4 aquaculture engineering

7/30/2019 4 Aquaculture Engineering

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AQUACULTURE

ENGINEERINGMS324 AQUACULTURE IN PACIFIC ISLAND

COUNTRIES



LEARNING OUTCOMES:Students will be able to describe, and demonstrate

understanding of: Aquaculture systems –longlines, rafts, cages, ponds, tanks,raceways

Seawater systems - open systems, and closed systems

Site selection – importance of a good site, site selection

criteria Seawater intakes - importance of a good intake, requirements Water filtration - types of particles, types of filters Water reconditioning - bio-filters

Water disinfection – reducing bacteria, fungi, viruses with UV-light or chemicals

Temperature control – heaters, chillers Aeration

Carrying capacity of an aquaculture system

Electrical safety



What do fish need?



GOOD FOOD

and

CLEAN WATER!



ENGINEERING ISSUES

The main engineering issue facing theaquaculturist is obtaining clean water for thefish farm.

A secondary issue is ensuring that the farmedfish do not escape.

NB Feeding fish is a nutritional issue, not an engineeringissue (unless a special automatic fish-feeder is to be used)



AQUACULTURE SYSTEMS

Various aquaculture systems are availableto obtain water, and prevent fish escaping.

These range from extensive to intensive



Re-stocking (Sea ranching)

Organisms are released into the naturalenvironment from a hatchery

No structures are needed at all



Longlines and rafts

Open-water structures – non-motile organism issuspended in the water column

mostly used for filter-feeding molluscs like

mussels or for seaweeds (do not needsupplementary feeding)

need fairly sheltered locations

do still require good water movement (rely onthe water column for plankton food or for inorganic nutrients).



Pacific oyster raft



Seaweed longline



Longlines and rafts

Degree of control?

Investment?

Operating costs?

Pathological risk?



Cages

Open-water structures – contains motileorganism (usually fish) and stops them escaping

Fish will need supplementary feeding

Cages require sheltered-water location and

strong moorings, so they are not uprooted byrough weather.

But still need sufficient water movement to bringclean water, and flush fish wastes away.

If cages are placed in bays with insufficientwater exchange, then water quality deteriorates.This is harmful to the farmed fish, and to naturalbiota in the area.



Grouper seacages



Site selection for cages is important



Cages

Degree of control?

Investment?

Operating costs?

Pathological risk?



Ponds

are closed systems which serve the purposeof:

preventing animals from escaping

enable some control of the animals’environment

help protect them from predation or other

hazards.

Ponds may be earthen, or may be lined with a

synthetic material like plastic or rubber.



Earthen ponds

soil chemistry must be studied to find out whateffect the soil may have on pond water quality.

Soil pH, alkalinity, and presence of toxicsubstances like heavy metals need to be testedto ensure they are all at safe levels for the fishor for humans that eat the fish.

Slightly acidic soils will need preparation by

liming before ponds are filled, to raise the pH. Acid sulphate soils (often found behind

mangrove areas) can have pH as low as 4.5,and should be avoided.



Earthen pond (tilapia, prawn)



Lined ponds

Installation of pond liners makes water quality independent of soil chemistry

This gives the farmer a lot of control over the pond water quality

It is expensive in terms of capital costs(money up front) though it can savemoney in farm operating costs (pondmaintenance) later on.



Lined pond (shrimp)



Pond construction

Ponds need to be constructed in a certainway, however this differs between speciesand culture methods, and from site to site.

Detailed information about pondconstruction will not be given here, but

may be explained during the lectures for particular species, for example tilapia.



Ponds

Degree of control?

Investment?

Operating costs?

Pathological risk?



Tanks and raceways

are built on land (often indoors) provide very good control of water quality for optimal

environmental conditions

The expense of building tanks and pumping water into them can usually only be justified for the mostintensive types of aquaculture, e.g:

(1) the short period of the lifecycle when fish arelarvae (hatchery operations), or;

(2) for grow-out of very high-value species like

ornamental fish.



Outdoor tanks



Indoor tanks



Raceways



Tank water systems can be divided intotwo categories:

1. Open systems - incoming seawater isflowing through all the time

2. Closed systems - there is no incomingseawater



Flow-through tank system

Seacages and longlines are called opensystems, because the farm is in the seaand water is flowing past all the time.

Land-based tank, raceway or pondsystems are also called open systems if water is being pumped through all the

time. This is called a flow-through system



Flow-through system

Water is only used once - it trickles intothe tank, then overflows down a drain andruns away to waste.

The advantage is that this guarantees thecleanest tank water, with continuousflushing of fish wastes.

