(a) For successful spawning, selected broodstock require water temperatures above 18°C. In the middle and lower reaches of the Yangtze River, the spawning season typically runs from mid-April to mid-September, with the peak occurring between June and July. The most active period is usually from mid-June to mid-July, when conditions are most favorable for reproduction.
(b) Spawning and hatching take place in specially designed cages. Broodstock spawn primarily between June and July, and these shrimp are generally larger in size, as they are the oldest individuals that have survived the winter. Shrimp that spawn after July 7 tend to be smaller, as they are younger and have grown during the breeding season. The entire process—from egg-laying to hatching—happens inside floating cages, which are divided into two parts: incubators and hatching cages.
The incubators are made of polyethylene netting with a mesh density of 196 holes per square centimeter. They measure 10 meters in length, 667 meters in width, and 1.7 meters in height. Each cage has polyethylene chain ropes at the bottom and top to secure it in place. These cages are open and float on the surface, with about 0.3 meters exposed above water to prevent shrimp from escaping. Inside each incubator, small hatching cages are placed—each made of polyethylene mesh with a mesh size of 12 holes per square centimeter. These hatching cages are 1.7 meters long, 1 meter wide, and 0.5 meters high. When installed, they are positioned so that about 5 centimeters of the cage is above the water surface. Small bricks are placed in each corner of the hatching cage’s base to stabilize it.
Before spawning, broodstock are moved into the incubators to feed and gain strength. Once the water temperature reaches 18°C, mating occurs, and eggs are laid within 24 hours. When a female becomes pregnant, her abdomen expands and bends slightly, while her back rises. The eggs are oval-shaped, filled with yolk, and cluster along the female’s abdominal appendages—typically one to four pairs. After overwintering, older shrimp can spawn twice in succession. The second spawning happens after the first batch of eggs has hatched. The number of eggs produced depends on the age and size of the broodstock. Older shrimp can lay up to 5,000 eggs, while those that matured during the same year, measuring around 3 cm in length, may produce up to 700 eggs.
Once the eggs develop compound eyes, the females are transferred to the hatching cages, with 700 to 1,000 eggs per cage. After 6 to 7 days, the larvae will break out of the eggs and fall into the incubator. At this point, the entire cage, including the hatched broodstock, is removed and prepared for the next stage of development.
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