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Aquaculturists have developed or adapted many
specific techniques to improve their operations -
some drawn readily from other fields and some which
have had to be devised by farmers and technicians
themselves. They range from simple field tricks
like moistening soil and rolling it into an
elongated shape to test whether there is enough
clay in the soil to make watertight pond dykes -
through to advanced biotechnology such as gene
transfer. As the sector has expanded to new
regions, new species and to achieve control over
more of the life cycle of farmed animals and
plants, fish farmers have proven very innovative in
devising solutions to the new problems they
faced.
The culture of carp was originally restricted to
the home range of each species, where fry (seed)
could be caught from the rivers and stocked in
ponds. A study of how water temperatures, changes
in day length and other factors affected the
reproductive cycle of fish subsequently led to the
ability to breed carp far from their native waters
and where the natural conditions would not normally
allow breeding. Manipulation of water temperatures
and day length remains important in the successful
hatchery production of many farmed species to this
day. As hormones became identified and their action
understood in higher vertebrates, fish farmers
began to experiment too, with extracts of hormone
producing organs in fish, and found that egg
development and spawning could be promoted in many
species by the injection of hormone extracts from
pituitary gland. These techniques are used today in
the production of fish like carp, salmon and bream.
Oysters and other molluscs are brought to produce
eggs by manipulating water temperatures and shrimp
are made to develop their ovaries by removing a
gland that produces an inhibitory hormone, sited in
the eyestalk. Hormones are also used in processes
like the sex-reversal of tilapia to produce
all-male populations that give better production.
There is a short period in the early life of the
fish when their sex is not fully determined and
feeding them with a hormone treated feed can push
them to develop male characteristics.
Many fish are stripped of their eggs (females)
and milt (males) in hatchery production and the
fertilisation is carried out externally. Typically
this is done in a bowl with the eggs and sperm
being mixed with a feather. Shrimp that do not
readily mate in captivity are artificially
inseminated by extracting the sperm capsule from
the male and attaching it to a female that has ripe
ovaries to replicate the natural mating
process.
The young stages of many farmed animals need
quite specific feeds to survive and many techniques
have had to be developed to produce reliable
supplies of feeds, both live and inert, to support
hatchery operations. Particular species of
microscopic algae are selected from the thousands
that occur in the sea or freshwater and grown in
tanks with just the right mixture of nutrients to
make them flourish. These algae are then fed to the
young fish or shrimp. Many cultured fish and shrimp
species require live microscopic animals at certain
stages of their development and the type of feed
they need can be quite specific. Aquaculturists
have found that in many cases, animals such as
Artemia and rotifers can fill this need and have
developed the techniques to rear these two to an
advanced level. Artemia (brine shrimp) are tiny
shrimp like creatures that grow in salty lakes in
places like Utah, USA and Iran. When the salt
content increases to a certain level the Artemia
turn into an egg-like cyst and this can be stored
dry for many years. When it is put back in water, a
tiny Artemia hatches out and this has proven to be
an ideal feed for the early stages of many fish and
shrimp.
Because of the problems and costs faced in
rearing live feeds however, techniques have also
been developed to produce artificial feeds with the
right density to float in the water, the right
taste and feel to be attractive to the fry and the
right nutritional content to give good growth and
survival. Vitamins dissolve out of such feeds quite
quickly and so methods have been developed to coat
the vitamins or hide them inside minute
'microcapsules'.
In ponds, it is often hard to see how much the
animals are eating - a fish farmer can not see how
much his animals leave, like a cattle or chicken
farmer can - and so techniques have had to be
developed to make sure the fish or shrimp are well
fed, but feed is not wasted. Some farmers use
demand feeders where the fish learn to push a lever
to get feed. Others place feed on trays and then
pull up the tray to check what feed is left. In
fish cages, farmers nowadays use close circuit TV
to see what is happening underwater.
Many techniques important to the industry are in
the health sector. Plating samples of water and
tissue on agar plates to test for bacteria and
fungi, the use of electron microscopy and DNA based
'probes' to check for viruses, the use of
'probiotics' or 'friendly' bacteria to keep water
in good condition, to mention just a few. Then
there are fields like cryogenics - the freezing of
eggs, sperm and embryos at ultra low temperatures
for storage and use at a later date; the use of
anaesthetics to calm fish down for live transport
(also possible by lowering the temperature);
treatments like dipping the shells of freshly
caught shrimp in an anti-oxidation mixture to keep
them fresh longer. The techniques useful to
aquaculture are many and will continue to expand
and improve, to help bring more cultured fish to
the table.
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