TECHNICAL PAPER # 52
Ira J. Somerset
Marilyn S. Chakroff
VOLUNTEERS IN TECHNICAL ASSISTANCE
Boulevard, Suite 500, Arlington, Virginia 22209 USA
Telephone: (703) 276-1800, Fax: (703) 243-1865
Telex 440192 VITAUI, Cable: VITAINC
firstname.lastname@example.org, Bitnet: vita@gmuvax
This paper is one of a series published by Volunteers in
Assistance (VITA) to provide an introduction to specific
state-of-the-art technologies of interest to people in
countries. The papers are intended to be used as guidelines
help people choose technologies that are suitable to their
situations. They are not intended to provide construction or
implementation details. People are urged to contact VITA or
similar organization for further information and technical
assistance if they find that a particular technology seems
meet their needs.
The papers in the series were written, reviewed, and
almost entirely by VITA Volunteers technical experts on a
voluntary basis. Some 500 volunteers were involved in the
production of the first 100 titles issued, contributing
5,000 hours of their time. VITA staff included Margaret
Crouch as Executive Editor, Suzanne Brooks handling
layout, and graphics, and James Butty as technical writer/editor.
The author of this paper, VITA Volunteer Ira J. Somerset, is
sanitary engineer working for the US Food and Drug
as an evaluator of shellfish sanitation programs in the
states. The reviewers are also VITA Volunteers. Marilyn S.
Chakroff, a technical writer and fishery trainer, is the
of Fresh Water Fish Pond Culture and Management, published
VITA; Robert Bettaso is an agricultural scientist with
in fish culture; and Martin Vincent is a self-employed
VITA is a private, nonprofit organization that supports
working on technical problems in developing countries. VITA
offers information and assistance aimed at helping
and groups to select and implement technologies appropriate
their situations. VITA maintains an international Inquiry
service, a specialized documentation center, and a
roster of volunteer technical consultants; managers
field projects; and publishes a variety of technical manuals
VITA Volunteer Ira J. Somerset
Aquaculture is the production of protein-rich foods through
controlled cultivation and harvest of aquatic plants and
Using inexpensive equipment and simple techniques,
can supply more protein than normally produced through
agriculture such as dairy, poultry, and cattle farming;
and traditional fishing.
Aquaculture is not new. More than 2,500 years ago the sticky
of some fish were collected on mats and bundles of reeds or
attached to posts in streams. Oyster and clam eggs were also
collected and transferred to other waters to hatch. This was
first form of aquaculture.
In the 11th and 12th centuries, pond culture developed. Carp
moved through a series of ponds where they reared young fish
grew to harvest size. Later, other fish were cultured in a
similar manner. Today, several types of fish and shellfish
grown in high density aquaculture operations throughout the
The techniques of animal husbandry improve the chances of
survival of the plants and animals being raised and speed up
their growth so that the food yield is quick and large.
any type of aquatic organism can be raised from its youth to
healthy, marketable adult. However, this paper in restricted
fish and shellfish culture. The reader is presented with
general considerations and approaches to aquaculture, since
requires specialization to address each possible cultural
ADVANTAGES AND DISADVANTAGES OF AQUACULTURE
Systematic aquaculture operations have a number of
over fishing for the production of protein foods. Some of
Economics (employment, new industry and
and increased foreign and domestic ex
No need for expensive fishing craft and
Low operating and maintenance costs;
Low capital investment (unless Ponds must
Reasonably predictable yields;
Less time lost due to bad weather or
Fewer equipment malfunctions and
Reduced health risks to consumers.
Aquaculture operations do have drawbacks, however. These
Water is necessary, in predictable
Large land area on which to construct
ponds or access
shallow area of water is required;
Knowledge of culture conditions may not
TYPES OF AQUACULTURE
There are five major types of aquaculture:
The movement of a species to a
location. This method in also used to introduce
Hatchery and Stocking:
The spawning, hatching, and
rearing of a
cultural species that will be transplanted
or desirable areas. This method is
supplement or replace the natural stock, or
The use of enclosures, such as
baskets, and strings, for aqua
Ponds with Supplemental Feed and
in natural or
artificial ponds with food and
provided to maintain algae and species
levels. In some systems, animal
used to provide fertilizer and some food.
Ponds without Supplemental Feed and
in natural or artificial ponds with the
species subsisting an natural available food
in the pond
water. This requires a high rate of
water for high growth rates.