The disadvantage is that large quantitiesof good-quality seawater must be available

at moderate cost.



Raceways



Static system

The simplest closed system is the static

system (sometimes called a batch culture)

a tank is filled with water and left with nowater flowing through it. Every so often apercentage of the dirty water is drained out,and refilled with clean water.

A marine aquarium is an example of a staticclosed system. It is used in situations whereseawater is very difficult to obtain.



Static system



Recirculating system

Another closed system is the recirculating

system.

Water overflows out of fish tanks, is collected

and treated (mechanical filtration and/or bio-filtration) then pumped back to a storage tank tobe re-used.

A percentage of the total water volume in the

recirculating system will need to be drained outperiodically and refilled with new, clean water.



Recirculation system

The advantage of recirculation is thatwater can be used more than once, whichsaves money in situations where quality

seawater is difficult or expensive to obtain.

The disadvantage is that, despite

treatment, the water quality will still slowlydeteriorate as fish metabolites accumulatein the water.



Summary of tank systems

A flow-through system is best - it guaranteesbest fish health with a minimum of expense onwater treatments. But it depends upon

availability of a site with an abundance of good-quality seawater.

A static system is worst in terms of fish health,with high operating costs and high-technology

required to keep the water clean. A recirculating system is in-between the other

two, in terms of maintaining good fish health at

reasonable cost.



Tanks and raceways

Degree of control?

Investment?

Operating costs?

Pathological risk?



Site selection

When choosing a site for aquaculture, threethings are very important:

1. LOCATION2. LOCATION

3. LOCATION

Bitter experience over the years shows thatselection of the right site is the single mostimportant factor in determining the success or failure of aquaculture projects.



Ideally a project proposer should go through a siteselection process, where a range of technicalfactors are considered:

water not too rough, or prone to heavy flooding

a water supply is available (river, well, dam,seawater)

water temperature in the optimum range for your species

water salinity, pH, alkalinity, nutrients etc inoptimum range

no toxins or pollution few diseases or predators in the area

road access, electricity, telephone, drinking water supply



There are also legal factors, such as:

Who owns the site?

Can it be bought or leased?

Is the area zoned in planning laws asavailable for aquaculture?

Social factors include:

Is labour available? Are there people nearby who may steal

farmed fish?



The reality is that few aquaculture sitesare ideal in every way

Often project proposers do not carry outany site selection process at all.

There may be good reasons for that.What could they be?



Few aquaculture sites may be available in thearea.

Or the site may have been determined right fromthe start, because the land being used is land

already owned by the project proposers.

In this case, the proposers should go through aspecies selection process, where different

species are analysed and one chosen withbiology and preferences that match theenvironmental conditions of the site.

Whi h i i t



Which species or organism toculture?

How do you decide which organism toculture?

1) Biological characteristics

2) Economic and Market Considerations

3) Introduction of Exotic Species



Biological Characteristics Growth Rate (some exceptions if slow growing but very

high value) Size and Age at Maturity- better if they reach marketable size

before becoming sexually mature. (many breeders available for hatchery but not ideal for growth).

Duration (Days of Culture)

Production under cultured condition- adaptability to captive environment.

Tropical species perform better at higher temp. but it is difficultand expensive to do so in a cold environment- may not beprofitable.

Can be cultured under semi or intensive systems- highpopulation/ crowding.

Organisms that are “Hardy” can tolerate unfavourable conditions- high/low temp or low DO.

Resistant to diseases.



Breeding in captivity- can produce seeds for stocking in a hatchery.

High fecundity and frequency of spawning is anadvantage.

Short larval rearing period is also desirable.

Larvae that consume inert feeds rather than live feedsmay also be desirable.

Wild breeders or juvenile availability.

Feeding Behaviour- a herbivorous or omnivorous maybe cheaper to culture.

Carnivores would require higher protein dietsand at a higher cost but they also tend to fetch ahigher market price.



Economic and Market Consideration

Proven technology-information/ technical

assistance or know-how available. Less info may require pilot studies and commercial

trials.

Are there any priorities- national/ regional.

Consumer acceptance and availability of markets. If no market exists it maybe developed but this can

take a long time and effort.

Consideration can be given to an introducedspecies whose technologies, economics andmarketability has already been demonstrated.



Introducing an Exotic species

Introductions must be done only if it is necessary. Proper procedures will reduce the risk of undesirableconsequences. Considerations for introduction: Fill a need because of the absence of a similar desirable species

in that locality.

Not compete with valuable native species, contributing to their

decline. Not cross with local native species to produce undesirable

hybrids.

Not be accompanied by pests, parasites or diseases that mightattack native species.

