Somos una red de investigadores que trabaja para la libre circulación del conocimiento y para mejorar el diálogo entre las ciencias del mar y el conjunto de la sociedad.

13 abr. 2011

Aquaculture, Part I.

Aquaculture is one of the fasted growing, food-producing sectors in the world. In 2008, production was estimated to 68 million tonnes with a total value of 106 billion US$ (source: FAO). Great hopes are associated with aquaculture production: end hunger in the world, produce resources for pharmaceutical purposes or energy production.

Figure source:

FAO - Fisheries and Aquaculture Information and Statistics Service – accessed on 23/03/2011

Reading a first book on the subject, one can take awareness what aquaculture actually is in practice, and what you need to go into business. The most fundamental component is clean water. Is there a continuous water supply close by or does it have to be pumped into the system from further away? Such considerations are important because every step in the process requiring energy will raise your cost of production. The water also needs to be at the right temperature so that your organism will grow at optimum rates. Oxygen to carbon dioxide ratios will have to be controlled, and the pH adjusted. If the chemical environment becomes unstable growth is not only slowed down but conditions can even become toxic for the culture. What exactly and how closely the chemistry needs to be monitored depends on the cultured organism.

Just like in agriculture, aquaculturing may involve growing plants or raising animals. Routinely cultured are algae (Laminarians, Chlorella), fish (salmon, trout, eels) or invertebrate species belonging to the bivalves (mussels, oysters, clams), crustaceans (shrimp), or echinoderms (sea urchins, sea cucumbers) – not everybody has the same taste! Also the rearing of ornamental fish for aquariums or outdoor ponds is part of the aquaculture business. As a precondition, you must know how to control the reproductive cycle of a species in an artificial environment. The cultured hatchlings or juveniles can be re-introduced into their natural environment to terminate growth, for example in lakes or streams. But most aquaculture production nowadays involves the organism being cultured all the way from the egg to the mature adult.

One of the most studied issues in aquaculture is how to feed the cultivated organism. In the natural environment, all species are embedded in an intricately evolved trophic network. There they find the variety of plant or animal food that they need during the different stages of growth. Creating the complexity of an artificial trophic network in the culture system is impossible (i.e. too costly!), even if you concentrate on the essential prey species. Rearing the first life stages of aquatic animals is be relatively easy, because these first life stages feed on phytoplankton that can be grown with comparatively simple methods. But as soon as the cultured organism develops into bigger, juvenile forms, diet requirements become more complex. Essential nutrients and metabolites are produced by phytoplankton and handed upward through the trophic network from the herbivorous (mussels, carp), to the omnivorous (shrimp) and the carnivorous top predators (salmon). Studying the growth physiology of potential aquaculture species, it is possible to identify the dietary needs and produce artificial feed of the right size, consistence and composition.

A series of negative side effects of aquaculture have become evident over the past 30 years. Maybe most grotesque from today’s point of view is the use of wild fish from already overexploited natural fish stocks in aquaculture feed. Water pollution is also a great concern and has been since the beginning of intensive aquaculture production. In coastal areas, excessive nutrient load from fish feed and excretion products leads to blooms of toxic phytoplankton, rendering the cultured organisms aquaculture improper for human consumption, or may even cause the culture to die off. Furthermore, common aquaculture species are often exotic to the locality where they are cultured and threaten to modify the natural ecosystem when they escape from the aquaculture system. Intensive aquaculture activities have substantially transformed and even destroyed the natural coastal environment, such as mangrove forests in tropical regions. Intensive culture has also led to the development of pathogens, which requires use of antibiotics in the production process. And finally, raising aquatic organisms in high densities has even called on the attention of animal protection leagues.

Intensive shrimp production in Ecuador in the 1970s and 1980s has created awareness of most of theses problems, but it was pioneering work that opened the way for an entire research field. Also the changes in social structure due to aquaculture expansion became obvious. The “aquacultural revolution” is taking place in areas that are already under intense anthropogenic pressure – the coastal zone. The majority of the world population lives within 100km of the coastline and is in competition for land and water resources with aquaculture. Also most of the natural biological productivity of the ocean occurs close to land over the continental shelves. Public policy now addresses this issue with coastal zone management strategies. Based on research data from sociologists, ecologists and oceanographers, stretches of coastline are classified for recreation, aquaculture or environmental protection. “An ecosystem approach to aquaculture is a strategy for the integration of the activity within the wider ecosystem such that it promotes sustainable development, equity, and resilience of interlinked social-ecological systems.”

Aquaculture production has its origin in Asia where it was included in human cultural activities thousands of years ago to cope with population growth. In her book “The sea-farm” from 1980, Elisabeth Mann Borgese wrote the following about aquaculture:

That aquaculture has a philosophical base in the East and a scientific base in the West has far-reaching implications. In the East, it is life: culture to improve life by providing food and employment. It is embedded in the social and economic infrastructure. All that science can and must do is to make this culture more effective. In the West, aquaculture is science and technology, embodied in industry and providing profits: money. It has no social infrastructure. In this, the West has much to learn from the East.”

Thirty years into the future, awareness has been created and research has progressed. These lines were true in 1980 when aquaculture production indeed started to grow fast due to its industrialization. There is a lot to explore how aquaculture has changed for the better, with a special focus on the contribution of research to this change.

To be continued.

Sabine Schultes, PhD