|By goGreen | July 29, 2012|
Aquaculture is the production of protein-rich foods through the controlled cultivation and harvest of aquatic plants and animals. Using inexpensive equipment and simple techniques, aquaculture can supply more protein than normally produced through conventional agriculture such as dairy, poultry, and cattle farming; and traditional fishing.
Aquaculture is not new. More than 2,500 years ago the sticky eggs of some fish were collected on mats and bundles of reeds or wood attached to posts in streams. Oyster and clam eggs were also collected and transferred to other waters to hatch. This was the first form of aquaculture.
In the 11th and 12th centuries, pond culture developed. Carp were moved through a series of ponds where they reared young fish and grew to harvest size. Later, other fish were cultured in a similar manner. Today, several types of fish and shellfish are grown in high density aquaculture operations throughout the world.
The techniques of animal husbandry improve the chances of survival of the plants and animals being raised and speed up their growth so that the food yield is quick and large. Almost any type of aquatic organism can be raised from its youth to a healthy, marketable adult. However, this paper in restricted to fish and shellfish culture. The reader is presented with only general considerations and approaches to aquaculture, since it requires specialization to address each possible cultural species.
Advantages and Disadvantages of Aquaculture
Systematic aquaculture operations have a number of advantages over fishing for the production of protein foods. Some of these are:
- Economics (employment, new industry and support services, and increased foreign and domestic ex change);
- No need for expensive fishing craft and gear;
- Low operating and maintenance costs;
- Low capital investment (unless Ponds must be constructed;
- Reasonably predictable yields;
- Less time lost due to bad weather or breakdowns;
- Fewer equipment malfunctions and injuries;
- Reduced health risks to consumers.
Aquaculture operations do have drawbacks, however. These include:
- Water is necessary, in predictable quantity and quality;
- Large land area on which to construct ponds or access to large shallow area of water is required;
- Knowledge of culture conditions may not be generally available.
Types of Aquaculture
There are five major types of aquaculture:
1. Transplantation: The movement of a species to a suitable location. This method in also used to introduce species into new environments.
2. Hatchery and Stocking: The spawning, hatching, and rearing of a cultural species that will be transplanted to suitable or desirable areas. This method is used to supplement or replace the natural stock, or for transplantation.
3. Enbayment Culture: The use of enclosures, such as ponds, cages, baskets, and strings, for aqua culture in natural waters.
4. Ponds with Supplemental Feed and Fertilizer: Aquaculture in natural or artificial ponds with food and fertilizer provided to maintain algae and species at desirable levels. In some systems, animal manures are used to provide fertilizer and some food.
5. Ponds without Supplemental Feed and Fertilizer: Aquaculture in natural or artificial ponds with the cultured species subsisting an natural available food in the pond water. This requires a high rate of exchange of water for high growth rates.
As can be seen, the basic theory of aquaculture is to obtain small animals and provide them with an environment that allows for their rapid, healthy growth. A desirable-sized fish can be harvested in a short period of time.
The most commonly cultivated species of fish are carp and tilapia. Shellfish such as oysters and mussels, which are low on the food chain, are also farmed extensively. While culture techniques must be adapted to the needs of specific species and to local needs and conditions, some general rules apply:
1. The species must be Suitable for cultivation under the proposed conditions.
2. The program must develop the best method of cultivating the identified species from physiological, geographical, and market points of view.
3. Adequate support must be available. This includes changing and aerating the water, feeding the fish, maintaining equipment, marketing, and so on. Experimentationis often necessary to improve yields substantially.
4. Predators must be controlled.
5. Cannibalism must be controlled.
6. The species life cycle must be understood, and good, inexpensive feed must be available.
A dense population of animals demands abundant food and oxygen and a means of removing metabolic wastes. There is a limit to the size of the biological community that can be supported before growth is limited by competition for food, oxygen, and space. The high density of cultured animals makes them susceptible to disease and predation. To prevent juveniles from being attacked by these diseases, drained ponds must be thoroughly dried to destroy parasites and disease-causing organisms. The water and stocking animals should be free of parasites and disease-causing organisms. Feed and feed supplements should not introduce parasites or disease-causing organisms.
On the positive side, the fertile fish and shellfish wastes can be used in the production of leaf crops requiring nitrogen. Shellfish wastes are best used on fruit trees.
OVERALL OPERATION AND MAINTENANCE
Aquaculture systems can be operated and maintained in three ways:
1. Communal: This is subsistence cultivation that is some times publicly funded. The conditions are often mediocre,and production is poor because duties are attended randomly.