As can be seen, the basic theory of aquaculture is to obtain
small animals and provide them with an environment that
for their rapid, healthy growth. A desirable-sized fish can
harvested in a short period of time.
II. CULTIVATION REQUIREMENTS
The most commonly cultivated species of fish are carp and
tilapia. Shellfish such as oysters and mussels, which are
the food chain, are also farmed extensively. While culture
techniques must be adapted to the needs of specific species
to local needs and conditions, some general rules apply:
The species must be Suitable for
The program must develop the best method
identified species from physiological, geographical,
points of view.
Adequate support must be available. This
and aerating the water, feeding the fish,
maintaining equipment, marketing, and so on. Experimentation
necessary to improve yields substantially.
Predators must be controlled.
Cannibalism must be controlled.
The species life cycle must be
understood, and good,
inexpensive feed must be available.
A dense population of animals demands abundant food and
and a means of removing metabolic wastes. There is a limit
size of the biological community that can be supported
growth is limited by competition for food, oxygen, and
high density of cultured animals makes them susceptible to
disease and predation. To prevent juveniles from being
by these diseases, drained ponds must be thoroughly dried to
destroy parasites and disease-causing organisms. The water
stocking animals should be free of parasites and
organisms. Feed and feed supplements should not introduce
parasites or disease-causing organisms.
On the positive side, the fertile fish and shellfish wastes
be used in the production of leaf crops requiring nitrogen.
Shellfish wastes are best used on fruit trees.
OVERALL OPERATION AND MAINTENANCE
Aquaculture systems can be operated and maintained in three
This is subsistence cultivation that is some
publicly funded. The conditions are often mediocre,
production is poor because duties are attended
This can range from subsistence cultivation to a
very sophisticated operation, depending
on the skill and
energy of the
owners. Under the worst of conditions, it
can be more
variable than communal; at its best, it can
standards of a dedicated system. The key to a
operation is the family's commitment to putting
effort necessary to produce a quality
This operation is designed to produce food
and is usually well-regulated with high
Each of these types of operation can be run as extensive or
Extensive Culture provides little or no control over the
Placing shellfish on a site and allowing them to grow on
their own, or trapping fish and invertebrates in special
and holding them until they reach market size, are examples
of extensive culture. In extensive culture, the fish depend
the natural food supply in the water. Only 20 to 50 percent
the stocked animals survive in this uncontrolled
Intensive Culture on the other hand provides full control,
the environment. An indoor culture of shellfish, in which
temperature, salinity (salt/water ratio), flow rate, feed
amount of feed, and light are fully controlled, is an
No matter which type of operation or which method of culture
selected, sufficient food and oxygen must be provided.
levels of 4 to 5 milligrams per liter (parts per million)
satisfactory. Water can be aerated by spraying it out at
0.6m (2 feet) in droplet form. Food requirements are
a later section.
There is one other general consideration in aquaculture that
extremely important: The size of the animals. The animals
in the aquaculture system must be large enough to grow to
size in the desired time. Some preliminary experimentation
needed to determine the minimum desirable size. only healthy
animals should be chosen for stocking the aquaculture system.
An aquaculture system can be operated on a shore, in an
region (zone between the high and low tides levels), in a
sub-tidal region (zone below the low tide level), on a water
in mid-water, or on a seabed. Certain culture systems are
better-suited to certain sites. A shore facility is usually
for fish and shrimp production. Full control (intensive
of the environment is characteristic of shore sites, and
may be needed to provide the water supply.
Controlled Pond Facilities
These are either man-made or natural areas that can be
from the water source. Water flows by gravity into the pond
pumped in. Ponds are suitable for such fish as tilapia or
or even game fish such as salmon.
Intertidal facilities take advantage of the movement of the
to replenish food and water. They are used for shellfish
and spat (larval shellfish) collection and can be controlled
properly constructed. The incoming high tides are let into
area that can then be closed off. The high water, with its
of baby fish or shellfish, is dammed off and is held until
fish reach marketable size. Pumps may be necessary to
Subtidal facilities have extensive culture (little
control) characteristics. No water pumps are needed, but
water quality analysis in required to ensure adequate
Fouling organisms must be regularly removed from your stock
Surface Floating Facilities
In this case, floating cages and rafts are used, which can
moved to protected areas if necessary. This is extensive
and usually does not require pumping of water. However,
organisms may restrict the flow of water, creating supply
feeding problems. Supplemental feeding may be necessary, and
fouling organisms must be removed regularly.
