Autotrophic lake aquaculture for sustainable and water-free food production.1
Ricardo Radulovich, Ph.D.
Department of Agricultural Engineering
University of Costa Rica, San José, Costa Rica
Email: [email protected]
Abstract
Water is becoming the most severe and widespread limitation to increasing world food production and
security. While irrigation is a very limited option precisely due to lack of water, rainfed agriculture is
affected by prolonged dry seasons and rainfall variability during the rainy seasons. Climate change may
aggravate this to an unforeseeable degree. Yet several countries in Africa are endowed with many lakes,
some very large, that occupy a surface of over 150,000 km2. Fisheries, however, a traditional source of
quality food, are severely dwindling and in many cases water eutrophication is increasing. These
conditions make essential that adequate food production systems are developed to take advantage of
lakes and lagoons while preserving and even improving their conditions. The concept of autotrophic
aquaculture is presented here as such an approach, in particular for Malawi, which will allow production
of massive amounts of food without spending additional water from the lakes, moreover taking
advantage of the excess organic matter and nutrients to the point of bioremediating the waters. Just like
agriculture, autotrophic aquaculture is based on photosynthesis, in this case in the water itself, both
directly by producing aquatic plants and indirectly by using filter-feeding fish and bivalves to feed on
phytoplankton plus organic matter and nutrients. Aquatic plants thus produced, given their high
nutritional value, can be used as human food or as feed for herbivorous fish production and even for
land livestock. Their use as biofuel is equally valuable. The production of horticultural crops in floating
conditions is also considered since their production is simple and their transpiration will take the place
of evaporation from the lake area where they are produced, again not representing additional water
expenditure. Several conditions for this are discussed, including the use of native species and of low cost
pens and flexible cages to allow for a wider base of participants and of low-investment, low-input
systems that do not require high returns. Evidently, the task is not a simple one, yet the rewards can be
so far reaching that a concerted effort should be made to develop such an approach or similar ones.
1
This paper is a proposal for discussion. The author will thank comments and criticism. The proposal was
originally presented at a workshop--and greatly enriched by participants--conducted at the Department
of Fisheries and Aquaculture, Bunda College of Agriculture, University of Malawi, Oct. 3-7, 2011, as part
of a program of the Food Security Center, Hohenheim University, Germany with the University of Costa
Rica, San José, Costa Rica, and the Bunda College of Agriculture, University of Malawi, Lilongwe, Malawi.
Recent research and applications leading to this proposal were developed through the ‘Sea Gardens’
project funded by grant 131-07 of the Development Marketplace Program of the World Bank. Contents
and opinions are exclusively of the author.
1
Introduction
As in many countries in the world, food production in Malawi is limited by lack of water to the point of
recurrent and severe food shortages, particularly during the prolonged dry season but also due to
rainfall variability during the rainy season. One approach being followed to confront this situation is to
enhance the potential of rainfed agriculture by distributing subsidized improved maize seed and
fertilizer nitrogen to farmers, something that has considerably increased yields yet so far coinciding with
years of moderate to good rainfall (Denning et al., 2009; Sanchez et al., 2009).
Irrigation, which already uses 70% of the world’s available freshwater, even 90% in some countries
(Pimentel and Pimentel, 2003; Madramootoo and Fyles, 2010), is a very limited option given the high
amounts of water needed for crop growth, particularly during the dry season when water levels of lakes
are at their lowest and demand at its highest. A crop, like soybean or maize, requires ca. 50,000 liters of
water per hectare per day, most of it for evapotranspiration since only a small fraction is used to
constitute live biomass (e.g. Allen et al., 1998). Thus, simple calculations allow to conclude that in the
order of 1,000 liters of water are needed to produce a single kg of grain, and from 15,000 to 200,000
liters (depending on how calculated) are needed to produce one kg of beef (Pimentel and Pimentel,
2003; Aiking, 2011), most of it for the production of feed since on-farm water use by animals, including
drinking, is only 1% of feed-associated water use (Verdegem et al., 2006).
Fishing from the abundant lakes and lagoons, particularly from Lake Malawi, which covers ca. 24,000
km2 of the country, is a major contributor to the Malawian diet, yet catch and subsequently per capita
consumption have been reduced substantially, to less than half of previous levels (Global Fish Alliance,
2002; World Fish Center, 2010).
