Sunday, August 23, 2009

Fish Culture 3: Fish Cage

Carp cultured in fish cage in Laguna Bay
Binangonan, Rizal

Abe V Rotor

The original fish cage was developed by Central Luzon State University. There are now modifications made from it for both freshwater and marine environments. How does a fish cage look like?

The simplest design looks like an inverted mosquito net with the four corners tied to pegs that also serve as post. The cage is installed in shallow water and you have a fixed fish cage.

The floating cage model is used in deep water. Nylon net or mesh wire is mounted on a cube-shape frame (1m x 1m x 1m), complete with cover that allows aeration and sunlight, and solid bamboo or styropore as float. About 500 Nile tilapia fingerlings weighing 20 grams each may be stocked per cubic meter of cage. Each fingerling may reach marketable weight of 60 grams in two months or 120 grams in four months. Thus a cubic meter of cage can yield 30 kg every two months or 60 kg every four months.

CLSU developed a low-cost, efficient feed formula which consists of 75% fine rice bran (cono) and 25% fish meal (local). It is served as moist pellets. The fishmeal and fine rice bran are mixed with just enough water to form a mash and divided into balls. The moist balls are force-fed into an ordinary meat grinder. The extruded product is noodle-like which breaks into pellets.

Using moist pellets, the feed conversion is 2.5 on the average, which means that 2.5kg of feed produce one kg of fish. Feeding rate can be determined with this formula. Fish weighing 50 grams or less are fed at 5% of total fish weight. For example, a stock of 1,000 fingerlings weighing 20 grams each will require one kg of feed per day. But as the fish grow, you will have to increase the rate of feeding every two weeks, using the same body weight basis. Feeding is done twice a day, splitting the ration, one at 6 to 8 AM, and the other at 4 to 6 PM. To economize on feeds and minimize wastage, place the feeds in a fine-meshed feeding box inside the cage.

A farm of 10 to 20 cages requires only about two hours of attention everyday. The culture period is 2 to 4 months depending on the desired marketable size. While diseases are rare, poaching may be a problem in certain areas.

Whatever is our reason to engage in fishing, hobby or business, there is something more that we derive out of it. Let me count the ways. Fresh fish, added income, aesthetic value, clean air, sunshine, good exercise, peace of mind, companionship with nature, good health – and the thought that we are close to the Greatest Fisherman who ever lived.
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Living with Nature, Volume 3. All Rights Reserved

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