Mid-Water Culture Facilities
Mid-water culture facilities consist of strings of mollusks
(shellfish) suspended through the water column. Since this
extensive culture, restricted flow may create fooding
Fouling organisms must be removed periodically.
Seabed Culture Facilities
These are also extensive culture sites and may be subject to
fouling organisms that restrict water flow and cause feeding
problems. Because of natural flow restrictions along the
oxygen and food supply may be reduced.
For all of those sites, you must evaluate the exposure to
pollution from land runoff (pesticides or siltation), and f
sewage and industrial wastes. Ways of protecting a site from
winds and waves must also be evaluated.
Enclosures are needed to keep predators away and to prevent
loss of stock through sluice gates and other outlets.
used in aquaculture must:
Have a long visible life.
Be resistant to fouling.
Be easily cleaned.
Structures supporting enclosures within the intertidal zone
be rigid to allow for the rise and fall of the tide.
rafts, nets, and cages must be anchored to allow for wind
waves. Wind and waves cause wear and abrasion of the
The structure may also need fine-mesh nets for protection
predators and coarse-mesh nets for protection from trash and
Surface floating units, consisting of a timber structure on
floatation barrels or floats, require much maintenance. The
condition of the floatation and framework should be checked
often, especially when used in salt water. Before using any
material in water, especially salt water, the effects of
predators on the material should be evaluated by installing
pieces for at least one growing season.
Organisms growth on equipment and shellfish can be removed
brushing, hand picking, or high-velocity water jet. Growth
prevented in some cases by periodically removing the
from the water. In removing growth, care must be exercised
ensure that the underlying material (rope, net, and shell)
FOODS AND FEEDING
Fish or shellfish cultured must be limited in number so that
animal can obtain enough food to grow. Insufficient food
result in slow growth, or even shrinkage, small animals
and a high potential for disease. Harvest has been found
to increase as much as 1,000 percent when animals are fed
regularly. Figure 1 shows how the growth rate can be
The conversion rate from feed to flesh varies with fish
food type, temperature, individual fish, and food
Generally, it in between 10 to 1 and 20 to 1. Cultured fist
shellfish should not be overfed, since unconsumed feed sinks
the bottom, decays, and aids the development of algae
while reducing oxygen levels through the decomposition
Although some of this fertilization is good, too much growth
creates low oxygen levels. Fish should be fed 6 days a week
the same time and place each day, ideally, 2 to 3 hours
sunrise or before sunset. To empty the digestive tract and
produce better-quality fish, don't feed them on the day
Feed only what will be eaten daily. If a floating feed is
feed what in eaten in 10-15 minutes. Observe the response to
feeding: If the fish do not appear hungry, there may be
reasons (abundant natural food available, low dissolved
poisons, etc.) and feeding should be discontinued until the
reason in found and corrected. If sinking food in used,
feeding response by placing a 1.2m x 1.2m (4 feet x 4 feet)
on the bottom in the feeding area. After 1 hour, raise the
slowly and carefully. Look for feed on the tray. If the feed
not been completely consumed, reduce the amount of feed.
fish will eat one tenth to one half their own weight per
Both natural and artificial foods say be used. Controlled
fertilization of ponds in order to increase their
and providing more natural food to the cultured species are
established practices. Artificial foods (those that will be
consumed directly without conversion to algae) consist of
processed food, and certain industrial wastes. Examples of
foods are the leaves of the cassava (tubers and peelings are
suitable), sweet potatoes, eddoes, banana, paw paw, maize,
canna plants. Processed foods include meal waste, cassava
flour, rice chips and balls, corn flour, and cotton and
oil cakes. Industrial wastes such as decomposed fruit,
sediment, coffee pulp, and local beverage wastes have also
Fertilizer is added to a pond to ensure that there are
amounts of nitrogen, phosphorous, and potassium in the water
support algae growth. The requirements will vary with the
quality and fish population. Fertilizer should be added
the fish-growing season and repeated at ten-day intervals to
produce the desired algae population, known as a bloom.
bloom, add fertilizer as necessary to maintain a light
density of the bloom must be adjusted for different seasons,
since too much algae will cause a reduction in the dissolved
oxygen levels and could kill fish. A desirable bloom will
out a bright object 0.3 - 0.5m (12-18 inches) below the
If 3 to 5 applications of fertilizer are made and a bloom is
observed, there may be other problems, such as filamentous
or other plants using the fertilizer. These must be killed
phytoplankton algae can grow, unless the aquaculture system
filamentous algae or large plants. If filamentous algae or
plants are consistent problem, you should consider adding
of fish that can eat then, thus converting then into useful
protein, rather than staying in a constant battle to remove
The pond can be fertilized in three ways: by spreading the
fertilizer over the water surface; by placing perforated
intervals around the pond edge to allow the wave action to
dissolve the fertilizer; or by placing the fertilizer on sub
merged floating or stationary platforms off the bottom. That
method provides the best results with the least fertilizer.
