Algae for AsiaThe cultivation of algae is less widespread than that of aquatic animals. It is only practised in about 30 countries throughout the world, predominantly in Asia. In most cases cultivation is of large algae such as kombu (Laminaria japonica), a Japanese seaweed which is several metres long. It is now farmed mainly in marine water and brackish water along the coast of China. Kombu is often used as a soup ingredient. Although the 19 million tonnes of algae produced in 2010 was much less than farmed aquatic animals, nonetheless its growth rate has been similarly strong in recent years – an average of 9.5 per cent per annum during the 1990s and 7.4 per cent in the past decade. In 1990 global algae production was 3.8 million tonnes. The most important regions are China (58.4 per cent of global production), Indonesia (20.6 per cent) and the Philippines (9.5 per cent). Most of the algae produced worldwide is used in the cosmetics, chemical and food industries. Only a small proportion is used for human consumption, as a base for soups. The tropical algae Eucheuma and Kappaphycus, harvested throughout the Indo-Pacific region between the island of Zanzibar and the Philippines, are also of significance. They offer many fishermen an additional income and are utilized in the chemical, health and biological industries as a bacterial growth medium.
- 4.5 > Fish can convert feed into body mass much more efficiently than birds or mammals. They provide a great deal more mass per kilogram of feed.
The strengths and weaknesses of aquacultureAquaculture has come in for some hefty criticism in recent years. For various reasons it still attracts controversy. Food, faecal and metabolic wastes from intensive fish farms can lead to the eutrophication (over-fertilization) of water in rivers and coastal bays. There have also been complaints that fish farmed under intensive conditions for maximum yields are more susceptible to disease than their relatives in the wild. Tremendous amounts of anti-biotics and other medications are used to fight disease, particularly in relation to shrimp on farms in South East Asia – with unforeseeable consequences for surrounding ecosystems and consumer health. In some cases these points are valid, but they should not detract from the fact that aquaculture can be a very efficient and sustainable method of supplying humans with animal proteins – and counteracting over-fishing. The farming of the classic common carp or mirror carp provides a positive example of environmentally-sound aquaculture. Carp are bottom feeders, generally eating small aquatic animals, plants, dead plant matter and waste material which gather on the pond floor. They also sieve the water to extract suspended solids, thus helping to keep the water clean. Carp ponds often have very clear water. Intensive mussel farming also helps to keep the water clean. Mussels filter large amounts of water, sieving out tiny particles of food, thus counteracting the over-fertilization of water and algal blooms.
- 4.6 > In Belize, in Central America, the construction of huge aquaculture facilities has involved the destruction of large tracts of land and mangroves. The effluent is discharged to the sea without any prior treatment. Such operations have brought the sector into disrepute.
- 4.7 > Aquaculture emits much less nitrogen and phosphorus per tonne of produced protein than livestock farming. Farmed mussels even lower nitrogen and phosphorus levels as they filter the water. However, this also means that mussels from highly polluted waters can themselves contain high nitogen and phosphor levels.
- Although the nutrient-rich effluents from aquaculture facilities can lead to problems in rivers or coastal areas, nonetheless many fish farms are more environmentally-friendly than, for instance, the intensive farming of pigs or cattle. The latter emit large quantities of nitrogen and phosphorus from the slurry and manure used to fertilize the land. Aquaculture produces far lower emissions of nitrogen and phosphorus and can roughly be compared with those from the much less problematic farming of poultry. This is made abundantly clear by the example of the Mekong Delta. Only about 1 to 2 per cent of nutrient inflows into the delta come from pangasius aquaculture. The majority comes from agriculture, the production of vegetables and fruit as well as from untreated municipal sewage and industrial effluent. Aquaculture also scores well when compared to livestock breeding because fish and other aquatic organisms need less nourishment to build body mass than land animals. Therefore a lot less feed is required to produce 1 kilogram of carp than to produce 1 kilogram of chicken, beef or pork. One reason for this is that fish are cold-blooded creatures, meaning that their body temperature is approximately the same as that of their surroundings. They therefore need far less energy to produce heat than warm-blooded mammals or birds. Also, it takes greater expenditure of energy to move on land than in the water. As water is denser than air, it provides buoyant lift to the body, meaning that fish are supported without the development of heavy skeletal mass. Many marine animals such as mussels, snails and sea cucumbers also manage without an internal skeleton. This saves them the energy they would otherwise use to build bones. Fish have another energy advantage, too: they are capable of releasing into the water (as ammonium, a simple chemical compound) any surplus nitrogen they may have absorbed with their food. In contrast, land-based animals have to use energy to convert nitrogen into urea or uric acid. Only in this chemical form are they able to excrete the nitrogen with their faeces or urine.
Fish for all?In an international collaboration scientists have investigated whether aquaculture and commercial fishing will be capable of meeting the global demand for fish in 2050. They are optimistic, believing that yes, they can. How-ever, this would depend upon the world’s fish stocks being managed sustainably in the long term. Also, the fish used as feed in aquaculture in the form of fishmeal and fish oil must be utilized more efficiently. Scientists have also queried the predicted direct impact of climate change and ocean warming on potential marine fisheries procduction. They have concluded that the amount of wild marine fish available for fisheries worldwide will probably be re-distributed due to climate change and predict a slight 6 per cent overall increase on marine fisheries potential.