fouling of nets in the marine environment can be a serious problem and requires frequent changing of nets. In the United States, legal restrictions on the use of cages and netpens and local opposition by adjacent property owners are serious impediments to their use. When cages are placed in static freshwater, production cannot be increased beyond that for a static pond without producing adverse water quality changes. Reuse systems potentially can be sited in areas with inadequate water resources or close to markets. They have great appeal to venture capitalists, business school graduates, and entrepreneurs, and also to shysters. Compared to pond or flow-through systems, reuse systems have significantly higher capital and operating costs (Muir, 1981). The successful economic use of reuse systems for the production of food animals in the United States remains to be demonstrated. Reuse systems seem to have their best potential for research systems, larval rearing systems, and highpriced specialty products such as tropical and ornamental fish. Size and Number of Rearing Units. The size of rearing units is usually a trade-off between decreased cost per unit volume (or surface area) vs diseconomies resulting from the greater operational difficulties and decreased efficiencies often associated with larger units (Huguenin and Colt, 1986). Increasing rearing unit size may also allow the efficient and advantageous use of expensive equipment. Another set of important considerations in

determining rearing unit size involves the operational advantages of having multiple independent units. These advantages may result from increased flexibility to meet marketing requirements and decreased consequence of individual failures. Material SeZection. The design of commercial aquatic culture systems involves serious material selection problems, especially in the marine area. This involves not only structural problems resulting from fouling, boring animals, and corrosion, but also the effects of metals and organic compounds leaching from materials or the adsorption of materials from the water. Many of the common plastic and rubber products may be toxic, at least initially, to sensitive species. Reliability. Reliability is a key concern in the design of aquatic culture systems. Intermption of the water or air supply for 1 to 6 h may result in total mortality in flow-through or recycle systems. On a yearly basis, the system reliability can be better than 99.9% but still result in dead animals. Operational problem areas tend to arise from two sources (Huguenin and Colt, 1989). One source is internal problems resulting from design errors or inadequate operating procedures and includes problems arising from material selection, use of chlorine, gas supersaturation, and monitoring and control limitations. Another source of problems is climate or weather-induced failures (Table 3) that are external to the facility. A good review of types of failures and emergency procedures can be found in the publication of Shepherd and Moms (1987). In some systems it may be necessary to provide secondary water sources, standby generators to power pumps and blowers, and a variety of alarms, phone dialers, and automatic control. Future Trends Increasing production costs and resource limitations create a strong pressure for the development of more cost- and watereffective production systems. In warm-water ponds, there is a trend toward the use of aeration to prevent oxygen depletion problems. Continuous aeration with electric paddlewheels is more economic than tractor-powered emergency units (Engle and Hatch, 1988). A number of potentially more efficient aerators for pond systems are currently under development. The intensity of flow-through systems is

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AQUACIXTURAL PRODUCTION SYSTEMS

increasing through the use of aeration and reuse of the water. The use of supplemental pure oxygen is becoming more common in both private and public sector facilities (Colt and Watten, 1988). A number of advanced reuse systems based on European technology have been constructed in the United States in the past several years. This construction and other factors have renewed interest in reuse systems. Further development in reuse technol-

ogy will result from this interest. Based on encouraging results in Israel, systematic r e search on the use of ecologically based pond/ reuse systems has started. These systems use natural pixesses such as algal uptake, photosynthesis, and bacterial activity to remove metabolic wastes and add dissolved oxygen and may have significantly lower capital and operating costs than conventional reuse systems. The integration of flow-through and

TABLE 3. CLIMATE- OR WEATHER-INDUCED SYSTEM FAILURES ~~

Component

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Impacts

Intake structures Biofouling of intake Clogging of intake structure due to debris Damage to intake structure due to ice, rocks,or floating debris Intake screen collapse due to clogging and pressure drop Wave damage Scouring (under mining) or deposition due to water currents Collision (anchors, boats, fuhing gear) damage Piping Clogging due to biofouling Collision damage inadequate burial and being run over by moving vehicle Gunshot damage Erosion due to enhainment of abrasive particles in water Ground movement or earth slides Earthquake damage Stom waves and current depositingintake piping 011 beach

