Aquaculture has been practiced worldwide in one form or another for centuries. Lowland fields and rice paddies would often be flooded by strong rains and monsoons. With these floods came an abundance of fish and aquatic organisms which flourished in this vegetation-rich environment. Once the rainy season ended and the water receded, the fish and their offspring would be harvested. Eventually it was realized that by leaving the smallest of the fish in these ponds, they would grow, spawn, and the cycle could be continued and managed as long as there was water and food available for the fish. In areas close to the sea, with concentrations of tidal ponds and lagoons that were affected by the ebb and flow of tides, traps would be installed that would block the exit of these fish.
The next steps in aquaculture were to gather up small fish (fry) from rivers, streams and oceans and transport them to controlled ponds where they were allowed to grow before being harvested. This technique was widely used in China with the common carp. It wasn’t until the eighteenth century that eggs and sperm from fish ready to spawn were removed and spawned in controlled conditions before being moved to tanks or ponds for cultivation. Initially these were all freshwater fish, but in the twentieth century, new techniques were developed to breed saltwater species.
With these new techniques has come expansion of farming high value seafood such as sea bass, salmon, shrimp and grouper, a practice that has dropped prices, but caused controversy for its possible environmental impact.
Fish farming techniques/methods
Aquaponics
Aquaponics is the process of combining aquaculture and hydroponics. This process utilizes the waste products and water from the fish for plant nutrients. The plants act as filters for the water, which is purified and recycled back into the tanks. No chemical fertilizers, pesticides or medications are needed for the plants or fish. The water needed in this process is about 95 percent less than normal fish farming and 1/10 the water required for normal vegetable growing. Aquaponics is viable for both large- and small-scale operations and can be accomplished with both natural and artificial light sources. Many species of fish, herbs and vegetables can be grown using this technique, which is an ideal sustainable form of both aquaculture and agriculture for the future.
Sea ranching
Sea ranching is an aquaculture technique that is becoming controversial in many parts of the world. Large schools of high-value fish such as tuna are captured through a well-orchestrated multi-boat process. The fish are rounded up in what amounts to an underwater cattle drive as they are herded out to sea and into waiting circular nets that float on the surface. These large netted enclosures are carefully towed out to sea where the fish are fed and fattened up over a period of months. The controversy over this technique arises because large amounts of fish are rounded up, often without regard to quotas, and in the process of the trapping there are casualties. Another problem is that many fish are carnivorous and require a diet of smaller fish such as herring and sardines. Because carnivorous fish do not metabolize carbohydrates well, the amount of food they consume exceeds the amount they produce at a rate of up to five to one. This oftentimes illogical number is consistent with most meat-eating farmed fish, putting a strain on many of the smaller species used to create fish protein and meal.
Cages
Tuna as well as salmon are held or raised in net-like enclosures anchored to the sea bottom. Large amounts of fish can be monitored remotely with cameras and automatic feeders. Because of the large concentration of fish and feed, pollution and algae bloom is possible. Additionally, there is fear that interbreeding and/or the spread of disease will eventually disrupt the wild species.
Recirculation systems
This method is a lot like a large, round aquarium. Located both indoors and outdoors, treated water is constantly recirculated through the system to raise a variety of species including salmon, bass and even sturgeon.
Raceways
These systems resemble long, deep lanes or channels through which diverted stream or river water is pumped. The fish, typically trout, are able to swim in these channels; their wastewater is treated before being returned to the source. Regulations are in place in many states minimizing environmental impact.
Ponds
Trout, catfish, shrimp and tilapia are examples of species raised in ponds. They are built in a variety of shapes and materials, including concrete and earth, and have the advantage of being placed near water sources both inland and in coastal areas. A constant supply of water is important to the delicate balance of this crowded environment and surrounding ecosystem.
Algaculture
Algaculture refers to the controlled farming of algae, or seaweed. Common to the Asian diet, it is highly nutritious, containing vitamins A, B1, B2, B6, C and niacin. Additionally, the omega-3 fatty acid docosahexaenoic acid (DHA) can be manufactured from algae and is used as a nutritional supplement. Many varieties of algae are used as natural dyes, livestock feed, fertilizer, or to control pollution in wastewater plants. It can also be made into bio-diesel. As its health benefits and versatility continue to be studied, algaculture will certainly increase in the coming years.
Shrimp farming
For over 30 years, shrimp farming has been on the rise worldwide. Limited supply of wild shrimp, high profits and relatively cheap start-up costs in depressed economic regions have fueled this expansion. Much of the growth is in developing countries such as Thailand, Indonesia, India, the Philippines and Ecuador, and has brought jobs and economic gains, as well as environmental degradation. The hope of quick profits has led to overexpansion and unrealistic goals, without proper capital and controls being invested in environmental safety. In question is whether this young industry can sustain itself amidst increasing world pressures to mitigate and end disruption of wetlands and control possible disease outbreak to wild shrimp.
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