Although agricultural runoff may help by providing nitrogen
phosphorous from the fields, pesticide and herbicide
destroy all of the fish in the pond. The direct application
animal manure has been shown to be effective in producing
bloom, but it does have two potential dangers. Oxygen may be
up and ammonium (a reduced form of nitrogen) may reach too
level. Both of these problems can be avoided if manures are
in moderation or if they are held in a pretreatment aeration
pond. In general, if used carefully, animal manures may be
excellent, inexpensive, source of fertilizer for the fish
The aquaculturist should, of course, be aware of any
cultural taboos against such use that may affect marketing.
taboos exist, the fish can be hold in "clean"
ponds, or use of
the manure can be suspended, for a week or two prior to
III. CULTURAL METHODS
Fish can be grown in open ponds or in cages in ponds.
on the other hand, often do better in what is called
culture. These three methods are described below.
POND FISH CULTURE
Types of Pond Culture
There are four general types of pond fish cultures:
groups, temporary age group mixing, separated age groups,
The Mixed Age Groups Method. This method produces all sizes
fish in great quantity. The level of production is
catching some fish while the fish are growing.
This may be done
with a hook and line or a limited number of traps. At the
the growth period, the pond is drained and all fish are
Some are selected for restocking the pond when it is
refilled. This method provides a high production rate if the
are well-fed. Fish from a different source should be put if
pond periodically to improve the fish quality.
The Temporary Age Group Mixing. This culture produces a
portion of equal-sized fish. The pond in stocked with young
of approximately the same size, which are fed and allowed to
and reproduce once. When the largest of the fish spawned in
pond are large enough to use for restocking, the pond is
and the fish harvested. All adults are sold or used for
smaller fish are used for restocking. In this method, the
per fish is usually small. A mixed size fishery usually
from temporary size mixing.
Separated Age Groups Method. In this method, two ponds and
feeding are used to produce table or market-size fish as
as possible. Adults of a single species are introduced into
reproduction pond. When the young spawned in the
pond are large enough to survive in a larger growing pond,
are transferred to the larger pond.
The "Natural" Predation Method. This method
attempts to balance
the fish's growth and reproduction through the introduction
predator. The results of this method are uncertain, since
over-predation will reduce or even eliminate the population,
leading to too many fish that are too small (dwarfing).
Controlled Reproduction Methods. These methods control the
and numbers of fish in the growth ponds by controlling
within a laboratory. Fish stock in the ponds do not
because conditions in the pond are not favorable for the
species used or because something is done in the laboratory
prevent fertility. One method that has been used with some
success if separation of fish by sex. Males and females are
simply placed in separate ponds. However, this is a very
method to use, because a small number of males in the
female pond (or vice-versa) will cause reproduction in the
pond (and in the male pond to a lesser extent).
Other methods include production of sterile hybrids,
fish to sexually denature them; or treating the fish to
Construction and Operation of Fish Ponds
Once pond cultivation has been decided on, the technical
must be addressed. A suitable location with an
adequate water supply must be chosen. The soil must be able
contain the water in the pond. The water quality must be
for the species, and the quantity must fill the pond in less
one month and replace losses due to seepage and evaporation.
Water Supply. There are several sources of water for pond
culture, including rainfall, surface water, springs, and
Surface water often contains unwanted fish, pollution,
and disease, and is the least desirable water source. It is
necessary to aerate to remove undesirable gazes and raise
oxygen level. Springs may also contain unwanted fish and can
up at the time water is most needed. Rainfall may be even
undependable and low in nutrients. But it will generally be
of pollutants and high in oxygen.
Well water in usually the highest quality (especially when
comes from covered wells). It does not contain unwanted fish
suspended material, and is protected from flood water. But
also may need aeration to remove undesirable gases and raise
oxygen level. If the well's water source is of uncertain
or quality, test wells should be constructed first.