Live and reproduce in equilibrium with its new environment.

Turner (1949) in Pillay T. V. R. (1990).



PILOT PROJECT

A small-scale pilot project can be done totest the chosen species at the chosen site,to find out any problems before too much

money is spent. A small pond may be dug and stocked, or

a small seacage tried out.

In seaweed farming, the pilot project maybe as simple as trying a test plot of one or two lines in a range of reef locations.



Poor site = ¯└ $$$ ┘¯

A bad site can be made better, but money willneed to be spent on improving it.

How much money can be spent will depend

upon economic analyses of the profitability of theventure. More money needed for improvementsmeans less money for profit.

Sometimes poor sites can be made into good

ones, but many end up being abandoned evenafter much investment of money and effort.



Seawater intakes

Many high-value marine species arefarmed in terrestrial environments, to givemaximum control over culture conditions.

Larvae hatcheries, and growout of specieslike Penaeid shrimp in ponds, requires

seawater to be pumped up onto the land.

S t i t k



Seawater intakes

The successful installation of a seawater

intake is the single most important factor inthe success of any land-based marine-species aquaculture operation.

More projects have failed because of problems and expense with seawater intakesthan from any other reason.

It does not matter how fancy the on-shorehatcheries and laboratories may appear. If areliable supply of quality seawater is notavailable, then the whole project is pointless.



Seawater intakes

Seawater intakes have to be in the sea.

They therefore need to be firmly anchored,and placed where storms or natural

disasters will not uproot them.

Such adverse events are usuallyinfrequent, so their severity at a particular

site may be difficult to predict. The farmer is taking a gamble.



Intake water quality

The land-based hatchery or farm willrequire good-quality seawater that suitsthe biology of the farmed species.

It is critical that the water body theseawater is being extracted from will be of good quality most of the time.

If rainfall or flooding causes periods of lowsalinity or high turbidity (muddiness) thenthe farm will be deprived of water andcannot function.

Intakes located in shallow water will



Intakes located in shallow water willnot provide quality water if:

the bottom mud is being stirred up bybreaking waves, or;

brackish water is floating on top of the

more-dense seawater, or;

rubbish is drawn up the pipe.

The deeper the intake (more than 5m), thebetter the seawater.



Intake screen

Intakes require a screen to prevent rubbleor debris being drawn up the pipe anddamaging the pump.

Mesh screens cannot be too fine,however, or bio-fouling (barnacles, oystersetc) will block the holes and prevent water being pumped.

Roughly one-inch holes in the screen areusually adequate.



Exercise:

Study the photos of the two seawater intakes shown on the next slides.

Discuss their advantages anddisadvantages.

Decide which intake will give bestseawater with least problems.



And if that water is no good then



And if that water is no good, thenwe have to do this …



Water filtration

Even good seawater sources usuallyrequire some sort of water treatmentbefore it can be added to the fish tanks.

Filtration is the term for straining particlesout of water.



There are usually three things that need to

be filtered:

1. Sediment, that could clog the gills of

animals2. Zooplankton, especially predators of

hatchery larvae, or larvae of biofoulingorganisms that can settle, grow, and clog

up hatchery pipes3. Bacteria, that may cause diseases



Stages of filtration

Filtration is usually done in stages, fromcoarse to fine. The number of stagesdepends upon the hatchery requirements.

The first stage is the intake screen,usually filtering out particles of size about

an inch (25mm).

Sand filter



Sand filter

The second stage is usually a sand filter , to

remove the worst of the larger sedimentparticles, the bigger zooplankton, and eggsof various kinds.

This requires filtration of particles in therange of 75-100 microns (thousandths of amillimetre).

Sand filters require periodic back-flushing,whereby the water flow is run backwards tounclog the sand and clean the filter beforewater is made to run forwards again.



Cartridge filter



Cartridge filter

The third stage is to remove phytoplanktonand zooplankton, usually done by acartridge filter .

Different cartridges can be fitted to provide

different pore sizes, and for phytoplanktonremoval are usually in the range of 2-10

microns.

To remove bacteria or very fine sedimentparticles (if this needs to be done) acartridge filter with pore size of 1 micron

or less is required.



It is important that coarse filtration is done



It is important that coarse filtration is donebefore fine filters are used, or the fine filters

will clog very rapidly. Filter cartridges used for removal of bacteria

will eventually clog, so their performancemust be regularly inspected.

Even if not clogged, the filter cartridge shouldbe removed every couple of days and soakedin a chlorine bath to disinfect it before re-use.

This is because of "bacterial creep" whereby,through cell division, living bacterial culturescan grow their way through from one side of the filter material to the other.



