METHODS OF FISH CULTIVATION.2.docx

7/31/2019 METHODS OF FISH CULTIVATION.2.docx

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Fish Culture in Dams and Reservoirs

Water contained by dams and reservoirs is sometimes used for fish culture. These waters can bestocked with fry or fingerlings; the adults are later harvested with nets. Raising fish in thesewaters is more difficult than in ponds because these waters cannot be drained, and the predatorscannot be removed. Also, it is not possible to feed, fertilize, or poison the water, so naturalnutrients must provide enough fish food. But if there is no other water source available, culturein dams and reservoirs can work.

Culturing fish in waters held by dams and reservoirs can be done more easily if the fish areplaced in fish cages and pens. These structures confine the fish to a certain place and give morecontrol over the fish.

In Cages

In many parts of the world, the only water available is flowing water or large bodies of waterwhere it is not possible to divert the water into a pond. In these waters, it is possible to grow fishin small cages. Cage culture can also be practiced in areas like swamps where there is water notbeing used for any other purpose.

Cages can be rectangular boxes, bamboo cylinders, or anything that can be floated in a watercurrent so that the water passes through.

In addition to bamboo, cages can be made out of such materials as wire screen, nylon mesh, andwood. All cages must be anchored so that they do not float away.



Cage culture is used in some countries in very fertile waters (polluted from sewage) with verygood results. Fish in cages usually get their food from the water as it floats past the stationarycage, but in some cases, the caged fish are fed pellets of food daily.

Fast flowing water is best for cage culture. If the water is not flowing very fast, problems such asoxygen lack and competition for food can occur. These can be big problems in cages becausethere are usually more fish placed in the small area of the cage than would normally be in thesame area in the pond.

Cage culture is still experimental, but in ideal conditions, good growth rates have been shown byfish that were grown in cages and given extra food.



Cages also are used inside ponds for holding fish between harvest and the time they are sold.And, sometimes, cages are used as breeding tanks -- like hapas. Cages are also used to carry fishcaught in rivers to market, strapped alongside a boat.

In Pens

Fish can also be cultured in pens inside lakes or offshore areas. Fish culture in pens has beendone in Israel and Scotland for years, and is now being done in some Asian countries. Pens areconstructed of bamboo or wooden poles that are forced down into the lake or shore bottom. Thennets are strung from pole to pole to form an enclosure. The nets are anchored into the lakebottom with weights or sinkers, and the fish are placed inside the pen for culture. Fish grown inpens can be controlled a little better than fish in cages because pens are larger (fish pens can becomparable in size to regular fish ponds) and provide more area and more food.



Fish pens placed in fertile (productive) lakes have very good growth rates. In a fish pen placed ina major lake in the Philippines, silver carp stocked at 7 grams gained an average of 4 grams a dayin a 52-day growing season.

Fish pens have many good points: they require no extra feeding of fish, no fertilization, and very

little maintenance (although a lot of care is given to the nets). The fish are stocked and harvestedlater at the end of their growing season. Fish pens can work in areas where the water is not veryproductive, but in these areas, the fish must be fed supplementary foods. Feeding rings are usedso the food will stay in the pen and not float out into the water. Fish in pens are usually harvestedby gill nets; seines also may be used.

There are some disadvantages to pens:

* Pens are expensive to build. The netting used must be nylon or plastic so it does not rot, andpoles must be treated so they do not become waterlogged and rot. In the Philippines, it costsabout $1,428 (U.S.) to build a one hectare pen, using nylon netting and bamboo poles. This iscomparable to the cost of a one-hectare fish pond, but a pen can be destroyed by a big storm anda pond will no+ be destroyed.

* A fish pen only lasts three to five years in the water.

* Fish pens are usually built in the shallow areas of a lake, where they use space many fish needto feed and spawn. The pens, therefore, reduce the natural production in some lakes.

* Fishermen must go further out into the water to fish when pens are in the shallow areas.

Fish pens can also be built like fish cages so that they float. Floating fish pens are used most formarine fish research studies; they also can be used in lakes. Floating fish pens can be as small asone hectare in size, or as large as 10 hectares. They are not destroyed by storms as easily as pens

anchored to the bottom, and they can-be moved from one site to another.

Fish pens may have an increasingly important role in future fish culture activities around theworld.

In Rice Paddies



This manual has already mentioned the practice of culturing fish in fields with rice. Here isfurther, brief mention of that subject.

The farmer digs deep trenches all along the dikes of the paddy. He then floods the field andplants the rice. After the rice has grown to a height of 5cm or so, fish can be placed into thepaddy field.

This culture method can be used only with fish that are resistant to low oxygen levels and are notherbivores - herbivores might eat the young rice plants. Clarias catfishes are good fish to culturein rice paddies because they ave accessory breathing organs which help them to breathe evenwhen the paddy gets dry and the water in the trenches gets very low.

After the rice is harvested, the fish are caught in hand nets and sold. This is not really a culture of fish, but a culture of rice with some fish added. It can be an easy way for a farmer who has noextra land on which to build fish ponds to increase the total production of his land.



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METHODS OF FISH CULTIVATION.2.docx