The minimum pond water depth depends on the air temperature,
seepage rates, and the dependability of the water supply. In
area dependent on seasonal rains, the water should be at
(10 feet) deep over at least 25 percent of the pond. In warm
areas with low seepage or sufficient water supply, the minimum
depth may be as little as 1m (3 feet). If the pond will be
covered for one month or more, the pond will have to be at
6m (20 feet) depth to prevent winter-kill.
Woods may grow in shallow water. Since this may be
removal will depend on whether the benefits outweigh the
associated with the additional use of nutrients, loss of
volume, and potential oxygen use when the plants decay.
areas with weeds are favorite brooding areas for mosquitoes.
is recommended that the pond be not less than 12 (3 feet)
minimize weed and mosquito growth, or herbivorous fish, such
grass carp, should be among the species stacked in the pond.
The pond should be constructed with side
slopes in a ratio of 2.5 to 1 and a gentle bottom slope of
least 6.4cm per 30m (2 1/2 inches per 100 feet). (see Figure
To stabilize side slopes, grass should be planted as soon as
possible after construction. If the bottom material consists
good stable soil, put in a drain well, or harvest basin.
most fish are harvested by netting, some will escape and be
easily caught in the drain well. The drain should be
1/10 of the size of the production area and 0.7m (2 feet)
deeper than the surrounding area.
It may be necessary to build a dam to trap the water for the
pond. If so, assistance should be gained from a qualified
engineer, as a break in the dam can have serious
emergency spillway that prevents water from flowing over the
of the dam should be constructed when the pond is created.
spillway must keep the flow shallow enough or must have a
so that large fish stay in the pond and unwanted fish cannot
enter. A vertical overflow from the spillway of 0.7m to 1m,
3 feet), or a turndown pipe, will keep out unwanted fish.
A drainpipe large enough to drain the pond in less than five
should be placed in the bottom of the pond through the dam.
trickle tube--a small adjustable-height pipe that allows
water to flow out without going over the spillway--may be
connected to the drain pipe. The trickle tube should be
enough to prevent small fish from swimming out. It can also
used to regulate the depth of the water behind the dam.
To prevent decaying material from reducing the oxygen levels
to allow harvesting with nets, all trees, bushes, rocks, and
stumps should be removed from the pond bottom and sides. Any
trees within 9m (30 feet) of the edge of the pond may have
cleared to reduce leaves, which can discolor the water and
promote algae growth. Algae and decaying leaves cause oxygen
depletion, which may endanger the fish. On the other hand,
can be a source of food and might be desirable depending on
species chosen for culture.
Operation. Unwanted fish must be prevented from entering the
wherever possible. Incoming water should be filtered and the
located so that the overflow from streams does not enter.
will also exclude disease-carrying organisms and parasites.
keep birds from landing and taking off in the pond, you may
to stretch crossed wires across the pond.
It is critical in pond operation that an adequate amount of
oxygen be dissolved from the air into the water. Without
dissolved oxygen, the fish will die. To maintain adequate
do not make the pond too deep and provide a means to aerate
water if necessary (Figure 4). Unless there is good
from the top to bottom, the bottom sediments will become
without oxygen) and produce hydrogen sulfide. This will
interfere with the ability of fish to use the available
without which they may die. Decay from dead fish also
oxygen, which reduces the oxygen available for the live
thus creating a deadly cycle. The pond must be filled with
water, ever-fertilization must be avoided, and dissolved
levels should be checked frequently, especially at daybreak.
Harvesting the fish may be done by partially draining the
and netting the fish. Make the not large enough to let
fish escape. Do not drain the pond down so far that the
undersized fish are killed. The water level should be
slowly enough to allow the fish to move to deep water to
their death from stirred-up sediment and a lack of oxygen.
Harvesting is best done in cool weather, but can be done at
time. After drying the pond and performing any necessary
refill and restock the pond.
Salt Water Ponds
Although most of the information in this section has related
primarily to freshwater fish ponds, the same approach can be
to grow salt water fish in ponds. With a salt water pond,
tide circulates new water through the pond frequently enough
prevent low dissolved-oxygen levels. Predatory fish and
must be kept out of the pond. Crabs entering the pond can be
trapped, but it is best to keep them out in the first place.
starfish and crabs that are found in weekly inspections
picked up and used for crop fertilizer, eaten, or grown in
another pond and used for human or animal food.
