An Australian fish farming expert, Mr J.L. MacLean, says that aquaculture or fish farming management aims to get higher yields by preventing the death or depletion of the fish being raised due to the harmful characteristics of the natural environment.
MacLean says the natural environment is hostile and full of dangers to fish life.
Therefore, management aims to control or eliminate as many of these natural dangers to increase the survival rate of fish.
The problems of fish farmers the world over arise from the harmful and limiting factors imposed by the natural environment.
Fish pests and diseases are harmful factors; not enough food for the fish is a limiting factor. Modern fish farming has developed a management system whose basic components would include a hatchery, an enclosure such as a pond, a fish pen or a floating cage, fertilizer, feed supplement, and a system of water circulation.
A hatchery eliminates the dangers that cause the death of fry. A hatchery prepares the fry or fingerlings for release to the sea or the fish farm. Left on its own, the fry is very vulnerable, and It can easily be killed by the harmful forces in the natural environment. Thus, the hatchery.
The enclosure – a fish pond or fish pen – lessens further the harmful effects of the environment by keeping the fish out of the reach of predators or other animals that prey on them.
The provision of organic or inorganic fertilizers makes the water in the pond more productive. With fertilizers, more organisms that serve as food for the fish, such as lablabs, can be grown.
Food – or not enough of it — is a limiting factor. Therefore, providing supplementary food enables you to raise more fish per unit area.
Finally, circulating the water through the fish pond or fish pen would remove the dangers caused by the accumulation of pollutants like a waste. At the same time, it makes available an unlimited supply of oxygen for the fish.
At this level of management, virtually all of the dangers in the environment are eliminated. As a fish culturist or fish farmer, you would then be faced with only one limiting factor – “space”.
In summary, modern fish culture incorporates the following practices:
– Protecting the fry from natural dangers and preparing them for release to the grow-out ponds or the sea.
– Protecting the fish from predators; increasing the fertility of the water.
– Adding feed supplement, and removing water circulation poisonous materials in the water.
Understanding The Pond Ecosystem Better
Fish farming, especially prawn farming, requires good knowledge of some basic information on how and why changes occur in the pond’s conditions.
These changes are mainly the result of interactions among the water, soil, air and the various organisms in the pond. Here are some of this information:
1. Soil, water, air and the various organisms in the pond constantly interact. How good or bad the interaction is due largely to available sunlight and weather condition.
2. Water takes in almost all substances — soils, gases and other liquids – whether beneficial like nutrients or harmful like chemical pollutants and biological wastes.
3. Salt makes the water denser or heavier. The amount of salt is known as salinity and is expressed in parts per thousand or ppt. Seawater’s salinity ranges from 32 to 34 ppt while freshwater has zero ppt.
Thus, freshwater will float over seawater. During dry
months, it is fairly common for fishpond water to reach a salinity of 60 ppt or more.
4. Temperature also affects water density. As the temperature rises, the density goes down. Warm water will float over cold water.
5. The ability of water to take in (dissolve) oxygen and other gases is reduced by temperature and salinity. Warmer waters hold less oxygen, as do saltier waters.
6. Although water is composed of hydrogen and oxygen, it is not this form of oxygen which is used by aquatic organisms for breathing.
7. Organic matter in the pond such as decaying plants, animals and uneaten food also uses up oxygen and produces harmful products such as ammonia and hydrogen sulfide.
8. Dissolved oxygen in the water can be increased by wind action on the surface, by stirring the water with a paddle, or by bubbling air in the water. Letting in new water also increases dissolved oxygen content.
9. Water, to a certain extent, contains free hydrogen and hydroxyl ions. The amount of free hydrogen ions is measured on a scale from 1 to 14 known as the pH value.
Pure water has equal amounts of hydrogen and hydroxyl ions and has a neutral pH of 7. With a pH below 7, water is acidic. Above 7, it is alkaline.
For the maintenance of plant and animal life, the pH value should be from 7 to 9.
10. Plants in the pond produce oxygen but just like animals, they breathe and use up oxygen. In the process, plants produce carbon dioxide. In the daytime, plants produce more oxygen than they can consume.
At night, they stop producing oxygen but continue to use it up and produce carbon dioxide. In so doing, plants lower the dissolved oxygen content in the pond sometimes to the point of depletion.
11. Water pH is affected by soil pH and the amount of carbon dioxide in the water. Some pond soils are by nature acidic. Highly acidic soil is usually reddish. Such soil is not favourable for fish fanning and therefore has to be treated to lower its acidity.
12. Salinity, temperature, dissolved oxygen and pH vary from one pond to another as well as from time to time. A fish farmer must be able to distinguish short-term changes from long-term changes.
Short-term changes are those which occur hour by hour within a day while long-term changes are brought about by seasonal variation and sudden changes such as those brought about by heavy rainfall.
13. During 24 hours the most pronounced change which can drastically affect the fish is the rise and fall of dissolved oxygen content. It is generally at its lowest an hour or two before sunrise. Then it slowly rises to its maximum in the early afternoon and declines as the sun sets until it goes down to the minimum level in the early morning hours before sunrise.
14. Temperature also fluctuates during the day but such changes are not usually serious except in very shallow, less than knee-deep ponds. The rise and fall of pH and salinity during 24 hours are also not serious.
15. In one year, however, the most significant change occurs in salinity, particularly in regions with pronounced wet and dry seasons. Salinity will rise to 60 or 70 ppt during the dry season unless fresh water is constantly supplied.
On the other hand, during the rainy season, salinity could become so low as to make water almost fresh.
16. The most serious changes are those brought about by heavy rainfall. Such changes could be disastrous. A big flood can suddenly lower pond water’s salinity.