Pond aquaculture has received attention during the last decades, and it has been considered an activity
of high potential to substitute the decrease in capture fisheries, particularly through low-input systems
(Global Fish Alliance, 2002; Kamtambe et al., 2009; Valeta, 2011). Yet, according to Windmar (2011),
“subsistence aquaculture has failed to increase the supply of fish in Africa.” A reason for this may be
that one kg of fish meat in freshwater pond aquaculture requires on average 5000 liters of water to
account for direct water losses from the pond such as evaporation and seepage (Pillay and Kutty 2005;
Bostock et al., 2010), to which water used to produce the feed on land must be added at a rate of
several thousand liters more per kilogram of edible weight acquired by fully-fed fish (though much less
so for low-input systems that rely mostly on feed generated in situ). On this issue, Windmar (2011)
reports that in extensive pond systems in Malawi the water consumption can be beyond 50 000 l/kg of
fish produced, adding that due to this low water productivity “Some of the smallholder fish farmers I
worked with in Malawi from 2006-2009 had to give up fish farming because they realized that they
could make money if they used the available water resources to produce potatoes, groundnuts or
maize.”
2
Cage aquaculture in lakes and other confined water bodies, an activity that is beginning to grow in Lake
Malawi (World Fish Center, 2010), is very limited in its sustainable growth potential--to the extent that it
is based on fully-fed fish--since added feed releases proportional amounts of organic matter and
nutrients into the water as fish excrement and unused feed. There is ample demonstration in marine
environments that fed-animal cage aquaculture leads to serious eutrophication conditions. For example,
in Xiangshan Harbor in China in 2000, it was estimated that cage aquaculture discharged over 15,500
tons of unconsumed feed (wet weight) and over 1,700 tons of fecal material (dry weight) (Huiwen and
Yinglan, 2007). An example of this in freshwater is Lake Taal in the Philippines, with 243 km2 of water
area and an average depth of 65 m, where close to 10,000 fish cages of tilapia and milkfish exceed
carrying capacity, creating a variety of environmental quality problems including bottom fouling close to
fish cages and eutrophication, attributed to fish excrement and feed spill, aggravated by 30%
overfeeding (White et al., 2007).
Moreover, to the extent that fish production relies on feed made from grain, grain sub-products and fish
meal and oil, and even if feed components were available and affordable, something that is not the case
for Malawi (Longwe et al., 2010), such fed-animal aquaculture cannot be considered food production
but the contrary, food transformation through reduction, since normally close to two kilograms of dry
concentrate feed are required to produce a kilogram of fish fresh weight (a ratio close to 10:1 when
correcting for water content).
Also, high investment, mainly in cages and feed, requires high returns. This not only alienates the poor
from participating but may promote the use of faster growing non-native species, which sooner or later
escape in large numbers altering native biodiversity.
To bypass these water, feed and investment limitations of traditional animal-based aquaculture, in order
to use sustainably the enormous water-based capabilities of lakes to produce food, something that has
been advanced for the sea (Radulovich, 2011), the concept of autotrophic (self-fed) aquaculture is
advanced here which, if applied as proposed, or in its many possibilities of which most remain to be
developed, should allow substantial aquatic food production without spending any water while not
polluting it, on the contrary cleaning the water from unwanted excess nutrients. This concept, as well,
can be implemented in association with some conventional aquaculture operations as well as with
efforts to recover fisheries through restocking or aquaculture-enhanced fisheries.
Sustainable autotrophic aquaculture
Since water is at the core of aquaculture growth and sustainability, it is convenient to establish at first
two conditions by which aquaculture does not require or consume water by itself to produce food. This
refers to both animal and plant production, and of course it represents water spent beyond the small
fraction of water included in fresh weight at harvest (i.e. it considers the water spent producing food
and not water in food). As explained earlier, water that comprises fresh weight is minimal compared to
3
other water expenditures such as evaporation, transpiration and seepage which together account for ca.
1,000 liters per kg of grain and 5,000 liters or more per kg of animal live weight produced.
Aquaculture does not require water by itself as long as two complementary conditions are met:
a) No water losses or expenditures can be attributed to the aquaculture production system. From a
lake and other permanent water bodies these water expenditures or losses (from the surface
like evaporation, spillage and runoff or from seepage into the soil) happen naturally anyway.
