Aquaculture sustainabilty

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					Aquaculture Sustainability and Food Security
Aquaculture is currently playing, and will continue to play, a big part in boosting global
fish production and in meeting rising demand for fishery products. A recent session of the
FAO Committee on Fisheries (COFI) stressed the increasingly important and
complementary role of aquaculture and inland capture fisheries in fish production for
human nutrition and poverty alleviation in many
rural areas.
Aquaculture, in common with all other food
production practices, is facing challenges for
sustainable development. Most aqua-farmers,
like their terrestrial counterparts, are
continuously pursuing ways and means of
improving their production practices, to make
them more efficient and cost-effective.
Awareness of potential environmental problems
has increased significantly. Efforts are under
way to further improve human capacity,
resource use and environmental management in
                                                         Members of a women's cooperative
aquaculture. COFI emphasized enhancement of
                                                            harvest their farmed trout in Lake
inland fish production through integrated
                                                                                 Titicaca, Peru
aquaculture-agriculture farming systems and
integrated utilization of small and medium-size
water bodies.Integrated aquaculture has a
variety of benefits for farmers in addition to the
production of fish for consumption or sale. In Asia, for example, rice farmers use certain
species of fish to fight rice pests such as the golden snail. With rice-fish farming, they
boost their rice yields and harvest the fish. Under FAO's Special Programme for Food
Security (SPFS), farmers in Zambia are introducing small ponds into their home gardens
for irrigation and aquaculture. Mud from the bottom of fish ponds is also an organic
mineral-rich fertilizer.In traditional, extensive aquaculture, fish can be bred in open
waters such as lakes, estuaries or coastal bays, where they feed on naturally available
nutrients, or in farm ponds, where they can be fed with by-products from the farm.
Traditionally in China, more than five species of carp are bred together to make the best
use of feeds and ponds.
The promotion of sustainable aquaculture development requires that "enabling
environments", in particular those aimed at ensuring continuing human resource
development and capacity building, are created and maintained. The FAO Code of
Conduct for Responsible Fisheries contains principles and provisions in support of
sustainable aquaculture development. The Code recognizes the Special Requirements of
Developing Countries, and its Article 5 addresses in particular these needs, especially in
the areas of financial and technical assistance, technology transfer, training and scientific
cooperation.
PRODUCTION LIMITS
There are biological limits in the production pond or aquatic environment. Stocking
densitiesand harvest yields are finite and determined by pond (environmental) carrying
capacity. Theavailability of dissolved oxygen is the primary factor determining maximum
pond biomass.Depending on temperature, salinity and atmospheric pressure, water can
only hold certainconcentration of oxygen. As the overall weight or biomass of a farmed
species increases in theculture pond, so does oxygen demand. When respiratory demand
exceeds the rate of oxygenreplacement from surface diffusion and photosynthesis, either
aeration is employed or oxygenbecomes depleted and the culture species suffocate.
The total biomass in production ponds is composed primarily of phytoplankton,
zooplankton, the culture species and other micro-organisms (bacteria, fungi, etc.).
Phytoplankton produce most of the oxygen consumed in the production pond through
photosynthesis. But phytoplankton consume oxygen as well. The waste products
(manure,uneaten feed and excreted ammonia) from the primary culture species release
nitrogen andphosphorus (fertilizer) into the pond which stimulate the growth of
phytoplankton. Thenitrogenous wastes can be toxic to aquatic animals. However, when
the phytoplanktonpopulation (or bloom) becomes too dense, nighttime oxygen
consumption becomes greater thanthe rate of replacement from surface diffusion and
photosynthesis. Production wastes capharvest biomass by increasing phytoplankton
growth beyond critical densities.Phytoplankton productivity and biomass are measured
indirectly as the chlorophyll aconcentration (μg/l). Contrary to the popular maxim that
"nutrients (e.g., phosphorus andnitrogen) are limiting" for plant (phytoplankton)
growth,in heavily stocked or intensive,production ponds, light can be the limiting factor.
The concentration of plants becomes so high
(400-600 μg/L chlorophyll a) that light can not penetrate to any appreciable
depth(Tucker,1996). This limits photosynthetic oxygen production and primary
productivity while respirationincreases or continues unattenuated. When phytoplankton
populations are sufficiently dense,even aeration will not maintain dissolved oxygen at
concentrations acceptable for aquatic life. Inaddition to oxygen depletions, the off-flavors
commonly associated with dense algal blooms will
hamper production (i.e., unmarketable product).