2. Family: This can range from subsistence cultivation to a very sophisticated operation, depending on the skill and energy of the owners. Under the worst of conditions, it can be more variable than communal; at its best, it can exceed the standards of a dedicated system. The key to a successful operation is the family’s commitment to putting forth the effort necessary to produce a quality product.
3. Dedicated: This operation is designed to produce food for market, and is usually well-regulated with high yields.
Each of these types of operation can be run as extensive or intensive culture.
Extensive Culture provides little or no control over the environment. Placing shellfish on a site and allowing them to grow on their own, or trapping fish and invertebrates in special enclosures and holding them until they reach market size, are examples of extensive culture. In extensive culture, the fish depend uponthe natural food supply in the water. Only 20 to 50 percent of the stocked animals survive in this uncontrolled environment.
Intensive Culture on the other hand provides full control, over the environment. An indoor culture of shellfish, in which temperature, salinity (salt/water ratio), flow rate, feed type, amount of feed, and light are fully controlled, is an example of intensive culture.
No matter which type of operation or which method of culture is selected, sufficient food and oxygen must be provided. Oxygen levels of 4 to 5 milligrams per liter (parts per million) are satisfactory. Water can be aerated by spraying it out at least 0.6m (2 feet) in droplet form. Food requirements are discussed in a later section.
There is one other general consideration in aquaculture that is extremely important: The size of the animals. The animals stocked in the aquaculture system must be large enough to grow to market size in the desired time. Some preliminary experimentation is needed to determine the minimum desirable size. Only healthy animals should be chosen for stocking the aquaculture system.
An aquaculture system can be operated on a shore, in an inter tidal region (zone between the high and low tides levels), in a sub-tidal region (zone below the low tide level), on a water surface, in mid-water, or on a seabed. Certain culture systems are better-suited to certain sites. A shore facility is usually used for fish and shrimp production. Full control (intensive culture) of the environment is characteristic of shore sites, and pumps may be needed to provide the water supply.
Controlled Pond Facilities
These are either man-made or natural areas that can be isolated from the water source. Water flows by gravity into the pond or is pumped in. Ponds are suitable for such fish as tilapia or carp, or even game fish such as salmon.
Inter tidal Facilities
Intertidal facilities take advantage of the movement of the tides to replenish food and water. They are used for shellfish culture and spat (larval shellfish) collection and can be controlled if properly constructed. The incoming high tides are let into an area that can then be closed off. The high water, with its load of baby fish or shellfish, is dammed off and is held until the fish reach marketable size. Pumps may be necessary to provide the water supply.
Subtidal facilities have extensive culture (little environmental control) characteristics. No water pumps are needed, but detailed water quality analysis in required to ensure adequate circulation. Fouling organisms must be regularly removed from your stock and equipment.
Surface Floating Facilities
In this case, floating cages and rafts are used, which can be moved to protected areas if necessary. This is extensive culture and usually does not require pumping of water. However, fouling organisms may restrict the flow of water, creating supply and feeding problems. Supplemental feeding may be necessary, and fouling organisms must be removed regularly.
Mid-Water Culture Facilities
Mid-water culture facilities consist of strings of mollusks (shellfish) suspended through the water column. Since this is extensive culture, restricted flow may create fooding problems. Fouling organisms must be removed periodically.
Seabed Culture Facilities
These are also extensive culture sites and may be subject to fouling organisms that restrict water flow and cause feeding problems. Because of natural flow restrictions along the bottom, oxygen and food supply may be reduced.
For all of those sites, you must evaluate the exposure to pollution from land runoff (pesticides or siltation), and from sewage and industrial wastes. Ways of protecting a site from high winds and waves must also be evaluated.
Enclosures are needed to keep predators away and to prevent the loss of stock through sluice gates and other outlets. Materials used in aquaculture must:
1. Have a long visible life.
2. Be resistant to fouling.
3. Be easily cleaned.
4. Be nontoxic.
Structures supporting enclosures within the intertidal zone must be rigid to allow for the rise and fall of the tide. Floating rafts, nets, and cages must be anchored to allow for wind and waves. Wind and waves cause wear and abrasion of the materials. The structure may also need fine-mesh nets for protection from predators and coarse-mesh nets for protection from trash and floating objects.
Surface floating units, consisting of a timber structure on floatation barrels or floats, require much maintenance. The condition of the floatation and framework should be checked often, especially when used in salt water. Before using any material in water, especially salt water, the effects of marine predators on the material should be evaluated by installing test pieces for at least one growing season.