This is not the case from ponds created for that purpose; and,
b) All and any feed is produced in the water (though as discussed below a balanced exchange
between land and aquatic plant and animal biomass can be made).
Aquaculture systems, particularly those in regions limited in freshwater availability or, as in a lake,
limited in replenishment, must consider these two conditions that in turn greatly impinge on
sustainability.
Of particular relevance, for aquaculture to become a net source of food it must begin with and rely on
photosynthesis in water. It must be autotrophic in a net sense, just as agriculture is and to the
equivalent point where thanks to crop photosynthesis livestock can be fed.
Currently, for aquaculture to become a net source of food, this is possible:
a) indirectly, by promoting or taking advantage of photosynthetic microalgal growth from which higher
organisms feed, either directly as filter-feeders or up the trophic web, with zooplankton for planktivores,
or after more trophic levels that produce multi-celled plants and animals on which omnivorous and
carnivorous fish and crustaceans feed; or,
b) directly, at sea through seaweed farming and on freshwater through the farming of aquatic plants
which are in turn used as human food or as feed for animals.
In fact, pond aquaculture that relies on fertilization of the water and soil to promote microalgal growth
from which fish or shrimp feed, is a very widespread autotrophic system, and the intentional production
of microalgae for these purposes is considered “the leading sector in world aquaculture” (Neori, 2010).
Autotrophic aquaculture can also be defined in trophic terms. While the average trophic level for
agriculture is 1.03 (with photosynthetic crops of trophic level 1.0 being produced over 20 times more in
quantity than herbivorous livestock of trophic level 2.0, and that without counting the substantial
though unaccounted contribution of plant biomass from grazing), that of capture marine fisheries is 3.1
and the top 25 aquacultured fish species in the world average a trophic level of 2.64, yet for salmon and
trout this is 4.4 (Tacon et al., 2010) and for tuna 5.0 (Duarte et al., 2009).
4
Developing-country aquaculture (mostly freshwater) has focused on lower trophic levels and “…is
increasingly a means to increase domestic fish supply to low-income consumers” (World Fish Center,
2011). In fact the two carp species that produce 26% of total finfish aquaculture have a trophic level of
2.0, i.e. fully herbivorous fish; however, developed-country aquaculture has focused on high value
omnivorous and carnivorous fish, and the nine groups of marine fishes being produced have a mean
trophic level of 3.5 (Duarte et al., 2009), higher than capture marine fisheries. Bivalves, which filter-feed
on phytoplankton, have a trophic level of 2.0 and seaweeds and freshwater aquatic plants, termed here
true autotrophs, a trophic level of 1.0.
The following analyses of autotrophic aquaculture in quantitative terms is based on an honored rule of
thumb in ecology that when energy passes (through ingestion and metabolism) from one trophic level to
the other, the energy within the living being in the lower trophic level that is consumed is reduced to
10% in the living being on the next level, something termed the ‘energy transfer efficiency’ (e.g., for fish
see Pauly and Christensen, 1995). This means that, on average, an animal keeps within its body only 10%
of the energy it consumes, whether it comes from plants or from other animals.
For a hypothetical animal aquaculture system for which aquatic plant production is practiced to feed the
animals, roughly, dry plant biomass produced must be ten times the dry animal biomass to be produced.
It follows that for each kg of fresh weight growth of a strictly carnivorous fish 10 kg of fresh fish weight
must be provided. In fact, the latter is only true during the fast growing phase of fish. It has been
reported that for large tuna, perhaps the most extreme case with very high maintenance requirements,
to achieve an extra kg of live weight around 20 kg of fish fresh weight must be fed (Volpe, 2005).
Assuming similar dry/fresh biomass ratios, to produce 1 metric ton (t) of herbivorous fish live weight 10
t of live aquatic plant biomass must be produced, while to produce 1 t of carnivorous fish 100 t of live
aquatic plant biomass must be produced to feed the 10 t of herbivorous fish needed to feed the
carnivorous ones. Nonetheless, carnivorous fish thus produced can still be a part of a larger autotrophic
system, yet it would be as expensive in trophic terms as producing tigers for food (Naylor and Burke,
2005), which is the proper equivalent to the growing trend in developed-country aquaculture to
emphasize carnivorous fish production, notwithstanding efforts to increase the vegetable share of their
diet. It is far more logical to produce herbivores (including filter-feeders), just as in agriculture,
particularly when producing meat for resource-poor consumers.
