Aquaculture and Aquacultural Engineering

Aquaculture Definition

• The farming of aquatic organisms in inland and coastal areas
• Involves intervention in the rearing process to enhance production
• Includes individual or corporate ownership of the stock being cultivated
• This involves freshwater and saltwater organisms like mollusks, crustaceans, and aquatic plants.
• Aquaculture, also aquafarming, implies cultivation of aquatic populations under controlled conditions, unlike fishing
• Mariculture: aquaculture practiced in marine environments
• Includes fish farming, shrimp farming, oyster farming, seaweed farming

Aquacultural/Aquaculture Engineering

• Considered a branch of Agricultural Engineering; Fishery and Aquaculture Resource Engineering
• Involves design, construction, installation, operation, maintenance, and management of machinery, equipment, and facilities
• These are needed for fishery and aquaculture production, processing, transporting, and marketing
• Includes fish ponds, fish pens/cages, aerators, fish handling equipment and machinery, and fish storage
• Aquaculture engineering is applying engineering principles to farming aquatic organisms or producing food from aquatic environments

Aquaculture Species

• Major aquaculture species in the Philippines include:
• Seaweed (mainly Kappaphycus and Eucheuma spp.)
• Milkfish (Chanos chanos)
• Tilapia (mainly Nile tilapia, Oreochromis niloticus)
• Shrimp (mainly giant tiger prawn Penaeus monodon)
• Carp (mainly bighead carp Aristichthys nobilis)
• Oyster (slipper cupped oyster Crassostrea iredalei)
• Mussel (green mussel Perna viridis)
• Pacific white shrimp or whiteleg shrimp (Litopenaeus vannamei, formerly Penaeus vannamei)
• Giant freshwater prawn or river prawn (Macrobrachium rosenbergii)
• Asian seabass (Lates calcarifer)
• Mudcrab (Scylla serrata; S. olivacea, S. tranquebarica)
• Catfish (Clarias macrocephalus and C. batrachus native catfish; C. gariepinus- African catfish)

Characteristics of Cultured Species

• Biological criteria for selection: consider the natural life cycle of the intended fish to meet its basic biological needs
• Adaptability to the culture environment: temperature, salinity, tolerance to other environmental parameters; the fish species should suit local conditions
• Hardiness: tolerance/adaptability to crowding/handling, resistance to disease, tolerance to poor water quality
• Feeding character: species should accept external food (carnivorous species); food from external source may be natural (“trash” fish) or artificial (dry, pelleted formulation); high food conversion efficiency
• Reproduction: availability of seed stock (fry/fingerlings) and brood fish capable of spawning, either wild-caught (natural) or hatchery-bred (artificial)

Economic and Other Criteria

• Consumer preference and market demand, acceptability, and possibilities
• Target market as fingerlings, food fish, sport fish, bait, and other purposes
• Possibility of value-added products; there has to be a market for the fish; the species must have a good demand and high market value
• Productivity and profitability

Production Cycle of Some Species

• Generic production cycle – Figure 1
• Tilapia - Figure 2
• Milkfish - Figure 3
• Giant Freshwater Prawn – Figure 4
• Giant Tiger Prawn – Figure 5
• Pacific White Shrimp or Whiteleg Shrimp – Figure 6
• Mud Crab life cycle – Figure 7; Growout of mud crab generally in ponds, net pens in coastal areas, or in mangrove pens (aquasilviculture) Mud crab juveniles may be wild caught, but the SEAFDEC Aquaculture Department has already established the hatchery procedures.
• Catfish - They reproduce during the rainy season (May to October) and, in ponds, perhaps all year round. Sexes can be recognized at the period of reproduction because the genital aperture is different and the belly of the female is swollen
• They make their nests in the shapes of holes of 20-30 cm (8-12 in) in diameter and of variable depths
• Holes are generally from 20-30 cm below the surface of the water, on the bottom of a rice swamp or in a bank with weeds and plants
• The eggs are laid in the nest and stick to the roots of the plants or to the bottom of the nest
• After spawning, the male watches over the eggs which are from 1.3 to 1.6 mm in diameter
• Eggs hatch out after 20 hours in temperatures from 25 to 32 °C
• There can be as many as 2,000 to 5,000 (15,000) fry to a nest
• Growout is generally in ponds at a stocking density from 10-20 fish/m² depending on water quality and supply
• Staggered stocking of ponds is done every 15 – 30 days

