Key Technical Points for Rearing Summer Fry and Newly Hatched Fry of Grass Carp

Grass carp is presumably familiar to everyone; in fact, there are many varieties of grass carp, among which the most common are summer fry grass carp and newly hatched grass carp fry. Nowadays many people also want to rear them, but there are also many techniques to master in the rearing process; if the technique is not up to standard, these grass carp being reared may develop some problems.

Summer Fry Grass Carp Rearing Techniques

1. Stocking fry: Summer fry are weak in constitution, so the water level of the fry pond should be shallow (about 30—50 cm), and about 100,000 fry can be stocked per mu. It is best to release the fry on a sunny morning; when there is wind, release the fry at the windward spot. Because summer fry are weak, transport and release operations must be done very carefully. For summer fry purchased from elsewhere, upon arrival at the destination, place the plastic bags containing the summer fry into the pond and soak them for about 20 minutes; once the water temperature inside the bags and in the pond is basically the same, slowly open the plastic bags and release the fry into the pond.

2. Feeding management: Within one week after the fry are put into the pond, feed them soybean milk twice a day, at 8—9 a.m. and 3—4 p.m. respectively. Each time use 2 kg of soybeans per mu, soak them in water and grind them into 20—30 kg of soybean milk, and splash it evenly around the pond. After one week, you can switch to feeding soybean powder or peanut cake soaked and dissolved in an appropriate amount of water. According to the fertility of the pond water and the amount of plankton, apply organic fertilizer appropriately. At the same time, note to add new water once every 3—5 days, raising the water level by 10 cm each time, gradually reaching a water depth of 1 m and a transparency of 20—30 cm.

Rearing Techniques for Newly Hatched Grass Carp Fry

1. Pond disinfection: In the rearing of newly hatched grass carp fry, pond disinfection begins every year from April 20 to 25. Pond disinfection generally maintains a water level of about 30 cm. Quicklime, tea seed cake, etc. are used for disinfection. If bleaching powder is used for disinfection, it can be postponed to the end of April for dry-pond disinfection. This kills wild fish and pathogens; add new water the next day, and the new water must be filtered through 60-mesh mesh cloth to avoid bringing in harmful organisms.

2. Time for releasing newly hatched fry: Every year from May 5—15, choose the appropriate time to release the newly hatched fry. If the time is too early, the water temperature is too low and the survival rate is affected; if the time is too late, beyond the 20th, the water temperature is too high, the water easily becomes thick, and bubble disease is likely, which likewise affects the survival rate.

3. Stocking density: For newly hatched fry, it is advisable to stock 100,000 per mu, with a survival rate of 30%, and each mu can produce 30,000 fry of about 3 cm for splitting. If the stocking density is too high, it causes insufficient feed, the rearing size cannot be reached, and wheel worm disease is likely to occur, causing losses.

4. Feeding management: Because the water temperature in mid-May is suitable, and the pond water is now rather fertile, it is generally unnecessary to apply fertilizer. A lighter water color is preferred. When releasing the fry, there should be smaller rotifers in the water for the newly hatched grass carp fry to feed on. If they are large cladocerans, the newly hatched fry cannot eat them, and the cladocerans compete with the fry for food and oxygen, causing the failure of rearing the newly hatched fry.

Feeding Techniques for Grass Carp

Mainly feed pelleted feed, with a feed protein content of 28 to 32%, supplemented with green forage. Feed according to the principles of “coarse first, fine later” and “four fixed and four look”; generally feed twice a day, with the feed eaten within 2 hours and the grass carp eating until 80% full as appropriate. After continuously feeding pelleted feed for a period, pellet feeding should be stopped for 1 week, and during the interval feed raw grain feed. At ordinary times, note to appropriately add vitamins and other drugs to the feed to avoid diseases such as hepatobiliary syndrome in grass carp that cause mass death.

Disease Control of Grass Carp

1. White spot disease. Control method: The fish pond should be thoroughly disinfected with quicklime to reduce pathogens. Sick fish can be soaked for 20 to 30 minutes in a mixed solution of 1 part in 50,000 copper sulfate and magnesium sulfate, plus 1% table salt, which can kill all small ichthyophthirius.

2. Lernaea disease. Control method: Thoroughly clear the pond with quicklime to kill Lernaea larvae and eggs. Strictly forbid sick fish from entering the pond and causing infection. Soak sick fish for 1.5 to 2 hours in a 1 part in 50,000 (when water temperature is 15 to 20 degrees C) or 1 part in 100,000 (when water temperature is 21 to 30 degrees C) potassium permanganate solution.

In fact, no matter which kind of grass carp it is, before rearing, disinfection work must be done well, and then stocking should be carried out reasonably. During the rearing process, management work must be done properly, and feeding and disease control must be timely; there are also some techniques involved. The above gives a detailed introduction, and I hope it can be helpful to everyone.