Filter-feeders (including bivalves and some fish) normally feed on phytoplankton and suspended organic
matter, though some planktivore fish feed mostly on zooplankton. However, disregarding momentarily
the formal trophic analysis, it is possible to consider filter feeders as “functional autotrophs” since they
do not require input of feed as such—(though perhaps of nutrients and fertilizers to promote microalgal
growth as done in ponds, and as it can eventually be done in lakes promoting a controlled nutrient
enrichment if it were needed at all). So for practical purposes, and both agriculture and aquaculture are
practical sciences, filter-feeders in these conditions can have a trophic level of 1.0. Of course, this
wouldn’t be the case if there were an opportunity cost for the microalgae and organic matter they feed
5
upon (e.g. if natural cycles were to be disrupted because of extensive filter-feeder production,
something that is not normally the case in over-fished water bodies subjected to organic matter and
nutrient inputs from agricultural runoff and other sources).
An interesting offshoot from the above is that, to the degree that they feed from natural pastures and
vegetation on land that would otherwise have no or very limited other uses, cattle, sheep and goats can
also be considered as “functional autotrophs”, and this has fed humanity since times immemorial and
pastoralism continues to be a very important component of food production in Africa and elsewhere.
Moreover, by uptaking suspended organic matter and microalgae that have fed on dissolved nutrients,
filter-feeders clean the water and their use in bioremediation is growing (Cuomo et al., 1997; Soto and
Mena, 1999; Troell et al., 2003).
Aquatic plant (macrophyte) culture can be very valuable by itself, not only to feed fish but for other
purposes like human food, given their high protein content, in cases similar to grain. Given these
nutritional qualities and high growth rate of several aquatic plant species, there is a growing interest in
cultivating them for human food and/or animal feed (Skillicorn et al., 1992; FAO 2009), or even for
bioenergy (Kresovich et al., 1982; Bhattacharya and Kumar, 2010). In fact, even the traditional ‘nuisance’
of their blooming is now being considered a benefit as uses for their biomass are understood and
valued, as well as their capacity to bioremediate by uptaking nutrients from water thus counteracting
eutrophication--they have even been used to efficiently treat domestic wastewater (Kanabkaew and
Puetpaiboon, 2004). The threat that aquatic plants will clutter water ways, particularly close to
hydroelectric facilities, should cease when both those plants are valued (and thus will not go
unharvested) and some measures are taken such as placing nets as barriers. Currently, where their
blooms are a nuisance and clutter water ways, the new trend is “harvest them, and use them”; the next
trend must be: “cultivate them”. All of this without even beginning selection and genetic improvement
programs, which in a few years with a fraction of what is spent in agricultural crop improvement can
lead to tremendous advances.
Regarding bioremediation, however, a word of caution is warranted since both generalized and localized
pollution is of concern. It is one thing to have a certain concentration of a pollutant distributed through
a large area and the water column in general, and another the fact that around intensive animal
production, where thousands of animals are confined in a rather small volume, large amounts of organic
matter settles close to the emission without traveling with the water any significant distance. The latter
is an important consideration and any aquaculture scheme that purportedly takes advantage of such
organic material and nutrients in the water might not in reality fully accomplish the task. This is closely
tied to the carrying capacity of a lake and of portions of it, which as a concept that determines how
much live biomass can an area or volume of water support relates to both native and enhanced
productivity aspects, that create and maintain such live biomass (i.e., precisely beginning with
autotrophy). Even though water and its constituents move, this is limited, and thus both bioremediation
and carrying capacity must be considered not only for the totality of the water body but for specific
locations as well, something that remains at the core of any aquaculture system.
6
So, in practical trophic terms, autotrophic aquaculture is a combination of plant and animal aquaculture
that begins with trophic level 1 (whether formally, i.e. for plants, or ‘functionally’, as defined above for
filter-feeding fish and bivalves) and from there part or all of this production can be used as feed for
heterotrophic fish. Thus, the key issue is that autotrophic aquaculture does not rely on external feed
inputs unless, as mentioned, a trade-off is established with production on land thanks to which, for
example, fish diet can be complemented with products and byproducts from agriculture, fishery and
aquaculture itself, as long as this input is accounted for in the biomass and nutrient balances of both the
water body and the autotrophic status of the production system.