Aquaculture in the Philippines

• The Philippines' aquaculture production of fish, crustaceans and mollusks in 2006 was 0.623 million metric tons
• This ranked 10th in the world with a 1.2% share of the total global aquaculture production of 51.7 million metric tons
• The country's aquaculture production of fish, crustaceans and mollusks has amounted to over 981.5 million dollars in value
• The Philippines is the world's 2nd largest producer of aquatic plants (including seaweeds) with 1.47 million metric tons
• This represents nearly 9.7% of the total world production of 15.1 million metric tons
• Aquaculture accounted for 47% of the 4,711,252.4 million MT total fish production in 2007

Aquaculture Structure and Production

• Classified/categorized according to environment, farming, farming technology and production scale
• Classified basically according to environment in terms of water type or source classified into freswater, brackishwater and mariculture:
• Freshwater aquaculture utilizes the major lakes, rivers, reservoirs, dams, small-water impoundments, catch basins, rice paddies, and land-based ponds
• Brackishwater aquaculture utilizes inter-tidal zones, mangrove swamps and estuarine areas
• Mariculture utilizes coastal waters (shallow or deep)

Farming System

• Varies by cultured commodity species and water source
• Freshwater species commonly cultured are tilapia, carp, catfish, snakeheads, milkfish and freshwater prawn
• Ornamental aquarium fish production also falls under this farming category
• Farming system varies from fish corrals/pens, fish tanks, fish cages, earthen ponds to hapa net in ponds for hatchery
• Mangrove swamp areas along the intertidal zone are converted into brackishwater fishponds that draw water from the sea and rivers
• The most cultured fish in brackishwater are milkfish and shrimp
• Mudcrab and grouper were recently introduced in commercial scale to maximize utilization of ponds
• Aquasilviculture and fishpen farming systems are also used
• Seawater-based farming is mainly categorized into three commodity sectors: shellfish culture, finfish farming and seaweed culture
• Shellfish are grown by stake or hanging methods using bamboo poles and ropes
• Seaweed farming is similar, but utilizes different plot designs (lines, afloat or bottom set, and racks)
• Finfish are mostly reared in fixed pen enclosures and floating net cages
• Basically mono-culture based regardless of water source/farming system for the species cultured, while polyculture also occurs in freshwater

Production Scale

• Classified as intensive, semi-intensive and extensive depending on stocking density of fish fry and amount of feeds
• Recently, Mariculture Parks grow commercially important marine species in zonified marine cages
• Similar to land-based industrial zones where fish farmers pay an annual lease which is a fraction of the cost to develop cage facilities themselves
• There are 11 mariculture parks all over the country catering to local, national and foreign investors
• These are mostly engaged in milkfish and other varieties of farming highly commercial valued species (groupers, siganids, cavallas, etc.)

Aquaculture Systems and Equipment

• Broad categories of aquaculture systems based on:
• Purpose or function – broodstock, hatchery, nursery, growout, combination
• Culture conditions: -- Water - freshwater, brackishwater, saline water/saltwater -- Temperature - warmwater/tropical, cool water/sub-tropical, cold water/temperate -- Levels of input/output and management - extensive, semi-intensive, intensive, super -intensive -- Water use: --- Open in natural or man-made bodies of water; use of enclosures, pens, or cages --- Semi-closed or flow-through - culture water makes one pass through the system and is discharged --- Closed or recirculating - water is reconditioned and recirculated -- Rearing, holding or culture unit – pen, cage, pond, tank, raceway -- Specific applications/species - mollusks and seaweeds – bottom or off-bottom culture, pole, rack, long-line, etc. -- Integrated systems for multiple resource use, waste recovery/recycling, environmental impact mitigation, energy-efficiency. Examples: --- Rice-fish/plant-fish culture --- Fish-livestock culture --- Crab-mangrove pen culture --- "Green water” system (shrimp-fish culture) --- Recirculating pond-reservoir systems --- Integrated culture of fish, mollusks, crustaceans, seaweeds --- Polyculture – mixed culture of several species in one rearing unit --- Aquaponics - integration of hydroponics and recirculating aquaculture