Run-off from the dikes in ponds with acidic soil could drastically lower the water’s pH from 8 to 3 in a short time. After heavy rainfall, a layer of freshwater is formed over saltwater thus blocking the interchange of gases between air and water.
This will easily deplete the oxygen content in the pond water especially when the air is perfectly still.
Preparations for the New Year Production
For fishpond raisers, here’s a checklist of jobs and preparations you may want to do at the start of the year:
1. Repair dikes, gates and other pond structures as well as nets and screens. Inspect your ponds and note where leaks are.
You could list down all the needed repair jobs and how much these would cost.
2. Check your water pumps and put them in proper operating conditions. You’ll need a reliable pump in the face of the hot summer months.
3. Obtain from the Bureau of Coast and Geodetic Survey a 1980 tidal table. Some calendars being given away by commercial firms also contain the tidal table.
4. Check the pH and fertility of your pond soil to find out if you have to apply lime and fertilizer.
5. You may want to start contacting fry dealers and suppliers. Plan your next year’s production scheme; find out where you can obtain fry at a good price and start developing closer business relations with the suppliers or their agents.
Your production plan should be able to tell you how many fries you need for the succeeding cropping seasons.
6. Check for signs of erosion around the farm and plant cover crops or install erosion checks. Planting a buffer zone of mangrove trees will go a long way in protecting your land from wave erosion.
7. Start looking into ways you can save on fuel. A smooth-running pump or delivery pick-up saves a great deal of fuel. Also, you may want to look into the possibility of installing some alternative pumping system such as a windmill.
8. See if you can integrate other agricultural operations into your fish farm. Cattle, hogs, ducks and poultry could be raised profitably with fish. And some crops raised for human food and feed supplement would enable more efficient use of your land and labour resources.
9. Your workers and farmhands might need some training in new skills and orientation along with better pond management practices. See how you can get them to be trained in new and more effective skills.
10. Review your performance last year and see where your management practices and operations can stand some improvement.
Take Care Of Your Pond Dikes
A good dike does not leak. Leaky dikes are the result of poor dike construction, improper soil used for making the dike, and animals that bore holes through them.
The kind of soil used to build the dike is important. Sandy or silty soil with very low clay content will cause dikes to leak after some time. If no puddle trench is dug during the construction, water tends to seep between the original soil surface and under the dike due to the difference in material consistency.
Crabs, eels, snakes and other burrowing animals may bore holes through dikes, so to prevent leak or seepage, always construct a puddle trench at the middle and bottom of the new dike.
Build the dike with enough thickness at the base to stand water pressure from either side. Remove all organic matter like roots, twigs, stumps and dead
leaves from the soil surface where a new dike is going to be built.
Use clayey soil for diking material. If seepage occurs after some time dig a new puddle trench along the inside of the dike and refill it with new clayey soil.
If holes are made by animals, kill the animals inside the holes by placing poisoned bait, putting hydrated lime into the hole, digging the animal out of the hole, and refilling the hole with new soil. If the dike is too narrow at the base, widen it by constructing a berm or a shoulder.
Grade Your Fry or Fingerlings Before Stocking
Grading fish to a uniform size before stocking can help fish farmers get a good estimate of the number of fish in the ponds. Of more importance, you reduce the number of fish that are too small to sell when the stock is harvested.
Sorting tables are commonly used to cull or select fingerlings for stocking. However, the use of sorting tables does not avoid careless and rough handling, especially if workers are in a hurry. Fingerlings are usually injured with this method.
A new idea is the use of fish grading panels which are of the same width as the holding tanks. Fish grading panels are placed in the tank with all the fish concentrated on one side of it.
Since the grading panels have slots of a predetermined size, the fingerlings smaller than the slots can pass through them. The ones that cannot get through are of the size you want for stocking.
Another way is to use floating grading boxes with panels of metal bars at the sides or bottom. The space between the metal bars determines the size of fish that cannot be retained for stocking.
Those small enough to pass between the bars escape. The ones that cannot get through are retained for stocking.
The advantage of this method of sorting fingerlings is that you avoid handling them with dipnets which can injure and cause stress.
DO’S AND DON’TS IN FISH FARMING
Here’s a list of what to do and what to avoid in fish farming.
These do’s and don’ts have been adapted from a list prepared by the Central Inland Fisheries Research Institute in India, whose scientists have successfully developed and promoted what has been called composite culture or polyculture (raising different kinds of fish in one body of water), particularly carps.
What to Do
1. Utilize all cultivable bodies of water for growing fish.
2. Remove weeds from your pond by economical methods
3. Remove all unwanted fishes and predators from the pond.
4. As much as possible, use any plant poison like tobacco dust – to treat your ponds.
5. Stock only after the effect of poisons has disappeared.
6. Fertilize the pond to increase the production of fish food.
7. Stock at the proper rate and ratio.
8. Select healthy fingerlings to get fast growth and lessen predation.
9. Try to feed the fish with cheap and balanced artificial feed.
10. Feed the fish at fixed hours and spots in the pond; observe how the fish consume the feed.
What Not to Do
1. Do not waste any water area because fish farming is lucrative.
2. Do not allow the growth of weeds because fish will grow poorly and harvesting is made more difficult.
3. Do not allow the entry of harmful and predatory fishes into the pond.
4. Avoid the use of chemical poisons because they may spoil the pond and leave harmful after-effects.
5. Never stock while toxicity is still present in the water.
6. Do not expect your fish to grow well without enough natural food.
7. Do not stock indiscriminately – too low or too high stocking will not give high production.
8. Do not stock with unhealthy and undersized fingerlings.
9. Do not expect a fast growth rate of fish without proper supplementary feeding.
10. Do not broadcast feed indiscriminately to avoid waste.