Culture techniques of silverfish

Silverfish is one of the most valuable aquatic products in China, which is regarded as a treasure at the table and enjoys a high reputation at home and abroad. On the basis of studying the success of silverfish culture on large water surface, the aquaculture department has explored the silverfish pond culture technology.

I. Pond conditions

The selection of Laokou pond requires fresh water quality, no pollution, shelter from the wind and the sun, and convenient entry and drainage. The single pond surface is 0.2-0.3 hectares (1 hectare is 15 mu), the pond surface is 0.3-0.6 hectares, the pond depth is more than 2 meters, the sediment thickness is 0.2 meters, and there is an appropriate amount of aquatic plants around the pond.

Note: do not mix with animal diet and omnivorous fish.

2. Seed and seedling cultivation

1. Prepare the seedling stocking pond.

The fertile pond where domestic fish are raised is netted, and after turning the surface of the sediment properly, the water of the pond is poured into the stocking pond after silt removal.

Because the temperature of the silverfish is low, the water quality of the pond is difficult to cultivate, especially the rotifer density is low, use the domestic fish pond fertilizer water, and input the rotifer dormant eggs to rapidly increase the bait density in the stocking pond. This work should be completed two weeks before stocking, and the pool water is 0.6 meters deep before stocking. 2. The source of seedlings.

For the first time, the mature parents can be collected in the natural waters, and the fertilized eggs can be obtained by artificial insemination on the spot (fertilized eggs are sold in the fish farm). The fertilized eggs can hatch in indoor still water. When the water temperature is kept at 4 ℃-6 ℃, the hatching rate is higher and the stocking effect is better when the water temperature is kept at 4 ℃-6 for 30-40 days. When the film comes out after the end of February, it is easy to get the opening bait, which is beneficial to improve the survival rate of seedlings.

3. Stocking method.

The effect of stocking in the egg embryo period is better than that of fish fry and hatched in the pond one week before hatching. Every 667 square meters (1 mu) put 20,000 fertilized eggs, and 30 kilograms of large silverfish can be caught from September to October. If the stocking amount is too large, it will result in insufficient bait for the young seedlings. The water depth of the pool should be 1-1.5 meters.

4. Cultivate technology.

The larvae feed on rotifers and nauplii. Hatching 10 days to eat, 3 days after feeding, if there is no bait will die, so the stocking pond should be fully fertilized in advance to ensure that there is enough bait when eating. When fully fermented manure and limewater were applied to the breeding bait, the rotifer could reach considerable density after 10-15 days. The silverfish can be fertilized frequently during the juvenile period, and the amount of fertilizer can be controlled according to the water color and water temperature, so that the transparency of the pond water can reach more than 40 cm and the water depth can be maintained at 2 meters.

III. Adult fish culture

1. Provide sufficient bait. During the adult period (more than 40 mm in length), the food intake is large, and the growth rate is significantly speeded up. It is necessary to fertilize frequently to maintain the density of plankton. When applying fertilizer, you should apply rotten fermented fertilizer, or sprinkle a small amount of soybean milk, using 250-500 grams of soybeans per 667 square meters of water surface every day. Flexible control according to the water quality. [8]

2. Strictly guard against floating head. Silverfish requires higher dissolved oxygen than ordinary fish, and mixed culture is always the first to float its head. Floating heads appear when the water temperature is 20 ℃. If emergency measures are not taken immediately, a large number of deaths may occur. The way to prevent floating head is to reduce the amount of fertilizer so as not to make the bait organisms reproduce excessively. If the water is too fertile, fresh water should be replaced as soon as possible. If necessary, an aerator or oxygenator can be used to increase oxygen.

3. Pay attention to the transformation of diet. The feeding habits of silverfish have a transformation period, which gradually changes from feeding Cladocera and copepod to carnivorous. When it is found that there are fish and shrimp in the intestines of silverfish with a body length of nearly 80 mm, it shows that the feeding habits are changing. Small fish and shrimp should be introduced in time and maintain a certain density in order to promote the growth of large silverfish. Reasonable egg-holding green shrimp can be introduced into the Yangtze River basin in May, and the hatched larvae can be eaten during the transition period of large silverfish.

4. Prevent high temperature. In the high temperature season, the pool water should be kept at a depth of more than 2.5 meters, and shading measures should be adopted if necessary to prevent the harm of high temperature.

Artificial incubation technology

Silverfish is a valuable small economic fish, which is suitable for growing in larger waters. In recent years, there are many large and medium-sized reservoirs in the north. It lays eggs in winter and the suitable water temperature is 0 ℃ ~ 8 ℃. The artificial incubation techniques are as follows:

Preparatory work

Prepare 2 50 ml and 200 ml cups, 3 200 ml and 500 ml measuring tubes, 5 burettes and 5 suction balls, 5 tweezers and 5 scissors, 2 thermometers, 4 trays, 1 balance, 50 grams of malachite green and 20 kg of salt. A number of 140 cm × 20 cm fertilization bags are made of 6-wire polyethylene film. Several incubators with a scale of 1.2 meters × 2 meters × 0.2 meters were built with bricks, then covered with polyethylene film and sterilized with 15% salt water.

Catch parent fish

Silverfish generally mature sexually in the middle and last ten days of December in the northern region, and artificial insemination begins when mature individuals reach 30%. To catch parent fish, use a Gill net with a mesh of 1.8 cm ~ 2.2 cm. The fishing area is generally in the area where the water depth is about 2 meters and the bottom is gravel.

Artificial insemination

(1) male and female identification of parent fish.

In a female fish, mature eggs can be seen arranged in the abdominal cavity through its transparent abdomen. Abdominal enlargement, gently press the abdomen, egg outflow. The male fin is thicker, the testis is only one and smaller, and there is a white vas deferens near the cloacal cavity. A mature male has a red heart.

2) artificial insemination.

Dry the parent fish with a dry towel and put it on the tray. Take the fertilization bag, fold it into a tube, clip the fertilization bag with the middle finger, ring finger and little finger of the left hand, then take the female fish, pick up the head, close the right thumb and the other four fingers, and gently press the thumb on the female's abdomen to squeeze the eggs into the fertilization bag. Then use the right hand to invert the male fish, the head of the fish pointing to the arm, the anal fin away from the eggs 1 cm, squeeze out the semen, put the male body on the eggs. Add 30 ml 0.7% saline to the fertilization bag and shake up and down the mouth of the bag to mix well. Fill the fertilization bag with air, then tie the mouth with a rubber band and rest for 30 minutes. Then take out the male fish from the fertilization bag, add 100 milliliters of filtered river water, and wait for them to be put into the incubator.

Incubation management

(1) add the filtered water to the depth of 5 cm ~ 7 cm in the incubator, remove the immature eggs and impurities in the fertilization bag, and then put the fertilized eggs in the incubator with a density of 500000 eggs per square meter.

(2) remove the unfertilized dead eggs with a straw every morning.

(3) the filtered water should be changed every day, and the difference of water temperature should not exceed 1 ℃.

(4) two days later, the fish eggs were bathed with malachite green medicine with a concentration of 0.1 × 10 ~ 6 for half an hour. The unfertilized egg whitens and floats in the upper layer, and the fertilized egg sinks quickly, transparent and bright, in the lower layer. The hatching is usually completed in 6 ~ 8 days.