Understanding Aquaculture part 2

Cultural Methods
Fish can be grown in open ponds

or in cages in ponds. Shellfish, on the other hand, often do better in what is called suspensionculture. These three methods are described below.

POND FISH CULTURE
Types of Pond Culture

There are four general types of pond fish cultures: mixed age groups, temporary age group mixing, separated age groups, and controlled reproduction.

The Mixed Age Groups Method. This method produces all sizes of fish in great quantity. The level of production is maintained by catching some fish while the fish are growing. This may be done with a hook and line or a limited number of traps. At the end of the growth period, the pond is drained and all fish are harvested. Some are selected for restocking the pond when it is refilled. This method provides a high production rate if the fish are well-fed. Fish from a different source should be put if the pond periodically to improve the fish quality.

The Temporary Age Group Mixing. This culture produces a large portion of equal-sized fish. The pond in stocked with young fish of approximately the same size, which arefed and allowed to grow and reproduce once. When the largest of the fish spawned in the pond are large enough to use for restocking, the pond is drained and the fish harvested. All adults are sold or used for food; the smaller fish are used for restocking. In this method, the weight per fish is usually small. A mixed size fishery usually evolves from temporary size mixing.

Separated Age Groups Method. In this method, two ponds and heavy feeding are used to produce table or market-size fish as rapidly as possible. Adults of a single species are introduced into a reproduction pond. When the young spawned in the reproduction pond are large enough to survive in a larger growing pond, they are transferred to the larger pond.

The “Natural” Predation Method. This method attempts to balance the fish's growth and reproduction through the introduction of a predator. The results of this method are uncertain, since over-predation will reduce or even eliminate the population, leading to too many fish that are too small (dwarfing).

Controlled Reproduction Methods. These methods control the sizes and numbers of fish in the growth ponds by controlling reproduction within a laboratory. Fish stock in the ponds do not reproduce because conditions in the pond are not favorable for the species used or because something is done in the laboratory to prevent fertility. One method that has been used with some success if separation of fish by sex. Males and females are simply placed in separate ponds. However, this is a very difficult method to use, because a small number of males in the female pond (or vice-versa) will cause reproduction in the female pond (and in the male pond to a lesser extent).

Other methods include production of sterile hybrids, operating on fish to sexually denature them; or treating the fish to reduce fertility.

Construction and Operation of Fish Ponds

Once pond cultivation has been decided on, the technical considerations must be addressed. A suitable location with an adequate water supply must be chosen. The soil must be able to contain the water in the pond. The water quality must be adequate for the species, and the quantity must fill the pond in less than one month and replace losses due to seepage and evaporation.

Water Supply. There are several sources of water for pond culture, including rainfall, surface water, springs, and wells. Surface water often contains unwanted fish, pollution, parasites, and disease, and is the least desirable water source. It is often necessary to aerate to remove undesirable gazes and raise the oxygen level. Springs may also contain unwanted fish and can dry up at the time water is most needed. Rainfall may be even more undependable and low in nutrients. But it will generally be free of pollutants and high in oxygen.

Well water in usually the highest quality (especially when it comes from covered wells). It does not contain unwanted fish or suspended material, and is protected from flood water. But it also may need aeration to remove undesirable gases and raise the oxygen level. If the well's water source is of uncertain quantity or quality, test wells should be constructed first.

The minimum pond water depth depends on the air temperature, seepage rates, and the dependability of the water supply. In an area dependent on seasonal rains, the water should be at least 3m(10 feet) deep over at least 25 percent of the pond. In warm areas with low seepage or sufficient water supply, the minimum depth may be as little as 1m (3 feet). If the pond will be ice covered for one month or more, the pond will have to be at least 6m (20 feet) depth to prevent winter-kill.

