In farming, to have healthy, fast growing, highly productive and low-cost fish…, rearing breed with a high quality and without diseases is a first issue.
Rearing fries into sweetfish
Selecting and cleaning the pond
This is a very important issue affecting the survival rate of fish. It is neccesary to choose the rearing pond near an irrigation system to provide clean water for the pond and to limit diseases in the breeding process.
The drainage system to the pond must be separated, the water supply and drainage are in the same canal. Depending on the conditions of the farmers, the pond has a suitable and different area for technical operations and care management. It should be from 500 m2 to 1,000 m2.
Cleaning ponds for rearing fries needs to be carried out more carefully than rearing sweetfish into breed fish because the fries are of a small size and swim badly, so they can be easily eaten up. The pond is must be drained, the bottom cleaned, all holes filled out. Mud in the bottom must be dredged if it is too thick to keep it only, from 15 cm to 20 cm. The pond hedges must be cleared and thoroughly restrained to prevent water leakage.
Use agricultural lime (CaO) to clean the bottom of the pond. For newly dug ponds or those with a lot of alum scum, the amount of lime is from 10 to 14 kg/100m2. For repeatedly rearing ponds, the amount is less than 7 to 8 kg/100m2. After liming, use a tool to flatten evenly the bottom so that lime and mud of the pond are well mixed; bacteria, shrimps, fish and crabs which still hide in the bottom of the pond killed; and pH of the bottom neutralized.
Use agricultural lime (CaO) to clean the bottom of the pond – Photo: Phan Thanh Cuong
The bottom of the pond may be exposed for from three to five days, or water is piped into the pond after a day of liming. The water must be clean, filtered through a thick filtering bag to prevent harmful of objects from entering the pond with the depth of water from 0.7 to 1 m. Cooked soy flour from 1 kg to 2 kg/100m2 and weakly fixed Urea dilute 0.2 kg/100m2 are put into the pond (for three consecutive days) to make coloring water and develop natural feed (Daphnia, Moina). Green plants (molluscs) that are bound into sheaves are immersed into the corner of the pond and become green manure, creating natural feed.
In order to prevent diseases and water pollution, farmers should not use manure for creating feed to rear fish. After feed is created, the clear water of the pond is from 35 to 40 cm. It is satisfactory that the water is bright green and the neutralized pH is from 7 to 7.5.
Rearing breed and taking care of it
Before buying fish breed, farmers need to find out information of fries so that they can buy high quality breeds, not inbreeding, and free of diseases. High quality fries are not forced to be born, not premature and must reach three days old. They are transported in nylon bags with oxygen and released in the morning and evening. Before stocking fish into the pond, these fish bags should be soaked in the pond for 15 minutes to balance the water temperature in the bags and that in the pond, then open the bags so that water can enter the bags (10 liters) and hold the bags for 5 – 6 minutes for adaption by the fish, after that gently slope fish bags out the pond.
The fish should be released at the upper reach of the wind so that the fish is evenly distributed in the pond with a density of 250 – 300 baby fish/m2. After a day, the fish can be fed with cooked and homemade feed (30 percent of bran + 70 percent of fish flour) and chicken and duck eggs. In the fist 10 days, they are fed with 0.2 kg of feed +10 egg yolks/ten thousand and filarias (0.5 – 0.7 kg/ten thousand/a day).
Every day, fries are fed 3 – 4 times. The yolk of boiled eggs are ground through thick mesh and mixed with cooked feed and water. All are evenly poured around the pond. After 10 days, an increase of feed is up to 0.1 – 0.2 kg/ten thousand/day. Industrial feed in the form of ground flour, grain and tablet with the protein content of over 45 percent can be used, following the dose instructions of manufacturers.
When the fish starts weaning, increase the amount of 50 percent above and continue to add eggs and filarias. Now, they can start weaning with well ground fresh fish. Operation and feed for the fish, water quality and depth must be observed in order to adjust the amount of feed and to replace or add water to the pond in a timely manner.
In the first week, fish are released in the morning. Check the pond and pick out the nests of native frogs (above the water) in the early morning. Limit hatching of the eggs of the frogs that develop into tadpoles and eat the fish.
After 25 – 30 days, fish reache a size of 2.5 – 3 cm (sweetfish), survival rate of 60 – 70 percent. Use soft nets with thick meshes to collect the fish and sell or sparsely divide to keep raising. Pay attention to use soft nets to catch the fish gently.
Rearing sweetfish into breeding fish
To rear sweetfish into breeding fish, the area and cleaning of the pond, water supply, fertilizing are the same as those of rearing fries. However, it is not too careful like rearing fries. The density of rearing is from 150 to 200 fish/m2.
The homemade feed is cooked, including bran, fish flour or minced fresh fish at the rate of 3/7, adding 1 percent of minerals and vitamins. Daily feed can accounts for 7 – 10 percent of the weight of the fish in the pond. Industrial food (>35 percent of protein) accounts for 2 – 3 percent of the weight of fish. They are fed 3 – 4 times/day.
During the rearing process, it is necessary to inspect the eating ability of the fish, the color of the pond water in order to adjust feed and replace water in a timely way so that fish can grow well.
After 30 – 50 days, fish reache a size of 6 – 8 cm/fish, the survival rate of 85 – 90 percent, so dredge can be used to collect fish and sell.
|>> In the process of rearing, pangasius often catches some diseases (achlya fungus, rotifera, white spot disease…). To prevent diseases, cattle and poultry manure should not be used, the density of fish must be kept moderate, clean water added, the depth of pond maintained and water replaced in a timely way. The pond must be periodically improved with lime (1.5 – 2 kg/100m2) monthly to stabilize pH and destroy the pathogens.|