If an autotrophic approach is not followed, which can be for an individual system or for a combination of
systems of which some are not but their overall value is, aquaculture in general, not only for lakes, will
continue to be subsidized by agriculture and fisheries, and it will not pass from being another branch of
livestock production just as poultry is—with the notable difference that poultry production, as efficient
as reputedly fish are in feed conversion, has evolved to the point that chicken acquire 2 kg in six weeks,
while fish hardly reach 1 kg in a year. In this sense, and counting the water and infrastructure needed in
many traditional aquaculture systems, when using feed of some quality it might be far better used to
raise chicken if meat protein for the population and markets is what is desired (as opposed to highpriced aquatic products to satisfy specific markets).
Species and production systems for autotrophic lake aquaculture
Several groups of species and aquaculture systems can be considered autotrophic, and some of them
are presented as examples of the existing potential for lake aquaculture in Malawi.
1. Filter-feeding fish
Several native fish species are filter feeders, fully or to a large extent, like Oreochromis shiranus and O.
karongae, and they can be used in a variety of production systems depending on conditions of the water
body, beginning with high native nutrition of eutrophic smaller lakes and lagoons and high microalgae
concentration down current from upwelling areas in Lake Malawi.
Such fish production can be implemented in three non-exclusive manners:
a) in cages;
b) in pens or other enclosures (e.g. closing with a net the entrance of a bay in a lake); and,
c) releasing fingerlings in an open area of known productive potential or depleted populations to
improve fisheries (restocking or aquaculture-enhanced fisheries).
The two latter options increase the feeding potential to the extent that fish can access bottoms, thus
allowing the use of other species such as a nibbler like Tilapia rendalli, besides filter feeders. Also, areas
in pens can be substantially larger than within cages, like the one shown in Figure 1 which corresponds
7
to a eutrophic area moreover devoid of fish due to overfishing. Cages, however, can be placed in deeper
waters allowing more access to the water column and permitting some dilution of organic matter and
nutrients.
Figure 1. An area of Khia Lagoon, Malawi, identified as a potential pen. The narrow entrance can easily
be closed with a net and be used as a large natural pond to grow filter-feeding fish and aquatic plants.
The water was considered eutrophic and thus has high natural feeding potential, and of course adding
feed would only worsen the situation.
Given the relatively tranquil waters of a lake as compared to the ocean, low-cost cages of any size can
be built with the utmost simplicity, preferably with a flexible frame made of rope, with the form
provided by tensional integrity from anchors and buoys, such as the one shown in Figure 2, which is
derived from the work being conducted at sea in Costa Rica. After some engineering input it should
become completely unnecessary to purchase from abroad cages that are for rough sea conditions, such
as salmon cages being used in Malawi (World Fish Center, 2010) and tend cost around $100/m3 when
they can be made locally at a much lower cost—with the many benefits associated to reducing
investment. Locally made cages for low-input aquaculture are being successfully used in Kenya (CharoKarisa et al., 2009).
Through some approximations and—brief—trial and error, the right carrying capacity of the water must
be considered for each production system, and fish size and density at harvest, as well as time to harvest
(i.e. rate of growth), must be adjusted accordingly. For example, density can vary from 1 to 500 fish/m3
depending on fish size and on phytoplankton and organic matter concentration and flux.
8
Figure 2. Flexible cage with rope frame being made. This cage is of the type developed and tested
successfully at sea in Costa Rica, and has even better applications in lakes where currents and waves are
less severe than at sea.
Seasonal variations should also be considered and in some instances supplemental feed may be added.
If the supplemental feed or some components of it are produced on land, this may not affect the
autotrophic nature of the system as long as such added feed or its equivalent in biomass and nutrients
are harvested with the fish (i.e., a net balance). The imperative of considering local carrying capacity
should not, however, be neglected.
2. Filter-feeding bivalves
Although not a preferred food in Malawi, there is a variety of native freshwater bivalves (Brooks et al.,
2011; Darwall et al., 2011), like clams and mussels, which can be produced in practical autotrophic
conditions and exported to markets where they are consumed. Although it may seem wasteful from
some perspectives, bivalve meat thus produced can also be used to supplement feeding of fish in a
completely autotrophic manner. Moreover, the fact that they are not consumed locally may work to the
advantage of their production as they will not be subject to theft. Their production techniques are very
simple and low cost yet commercial-level reproduction of some species may require experimentation.