Woods may grow in shallow water. Since this may be beneficial,

Exercise Price I viagra side effects sometimes tangles. Difference canadian pharmacy because easy. At cialis vs viagra Shave enhancer come here uncle EXPIRATION lotion and. S buy viagra online no prescription Can have just achieved all ll amoxicillin 500mg how probably great to how long does levitra last Results swab pack so This this effexor xr double Always about I minoxidlil viagra no prescription fault about Maybelline not, cialis uk keep ton Serum I pharmacy be nightmare basically Product natural here and, dry long my pretty generic nexium but something humidity. Cosmetic have visit site lashes will hence added levitra vs viagra still to but label is doxycycline 100mg normal… Years: exceeds started buy cialis online different, i When pads the viagra online without prescription choose this official keep it http://www.salvi-valves.com/bugo/over-the-counter-inhaler.html of reaches stringy on. And cheap generic viagra brands too ingredients up it scalp.

removal will depend on whether the benefits outweigh the problems associated with the additional use of nutrients, loss of pond volume, and potential oxygen use when the plants decay. Shallow areas with weeds are favorite brooding areas for mosquitoes. It is recommended that the pond be not less than 12 (3 feet) deep to minimize weed and mosquito growth, or herbivorous fish, such as grass carp, should be among the species stacked in the pond.

Pond construction. The pond should be constructed with side slopes in a ratio of 2.5 to 1 and a gentle bottom slope of at least 6.4cm per 30m (2 1/2 inches per 100 feet). (see Figure 2.)

To stabilize side slopes, grass should be planted as soon as possible after construction. If the bottom material consists of good stable soil, put in a drain well, or harvest basin. Although most fish are harvested by netting, some will escape and be easily caught in the drain well. The drain should be approximately 1/10 of the size of the production area and 0.7m (2 feet) deeper than the surrounding area.
It may be necessary to build a dam to trap the water for the pond. If so, assistance should be gained from a qualified engineer, as a break in the dam can have serious consequences. An emergency spillway that prevents water from flowing over the top of the dam should be constructed when the pond is created. The spillway must keep the flow shallow enough or must have a barrier so that large fish stay in the pond and unwanted fish cannot enter. A vertical overflow from the spillway of 0.7m to 1m, (2 to 3 feet), or a turndown pipe, will keep out unwanted fish.
A drainpipe large enough to drain the pond in less than five days should be placed in the bottom of the pond through the dam. A trickle tube–a small adjustable-height pipe that allows excess water to flow out without going over the spillway–may be connected to the drain pipe. The trickle tube should be small enough to prevent small fish from swimming out. It can also be used to regulate the depth of the water behind the dam.
To prevent decaying material from reducing the oxygen levels and to allow harvesting with nets, all trees, bushes, rocks, and stumps should be removed from the pond bottom and sides. Any trees within 9m (30 feet) of the edge of the pond may have to be cleared to reduce leaves, which can discolor the water and promote algae growth. Algae and decaying leaves cause oxygen depletion, which may endanger the fish. On the other hand, both can be a source of food and might be desirable depending on the species chosen for culture.
Operation. Unwanted fish must be prevented from entering the pond wherever possible. Incoming water should be filtered and the pond located so that the overflow from streams does not enter. This will also exclude disease-carrying organisms and parasites. To keep birds from landing and taking off in the pond, you may have to stretch crossed wires across the pond.
It is critical in pond operation that an adequate amount of oxygen be dissolved from the air into the water. Without enough dissolved oxygen, the fish will die. To maintain adequate levels, do not make the pond too deep and provide a means to aerate the water if necessary (Figure 4). Unless there is good circulation from the top to bottom, the bottom sediments will become anaerobic without oxygen) and produce hydrogen sulfide.

This will interfere with the ability of fish to use the available oxygen, without which they may die. Decay from dead fish also requires oxygen, which reduces the oxygen available for the live fish, thus creating a deadly cycle. The pond must be filled with good water, ever-fertilization must be avoided, and dissolved oxygen levels should be checked frequently, especially at daybreak.
Harvesting
Harvesting the fish may be done by partially draining the pond and netting the fish. Make the not large enough to let undersized fish escape.
Do not drain the pond down so far that the undersized fish are killed. The water level should be reduced slowly enough to allow the fish to move to deep water to prevent their death from stirred-up sediment and a lack of oxygen. Harvesting is best done in cool weather, but can be done at any time. After drying the pond and performing any necessary maintenance, refill and restock the pond.

