Aquaculture
Aquaculture is the rough equivalent of agriculture on land. Aquaculture is the raising of fish, shellfish, or aquatic plants to supplement the natural supply. Although aquaculture includes the growing of aquatic plants, most people use the term to mean fish and shellfish farming. Fish and shellfish are raised as food under controlled conditions all over the world. The goal of fish and shellfish culture is to increase the yield of useful products, including increased food production.
While most aquacultural production is in food items such as fish, mollusks, and crustaceans, some marine algae, kelp, and other aquatic plants are raised commercially. Cultured pearls are created by placing small bits of material in the shells of young oysters. Various types of floating algae and phytoplankton are also grown, primarily as food for animals
Aquatic animal husbandry includes all of the activities terrestrial farmers and ranchers have used, such as selective breeding, care of the young,feeding, sanitation, environmental modifications, and harvesting. Species having characteristics that make them suitable and practical for culturing are selected for extensive cultivation. This includes considerations of con sumer choice. Aquaculture is relatively expensive, so most aquacultural products are luxury items such as trout, oysters, and shrimp. Some less expensive fish species, such as carp and tilapia, are successfully cultured in China, India, and southeast Asian countries.
History of Aquaculture
Aquaculture has been practiced for thousands of years. Chinese in the fifth century C.E. practiced aquaculture, and temple friezes (ornamented bands on a building) dating from the Middle Kingdom of Egypt (2052–1786 B.C.E.) depict what appear to have been intensive fish farming. The ancient Romans are known to have cultivated oysters.
Commercial Importance
As suitable arable land diminishes and the world’s population increases,aquaculture is expected to become increasingly important. Aquaculture is an environmentally friendly source of high-quality animal protein. Many countries with limited arable land, such as Japan, are actively developing an aquaculture industry.
Problems of Aquaculture
Aquacultural practices are not as efficient as they could be. Lack of capitalization in developing countries, inefficient and outdated techniques, and poor marketing all contribute to the lack of commercial success in aquaculture. Another factor limiting production is the lack of suitable domesticated species. Only a few aquatic animals are used, and much of the life cycle of these animals is not controlled. Research into new species, development of commercially viable hybrids, and new techniques of breeding should improve the efficiency of commercial aquaculture. Continued research and the dissemination of new skills and techniques holds promise for substantially increased aquacultural production, perhaps exceeding 30 million metric tons (33 million short tons) per year.
Selection of Suitable Species
In order to be aquaculturally useful, species must be able to reproduce in captivity, have robust eggs and larvae, feed on inexpensive food, and grow quickly to harvestable size. For example, trout and carp have large, hardy eggs; mullet fry are easily collected; and young oysters are easily collected and grown. So these were the species of choice for aquaculture. The feeding habits of species also limit suitability. Wide-ranging plankton feeders, such as herring, are not suitable. Sessile animals, such as oysters and mussels, which filter the water for their food, can be cultured extensively but still must be supplied with a rich food supply if they are to grow rapidly.
Selective Breeding
Aquaculturists, like their terrestrial counterparts, selectively breed for desirable traits in captive organisms. Since the traits that enhance success in a wild population are often inconsistent with a successful captive population, these traits must be eliminated through breeding. Desirable characteristics include fast growth and a body shape that provides more edible tissue. Since captive populations are usually held at a higher density than wild populations, disease is a problem. So resistance to disease is desirable. Since aquatic animals usually produce many offspring per generation, selective breeding is somewhat easier than with terrestrial animals.
One desirable characteristic of captive populations is an accelerated onset of sexual maturity. This event is triggered in the wild by a combination of factors, including water temperature, length of daylight hours, and salinity. These factors in turn act on the animal’s pituitary gland, which controls the output of sexual hormones. Attempts to control environmental factors to accelerate spawning have been largely unsuccessful, except in the cases of oysters and shrimp. A more generally successful method involves the injection of pituitary hormones. This is expensive and labor intensive so alternatives are being sought.
Evolving Technologies
Large-scale fish culture projects, if properly managed, have the potential to produce thousands of tons of fish. Community ponds and reservoirs created by the damming of tropical rivers are often designed to include largescale fish farming. When a new reservoir is created, nutrients from the soil trigger the growth of abundant algae and aquatic plants. So herbivorous fish must be included in the plans. These fish can provide the first harvested “crops.”
Fish “ranching” is also widely practiced. For example, salmon are raised in hatcheries then released into wild streams. This allows the establishment of new salmon runs, the reintroduction of salmon into previously used streams, and the replenishment of depleted stocks. This form of aquaculture also helps alleviate losses due to human induced environmental degradation.
Hybridization is another technique coming into use in aquaculture. Crossing one trout with another trout having seagoing tendencies enables breeders to send fish to new oceanic pastures and then to harvest them when they return to freshwater to spawn. Promising crossbreeding experiments with tilapia have also resulted in species exhibiting hybrid vigor.
Both coal-fired and nuclear power plants use water for cooling. This water is generally discharged into a reservoir of evenly warmed water. This water has significant potential to be used in aquacultural programs. Many aquatic animals grow more rapidly in somewhat warmer water. Other species, such as carp and catfish, prefer warmer water. Many of the farmraised catfish available in supermarkets are grown in ponds warmed by water from power plants.
Pelagic (open ocean) fish have not been raised in captivity with any great success. They are desirable species because they grow fast. But they require huge quantities of food fish or other pelagic organisms, which are also hard to raise in captivity. As research continues, it is likely that new aquacultural techniques will be developed that will permit the farming of many new species such as spiny lobsters, crayfish, octopus, and others not presently husbanded. Improved techniques will increase the yield of existing aquacultural species. As demand continues to increase for world food supplies, aquaculture promises to grow into a thriving and productive industry. SEE ALSO Farming.