Other types of filter technology areavailable, for example diatomaceous-earthfilters, filter bags, micro-screens, and

sedimentation tanks.

However the methods described above

are the main ones.

Water Reconditioning



Water Reconditioning

Reconditioning refers to removal of toxic

metabolites (fish waste products) of which thevarious forms of inorganic nitrogen are the mostcritical.

Marine organisms excrete nitrogenous waste inthe form of ammonia, mainly through their gills.

Faeces and uneaten food in the water arebroken down by bacteria, releasing more

ammonia. Ammonia exists in two forms in seawater. Un-

ionized ammonia (NH3) is very toxic to fish.

Ionized ammonia (NH4+) is not very toxic.

Monitoring ammonia



Monitoring ammonia

It is important that large-scale hatcheryoperators monitor levels of un-ionizedammonia and ensure that it remains less thanvalues known to be toxic for their organism.

Remember, however, that analytical chemistsare in the habit of measuring total ammonia(NH3 + NH4+) so you will need to make aspecial request for them to measure un-

ionized ammonia only. If ammonia reaches problem levels (>1ppm)

in an open system, then the flow of incoming

water will need to be increased.

Bio-filtration



Bio-filtration In a closed system, removal of ammonia can be

achieved by bio-filtration. Ammonia released by fish enters the nitrogen cycle

in seawater. Naturally-occurring aerobic bacteriacalled nitrifying bacteria can convert ammonia

first to nitrite, which is also highly toxic to fish(>1ppm), and then to nitrate which is not very toxic(up to 100ppm before it is toxic).

This process is called nitrification, and results in

ammonia-rich water being converted to a less toxicstate.

In hatchery tanks there are usually insufficientnitrifying bacteria to handle the large output of

wastes from high stock densities of fish.

Bio-filters



Bio filters

Bio-filters can be included in recirculation

systems to provide a greatly increasedaerobic surface area for growth of nitrifyingbacteria.

The bio-filter may consist of rolled-up plasticnetting, or specially molded plastic "bio-balls", and have water trickled through it likea waterfall.

Live rock is also a bio-filtration medium, nowvery popular for use in marine aquariumtanks.



f



Water Disinfection

Disinfection is reduction in the number of bacteria, fungi and viruses to safe levels.

Sterilization is the complete elimination of such organisms, however this is usuallynot needed, or is not possible, or is not

even desirable if bio-filtration is being usedin the system.

Di i f ti i d d f t it ti



Disinfection is needed for two situations:

1. Surface disinfection of tanks, pipes, scoop-nets, filters, hoses, buckets or other equipment

2. Disinfection of the water itself

The first is easier to do, because after disinfection with toxic chemical agents, theequipment can be rinsed off with clean water.

The second is more difficult because chemicalagents must be removed before animals canbe placed in the disinfected water.

Chemical disinfectants



Chemical disinfectants

include chlorine, ammonium compounds, formalin,

and iodine compounds. Chlorine is the most common one used in

hatcheries, usually applied as sodium hypochloritesolution (common household bleach, for example

Janola). After surface sterilization the bleach must beremoved by liberal rinsing with a freshwater hose,or by exchange of 6 - 10 tank volumes beforeanimals are introduced to the tank..

To disinfect water, chlorine can be added at 1 -5ppm concentration and then removed by allowingthe water to stand in the tank for a couple of dayswith air bubbling through it.

Ultra-violet light



Ultra violet light

can be used to disinfect both surfaces, and water.

UV light causes chromosome damage to bacteriaand prevents them from replicating.

Inoculation of micro-algal cultures often requiressterilization of work surfaces and equipment before

and after the inoculation steps are carried out. Water passing through a pipe can also be

disinfected by having it flow through a transparentportion surrounded by a jacket of UV lamps.

It has the advantage that nothing gets added to thewater that can affect cultured organisms. It has thedisadvantage that high flow rate or high turbidity of water will reduce its effectiveness.



Temperature control



Temperature control

Despite being located in the tropics, hatcheries in

Pacific island countries often have incoming water that is either too cold or too hot. Sea shrimp Penaeus monodon larvae require tank

temperature close to 27-28 degreees Celsius. In Fiji during the cool months, hatchery tank water

can fall as low as 23 degrees Celsius, and needs tobe heated.

During the hot months it can rise to 32 degreesCelsius, and needs to be chilled.

One of the properties of water is that it is thermallyvery conservative (resistant to temperature change).This means that a lot of energy is required to changethe temperature of a volume of water even by onedegree.

Chiller



Chiller

A seawater chiller is a refrigeration unit used to

cool seawater. It works the same way as an air conditioner, but

acts on seawater.