Pumps and motor Gunshotdamage Loss of eleceical power or loss of one leg in three-phase powex Poor regulation of frequency or voltage Power transients Poor alignment of motor, sbafts, and pumps Debris lodged in impeller or against the shaft Cavitation due to blockage of suction lines Flooding of controls Inadequate lubrication or maintenance Corrosion Overspeed due to being run dry Overheating due to being run against a closed valve Blowers

Flooding with water when shut down Excessive pressure resulting in surging Electrical supply

Tree or animaldamage to power lines Flooding of conduit and shorting of lines Wind or storm damage to power lines Culture systems Foulii of valves, drains, and pipes due to biofouling or silt Collapse damage Excessive freshwater or waste water M o w Earthquake damage Sinking of criticalfloating componentsdue to biofoulii Direct wave damage including breaching of dikes Excessive higbwater due to storms and flooding Clogging of fiters and other equipment due to storm-related turbidity Loss of temperature control due to storm efftxts Oxygen depletion resulting from several days of cloud cover

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pond system with conventional agriculture may have the potential to expand aquacultural production in areas of limited water. Two regulatory areas will have a major impact on aquatic system design and operation. Following the lead of Europe, stricter limits on the discharge of nutrients, solids, organic compounds, and therapeutics are being a p plied. Flow-through systems are the most affected by these regulations. Control of bird predation in ponds is becoming more difficult because of restrictions on the use of lethal control measures. The impact of these two regulatory areas coupled with economic pressures will tend to change significantly the characteristics of aquatic production systems in the United States. Implications

New and more intensive types of aquatic production systems are being driven by economic and regulatory pressure. Advances in aquaculture and aquacultural production systems will be based on a fundamental understanding of the physiological, nutritional, and behavioral requirements of the culture animals. The ability to predict reliably the interaction between the culture animal and the physical, chemical, and biological environment will be needed for design and operation. Long-term fundamental and applied research at the regional and national level is needed to accelerate aquacultural development. Literature Clted

Bowden, G. 1981. Coastal AquaculturalLaw and Policy: A Case Study of California. Westview Press, Boulder,

co. Buss, K., D. R.Graff and E. R Miller. 1970.Trout culture in vertical units. Rog. Fish-Cult. 32187. Colt, J. and K.Orwicz. 1991. Modeling production capacity of aquaticculturesystemsunder freshwater conditions.

Aquacult.

Ew. rn P S S ) .

Colt, J. and B.Wattcn. 1988. Application of pure oxygen in fish culture. Aquacult. Eng. 7:397. Engle, C. R and U. Hatch. 1988. Economic assessment of altexnative aquaculture aeration strategies. J. World Mar. Soc. 19:85. HuguCnin, J. E.and J. Colt. 1986. Applicationof aquaculture technology. In: M. Bilio, H. Rosenthal and C. I. Siden!iarur (Ed.) Realism in Aquaculture: Achievements, Constraints, Perspectives. pp 495-516. European Aquacult. Society, Bredene, Belgium. Huguenin, J. E. and 1. Colt. 1989. Design and Operating Guide for Aquaculture Seawater Systems. Elsevier, Amsterdam, Netherlands. Krom, M.D., A. Neori and J. van Rim. 1989. Importanceof water flow rate in controlling water quality processes in marine and freshwater fish ponds.Bamidgeh 41:23. Meade, J. W. 1988. A bioassay for production assessment. Aquacult. Fing. 7:139. Muir, J. P. 1981. hbnagement and cost implications in recirculating water systems. In: L. I. Allen and E. Kinney (Ed) Bio-engineering Symposium for Fish Culture. pp 11G127. Am. Fisheries Soc., Bethesda,

m.

Nasb, C. E.and C. B. Kensler. 1990. A global overview of quaculture production in 1987. World Aquacult. 21: 104. Shepherd,B. G. and J. G. Moms. 1987. A review of practical emergency procedures for fuh culturists. Aquacult. Eng. 6:155. Tiews, K. (Ed.). 1981. Aquaculture in Heated Effluent and Recirculation Systems. H e e n e m a ~ Verlagsgesellschaft, Berlin, FRG. Tucker, L., C. E.Boyd and E. W. McCoy. 1979. Effects of feeding rate on water quality, production of channel catfish, and economic return. Trans. Am. Fish. SOC. 108:389. Webber, H. H. 1971. The design of an aquaculture enterprise. Proc.of the Gulf and Caribbean Fish. Inst. W117. Wheaton, F. 1977. AquaculturalEngineering.John Wiley & Sons, New Yo&.

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