Organisms growth on equipment and shellfish can be removed by brushing, hand picking, or high-velocity water jet. Growth may be prevented in some cases by periodically removing the material from the water. In removing growth, care must be exercised to ensure that the underlying material (rope, net, and shell) is not damaged.
Foods and Feeding
Fish or shellfish cultured must be limited in number so that each animal can obtain enough food to grow. Insufficient food will result in slow growth, or even shrinkage, small animals (dwarfism), and a high potential for disease. Harvest has been found to increase as much as 1,000 percent when animals are fed regularly. Figure 1 shows how the growth rate can be graphed.
The conversion rate from feed to flesh varies with fish species, food type, temperature, individual fish, and food availability. Generally, it in between 10 to 1 and 20 to 1. Cultured fist and shellfish should not be overfed, since unconsumed feed sinks to the bottom, decays, and aids the development of algae growth, while reducing oxygen levels through the decomposition process. Although some of this fertilization is good, too much growth creates low oxygen levels. Fish should be fed 6 days a week at the same time and place each day, ideally, 2 to 3 hours after sunrise or before sunset. To empty the digestive tract and produce better-quality fish, don’t feed them on the day before harvest.
Feed only what will be eaten daily. If a floating feed is used, feed what in eaten in 10-15 minutes. Observe the response to feeding: If the fish do not appear hungry, there may be logical reasons (abundant natural food available, low dissolved oxygen, poisons, etc.) and feeding should be discontinued until the reason in found and corrected. If sinking food in used, check the feeding response by placing a 1.2m x 1.2m (4 feet x 4 feet) tray on the bottom in the feeding area. After 1 hour, raise the tray slowly and carefully. Look for feed on the tray. If the feed has not been completely consumed, reduce the amount of feed. Generally, fish will eat one tenth to one half their own weight per day.
Both natural and artificial foods say be used. Controlled fertilization of ponds in order to increase their productivity and providing more natural food to the cultured species are established practices. Artificial foods (those that will be consumed directly without conversion to algae) consist of plants, processed food, and certain industrial wastes. Examples of plant foods are the leaves of the cassava (tubers and peelings are not suitable), sweet potatoes, eddoes, banana, paw paw, maize, and canna plants. Processed foods include meal waste, cassava bran, flour, rice chips and balls, corn flour, and cotton and groundnut oil cakes. Industrial wastes such as decomposed fruit, brewery sediment, coffee pulp, and local beverage wastes have also been used successfully.
Fertilizer is added to a pond to ensure that there are minimum amounts of nitrogen, phosphorous, and potassium in the water to support algae growth. The requirements will vary with the water quality and fish population. Fertilizer should be added before the fish-growing season and repeated at ten-day intervals to produce the desired algae population, known as a bloom. After the bloom, add fertilizer as necessary to maintain a light bloom. The density of the bloom must be adjusted for different seasons, since too much algae will cause a reduction in the dissolved oxygen levels and could kill fish. A desirable bloom will shade out a bright object 0.3 – 0.5m (12-18 inches) below the surface. If 3 to 5 applications of fertilizer are made and a bloom is not observed, there may be other problems, such as filamentous algae or other plants using the fertilizer. These must be killed before phytoplankton algae can grow, unless the aquaculture system uses filamentous algae or large plants. If filamentous algae or larger plants are consistent problem, you should consider adding species of fish that can eat then, thus converting then into useful protein, rather than staying in a constant battle to remove them.
The pond can be fertilized in three ways: by spreading the fertilizer over the water surface; by placing perforated bags at intervals around the pond edge to allow the wave action to dissolve the fertilizer; or by placing the fertilizer on sub merged floating or stationary platforms off the bottom. That last
method provides the best results with the least fertilizer. Although agricultural runoff may help by providing nitrogen and phosphorous from the fields, pesticide and herbicide residues may destroy all of the fish in the pond. The direct application of animal manure has been shown to be effective in producing algae bloom, but it does have two potential dangers. Oxygen may be used up and ammonium (a reduced form of nitrogen) may reach too high a level. Both of these problems can be avoided if manures are used in moderation or if they are held in a pretreatment aeration pond. In general, if used carefully, animal manures may be an excellent, inexpensive, source of fertilizer for the fish pond. The aquaculturist should, of course, be aware of any religious or cultural taboos against such use that may affect marketing. (If taboos exist, the fish can be hold in “clean” ponds, or use of the manure can be suspended, for a week or two prior to harvest.
Related Posts: Understanding Aquaculture- Part 2
Source: Technical Paper #52
UNDERSTANDING AQUACULTURE By Ira J. Somerset