9
3. Aquatic plants
There are many species of aquatic plants which have through history been known as ‘aquatic weeds’,
and several species grow naturally in lakes and lagoons of Malawi (Brooks et al., 2011; Darwall et al.,
2011). Cultivation techniques will have to be developed and tested, and evidently larger plants lend
themselves better to be grown tied to ropes or confined by a floating ‘fence’ made of net and bouys.
Smaller plants, like Lemna, can perhaps be better grown in pens and other areas less subject to wind
and currents.
The cultivation of aquatic plants to be used as fish feed opens up a variety of options in fish species that
can be produced, up to all the herbivorous species and even omnivorous ones if such vegetal feed is
supplemented with small fractions of animal meat and byproducts, both from the processing of fish and
that of bivalves as indicated above. The most interesting application, of course, is as human food, and
initial applications can be partial, such as combining an aquatic plant meal with maize flour, very
possibly enriching it nutritionally.
4. Aquaponics
A variety of land plants can be grown with their roots directly in an aquatic medium (e.g. lettuce) or in
floating rafts irrigated with water from the lake (White et al., 2007). The latter option, an example of
which is shown in Figure 3, has already been implemented for years at sea using a variety of
horticultural crops such as tomato and cucumber, though with the severe limitation that irrigation water
must be produced through in situ distillation or harvesting and storing rainwater (Radulovich, 2010).
This fully autotrophic aquatic production system can also take advantage of nutrients in water, though
controlled fertilization may have to be practiced depending on the intensity of the production system. In
water high in fecal coliforms, the production of ornamental horticultural crops can be implemented as a
cash crop.
Moreover, as it is the experience in Costa Rica, when producing land crops away from the coast insect
and pathogen pests are almost not existent, and thus not only production is far easier and less
expensive, but also organic production can be implemented with much higher market price. Although it
is obvious, the production of such horticultural crops will not require additional water since their
transpiration will be equivalent to the evaporation from the water surface that will have occurred
anyway.
10
Figure 3. Example of metal dome with horticultural crops floating at sea (from Radulovich, 2010). For
freshwater conditions, where avoiding contact or spray of saltwater on crops does not exist, designs
could be far simpler.
5. Polyculture
Analogous to agriculture, and aquaculture is agriculture, although commercial operations with high
investment and thus high profit usually require high degrees of specialization (i.e. monoculture of high
yielding species and varieties with a high optimal input level), low-input production benefits from
diversity in a variety of ways. One of them is the trophic aspect, which has been abundantly promoted in
the literature under the concept of ‘multi-trophic’ and its applications to bioremediation, whereby the
organic matter and nutrients released by fed-animal operations are uptaken by filter-feeders and plants
(e.g., Chopin and Bastarache, 2004; Neori, 2008).
But polyculture goes beyond trophic aspects, particularly in water where multi-strata can be used, and
while plants are kept at the surface, below surface animals can be produced, making more intensive use
of a given area (Radulovich, 2006). Another major benefit is that once an operation is established, which
requires a variety of initial and maintenance costs, including care, to add other production options can
be done at a marginal cost. For example, suspended bivalve culture can be established from the same
moorings and rope system used for fish cages, even within fish cages. Another advantage of polyculture
in small-scale production is that a variety of foods can be obtained and in the case of failure of one
element the others are there to buffer the loss.
11
Figure 4. View of an autotrophic aquaculture system showing a large area cultivated to aquatic plants
using long-lines, from where bivalves hang suspended, and a low-cost flexible fish cage. The mooring is
shown only as an illustration.