The seawater inflow pipe runs through a heatexchanger alongside another counter-flowing pipecontaining a refrigerant maintained at a settemperature by the chiller's refrigeration unit.

This works best in a recirculation system, wherechilled water an be re-used, rather than on a flow-through system where the water is chilled oncethen thrown away.



Heater



Heater

A seawater heater can be as simple as an electrical

element, the same as that used in an electric kettlefor making tea.

The element is usually contained in a glass or titanium tube, that is immersed in the seawater tank.

At one end of the heater is a thermostat unit for temperature level adjustment. The heaters aresealed units that can be placed completelyunderwater.

Three 300Watt units or one 1000W unit are usuallyenough to raise one tonne of seawater from 24degrees to 28 degrees Celsius.

H t h



Heat exchanger

To create large volumes of heated or chilled water in a flow-through system, aheat exchanger must be used.

These can be several metres long withpipework operating on the counter-flow

system. They require a lot of electricity tooperate, so your power bill will be high.

Aeration



Aeration

Air bubbled through the water column has

two purposes:

1. Increases dissolved-oxygen (DO) level in

the tank water, and;2. Creates water movement, to keep larvae

up in the water column and evenly

spread out in the tank space.

Aeration can be provided by compressors,or by blowers

C



Compressor

Provides air at highpressure but at lowvolume

Good for makingbubbles in deep water

Bad at making the air “wet” (a source of tank

contamination” Wear out quickly

Bl



Blower Provides air at low

pressure but at highvolume

Good for supplying alot of tanks, but thewater must stayshallow (less than 1mapprox.)

Delivers very dry,clean air

Not many wearingparts

Carrying capacity



y g p y Carrying capacity refers to the amount of farmed

organism that can be placed in an aquaculture systemwithout adversely affecting growth or survival.

There are a variety of units for measuring carrying

capacity, including:

Volumetric density = mass of animal (kg)/volume of water (L)

Volumetric abundance = nos. of animal (kg)/volume of water (L)

Areal density = mass of animal (kg)/area of water (m2)

Areal abundance = nos. of animal/ area of water (m2)



It is difficult to provide any general rules for carrying capacity, since every aquaculturesystem is different in its characteristics, andevery species is different in its requirements.

Aquaculturists will need to become familiar with the published literature on the tolerancesof their organism, and;

will have to monitor water quality on a regular basis to ensure that safe carrying capacitylimits for that species are not being exceeded.

Water quality monitoring



q y g

The two most important water quality parameters

are the level of un-ionized ammonia, and the levelof dissolved oxygen.

Excessive un-ionized ammonia indicates that toomany fish are excreting wastes into the water.

Low dissolved oxygen indicates too many fish aretaking up oxygen from the water.

It also indicates that too many fish are excreting

wastes, since the bacteria that decompose fishwastes are themselves aerobic and consumeoxygen.

Levels of ammonia increase if pH increases,d th t f di l d i d d



and the amount of dissolved oxygen is reducedif temperature increases.

There are therefore four water qualityparameters that conscientious aquaculturistsmeasure regularly:

- un-ionized ammonia NH3 - dissolved oxygen

- pH

- temperature

For marine organisms, a fifth parameter must

also be monitored - salinity

Electrical safety



Electrical safety

Electricity and seawater do not mix very well.

Seawater is a salt solution that is a goodconductor of electricity.

A current leak that might only give you a"tingle" in a freshwater system could bedeadly in a seawater system.

You must be very careful when usingelectrical equipment or appliances in aseawater aquaculture system.

Good advice when using electricity:



g y All electrical circuits should have ground fault interrupters,

either in the switchboard itself or by plugging your appliance

into a portable transformer unit. Make sure your electrical appliances and all power cords are in

good condition Avoid splashing seawater around, and regularly hose down the

place with freshwater, to prevent salt cake buildup on surfaces

and around electrical sockets Do not place any electrical equipment under water pipes, or

tanks, or anywhere that water can fall or splash onto it, or dripfrom condensation on outside of pipes. Even aeration of seawater with air stones can cause a salt aerosol spray to drift

through the air and onto electrics. Overhead placement of electrical sockets are better than wall-

mounted sockets. Every so often, mains power should be turned off and power

sockets and extension leads be rinsed thoroughly in fresh water

and dried out again with methanol, to remove salt build-up.

Reading (in PIMRIS Library)



g ( y)

Hugenin & Colt “Design and operatingguide for aquaculture seawater systems”

TVR Pillay “Aquaculture Principles andPractices” Chpt. 4, 6.

Swift DR “Aquaculture Training Manual”

4 aquaculture engineering

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