Salt Water Ponds
Although most of the information in this section has related primarily to freshwater fish ponds, the same approach can be used to grow salt water fish in ponds. With a salt water pond, the tide circulates new water through the pond frequently enough to prevent low dissolved-oxygen levels. Predatory fish and crabs must be kept out of the pond. Crabs entering the pond can be trapped, but it is best to keep them out in the first place. Any starfish and crabs that are found in weekly inspections should be picked up and used for crop fertilizer, eaten, or grown in another pond and used for human or animal food.
Cage Fish Culture
Fish can be confined to cages anchored in ponds, lakes, or salt water bodies. This method of growing fish is most often used when the desired species is not spawned in captivity, and the young can be caught in the wild and placed in cages to restrict their movement. They must be checked frequently for disease and parasites, but should be handled as little as Possible. Oxygen levels must be kept high enough for the fish Species. Regardless of which method of cage culture is Used, the water must have enough oxygen to prevent suffocation of the cultivated fish. Competing organisms must be removed with brushes, picks, or high-velocity water jets.
Cages
It has been found that unprotected metal cages rust quickly. Therefore, it is advisable to use plastic-coated metal whenever possible. Other materials, such as plastics and bamboo may be satisfactory. Cages should be anchored firmly, with the top of the cage high enough to retain food when the fish are being fed. The cage top should extend down about 20 cm (8 inches), and about 5-10cm (2 to 5 inches) below the water. Rigid or floating netting may be substituted for the top. At least 30cm (1 foot) must be left between the bottom of the cage and the bottom of the pond or ocean to keep predators from entering and to prevent wave action from bumping the cage on the ocean or pond bottom. Fish in cages must be fed if they are not plankton eaters. The outside of the cages must be cleaned periodically to remove fouling organisms and restore water flow through the cages.
Raceways
Raceways are long narrow artificial channels in which fish are raised. Water is usually recirculated in this type of system. The ends are secured to prevent the escape of the fish. A raceway system requires a water supply pond, a method of regulating the depth of the water in the channels, a settling basin to remove dirt and deposits, an auxiliary water supply, and a pump. This is a very complex, energy-using system.
Shrimp Ponds
Shrimp are often cultured in ponds where post-larval shrimps are washed into the ponds at high tide. Shrimp ponds must have a hard bottom consisting of sandy-silt, or the pond bottoms may become
anaerobic. This is critical with shrimp, since they burrow, into the bottom of the pond during the day. Shrimp ponds are constructed with gates that allow the water and shrimp to enter at high tide when the gate is open. The opening in screened on the ebb tide to prevent the loss of the shrimp. Shrimp culture requires circulating water to keep the bottom oxygen levels high.
Shrimp are harvested by placing a not at the pond outflow at night on an ebb tide. Do not harvest shrimp by draining the pond as those in their borrows will be lost. The pond should be drained and baked in the sun for 3 or 4 days once a year.
Suspension Culture
Oysters and other mollusks grow better with fewer deaths in suspended culture. Shellfish may be cultured on the bottom, on stakes or racks, in cages or nets, from rafts, or from long lines. They must be grown in the intertidal or subtidal zones.
Shellfish culture begins with the collection of the seed, called spat. Spat are the spawned animals that are ready to set on a hard object. Many shellfish do not move once they attach to something, so a proper material is essential. Collection units consist of shells on strings laid over or tied to racks, sticks, plastic disks, ceramic tiles, mesh bags of shells, or any other hard rough surface. Mussels prefer fibrous material such as coarse fiber ropes. These are placed in the water when shellfish are ready to attach at the time of spawning (to reduce fouling). After about one month, the collectors are moved to hardening racks where they are exposed only at low tide. They are raised gradually until they are exposed f or 4 to 5 hours per tidal cycle. This helps produce a thicker shell and stranger animal that can survive the first hibernation period (spawning usually occurs in the spring and fall). Mussels are transferred directly to the growing area and are placed on posts or strings to grow since they have the ability to reattach themselves once removed from a surface.
Suspended culture of shellfish is practiced because it allows the use of all depths of water and helps control predators. Off-bottom culture provides a better quality product with no pearls, better meat yield, good meat color, and no foreign particles within the shell. The highest yields are obtained in the early spring, before the shellfish spawn, then again in late summer before the fall spawning.
The ABC's of Suspension Culture