Potential benefits
A simple analysis for Lake Malawi reveals that if 10% of its surface were to be eventually farmed with
aquatic plants, i.e. 240,000 ha, with yields of all-year-round production set equivalent to 10 t of
grain/ha/yr, then can be produced, which is similar to the total maize requirement of the country. With
a cost of $500/t of grain, which has been established at over $800/t via international aid (Sanchez et al.,
2009), this operation would have a value of $5,000/ha/yr and for 10% of the lake surface the value
would be $1.2 x 109 (1.2 billion dollars) per year. All of this without spending water from the lake save
for that taken with the harvest, and certainly without the vagaries associated with rainfed crop
production on land, moreover, cleaning the water from excess nutrients. In virtual water terms, the
amount of water that would be needed to produce 2.4 x 106 t grain equivalent/yr is 2.4 x 109 liters/yr. A
staggering amount of water that will have been made available as food without spending additional
water from the lake.
If low-density filter-feeding bivalve and fish production is established within the aquatic plant
production systems, yielding only 1 t/ha/yr of edible meat, at ca. $4/kg this represents a value of
12
$4,000/ha/yr which for 1% of the area of the lake, i.e. 24,000 ha, means $0.96 x 108 (96 million dollars)
per year.
A similar analysis, including aquaculture-assisted fisheries and floating horticulture, can be conducted
for all the many lakes and lagoons of Africa, which cover more than 150,000 km 2. Indeed a billionaire
opportunity waiting to be developed within the proper sustainability and equity aspects, perhaps acting
as the decisive factor to eradicate famine while providing an economic boost for development.
Of course, perhaps the technological aspects of this proposal are the simplest part of such a major
endeavor, through which aquaculture will evolve towards its true potential. Social organization and
cultural change (including food habits) can perhaps be larger challenges, not forgetting the need to
count with the proper policy frame, the concerted effort of national institutions, international aid in the
many manners required, and a strong political will to carry on in spite of the many obstacles that will be
presented by individuals and organizations. Yet quality of human life must take precedence now, not
only for the future. If people need it, and they do, the water environment must be used intelligently,
and even changed to an extent without meaning a biological or environmental chaos, moreover taking
pressure off from land and other freshwater resources. A win-win situation for all.
References
Aiking, H. 2011. Future protein supply. Trends Food Sci Technol, 22:112-120.
Allen, R. G. et al. 1998. Crop Evapotranspiration – Guidelines for computing crop water requirements.
Irrigation and Drainage Paper 56, FAO, Rome.
Bhattacharya, A. and P. Kumar. 2010. Water hyacinth as a potential biofuel crop. E J Environ Agric Food
Chem, 9:112-122.
Bostock, J. et al. 2010. Aquaculture : global status and trends. Phil Trans R Soc B, 365:2897-2912.
Brooks, E. G. E., D. J. Allen and W. R. T. Darwall (compilers). 2011. The status and distribution of
freshwater biodiversity in Central Africa. IUCN, Gland, Switzerland and Cambridge, U.K.
Charo-Karisa, H. et al. 2009. Low-input cage culture: towards food security and livelihood improvement
in rural Kenya. Sarnissa African Aquaculture Case Study, www.sarnissa.org.
Chopin, T. and S. Bastarache. 2004. Mariculture in Canada: Finfish, shellfish and seaweed. World
Aquaculture, 35:38-41.
Cuomo, V. et al. 1997. Mariculture with seaweed and mussels for marine environment restoration and
resources production. Int J Env Stud, 52(4):297.
13
Darwall, W. R. T. et al. (eds). 2011. The Diversity of Life in African Freshwaters: Under Water Under
Threat. An analysis of the status and distribution of freshwater species throughout mainland Africa.
IUCN, Cambridge, U.K. and Gland, Switzerland.
Denning G, Kabambe P, Sanchez P, Malik A, Flor R, et al. (2009). Input subsidies to improve smallholder
maize productivity in Malawi: Toward an African green revolution. PLoS Biol 7(1):e1000023.
doi:10.1371/journal.pbio.1000023
Duarte, C. M. et al. 2009. Will the oceans help feed humanity? Bioscience, 59:967-976.
FAO. 2009. Use of algae and aquatic macrophytes as feed in small-scale aquaculture. Fisheries and
Aquaculture Technical Paper 531, FAO, Rome.
Global Fish Alliance. 2002. The importance of fisheries for food security in Malawi. The Global Fish
Alliance, www.globalfishalliance.org.
Hardin, G. 1968. The tragedy of the commons. Science, December 13: 1243-1248.
Huiwen, C. and S. Yinglan. 2007. Management of marine cage aquaculture. Environmental carrying
capacity method based on dry feed conversion rate. Env Sci Pollut Res, 14:463-469.
