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Aquaculture began by man making small
modifications to natural habitats so as to improve
the survival and growth of his target species. Some
of the oldest examples are in the rearing of
freshwater fish in ponds, something that has been
practised for thousands of years in Asia and at
least for many centuries in Europe. The simple act
of putting a mesh barrier across the outlet of a
small pond or lake to prevent the fish escaping
could make a big improvement in the food that could
be supplied from the pond in the following months.
Similarly along the coasts, tidal lagoons occur
that can be turned into ponds with a minimum of
effort. Closing off such naturally occurring water
bodies was the start, centuries ago, of much fish
and shrimp aquaculture in Asia and, in modern
times, in South America.
Removing predators and improving the conditions
within the pond, (for instance by providing more
area of preferred water depth), supplying
additional food and later, adding seed animals
collected outside, were further steps that moved
aquaculture production close to where it is today.
The farming of seaweeds and molluscs (oysters,
clams, mussels etc) developed similarly, as people
made improvements such as providing more settlement
areas for the young, or the removal of predators
from the growing area.
Farmers had a natural desire to improve the
productivity of their systems and, as knowledge
grew, they learned to stock more animals, increase
feeding and manage the exchange of water to
maintain the conditions, such as adequate oxygen
levels, that the animals needed to survive.
The range of facilities used for aquaculture
subsequently broadened for a number of reasons.
Farmers encountered difficulties with more
intensive rearing because of the uncontrolled
influence of pond soils, local water quality,
weather. Some of these problems could be resolved
by rearing in ponds built of concrete, or lined
with plastic, by bringing the ponds indoors under
cover, or treating the water before flowing it to
the culture ponds. Secondly, as the naturally
occurring ponds and lagoons all became utilised,
prospective farmers had to take a broader approach
and develop the technology to be able to use less
naturally favoured sites. Net cages floating in
protected coastal or inland waters were developed
for fish culture, or fish were stocked in fenced
areas of the sea or of large lakes.
At the same time, the need for supplies of young
animals (fry, seed) to stock the systems led to the
development of hatchery techniques and dedicated
hatchery facilities. For most species this aspect
of production has proved more successful when
conditions can be more closely controlled, for
instance in indoor concrete and fibreglass tank
systems, rather than in outdoor ponds. Often, the
younger stages of aquatic animals are more
sensitive than adults to physical and chemical
conditions and these have to be managed within a
smaller range, if production is to be successful.
Thus hatchery facilities developed as a separate
branch of the industry.
More recently, our knowledge has improved
greatly regarding the complex interactions that
occur in a rearing system, between nutrients,
bacteria and the cultured organism. This and
technological developments have allowed many
aquatic organisms to be reared in completely closed
recirculating facilities, including the farming of
marine organisms at locations far from the sea.
Closed systems have the added advantage of offering
greater protection from the danger of disease
entering from the natural environment and also of
minimising adverse effects of the production system
on that external environment.
Technology has also begun to open up the
possibilities of growing fish in enclosures in the
open ocean, something that could one-day transform
the nature of human food production on the planet.
With 70% of the earth's surface covered by water,
the potential is clear. Earlier technology has
restricted the cage farming of fish to sheltered
coastal waters. Here the number of available sites
is limited, environmental damage is more likely and
conflicts exist with other users. As cages are
developed that can withstand the demanding
conditions of the open ocean, or which can be
operated below the ocean surface, farming could
move further offshore.
The farming of the sea without enclosures has
also made a small start, through so called
'ranching' programmes, notably in Japan, where fry
are released in large numbers into the ocean with
the aim of improving returns from the capture
fishery. Sometimes artificial reef structures are
created underwater as well, to increase the
available habitat and natural food for the fish.
Results with such initiatives have been mixed, but
as we reach a better understanding of species
interactions on the High Seas, ranching could
become more successful and make a difference to
world fisheries production.
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reference sources
Baluyut, E.A. 1989 Aquaculture systems
and practices: a selected review. Rome,
FAO/UNDP.
Mathias, J.A., Charles, A.T., &
Baoteng, H.W. (Eds). 1994. Integrated fish
farming. New York, U.S.A., CRC Press. ISBN
1-56670-260-7. 420 pp.
Nash, C.E. & Vovotny, A.J. (Eds).
1991. Production of aquatic animals:
crustaceans, molluscs, amphibians and
reptiles. World Animal Sci. C4. Amsterdam,
Netherlands. Elsevier. ISBN 0-444-88312-6.
244 pp.
Nash, C.E. & Vovotny, A.J. (Eds).
1995. Production of aquatic animals:
fishes. World Animal Sci. C8. Amsterdam,
Netherlands. Elsevier. ISBN 0-444-81950-9.
405 pp.
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