Ponds

• Basic types:
• Watershed ponds: -- Hill pond, upland pond, sky pond -- dam the narrow section or “throat" of natural valleys; must have emergency spillway -- rainfall and runoff from watershed as water source; watershed must be contaminant-free -- depth is a function of topography -- requires 5-7 hectares of watershed per hectare of water
• Excavated ponds: -- Dug below ground level -- Normally no levees are constructed -- Primary disadvantage are their need to be constructed in a relatively flat topography, and the cost of removing large amounts of soils -- Need for pumping to remove water, else a need for drainage system -- Sometimes called "borrow-pit" ponds (soil is/has been used for construction or other purposes elsewhere)
• Embankment ponds: -- Levee pond, dike pond, bund pond -- Principal type used for aquaculture -- Can be constructed in a wide range of topographic conditions; have simple construction; permits lower pumping cost and easier harvesting -- Generally with both excavation and levee construction (ideally using the same excavated soil)
• Pond type, size and depth depend on soil type, topography, water supply and drainage, type of production, specific uses/managment and personal preference
• Size affects development cost and management; smaller pond units, the greater the construction/maintenance costs
• Deeper ponds more expensive to construct; large pond management considerations
• Oxygen depletion less likely because of better wind action but wind action promotes wave formation that erode dikes and concentrate food; harvesting more difficult

Pond Shape

• Circular, square, rectangular, octagonal, triangular, irregular
• The same pond area has the shortest levee requirement for circular, followed by square, then rectangular ponds
• Layout/construction easier for straight dikes
• Rectangular ponds are the most common, with a preference for length of 1.5-2 times width

Levee Pond Features

• • Height -- Freeboard: --- Height of the levee from the water surface to the top of the levee --- Prevents overflow/overtopping by wave action --- Should be at least 30cm for erosion control
• Side Slope (horizontal run distance : unit rise) -- Sandy Loam: Inside Slope 2:1-3:1; Outside Slope 1.5:1-2:1 -- Sandy Clay: Inside Slope 1.5:1; Outside Slope 1.5:1 -- Firm Clay: Inside Slope 1:1; Outside Slope 1:1 -- Inside Brick-Lined: Inside Slope 1:1-1.5:1; Outside Slope 1.5:1-2:1 -- Inside Concrete-Lined: Inside Slope 1:1-1.3:1; Outside Slope 1.5:1-2:1
• Bottom slope - gently sloping at % of rise/run of 0.05 to 0.2% or slope of 2000:1 to 500:1
• Core Trench: -- Dug to anchor levee to existing topography and prevent seepage -- Core depth equal depth of pond -- Filled with high clay content soil -- Compacted
• Height and Width: -- Height of Dam ≤ 3m: Minimum Top Width 1.8m -- Height of Dam 3.4-4.3m: Minimum Top Width 2.4m -- Height of Dam 4.6-5.8m: Minimum Top Width 3m -- Height of Dam 6.1-7.3m: Minimum Top Width 3.7m -- Height of Dam 7.6-10.4m: Minimum Top Width 4.3m
• Water supply and drainage: ponds should fill in 7 days or less, and completely drain in 2 days or less

Anti-Seep Collars

• Provided in pipe drains to prevent seepage around the pipe; collar should be about 3 times the diameter of the pipe
• Monk sluices (sluice gates) are structures generally used for supplying/draining water in fish ponds (especially in coastal areas)
• the operator can release the upper or lower layer from the pond by means of stop-log closures and fish screens/racks
• Irrespective of the material used to construct gates (wood, reinforced concrete, ferro-cement), have adequate capacity, be constructed in a position for total discharge, have grooves for placement of filter screens, slabs/harvest nets, and be firmly placed

Pens and Cages

• Open systems, where interaction between fish/environment occurs with few restrictions; located in publicly-owned multipurpose water bodies
• Cage and pen culture are types of enclosure culture, involving holding organisms captive within an enclosed space while maintaining water exchange

Cage and Pen Differences

• Cages are totally enclosed on all or all but the top/sides by mesh/netting
• Pens have the bottom of the enclosure formed by the lake or sea bottom
• Classification system for cages - Figure 9
• Cage system components – Figure 10

Tanks and Recirculating Systems

Aeration

• Oxygen budget in ponds – Figure 11
• Common types of aerators: -- Paddle-wheel aerator -- Aspirating aerator -- Vertical pump aerators -- Diffused/bubble aeration using regenerative/centrifugal blowers or air pumps (diaphragm, vane, rotary lobe, piston)
• Basic approach in aerator selection: determine oxygen demand of the system; select type of aerator based on particular system needs/economics
• Determine standard aeration efficiency (SAE) of the aerator (manufacturer specifications); correct data for operating temperature/DO gradient; select standard/available aerator size/required number; distribute aerators roughly with equal volumes