Kanabkaew, T. and U. Puetpaiboon. 2004. Aquatic plants for domestic wastewater treatment: Lotus
(Nelumbo nucifera) and Hydrilla (Hydrilla verticillata) systems. Songklanakarin J Sci Technol, 26:749-756.
Kamtambe, K. M., J. Kang’ombe and E. K. W. Kaunda. 2009. A case study of Hangere integrated
agriculture-aquaculture farm in Malawi. Sarnissa African Aquaculture Case Study, www.sarnissa.org.
Kresovich, S. et al. 1982. The utilization of emergent aquatic plants for biomass energy systems
development. Solar Energy Research Institute, Golden, Colorado, USA.
Longwe, P. M., J. Kang’ombe and E. K. W. Kaunda. 2010. A case study of GK Aqua Farms in Chikwawa
District, Malawi. Sarnissa African Aquaculture Case Study, www.sarnissa.org.
Madramooto, C. A. and H. Fyles. 2010. Irrigation in the context of today’s global food crisis. Irrig Drain,
59:40-52.
Naylor, R. and M. Burke. 2005. Aquaculture and ocean resources: raising tigers of the sea. Ann Rev
Environ Resour, 30:185-218.
Neori, A. 2008. Essential role of seaweed cultivation in integrated multi-trophic aquaculture farms for
global expansion of mariculture: an analysis. J Appl Phycol, 20:567-570.
14
Neori, A. 2010. “Green water” microalgae: the leading sector in world aquaculture. J Appl Phycol,
23:143-149.
Pauly, D. and V. Christensen. 1995. Primary production required to sustain global fisheries. Nature,
374:255-257.
Pillay, T. V. R. and M. N. Kutty. 2005. Aquaculture Principles and Practices. Second Ed., Blackwell
Publishing, Oxford, U.K.
Pimentel, D. and M. Pimentel. 2003. Sustainability of meat-based and plant-based diets and the
environment. Am J Clin Nutr, 78(suppl):660S-663S.
Radulovich, R. 2006. Cultivando el mar. Agron Costarric, 30:115-132.
Radulovich, R. 2010. Marine agriculture: land plants cropped floating at sea. World Aquaculture, 41:4346.
Radulovich, R. 2011. Massive freshwater gains from producing food at sea. Water Policy, 13:547-554.
Sanchez, P.A., G.L. Denning and G. Nziguheba. 2009. The African Green Revolution moves forward. Food
Sec, 1:37-44.
Skillicorn, P., W. Spira and W. Journey. 1992. Duckweed aquaculture. A new farming system for
developing countries. Technical Working Paper, The World Bank, New York, USA.
Soto, D. and G. Mena. 1999. Filter feeding by the freshwater mussel, Diplodon chilensis, as a biocontrol
of salmon farming eutrophication. Aquaculture, 171:65-81.
Tacon, A. G. J., M. Metian, G. M. Turchini and S. S. De Silva. 2010. Responsible aquaculture and trophic
level implications to global fish supply. Rev Fish Sci, 18:94-105.
Troell, M. et al. 2003. Integrated mariculture : asking the right questions. Aquaculture, 226:69-90.
Valeta, J. M. H. S. 2011. A case study on the experiences of innovative, small-scale fish farmers in
Malawi. Sarnissa African Aquaculture Case Study, www.sarnissa.org.
Verdegem, M. C. J., R. H. Bosma and J. A. J. Verreth. 2006. Reducing water use for animal production
through aquaculture. Intern J Water Resourc Dev, 22:101-113.
Volpe, J. P. 2005. Dollars without sense: the bait for big-money tuna ranching around the world.
Bioscience, 55:301-302.
15
White, P. et al. 2007. Final Report – Taal Lake. Environmental monitoring and modeling of aquaculture in
risk areas of the Philippines. Akvaplan-niva AS, Norway.
Windmar, L. 2011. Posting on Sarnissa on the issue of land grab and water resources. Sarnissa-africanaquaculture Digest, 43(59).
World Fish Center. 2010. Cage aquaculture in Malawi. The World Fish Center, Malawi.
World Fish Center. 2011. Aquaculture, Fisheries, Poverty and Food Security. Working Paper 2011-65, The
World Fish Center, Penang, Malaysia.
*******
16