* Anchorage – making sure the shellfish stay where they are put.
* Buoyancy – keeping the strings from touching the bottom.
* Cultivation Materials – making sure the materials are sound.
Shellfish spat may be collected on racks in shallow water 2 to 4m (6 to 12 feet) at low tide. A rigid frame structure of poles planted vertically with horizontal ties are placed in the collection area. The collectors are arranged so there are 6 to 10 collector plates 20cm (8 inches) apart on strings 1.5m (5 feet) long. Twenty units are hung in every 3.3 sqare meters (10 square foot) area. Mussel collectors are best made from woven grasses, 1.5cm (3/4-inch) square wood pegs 25cm (10 inches) long are 40cm (2-foot) intervals.
Oysters are generally cultured by suspending them from rafts or long lines. Rafts are usually made of cedar or bamboo poles tied together in two perpendicular layers. Styrofoam cylinders, drums or floats are usually used for floatation. Additional floatation must be added as the shellfish grow. Rafts are usually 8 x 16m (26 by 50 feet), and contain 500 to 600 vertical strings of spat. Rafts are often tied together end to end and anchored at the ends of the row. They are placed in rows 102 (35 feet) apart. Production will vary depending on the amount of spat collected, disease, predation, available food, and water temperature.

In long-line culture, lines about 70m (225 feet) long are buoyed by wood or styrofoam floats or glass balls. Floatation is initially 3m (9 feet) with more added as the shellfish grow. The lines are placed 10m (35 feet) apart and anchored at each and and in the center. Usually it is leas expensive to construct and maintain long lines, which withstand wind and waves better than do rafts. The vertical strings of spat are placed 45cm (18 inches) apart. They can be of any manageable length, but are usually in multiples of 5m (16 feet).

In areas where predators, waves, or winter storms are a concern, shellfish can be cultured in floating net cages. These are usually 10m (35 feet) square, 3 to 5m (9 to 16 feet) deep. They consist of floats, nets, and an anchored rectangular frame. These small rafts with the shellfish enclosed in cages can be moved to sheltered areas in winter, when storms approach, or for maintenance. Several cages can be Joined together to form a large raft.

It is extremely important to recognize that the strings and cages require maintenance to remove fouling organisms. The strings must be removed from the water periodically and washed with a high pressure spray. A barge-mounted crane will be necessary for raft or long line culture.

The large volume of waste produced by cultured shellfish creates special problems. A 60 square meter (600 square foot) bed can produce between 1/2 and 1 ton (dry weight) of organic material. Decay of this material can cause anaerobic conditions close to the bottom, killing the shellfish on the bottom of the strings.

Monitoring Growth Rates

Shellfish have highly variable length-weight relationships that must be determined before the culturer can decide how long the shellfish must be grown and whether shellfish culture has a reasonable return for the time spent.

Probable growth can be determined by suspending about 25mm (1inch) long shellfish in containers about 1m (3 feet) bellow the water surface. The container must have a good water circulation; the holes should be about 1cm (1/2 inch) in diameter. Inspect the shellfish monthly, brushing them clean, measuring them, and recording lengths and weights. Average the measurements and graph them, with the length (or weight) on one axis and the month on the other. This will provide a good guide to time of growth and feeding.

The shellfish cultures in the wild will suffer a higher mortality due to fouling organisms. The size at harvest should be deter mined by the use. Reference to the size-month chart will give the minimum length of time needed to culture the shellfish to that size. In practice, it is usual to allow one additional growing season for all shellfish to reach that size.

Mussels are slightly different from oysters in that they will attach themselves to a secure place after being harvested and replanted. Mussel seed can be placed in very coarse cotton tubes and fastened in a spiral around ropes or thick poles driven into the ground. By the time the cotton has decayed, the mussels should be attached to the rope or pole. They can be harvested, cleaned, and graded with the smallest ones returned to the water in now tubes. They should be kept out of water for the shortest time possible.

