Aquaculture

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Workers harvest catfish from the Delta Pride Catfish farms in Mississippi
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Workers harvest catfish from the Delta Pride Catfish farms in Mississippi

Aquaculture is the cultivation of the natural produce of water (such as fish or shellfish, algae and other aquatic organisms). The term is distinguished from fishing by the idea of active human effort in maintaining or increasing the species involved, as opposed to simply taking them from the wild. Subsets of aquaculture include Mariculture (aquaculture in the ocean); Algaculture (the production of kelp/seaweed and other algae); Fish farming (the raising of catfish and tilapia in freshwater ponds or salmon in marine ponds); and the growing of cultured pearls.

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[edit] History

The practice of aquaculture is ancient and found in many cultures.

Aquaculture was used in China circa 2500 BC. When the waters lowered after river floods, some fishes, namely carps, were held in artificial lakes. Their brood were later fed using nymphs and feces from silkworms used for silk production, and they were used as a source of food protein as well as food for the hunger season. The Hawaiian people practiced aquaculture by constructing fish ponds (see Hawaiian aquaculture). A remarkable example from ancient Hawaii is the construction of a fish pond, dating from at least 1,000 years ago, at Alekoko. According to legend, it was constructed by the mythical Menehune. The Japanese practiced cultivation of seaweed by providing bamboo poles and, later, nets and oyster shells to serve as anchoring surfaces for spores.

The Romans were quite adept in breeding fish in ponds. In Europe it became common again in monasteries during the Middle Ages, since fish was scarce and thus expensive. Transportation improvements in the 19th century made fish easily available and inexpensive, even far from the seas, causing a decline in aquaculture.

Americans were rarely involved in aquaculture until the late 20th century, but California residents harvested wild kelp and made legal efforts to manage the supply starting circa 1900, later even producing it as a wartime resource. (Peter Neushul, Seaweed for War: California's World War I kelp industry, Technology and Culture 30 (July 1989), 561-583)

The current boom in aquaculture started in the 1960s as prices for fish began to climb. Wild fish capture was reaching its peak and the human population was continuing to rise. Today, commercial aquaculture exists on an unprecedented, huge scale. In the 1980s open-netcage salmon farming was also expanding; this particular type of aquaculture technology is still a minor part of the production of farmed finfish worldwide, but possible negative impacts on wild stocks, which have come into question since the late 1990s, have caused it to become a major cause of controversy.[1]

[edit] Economic importance

In 2003, the total world production of fisheries product was 132.2 million tonnes of which aquaculture contributed 41.9 million tonnes or about 31% of the total world production. The growth rate of world wide aquaculture is very fast (> 10% per year for most species) while the contribution to the total from wild fisheries has been escentially flat for the last decade. In the US, approximately 90% of all the shrimp consumed is farmed and imported. [1]

[edit] Criticism

A wide range of scientists and non-profits have raised concerns about aquaculture, particularly for its impact on the environment and on animal welfare. There are two main concerns:

First, most farmed species are carnivorous and so must be feed on other fish, usually caught in the wild. Because it takes at least two pounds of wild-caught fish (used as feed) to produce one pound of farmed fish[citation needed], environmentalists dispute claims that fish farms are more environmentally sustainable than ocean fishing. It is also claimed that most fishing is used to support fish farming rather than human consumption.

However, with modern knowledge of fish nutrition, the protein component of the diet can be from non-aquatic sources such as soybean protein concentrate and similar highly processed sources of protein that have had the anti-nutritional factors removed. This means that a linear programming economic/nutritional model, which provides the least cost diet formulation, determines the choice of ingredients in the diet. Whether fish meal and/or soy and/or corn gluten meal are used in the feed pellets has nothing to do with whether the fish are carnivorous and eat fish in the wild, but it has everything to do with economics relative to other animal feed producers (chickens, pigs, cows, etc.) who are competing for the same protein sources. [2].

Secondly, farmed fish are kept in concentrations never seen in the wild (e.g. 50,000 fish in a two-acre area. [3]) with each fish occupying less room than the average bathtub. This can cause several forms of pollution. Packed this tightly, fish rub against each other and the sides of their cages, damaging their fins and tails and becoming sickened with various diseases and infections.[4]

However, fish are also a type of animals that often aggregates into large schools at high density. Most successful aquaculture species are schooling species, which don't have social problems at high density. Aquaculturists know that operating a rearing system above it design capacity or above the social density limit of the fish will result in decreased growth rate and increased FCR (food conversion ratio - kg dry feed/kg of fish produced), which will result in increased cost and risk of health problems along with a decrease in profits. Stressing the animals is not desirable, but the concept of and measurement of stress must be viewed from the perspective of the animal using scientific methods and not anthropomorphic assumptions. [5].

On many fish farms, parasites such as sea lice are endemic. Lice damage around the head can be so severe that the bone of the living fishes' skulls can be exposed - a condition known as the 'death crown' [6] Such parasites can then attack passing wild fish, significantly affecting the wild population.

For these reasons, aquaculture operators frequently need to use strong drugs to keep the fish alive (but many fish still die prematurely at rates of up to 30% [7]) and these drugs inevitably enter the environment.

The lice and pathogen problems of the 90's were the driving forces for developing the modern treatment methods for lice and vaccines for many of the pathogens. These developments reduced the stress from parasite/pathogen problems. However, being in an ocean environment, the transfer of disease organisms from the wild fish to the aquaculture fish is an ever-present risk factor. [8].

Given the high fecundity of most fish, a 30% loss in the larval stage is often of no significance (some species spawn several 100,000 to a few million eggs per spawn). However if a farmer is taking 30% losses on near-harvestable fish, he will not be in business for long.

The very large number of fish kept long term in a single location produces a significant amount of condensed feces, often contaminated with drugs, which again affect local waterways and their wild cousins. However, these effects are very local to the actual fish farm site and are minimal to non-measurable in high current sites. Finally, the farming of an alien species can lead to escapees with effects on the local wild population.

Other potential problems faced by aquaculturists are the legal hurdles of obtaining various permits and water-use rights, profitability, concerns about invasive species and genetic engineering depending on what species are involved, and interaction with the UN Law of the Sea Treaty. This problem has not been solved in the US, though significant marine fish aquaculture exists and is expanding throughout the world, including Canada and Mexico, with relatively little US marine aquaculture. life

[edit] References

[edit] External links

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