POND BIOMASS
From a commercial standpoint, it is easy to view the cash crop as being the only
significantspecies in a production pond. As discussed previously, pond biomass consists
of several aquaticlife-forms, not the least of which are planktonic. Little empirical data
exist about zooplanktonproductivity in aquaculture ponds (eutrophic waters) and even
less practical information isavailable for predicting standing, zooplankton biomass.
However, there is some knowledgeabout phytoplankton productivity, respiration and
standing biomass in intensively farmed ponds
 (1995) reported that for every 1,000 kg of live channel catfish harvested, total
phytoplankton
productivity is 2,500 kg/ha dry weight or approximately 50,000 kg/ha wet weight. Each
seasonthe plankton biomass is lost when these organisms die, break down, and return to
their basiccomponents: water, carbon dioxide, nitrogen and phophorus.
On a dry weight basis, phytoplankton and zooplankton could easily account for almost
half of the total, daily biomass in a culture pond. At harvest, there would be a standing
biomass(dry weight) of approximately 900-1,000 kg/ha of plankton for 1,000 kg/ha
(5,000 kg/ha wetweight) of channel catfish. Because of their smaller size and greater
surface area to volumeratio, phytoplankton and zooplankton have significantly greate
rmetabolic rates and therefore,much higher respiratory rates. In a commercial production
pond, phytoplankton alone can
consume greater than five times more oxygen per day than channel catfish (Table 3).

PLANKTON HARVEST
The most obvious way to increase the harvest biomass of a culture species is to lower
oxygendemand by reducing plankton biomass. Greater oxygen availability would permit
higher stocking densities and bigger yields. Plankton could be harvested either
mechanically orbiologically. Mechanical harvest would involve pumping water through
filters and collecting the plankton retained. Because the mesh or screen size determines
the size of the particle harvested, filter screen selection and placement would be critical.
Screen mesh must be small enough to retain the size of plankton desired but large enough
to allow smaller plankton and particles to pass through unobstructed. Larger particles
such as zooplankton must be removed before filtering smaller particles like
phytoplankton and minute zooplankton. Otherwise, the small mesh screens for
phytoplankton would become clogged rapidly by the large zooplankton, and
filtering would be disrupted. While mechanical harvest of plankton may be
technologically feasible, it is likely that economic obstacles and the current lack of
markets for plankton products would make this approach impractical.

MODIFIED POLYCULTURE
The traditional polyculture practice of allowing both zooplankton and phytoplankton
feeders to roam freely in the same pond has some drawbacks. This technique can be
inefficient and problems like those discussed for mechanical filtration exist. Species that
feed on phytoplankton are filtering smaller particles from the water than animals that
consume large zooplankton. Both types of filter feeders are grazing simultaneously, or
parallel to one another. In addition to removing phytoplankton, herbivorous planktivores
remove large zooplankton from the pond non-selectively, because they strain their food
from water on the basis of size (i.e., small mesh screens vs. large mesh screens). The net
effect is a lowered concentration of zooplankton which reduces the filtration efficiency
and potential biomass of zooplankton feeders.
As with mechanical harvest, the most efficient method of plankton harvest would be to
place zooplankton feeders in front of phytoplankton feeders and those animals that
consume much smaller zooplankton. Each of the different species would have to be
compartmentalized
Poverty and food security

Poverty is a generally considered as being one of the major causes of food insecurity.
Poverty eradication is essential to improve access to food. The World Bank defines
poverty as a "multidimensional phenomenon, encompassing inability to satisfy basic
needs, lack of control over resources, lack of education and skills, poor health,
malnutrition, lack of shelter, poor access to water and sanitation, vulnerability to shocks,
violence and crime, lack of political freedom and voice". It is estimated that about one-
fifth of the world's population is currently living in extreme economic poverty; defined as
living on less than US$1 per day (in 1993 dollars, adjusted to account for differences in
purchasing power across countries).

Role of aquaculture
Fish contributes to national food self-sufficiency through direct consumption and through
trade and exports. In traditional fish eating countries in Asia and Oceania, per capita
consumption are mostly above 25 kg. In some island countries in the Pacific the per
capita consumption are above 50 kg per year or even as high as 190 kg as is the case in
Maldives. The extreme importance of fish to food security and nutrition may be
illustrated by assessments on the situation in Africa. FAO estimates that fish provides 22
percent of the protein intake in sub-Saharan Africa. This share, however, can exceed 50
percent in the poorest countries (especially where other sources of animal protein are
scarce or expensive). In West African coastal countries, for instance, where fish has been
a central element in local economies for many centuries, the proportion of dietary protein
that comes from fish is extremely high: 47 percent in Senegal, 62 percent in Gambia and
63 percent in Sierra Leone and Ghana.

In general terms, aquaculture can benefit the livelihoods of the poor either through an
improved food supply and/or through employment and increased income. However, at
present little or no hard statistical information exists concerning the scale and extent of
rural or small-scale aquaculture development within most developing countries and
LIFDCs, nor concerning the direct/indirect impact of these and the more commercial-
scale farming activities and assistance projects on food security and poverty alleviation.
Despite the lack of information concerning the role of rural aquaculture, there is one sure
benefit of consuming fish, and that is the nutritional and health benefit to be gained from
its valuable nutritional content. Food fish has a nutrient profile superior to all terrestrial
meats. It is an excellent source of high quality animal protein and highly digestible
energy, as well as an extremely rich source of omega-3 polyunsaturated fatty acids
(PUFAs), fat soluble vitamins (A, D and E), water soluble vitamins (B complex), and
minerals (calcium, phosphorus, iron, iodine and selenium). In fact, if there is a single
food that could be used to address all of the different aspects of world malnutrition, it is
fish - the staple animal protein source of traditional fishers.

				
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posted:7/25/2012
language:English
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