What preparatory work is needed before stocking Pacific white shrimp

The preparatory work before stocking Pacific white shrimp mainly includes repairing the shrimp ponds, drainage and irrigation systems and other production facilities, clearing the ponds with chemicals, and cultivating basic bait organisms.

I. Shrimp pond preparation

(1) Drying the pond

The purpose is to restore the pond bottom. Generally, after harvest, the pond water should be drained and the bottom allowed to dry in the sun until the sediment cracks. Pond drying lasts from 15 to 30 days, or even 45 to 60 days using the empty pond period in winter. Then, depending on the degree of contamination of the pond bottom, further treatment is carried out.

1. Where the bottom sludge is 3 to 10 cm thick, the pond water should be drained, the pond bottom exposed to the sun so the soil oxidizes, and then quicklime applied at 100 to 150 kg per mu.

2. Where the bottom sludge reaches 10 to 20 cm or more, after treatment as above, plow the bottom soil with an ox plow or machinery so that the lower sludge also receives sunlight; this gives better restoration. Then spread 100 to 150 kg of lime per mu.

(2) Rinsing

If the pond water cannot be drained, repeatedly fill and drain to soak and rinse.

(3) Soil replacement

If the pond bottom is too heavily contaminated and both drying and rinsing are difficult, the aged soil at the bottom can be dug up and hauled away, and new sandy mud refilled to 8 to 10 cm. This method costs more but gives good results.

II. Clearing the pond with chemicals

After the above shrimp pond preparation, let in tidal water and rinse 3 to 4 times until the pond has no rusty water and the pond water pH is stable above 7.8, then clear the pond with chemicals. If the pond bottom is fairly acidic, add appropriate lime to neutralize the acidity, and once the pond water pH is stable, clear the pond with chemicals.

The purpose of pond clearing is to kill harmful organisms, including fish, shrimp and pathogens. If shrimp have been farmed for many years, the pond is fairly heavily contaminated and the ditches also have varying degrees of silt accumulation and contamination; first apply quicklime at 100 to 150 kg per mu or bleaching powder at 30 to 50×10-6 for disinfection, mainly to kill pathogenic bacteria and predator organisms in the bottom soil and water body; lime also improves the pond bottom and adjusts the water pH; then clear the pond with tea seed cake or trichlorfon, fenvalerate and other chemicals. Fenvalerate is very effective at killing white shrimp (commonly called five-whisker shrimp), usually used at a concentration of 0.1 to 0.3×10-6. The five-whisker shrimp is a predator organism that attacks shrimp fry or molting shrimp.

III. Letting in water

Two to 3 days after chemical pond clearing, the sluice gate can be opened to let in water. Water should be let in and drained several times to dilute and discharge residual chemical toxicity.

At the water inlet gate, install a filter screen to filter the seawater; the screen is made of 60-mesh nylon thread or nylon bolting silk as a straight flat screen or a conical net. For large shrimp ponds, a conical net should be used, with the net length 5 to 6 times the width of the net mouth. Before opening the gate, check whether the gate board and filter screen are properly installed, whether the gate groove leaks, and remove debris or sand and stones at the gate bottom. Install a larger mesh (about 1 cm mesh) straight flat screen on the outer gate groove to block debris. When letting in water, decide the gate opening height according to the bearing capacity of the filter screen, so that the screen is not burst and predator organisms do not enter. If the screen breaks and predators enter, the pond must be cleared with chemicals again.

The first water filling should be 30 to 40 cm, to facilitate fertilizing and culturing bait organisms, and then the water level is gradually raised.

IV. Culturing bait organisms

Culturing and propagating bait organisms (basic bait) in the shrimp pond is an effective measure to provide suitable feed for shrimp fry and accelerate shrimp growth, and is one of the effective ways to make full use of the pond's natural productivity and reduce shrimp farming costs. Because basic bait organisms reproduce quickly, are simple and feasible to culture, and have obvious nutritional effects, this has become an indispensable production step in the farming procedure. Practice shows that if the basic bait is abundant, shrimp fry can grow to about 8 cm within one month of being stocked.

Guangxi has a warm climate and bait organisms multiply rapidly; after about 7 days, the bait organisms can reach a considerable density. After fertilizing, the concentration of bait organisms is mostly expressed by transparency, and a transparency of 30 to 40 cm is generally appropriate. Considering that the pond bottom in the coastal shrimp ponds of Guangxi is mostly acidic soil, organic fertilizer gives better results than inorganic fertilizer. The specific method is:

After the shrimp pond is cleared, store water to 30 to 40 cm, and fertilize the pond; each fertilization amount: nitrogen fertilizer 1×10-6, phosphate fertilizer 0.1×10-6. Fertilize every 2 to 3 days to keep the pond water yellow-green or yellow-brown. Gradually add water to 80 cm, keeping water transparency at 30 to 40 cm. To avoid a single type of bait organism, let in water regularly to introduce bait organisms so that the bait organisms the shrimp feed on are diversified. Fertilization in the shrimp pond should be small and frequent, following the "three no fertilization" rule: do not fertilize when the water color is dark, do not fertilize on cloudy and rainy days, and do not fertilize at midday or evening.

Commonly used nitrogen fertilizers include urea and ammonium sulfate; phosphate fertilizers include superphosphate and Thomas phosphate; organic fertilizers can include chicken manure and cow manure. The ratio of nitrogen to phosphorus is 10:1. When fertilizing, the nitrogen fertilizer and phosphate fertilizer must each be stirred and diluted with water, then splashed evenly. Fertilize once every 3 to 5 days in the early stage, and once every 7 to 10 days in the later stage. If the water body maintains sufficient and abundant bait organisms, from stocking the shrimp fry until they reach 8 cm in body length, depending on the stocking density, it may not be necessary to feed or only feed a small amount; after 8 cm, begin artificial feeding of bait.