CAGE FISH CULTURE
Fish can be confined to cages anchored in ponds, lakes, or
water bodies. This method of growing fish is most often used
the desired species is not spawned in captivity, and the
can be caught in the wild and placed in cages to restrict
movement. They must be checked frequently for disease and
parasites, but should be handled as little as Possible.
levels must be kept high enough for the fish Species.
of which method of cage culture is Used, the water must have
enough oxygen to prevent suffocation of the cultivated fish.
Competing organisms must be removed with brushes, picks, or
high-velocity water jets.
It has been found that unprotected metal cages rust quickly.
Therefore, it is advisable to use plastic-coated metal
possible. Other materials, such as plastics and bamboo may
satisfactory. Cages should be anchored firmly, with the top
the cage high enough to retain food when the fish are being
The cage top should extend down about 20 cm (8 inches), and
5-10cm (2 to 5 inches) below the water. Rigid or floating
may be substituted for the top. At least 30cm (1 foot) must
left between the bottom of the cage and the bottom of the
ocean to keep predators from entering and to prevent wave
from bumping the cage on the ocean or pond bottom. Fish in
must be fed if they are not plankton eaters. The outside of
cages must be cleaned periodically to remove fouling
and restore water flow through the cages.
Raceways are long narrow artificial channels in which fish
raised. Water is usually recirculated in this type of
The ends are secured to prevent the escape of the fish. A
system requires a water supply pond, a method of regulating
depth of the water in the channels, a settling basin to
dirt and deposits, an auxiliary water supply, and a pump.
a very complex, energy-using system.
Shrimp are often cultured in ponds where post-larval shrimps
washed into the ponds at high tide. Shrimp ponds must have a
bottom consisting of sandy-silt, or the pond bottoms may
anaerobic. This is critical with shrimp, since they burrow,
the bottom of the pond during the day. Shrimp ponds are
with gates that allow the water and shrimp to enter at
high tide when the gate is open. The opening in screened on
ebb tide to prevent the loss of the shrimp. Shrimp culture
requires circulating water to keep the bottom oxygen levels
Shrimp are harvested by placing a not at the pond outflow at
night on an ebb tide. Do not harvest shrimp by draining the
as those in their borrows will be lost. The pond should be
drained and baked in the sun for 3 or 4 days once a year.
Oysters and other mollusks grow
better with fewer deaths in
suspended culture. Shellfish may
be cultured on the bottom, on
stakes or racks, in cages or
nets, from rafts, or from long
lines. They must be grown in the
intertidal or subtidal zones.
Shellfish culture begins with
the collection of the seed,
called spat. Spat are the spawned
animals that are ready to set
on a hard object. Many shellfish
do not move once they attach to something, so a proper
is essential. Collection units consist of shells on strings
over or tied to racks, sticks, plastic disks, ceramic tiles,
bags of shells, or any other hard rough surface. Mussels
fibrous material such as coarse fiber ropes. These are
the water when shellfish are ready to attach at the time of
spawning (to reduce fouling).
After about one month, the
collectors are moved to hardening racks where they are
only at low tide. They are raised gradually until they are
exposed f or 4 to 5 hours per tidal cycle. This helps
thicker shell and stranger animal that can survive the first
hibernation period (spawning usually occurs in the spring
fall). Mussels are transferred directly to the growing area
are placed on posts or strings to grow since they have the
ability to reattach themselves once removed from a surface.
Suspended culture of shellfish is practiced because it
use of all depths of water and helps control predators.
culture provides a better quality product with no pearls,
better meat yield, good meat color, and no foreign particles
within the shell. The highest yields are obtained in the
spring, before the shellfish spawn, then again in late
before the fall spawning.
The ABC's of Suspension Culture
Anchorage - making sure the shellfish
stay where they
Buoyancy - keeping the strings from
Cultivation Materials - making sure the
Shellfish spat may be collected on racks in shallow water 2
(6 to 12 feet) at low tide. A rigid frame structure of poles
planted vertically with horizontal ties are placed in the
collection area. The collectors are arranged so there are 6
collector plates 20cm (8 inches) apart on strings 1.5m (5
long. Twenty units are hung in every 3.3 sqare meters (10
foot) area. Mussel collectors are best made from woven
1.5cm (3/4-inch) square wood pegs 25cm (10 inches) long are
Oysters are generally cultured by suspending them from rafts
long lines. Rafts
are usually made of cedar or bamboo poles tied
together in two perpendicular layers. Styrofoam cylinders,
or floats are usually used for floatation. Additional
must be added as the shellfish grow. Rafts are usually 8 x
(26 by 50 feet), and contain 500 to 600 vertical strings of
Rafts are often tied together end to end and anchored at the
of the row. They are placed in rows 102 (35 feet) apart.
will vary depending on the amount of spat collected,
disease, predation, available food, and water temperature.