Aerator Efficiency

• Standard aeration efficiency (SAE) is measuring the aerator's oxygen transfer and energy used per hour, under standard conditions
• SAE is based on oxygen transfer rate at 20°C, 1 atm, in clean, pure water with zero initial DO (SOTR)
• SAE = SOTR / Power
• SAE needs to be corrected for actual temperature, saturation/actual DO in aquaculture water, and ratio of actual OTR to SOTR
• An SAE of 2.1: 2.1 pounds of oxygen per horsepower per hour are transferred to the water under standard conditions (metric = g/kW-hr)
• The higher the SAE, the higher the oxygen transfer/efficiency
• SAE numbers only a fair comparison when comparing equipment of the same type
• Choose the right type of aerator/oxygenator for the application before looking at SAE numbers -- Vertical pump aerator (SAE of 2.9) may be a good choice when there's little water/high stocking density -- Vertical pump aerators would be a poor choice for a large or deep pond -- Surface aerators may be excellent in emergencies because it quickly raises the oxygen level in a small area -- Diffused air system (SAE = 1.0 to 4.0) may be the best choice for multiple tanks/ponds because the energy source (blower) can be centralized, and less SAE is offset by application efficiency -- Water-moving aeration devices (aspirating/paddle-wheel aerators (SAE = 2.5 to 4.0) are excellent choices for medium/large ponds

Water Quality Requirements

• Water determines the success/failure of aquaculture
• Properties Important in Aquaculture Water Quality Management:
• Physical Parameters: -- Temperature Range (daily/seasonal variability) -- Salinity Range (tidal/seasonal variability) -- Particulates (solids) -- Turbidity and Color -- Light
• Chemical Parameters: -- pH and Alkalinity -- Gases -- Nutrients: nitrogen compounds, phosphorus compounds, trace metals and speciation -- Organic Compounds – biodegradable, non-biodegradable -- Toxic Compounds - heavy metals, biocides
• Biological Parameters - bacteria (type and concentrations), virus, fungi, others Acceptable range of water quality parameters for aquaculture applications: -- pH: 6.0-8.5 -- Alkalinity (as CaCO3): 100 - 400 ppm or mg/L -- Total Hardness: 100-400 -- Carbon Dioxide: 0-15 -- Iron-Ferrous (Fe2+): Less than 0.1 ppm -- Unionized ammonia (NH3): Less than 0.02 ppm -- Nitrate-N(NO3-N): 0-3.0 (but not as critical) -- Nitrite-N (NO2-N): 0.1ppm

Flow-Through and Recirculating Systems

Fish Tanks

• Non-toxic and durable
• Made of fiberglass, concrete, plastic, acrylic, glass or wood with impervious liner
• Various shapes exist
• Circular tanks provide a uniform environment
• Tank hydraulics distribute feed and fish, produce optimum velocity, and swimming motion
• Velocities in a doughnut-shaped region around the tank center are reduced

Raceway Information

• Long and narrow rectangular tanks (or ponds)
• A 10:1 length:width ratio aids in water flow and easier management
• Depth should be between 0.75-1.25m
• Water quality gradient exists along length
• Serial raceways maximize water use, with high water velocity for flushing wastes
• Parallel raceways can be built side by side to share common walls, reduce floor space/construction cost
• Combination serial and parallel systems are used
• Management considerations: low dissolved oxygen, nitrogenous waste build up, solids will accumulate, need for effluent treatment

Impact of Fish

• Constant waste excretion rates per kg feed:
• 30 g Total Ammonia Nitrogen (TAN)
• 300-500 g dry Fecal Solids
• 8gP
• 340g CO2, and require
• 250g O2
• Flow-through systems are single-pass systems in tanks/raceways/ponds
• Stocking densities can be high, but must supply the oxygen and prevent toxic metabolites
• Water quality may be subject to fluctuations in the source
• Carrying capacity: 1.0 liter/min (Lpm) of good quality water ≈ 1.0 kg of fish

Recirculating Systems

• Designed to approximate the fundamental aspects of natural systems in order to support aquatic life
• This may involve tank, pond, other culture systems
• Critical processes are gas exchange, solids removal, and biological filtration
• Other treatment processes include denitrification, ozonation, and ultraviolet sterilization

Other Info

• Heaters and/or chillers may be provided for temperature control
• Waste in recirculating aquaculture systems are characterized by a broad size spectrum, high organic content, and low density
• Two fractions are dissolved solids and suspended solids
• Removal is a solid-liquid separation process, and may involve gravity separation, swirl separation, or filtration
• Biofiltration uses living organisms to treat the water
• In pond systems this includes aquatic plants/animals other than the culture species
• In recirculating tank systems, this refers primarily to nitrification or toxic ammonia conversion
• Common equipment includes submerged, trickling, sand, and other granular media filters
• Biofilters need acclimation to become functional
• Acclimation takes about 30 days or more with introduction of culture animals with gradual increase