The long, thin beetle known as *C. longicornis*, listed in the Red Book of Endangered Animals of China, belongs to the genus *Polygonidae* and is commonly referred to as *S. striata* or *Blattella*. It is recognized as the fastest-growing and largest species among carps, with typical individuals weighing between 0.2 kg and 0.4 kg. The largest recorded specimen weighed up to 3.0 kg. This species is primarily found in the upper reaches of the Yangtze River and its tributaries. In recent years, numerous research institutions in China have focused on conserving and developing *C. longicornis*, conducting seed collection, pond domestication, and artificial breeding efforts. However, most of these attempts have been carried out under natural conditions in southern regions.
In 2006, a breakthrough was achieved when researchers from the Fish Disease Prevention and Control Center of Heilongjiang Institute of Special Fish Research collaborated with scientists from the Special Aquaculture Research Unit of Heilongjiang Forestry Research Institute. They successfully conducted indoor artificial propagation trials on *C. striata*, marking a significant step forward in conservation efforts.
For the trials, fish were sourced from the Sichuan Aquatic Fish Institute, with parent stock originating from wild populations in the Jinjiang River, a tributary of the Yangtze. Only healthy adults over three years old, free from injury and with normal mucus cover, were selected. Males needed to weigh more than 800g with visible sexual characteristics, while females should exceed 1500g. These crayfish are widely distributed across provinces like Jiangsu, Zhejiang, Hubei, Hunan, Anhui, and Shanghai, with increasing natural populations over the years. This suggests strong adaptability and high potential for successful transplantation.
Freshwater crayfish have specific environmental requirements. They can survive in water temperatures ranging from 0°C to 35°C, but thrive best between 20°C and 30°C. Below 15°C, their activity declines, and below 10°C or above 35°C, feeding decreases significantly. At temperatures below 8°C, they enter winter dormancy, digging into the substrate to survive. In northern regions like Heilongjiang, where average annual temperatures range from -5°C to 4°C, the growing season lasts about 120–150 days. Despite this, if heat sources such as hot springs or industrial waste heat are utilized, freshwater crayfish can be successfully farmed in the north.
Water quality is also crucial. Freshwater crayfish prefer pH levels between 5.8 and 8.2, with dissolved oxygen levels above 1.5 mg/L. Optimal conditions include a pH of 7.5–8.2 and dissolved oxygen over 3 mg/L. Transparency should be around 30–40 cm. In Heilongjiang, lake waters typically have a pH of 6.8–7.7, with dissolved oxygen levels sufficient for survival and growth.
Biologically, freshwater crayfish are omnivorous, feeding on aquatic plants, benthic organisms, zooplankton, and even dead fish and shrimp. They can also consume artificial feeds like soybean cake or compound feed. Natural waters in Heilongjiang provide ample food sources, including abundant phytoplankton, zooplankton, and benthic organisms, making them suitable for crayfish farming.
Despite their resilience, there are challenges. Freshwater crayfish can damage levees by burrowing, threatening infrastructure. They are also invasive, capable of rapidly establishing populations and disrupting local ecosystems. Additionally, their meat quality depends heavily on water cleanliness, requiring strict aquaculture management, pollution-free practices, and adherence to safety standards like HACCP and health certifications.
Overall, while freshwater crayfish offer great potential for aquaculture and conservation, careful planning and environmental monitoring are essential to ensure sustainable and safe cultivation.
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