In long-line culture, lines about 70m (225 feet) long are
by wood or styrofoam floats or glass balls. Floatation is
initially 3m (9 feet) with more added as the shellfish grow.
lines are placed 10m (35 feet) apart and anchored at each
in the center. Usually it is leas expensive to construct and
maintain long lines, which withstand wind and waves better
do rafts. The vertical strings of spat are placed 45cm (18
inches) apart. They can be of any manageable length, but are
usually in multiples of 5m (16 feet).
In areas where predators, waves, or winter storms are a
shellfish can be cultured in floating net cages. These are
usually 10m (35 feet) square, 3 to 5m (9 to 16 feet) deep.
consist of floats, nets, and an anchored rectangular frame.
small rafts with the shellfish enclosed in cages can be
sheltered areas in winter, when storms approach, or for
Several cages can be Joined together to form a large
It is extremely important to recognize that the strings and
require maintenance to remove fouling organisms. The strings
be removed from the water periodically and washed with a
pressure spray. A barge-mounted crane will be necessary for
or long line culture.
The large volume of waste produced by cultured shellfish
special problems. A 60 square meter (600 square foot) bed
produce between 1/2 and 1 ton (dry weight) of organic
Decay of this material can cause anaerobic conditions close
the bottom, killing the shellfish on the bottom of the
Monitoring Growth Rates
Shellfish have highly variable length-weight relationships
must be determined before the culturer can decide how long
shellfish must be grown and whether shellfish culture has a
reasonable return for the time spent.
Probable growth can be determined by suspending about 25mm
inch) long shellfish in containers about 1m (3 feet) bellow
water surface. The container must have a good water
the holes should be about 1cm (1/2 inch) in diameter.
shellfish monthly, brushing them clean, measuring them, and
recording lengths and weights. Average the measurements and
them, with the length (or weight) on one axis and the month
the other. This will provide a good guide to time of growth
The shellfish cultures in the wild will suffer a higher
due to fouling organisms. The size at harvest should be
mined by the use. Reference to the size-month chart will
minimum length of time needed to culture the shellfish to
size. In practice, it is usual to allow one additional
season for all shellfish to reach that size.
Mussels are slightly different from oysters in that they
attach themselves to a secure place after being harvested
replanted. Mussel seed can be placed in very coarse cotton
and fastened in a spiral around ropes or thick poles driven
the ground. By the time the cotton has decayed, the mussels
should be attached to the rope or pole. They can be
cleaned, and graded with the smallest ones returned to the
in now tubes. They should be kept out of water for the
To harvest mussels from strings, a collecting basket must be
placed under the string when it in lifted to catch those
that drop off.
IV. DECISION MAKING FACTORS
The management of a high density aquaculture operation is
complex, requires hard work, and is subject to the whims of
nature. An difficult as it might appear, aquaculture has
for thousands of years and is the source of food for many
people today. Even though there will always be problems, the
beginner aquaculturist is encouraged to start on a small
allowing the aquaculture operation to grow an the product
in a controlled manner.
Researchers are working an improving aquaculture techniques.
Specifically, they are working toward identifying additional
species suitable for culture, producing industrial fish (for
meal), and improving methods of managing various aspects of
aquaculture such as seed supply availability and disease,
predator, and water quality control. other areas of research
include genetic improvement, manipulating water temperature,
treating fish with hormones to promote spawning, and
new protein sources (e.g., agriculture wastes and yeasts
petroleum products or wood pulp) to replace fish meal in
formulations and to reduce the cost of feeding fish.
Some of the problem the aquaculturist will likely face include
the effects of corrosion, fouling, weather, and climate. The
aquaculturist will also encounter conflicting complaints and
demands from those concerned about land and coastal areas,
use, and pollution. Aquaculture risks may be natural
weather, disease), economic (price and market changes), or
One major constraint on aquaculture development has been the
limited supply and high cost of juvenile animals obtained
nursery areas. This can be solved locally by raising animals
producing juveniles, or by harvesting juveniles from their
natural habitat. Once the basic problem of mating, spawning,
raising the juvenile stages have been solved, the hatchery
production of large numbers of juveniles becomes routine and
inexpensive. It does not require large or expensive
By contrast, many variables make reliance on the harvest of
juveniles a very risky long-term undertaking.
