The long and slender beetle, listed in the Red Book of Endangered Animals of China, belongs to the genus Polygonidae, specifically *S. striata* and *Blattella*. It is the fastest-growing and largest species among carps. Common individuals weigh between 0.2 kg and 0.4 kg, while the largest recorded specimen reached 3.0 kg. This species is mainly found in the upper reaches of the Yangtze River and its tributaries. Over the past decade, numerous research institutions in China have focused on the conservation and utilization of *C. longicornis*, conducting seed collection, pond domestication, and artificial breeding trials. Most of these efforts are still conducted under natural conditions in southern regions.
In 2006, researchers from the Fish Disease Prevention and Control Center of the Heilongjiang Institute of Special Fish Research collaborated with scientists from the Heilongjiang Forestry Research Institute for the first time to successfully conduct indoor artificial propagation of *C. striata*.
The test materials included a species of sea bream introduced from the Sichuan Aquatic Fish Institute. The parent stock was wild *Jinjiang* pupae from the upper reaches of the Yangtze River. Breeding individuals must be over three years old, healthy, with no injuries or abnormal mucus. Males should weigh over 800g with visible sexual characteristics, while females should weigh over 1500g. These crayfish are widely distributed across more than ten provinces, including Jiangsu, Zhejiang, Hubei, Hunan, Anhui, and Shanghai. Natural populations are increasing, showing strong vitality and high potential for successful transplantation. However, in northern regions like Heilongjiang, where freshwater crayfish were introduced later, wild populations are limited due to environmental degradation. Improving their living conditions could lead to both ecological and fishery benefits.
Freshwater crayfish require specific water conditions. They can survive in temperatures ranging from 0°C to 35°C, but grow best between 20°C and 30°C. Below 15°C, their activity decreases, and below 10°C or above 35°C, feeding declines significantly. At 8°C, they enter hibernation. In Heilongjiang Province, which has a continental monsoon climate, the average annual temperature ranges from -5°C to 4°C, with about 120–150 days above 10°C. The region also receives ample sunlight, especially in July, making it suitable for crayfish growth. Using heat sources such as hot springs or industrial waste heat could further improve breeding success.
Water quality is also critical. Freshwater crayfish thrive in pH levels between 5.8 and 8.2, with dissolved oxygen above 1.5 mg/L. Ideal conditions are pH 7.5–8.2 and dissolved oxygen above 3 mg/L. Water transparency should be 30–40 cm. In Heilongjiang, water pH typically ranges from 6.8 to 7.7, with low salinity and sufficient oxygen levels, meeting most of the needs for survival and reproduction.
Biological factors include food availability, pathogens, competitors, and predators. Freshwater crayfish are omnivorous, feeding on aquatic plants, small organisms, and even dead fish. They can also consume artificial feed. Natural waters in Heilongjiang are rich in nutrients, phytoplankton, zooplankton, and benthic organisms, supporting their dietary needs. The fauna in the region is relatively simple, with few diseases, reducing competition and enhancing transplant success.
However, several challenges exist. Freshwater crayfish can damage levees by burrowing, posing risks to water infrastructure. Their invasive nature allows them to spread quickly, threatening native species and ecosystems. Additionally, their ability to adapt to polluted environments raises concerns about meat quality. Therefore, aquaculture should focus on clean water areas, follow strict hygiene protocols, and implement systems like HACCP to ensure safety and sustainability.
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