Key technical points and management methods for icefish (noodlefish) farming

Icefish is one of China's valuable aquatic products, regarded as a delicacy on the table, and long famous at home and abroad. On the basis of successful research on icefish farming in large water bodies, aquatic research departments have also explored pond farming techniques for icefish.

I. Pond conditions

Choose an old pond, requiring fresh, pollution-free water, shelter from wind and good sun exposure, and convenient water intake and drainage. A single pond surface of 0.2-0.3 ha (1 ha equals 15 mu), a polyculture pond surface of 0.3-0.6 ha, a pond depth above 2 m, bottom mud thickness 0.2 m, and an appropriate amount of aquatic grass around the pond.

Note: Do not polyculture with carnivorous and omnivorous fish.

II. Seedling cultivation

1. Prepare the seedling stocking pond.

Seine the fertile pond used for raising domestic fish, properly turn over the surface layer of bottom mud, and then fill this pond water into the stocking pond after dredging and pest elimination.

Because the air temperature is low when icefish begin feeding, it is difficult to cultivate pond water quality, especially when rotifer density is low. Using the fertile water of a domestic fish pond and introducing rotifer resting eggs can rapidly increase the food density in the stocking pond. This work should be completed two weeks before stocking, and the pond water depth before stocking should be 0.6 m. 2. Source of seedlings.

For the first rearing, the required seedlings can be obtained by collecting mature parent fish from natural waters and performing artificial fertilization on site to obtain fertilized eggs (fish seed farms sell fertilized eggs). Fertilized eggs can be hatched indoors in still water. When the water temperature is kept at 4°C-6°C, they hatch in 30-40 days, with a relatively high hatching rate and good stocking results. Hatching after the end of February makes it easier to obtain first food, which helps increase the survival rate of fry.

3. Stocking method.

Stocking at the egg embryo stage gives better results than fry. One week before hatching, place them in the pond to hatch. Stock 20,000 fertilized eggs per 667 sq m (1 mu), and 30 kg of large icefish can be caught in September-October. If the stocking amount is too large, it will cause insufficient food for the fry. The pond water depth should preferably be 1-1.5 m.

4. Cultivation techniques.

Larvae feed on rotifers and nauplii. They begin feeding 10 days after hatching. If there is no food for 3 days after first feeding, they will die, so the stocking pond must be sufficiently fertilized in advance to ensure adequate food at first feeding. For cultivating food organisms, apply fully fermented manure and appropriately apply limewater. After 10-15 days, the water becomes denser and rotifers can reach a considerable density. During the juvenile stage of icefish, fertilizer can be applied frequently. The amount applied should be controlled according to water color and water temperature, trying to keep pond water transparency above 40 cm and water depth at 2 m. 

III. Adult fish farming

1. Supply sufficient food. During the adult stage (total length above 40 mm), food intake is large and growth speed increases markedly, so fertilizer must be applied frequently to maintain the density of plankton. Apply decomposed fermented manure when fertilizing, and a small amount of soybean milk can also be splashed on. Use 250-500 g of soybeans per 667 sq m of water surface per day, flexibly adjusted according to water quality.[8] 

2. Strictly prevent floating head. Icefish have higher dissolved oxygen requirements than ordinary fish and are always the first to show floating head in polyculture. At a water temperature of 20°C, floating head occurs, and if emergency measures are not taken immediately, mass death may occur. The way to prevent floating head is to reduce the amount of fertilizer applied and prevent excessive reproduction of food organisms. If the water is too fertile, replace it with fresh water as soon as possible, and if necessary use an aerator or oxygen-increasing agent to increase oxygen.

3. Pay attention to dietary conversion. Icefish have a conversion period in feeding habits, gradually shifting from feeding on cladocerans and copepods to carnivory. If fish and shrimp are found in the intestinal tract of icefish with a body length close to 80 mm, it indicates that the feeding habit is converting, and small fish and shrimp should be introduced in time and kept at a certain density to promote the growth of large icefish. In the Yangtze River basin in May, suitable berried freshwater shrimp can be introduced. The hatched young shrimp are just right for large icefish to eat during the diet conversion period.

4. Prevent high temperatures. In hot seasons, pond water should be kept deeper than 2.5 m, and shading measures should be used if necessary to prevent high-temperature damage.

Artificial hatching techniques

Icefish are valuable small economic fish, suitable for growing in relatively large water bodies. In recent years, many large and medium-sized reservoirs in the north have farmed them. They spawn in winter, and the suitable water temperature is 0°C-8°C. The artificial hatching techniques are as follows:

Preparation work

Prepare 2 each of 50 mL and 200 mL measuring cups, 3 each of 200 mL and 500 mL graduated cylinders, 5 each of burettes and suction bulbs, 5 each of tweezers and scissors, 2 thermometers, 4 trays, 1 balance, 50 g malachite green, and 20 kg table salt. Several fertilization bags of 140 cm × 20 cm, made of 6-thread polyethylene film. Build several hatching ponds with dimensions of 1.2 m × 2 m × 0.2 m, made of brick, then lined with polyethylene film and disinfected with 15% saline.

Catching parent fish

In northern regions, icefish generally mature sexually in mid-to-late December. When mature individuals reach 30%, begin artificial fertilization. Catch parent fish with gill nets of 1.8 cm-2.2 cm mesh. The fishing area is generally where the water depth is about 2 m and the bottom is gravel.

Artificial insemination

(1) Identification of male and female parent fish.

For female fish, mature eggs can be seen arranged in the abdominal cavity through the transparent abdomen. The abdomen is enlarged; pressing lightly on the abdomen causes eggs to flow out. Male fish have thicker fin rays, only one relatively small testis, and a white vas deferens near the cloaca. Well-matured males are red at the heart area.

(2) Artificial insemination.

Wipe the parent fish dry with a dry towel and place it in a tray. Take the fertilization bag, fold it into a tube shape, hold the fertilization bag with the middle, ring, and little fingers of the left hand, then take the female fish, lift it by the head, close the thumb and remaining fingers of the right hand, press the female fish's abdomen lightly with the thumb, and squeeze the eggs into the fertilization bag. Then hold the male fish upside down with the right hand, with the fish head pointing toward the arm, the anal fin 1 cm away from the eggs, squeeze out the semen, and place the male fish body on the eggs. Add 30 mL of 0.7% physiological saline to the fertilization bag, grasp the bag opening and shake up and down to mix fully. Fill the fertilization bag with air, tie the opening with a rubber band, and let it stand for 30 minutes. Then remove the male fish from the fertilization bag, add 100 mL of filtered river water, and let it stand while waiting to be placed in the hatching pond.

Hatching management

(1) Add filtered water to the hatching pond to a depth of 5 cm-7 cm, remove immature egg masses and impurities from the fertilization bag, then place the fertilized eggs into the hatching pond at a density of 500,000 eggs/sq m.

(2) Every morning, use a pipette to remove unfertilized dead eggs.

(3) Replace 1/2-1/3 of the filtered water every day, with a temperature difference not exceeding 1°C.

(4) After two days, bathe the fish eggs for half an hour in malachite green at a concentration of 0.1×10—6. Unfertilized eggs turn white and float on the upper layer; fertilized eggs sink quickly, transparent and bright, in the lower layer. Hatching is generally completed in 6-8 days.