In evaluating the economics of aquaculture, it must be
that the price of the product is very important and will
as the fish supply increases. The price must exceed the cost
the project is to succeed. The cost of the right to use the
property or the right of access to the culture area must be
considered in addition to the equipment, maintenance, and
In marketing your aquaculture products, you need to:
Develop a marketing system, including
information and identifying products that
will want to buy.
Set or adhere to quality control standards.
Consider transportation and marketing
Preserve your fish products to prevent
they can be sold.
Social factors that may affect your decision to pursue
The williness of your community to respond
technology (e.g., from the technology of ocean
that of aquaculture).
Acceptance of your aquaculture products.
traditional food preferences and religious or
taboos may impede the acceptance of your
Establishing an aquaculture operation may cause degradation
the environment through dredging and filling, pond effluent
discharges, increased mosquito population, and exploitation
Care must be exercised when a new or foreign species is
considered for culture. A new species could escape into the
and, without natural predators, multiply rapidly with
consequences for the overall ecological balance.
Consult your local authorities to find out whether there are
laws or regulations that may prohibit you from developing an
aquaculture system or using an aquaculture area.
Anaerobic - Without free available oxygen
Aquaculture - The controlled cultivation and harvest of
plants and animals.
Filter Feeders - Shellfish that food by filtering food
from the water through their gills.
Food Chain - Transfer of food energy through a series of
organisms with many stages of eating and being eaten.
Invertebrates - Lower animals, without backbones.
Larval Stage - An immature stage of an invertebrate animal.
animal in this stage is called larva (plural, larvae).
Mollusk - Invertebrate characterized usually by a hard,
limy, one or more part shell that encloses a soft,
Parasitic Organisms - Organisms growing on cultured
and competing for the available food and oxygen.
Predation - The act of an animal eating another animal,
smaller and of a different species.
Spat - Young mollusks past the free-swimming stage and ready
settle and attach to a hard object.
Burrill, G., and Lynch, K. An Evaluation of the Aquaculture
at Goddard College: Report to the ARCA
Bennington, Vermont: Goddard College,
Freshwater Fish Pond Culture and Management.
Volunteers in Technical Assistance (VITA),
"The State of Aquaculture,"
8, 1976, pp. 3-7.
Cramer, D. L., Slabji, B.M., True, R.M.
"Seasonal Effects on
composition, and Quality of Blue Mussels,
Meats obtained from Cultivated and Natural
Fisheries Review (Volume 40, August 1978), pp.
U.S. Department of Commerce, National
Oceanic and Atmospheric
Cuyvers, L. Aquaculture 1980. Newark, Delaware: University
Delaware Sea Grant
College Program, 1981.
Gates, J.M. "Aquaculture in Less Developed Nations,
Considerations." Presented at the
Conference of the
Society, Washington, D.C., 1971.
Grinzell, R.A.; Dillon, O.W., Jr.; and Sullivan, E.G.
Farmers Bulletin, No. 2260. Washington,
U.S. Department of
Imai, T. Aquaculture in Shallow Seas:
Progress in Shallow Sea
Culture. Now Delhi,
India: Amerind Publishing Co., 1971.
Home-Grown Fish from Cages.
Alabama Cooperative Extension Service, Auburn
Landis, R. C. A Technology Assessment Methodology.
McLean, Virginia: The Mitre Corporation,
Lutz, R.A, Bivalve Molluscan Mariculture: A Mytilus
138. Walpole, Maine: Ira C. Darling Center,
Meyers, E. The
Husbandry of Mussels in a Maine Estuary:
Approach to a
Commercial Enterprise (Publication No. UNH-SG-164).
U.S. Department of
Commerce, National Oceanic and Atmospheric
University of New Hampshire/University
of Maine Sea Grant
College Program. Washington, D.C. 1981.
Milne, P. H. Fish
and Shellfish Farming in Coastal Waters.
Fishing News Ltd., 1972.
Missouri Conservation Department.
Fish Farming: What You
City, Missouri: Missouri Conservation Department,
"Sea Farming: An Appropriate Technology for
Food," Appropriate Technology,
Volume 6, 1979,
Shapiro, S. Our
Changing Fisheries. Washington,
Protein for the Third
The Commercial Fish Farmer.
Little Rock, Arkansas:
Catfish Farmers of
U.S. Department of Agriculture.
The Yearbook of Agriculture.
D.C.: U.S. Department of Agriculture,