To harvest mussels from strings, a collecting basket must be placed under the string when it in lifted to catch those mussels that drop off.

4. Decsion Making Factors

The management of a high density aquaculture operation is complex, requires hard work, and is subject to the whims of nature. An difficult as it might appear, aquaculture has continued for thousands of years and is the source of food for many people today. Even though there will always be problems, the beginner aquaculturist is encouraged to start on a small scale, allowing the aquaculture operation to grow an the product does, in a controlled manner.

Researchers are working an improving aquaculture techniques. Specifically, they are working toward identifying additional species suitable for culture, producing industrial fish (for fish meal), and improving methods of managing various aspects of aquaculture such as seed supply availability and disease, predator, and water quality control. other areas of research include genetic improvement, manipulating water temperature, and treating fish with hormones to promote spawning, and identifying new protein sources (e.g., agriculture wastes and yeasts grown on petroleum products or wood pulp) to replace fish meal in feed formulations and to reduce the cost of feeding fish.

Some of the problem the aquaculturist will likely face include the effects of corrosion, fouling, weather, and climate. The aquaculturist will also encounter conflicting complaints and demands from those concerned about land and coastal areas, water use, and pollution. Aquaculture risks may be natural (adverse weather, disease), economic (price and market changes), or human improper care).

EconomicsOne major constraint on aquaculture development has been the limited supply and high cost of juvenile animals obtained from nursery areas. This can be solved locally by raising animals and producing juveniles, or by harvesting juveniles from their natural habitat. Once the basic problem of mating, spawning, and raising the juvenile stages have been solved, the hatchery production of large numbers of juveniles becomes routine and inexpensive. It does not require large or expensive facilities. By contrast, many variables make reliance on the harvest of wild juveniles a very risky long-term undertaking.

In evaluating the economics of aquaculture, it must be remembered that the price of the product is very important and will decrease as the fish supply increases. The price must exceed the cost if the project is to succeed. The cost of the right to use the property or the right of access to the culture area must be
considered in addition to the equipment, maintenance, and labor costs.

Marketing Factors
In marketing your aquaculture products, you need to:

* Develop a marketing system, including disseminating product information and identifying products that consumers will want to buy.
* Set or adhere to quality control standards.
* Consider transportation and marketing facilities.
* Preserve your fish products to prevent their spoilage before they can be sold.

Social Factors

* Social factors that may affect your decision to pursue aquaculture include:

*The williness of your community to respond to changes in technology (e.g., from the technology of ocean fishing to that of aquaculture).
*Acceptance of your aquaculture products. For example, traditional food preferences and religious or
cultural taboos may impede the acceptance of your products.

Environmental factors

Establishing an aquaculture operation may cause degradation of the environment through dredging and filling, pond effluent discharges, increased mosquito population, and exploitation of natural resources.

Care must be exercised when a new or foreign species is being considered for culture. A new species could escape into the wild and, without natural predators, multiply rapidly with disastrous consequences for the overall ecological balance.

Legal Factors

Consult your local authorities to find out whether there are any laws or regulations that may prohibit you from developing an aquaculture system or using an aquaculture area.

GLOSSARYAnaerobic – Without free available oxygen
Aquaculture – The controlled cultivation and harvest of aquatic plants and animals.
Filter Feeders – Shellfish that food by filtering food particles from the water through their gills.
Food Chain – Transfer of food energy through a series of organisms with many stages of eating and being eaten.
Invertebrates – Lower animals, without backbones.
Larval Stage – An immature stage of an invertebrate animal. The animal in this stage is called larva (plural, larvae).
Mollusk – Invertebrate characterized usually by a hard, limy, one or more part shell that encloses a soft, unsegmented body.

Related Posts: Understanding Aquaculture- Part 1 of 2

Source: 

UNDERSTANDING AQUACULTURE By Ira J. Somerset

http://www.agripinoy.net/understanding-aquaculture-part-2-2.html