"Give a man a fish and you feed him for a day, teach the man how to grow that fish and you feed him for life."
-Ancient Chinese Proverb 500 B.C.
What is aquaculture? Aquaculture is one of the fastest growing sectors of food production in the world and there is much hope that it will be the supplement to dwindling wild fisheries (9). Fish is the most important source of protein for many diets, particularly those in rural, coastal communities. A UN Food and Agriculture (FAO) report estimates that fish provides close to 50% of people's animal protein intake per year (8). Continually depleting stocks in wild fish populations have led to an increased interest in the aquaculture of commercial fish to supply this protein, as well as reducing the pressure put on wild populations. Aquaculture itself is the cultivation of the natural production of fish, shellfish and aquatic plants through close husbandry efforts (8). Mariculture specifically refers to marine aquaculture; it is a specialized subset of aquaculture. Typically, aquaculture is used to cultivate fish and shell fish for seafood markets and human consumption, however, it also supplies exotic fish for the hobby industry and game fish for the growing sportfish industries. The aquaculture of seahorses looks promising. Industrialized nations have succeeded in rearing them, but not yet to the level which alleviates the harvesting pressures caused by the medicinal and hobby trades. The hope is that eventually seahorse aquaculture will become simple enough that it could be practiced by poor fishermen, thus providing an alternative to catching wild seahorses.
Aquaculture has been around for thousands of years. Ancient Chinese manuscripts from the 5th century B.C. indicate that the Chinese practiced the fish culture of Carp in rice patties (4). The ancient Hawaiians furthered these methods by building pens to breed and raise Carp and Talapia (7). Since then, aquaculture has been vastly improved and separated into two major categories: intensive and extensive aquaculture.
Intensive aquaculture relies on technology to raise fish in artificial tanks at very high densities. Aquaculturalists must have a thorough understanding of the targeted species so that water quality, temperature levels, oxygen levels, stocking densities, and feed are set at the optimal level to promote growth, reduce stress, control disease, and reduce mortality (Figure 1) (4). Due to the complete control of these factors, intensive aquaculture produces high yields and since it can be done throughout the year, it can be planned to correspond with foreseeable shortages in desired fish. Intensive aquaculture has a very high start up cost and requires much labor and currently, only rich countries have developed this into a profitable business. Research is being done to find viable species which can thrive in an aquaculture setting.
Although intensive aquaculture is completely mechanized and self-contained it can have a detrimental impact on the environment. The biggest problem caused by intensive aquaculture is the difficulty in properly dealing with the nutrient rich effluent (4). Effluent contains high levels of both organic and inorganic nutrients like ammonia, phosphorus, dissolved organic carbon, dissolved organic nitrogen and dissolved organic phosphorus (19). If not disposed of correctly the effluent could cause a number of problems including eutrophication, and hypernutrification (10). Ingenious solutions have been developed to reduce the negative effects to the environmental caused by this effluent. The most effective solution is the advent of aquaponics. Aquaponics is the combination of intensive aquaculture (fish farming) and hydroponics (growing plants without soil) (Figure 2). Aquaponic systems use the nutrient rich effluent from fish tanks as fertilizers for produce. The advent of aquaponics has made the aquaculture industry into a sustainable and eco-friendly business (4).
Extensive aquaculture is the other form of fish farming. Extensive aquaculture is more basic than intensive aquaculture in that less effort is put into the husbandry of the fish. Extensive aquaculture is done in the ocean, natural and man-made lakes, bays, rivers, and Fiords. Fish are contained within these habitats by multiple mesh enclosures which also function as trapping nets during harvest (Figure 3) (4). Since fish are susceptible to the elements, site placement is essential to ensuring rapid growth of the targeted species. The drawback of these facilities is that they depend on the surrounding area for good water quality in order to reduce mortality and increase the survivorship and growth rate of the fish (19). Fish chosen for extensive aquaculture are very hardy and often do well in high densities. Seaweed, prawns, muscles, carp, talapia, tuna and salmon are the most prominent forms of extensive aquacultured seafood (8).
Picture of Aquaponics facility provided by acuaponiaGranja.jpg
Extensive aquaculture facilities have negative impacts on the environment as well. Natural habitats are destroyed in the development of man made ponds used for extensive aquaculture. In the Philippines, shrimp aquaculture is responsible for the destruction of thousands of acres of mangrove fields which serve as nurseries and living habitats for many marine organisms. Benthic habitats are being depleted due to the high amount of organic waste produced by the fish which settles below their pens(4). Phytoplankton and algae breakdown fecal matter and residual fish meal reducing the amount of available oxygen in the water column,which chokes and kills the Benthic organisms. Another serious problem acquainted with extensive aquaculture is the introduction of invasive species into ecosystems (10). Escaped fish increase the competition between organisms for limited resources. Also, when foreign fish interbreed with wild species, they upset the genetic variability of the species, making them more prone to disease and infection. The high density of fish in these mesh tanks is very tempting for predators of the sea and air (19). To protect the harvest from predators protective netting is set up at a high cost. Often times predatorial fish and mammals like seals, sharks, and tuna get caught in these barrier nets and die. Some farmers protect their stocks from predatorial birds such as pelicans and albatross by shooting these sometimes endangered creatures.
Figure 3. Example of fish cages used in extensive aquaculture of catfish (35)
Today, only industrialized nations have the funds to invest in intensive aquaculture. Much like how industrialized farms in the U.S. have out-competed the small time farmer off of their land, industrialized aquaculture is driving the small time fishermen out of the sea. Mass produced aquacultured fish has lowered the wholesale price of fish, thus drawing customers away from the already poor fishermen. Today, the only form of aquaculture available to small time fishermen is in the form of grow out pens for juvenile fish. Research is being done to create more complex and affordable forms of extensive aquaculture for subsistence fishermen in order to increase their standard of living, and more importantly, act as an incentive to protect endangered species (see sustainable fishing methods).
View my extensive aquaculture experiment here
Look at pictures of my Pygmy Seahorses here
Look at a sustainable aquaculture facility here.
On to Conservation Policy