(a) The optimal water temperature for spawning by selected broodstock is 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, especially from mid-June to mid-July. During this period, environmental conditions are most favorable for successful reproduction.
(b) Spawning and hatching take place in specially designed cages. Broodstock usually spawn between June and July, and the individuals involved are generally larger, as they are the oldest shrimp 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 spawning and hatching process occurs within these cages, which are divided into two types: incubators and hatching cages.
The incubator is made of polyethylene netting with a mesh size of 196 holes per square centimeter. It measures 10 meters in length, 667 meters in width, and 1.7 meters in height. Both the bottom and top of the cage are equipped with polyethylene chain ropes to secure it in place. The cage floats on the water surface, with about 0.3 meters exposed to prevent shrimp from escaping. Inside the incubator, small hatching cages are placed—each made of polyethylene mesh with a mesh size of 12 holes per square centimeter, measuring 1.7 meters in length, 1 meter in width, and 0.5 meters in height. These hatching cages are positioned so that their tops are just 5 centimeters above the water surface, and small bricks are placed in each corner of the incubator’s base to stabilize them.
Before spawning, broodstock are moved to the incubator for fattening. Once the water temperature reaches 18°C, mating occurs, and eggs are laid within 24 hours of mating. When females become pregnant, their abdomens extend and curve, and their backs lift slightly. The eggs produced are oval-shaped, rich in yolk, and cluster along the female’s abdominal appendages, typically 1–4 pairs. After wintering, older shrimp can spawn twice in succession, with the second spawning occurring after the first batch of eggs has hatched. The number of eggs a shrimp lays depends on its age and body length. Older shrimp can produce up to 5,000 eggs, while shrimp that matured during the same year and measure around 3 cm in length may lay up to 700 eggs.
When the eggs develop compound eyes, the females are transferred to hatching cages, with 700–1,000 eggs per cage. After approximately 6–7 days, the larvae will break out of the egg membranes and fall into the incubator. At this stage, both the incubator and the hatched broodstock are removed from the cage for further care and development.
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