Artificial breeding techniques for whiteleg shrimp (Litopenaeus vannamei) farming

The whiteleg shrimp (Litopenaeus vannamei) is native to the area around Ecuador in South America. It was first introduced to China from the Americas in 1988, and it is one of the three most heavily farmed shrimp species in the world by production volume known to date. Compared with the Chinese white shrimp, the whiteleg shrimp has such advantages as a longer breeding season, a shorter larval rearing period, strong disease resistance, fast growth, strong resistance to changes in the water environment, a long growth lifespan, low feed requirements, a long survival time out of water, and a high meat content in the body. The whiteleg shrimp has become one of the better alternative species for the development of shrimp farming in China today. The artificial breeding techniques for this shrimp are described below.

I. Selection of broodstock

Where conditions permit, specific-pathogen-free (SPF) whiteleg shrimp broodstock should be introduced from the United States. The broodstock should have intact limbs, normal body color, a glossy appearance, and no injuries or disease. Females should reach a body length of 13 cm to 16 cm, be 12 to 18 months old, and have ovaries developed to stage III. Males should have a body length of 12 cm to 15 cm, with milky white spermatophores and no melanization. The female-to-male ratio is 1:1 to 2.

II. Broodstock rearing

Generally, broodstock are first reared in outdoor ponds by conventional low-temperature methods for a period, then moved indoors before breeding to induce mating and spawning. The spawning tanks are mostly round, 3 m to 5 m in diameter, with a water depth of 0.6 m to 1.2 m. The tank bottom is funnel-shaped, sloping toward the center at a gradient of 5%.

Before the broodstock are placed in the tank, they are soaked in 80×10-6 to 100×10-6 bleaching powder for 3 to 5 minutes. After the broodstock enter the maturation-promoting rearing tank from the overwintering tank at a water temperature of 16°C, the temperature is raised continuously over 8 days at an increase of 0.5°C per day (rising 0.3°C from 20:00 to 8:00 the next day, and 0.2°C from 8:00 to 20:00) to 20°C. After 2 days at a constant temperature, it is raised again at an increase of 0.5°C per day to 26°C. During rearing, the water quality parameters are: water temperature 23°C to 26°C, light intensity <1000 lux, dissolved oxygen >5 mg/L, pH 7.7 to 8.3, salinity 27 to 32, and ammonia nitrogen <0.6 mg/L. The stocking density of broodstock is 20 to 25 shrimp per sq m. They are fed wet feed made from live feed such as sandworms, brine shrimp, shellfish meat, and trash fish mixed with compound feed (at a ratio of 6 to 7:4 to 3), fed at 9:00, 15:00, and 22:00, with a feeding amount of 10% to 15% of body weight, adjusted according to water temperature, weather, water quality, and the shrimp's feeding situation. The daily water exchange rate is 1/3 to 1/2.

III. Maturation promotion

The ovaries of mature female shrimp are red and broad-band shaped. In male shrimp, a pair of white spermatophores can be seen on the outer side of the base of the fifth pair of walking legs; viewed from the ventral side, the genital papillae on the inner side of the base of the fifth pair of walking legs are particularly swollen, and are not usually easy to see. At this point, after unilateral eyestalk ablation by the forceps-cautery method (left in males, right in females), the gonads can mature in 7 to 15 days. Operated broodstock are best reared under low light (200 lux), and gonad development should be checked once every 2 to 3 days. Any female whose ovaries reach stage V, or male with a pair of white spermatophores on the outer side of the base of the fifth pair of walking legs, should immediately be caught out with a dip net and placed in the induction tank.

IV. Egg collection and hatching

After mating, females spawn at night until early morning. The next morning, check the quality of the eggs, then collect, wash, and count the eggs before placing them in a hatching tank or barrel to hatch. The hatching water temperature is 29°C to 30°C. The hatched nauplii are collected by the light attraction method.

Feed is the material basis for larval development. Stage 1 to 2 zoea larvae are mainly fed spirulina powder, soybean milk, and egg yolk, supplemented with yeast; stage 3 zoea larvae are mainly fed egg yolk and rotifers, with yeast fed regularly; stage 1 to 2 mysis larvae are mainly fed egg yolk, rotifers, and shrimp flake feed; stage 3 mysis larvae are mainly fed brine shrimp nauplii, supplemented with rotifers and the like; postlarvae are mainly fed brine shrimp nauplii, with a small amount of chopped adult brine shrimp. Experiments have shown that feeding a mixed feed of unicellular algae, artificial micro-particulate feed, and brine shrimp larvae from stage 2 zoea to the early postlarval stage results in a high larval survival rate. The salinity of the nursery water should be 25 to 30, the pH value 7.8 to 8.2, and the dissolved oxygen content not less than 6.0 mg/L. Viral diseases and vibriosis often occur during the nursery period, so some broad-spectrum antibiotics should be appropriately fed, such as chloramphenicol (1 mg/L), oxytetracycline (0.5 mg/L to 1.0 mg/L), and furazolidone (0.3 mg/L to 0.5 mg/L).