What are the environmental requirements for crayfish farming?
When it comes to crayfish, the first thing most people probably think of is how dirty they are, because before eating crayfish you have to scrub them clean with a brush, so many people believe crayfish like living in dirty environments. Is that really true? Let's find out together with the editor below!
Crayfish farming environment
Do crayfish like dirty environments? [Investigation] In dirty environments they have poor vitality and struggle to reproduce. Many netizens believe that crayfish are often found in sewage ditches, and wonder whether this shows that crayfish prefer to live in dirty environments. Is that really the case?
Tang Jianqing, director of the breeding office at the Jiangsu Freshwater Fisheries Research Institute, told reporters that their experiments showed that when putrid food and fresh food were placed in front of crayfish, the ratio of crayfish choosing putrid food to fresh food was 1:10.
Huang Cheng, associate professor at the School of Life Sciences at Nanjing University, demonstrated a “maze experiment” for reporters: a 2-meter-long Y-shaped trough was filled with clean water, a sponge soaked in ammonium chloride solution (a common substance in dirty water) was placed at the left front end of the trough, and a sponge soaked in clean water was placed at the right front end. He then placed a crayfish at the rear end of the trough. When the crayfish crawled along the trough to the junction of the paths ahead, after testing left and right, it finally chose to crawl toward the clean-water trough on the right end.
“Judging that crayfish like to live in dirty environments based on ‘you can catch them as soon as you scoop in a sewage ditch, but you can't catch them in clean water’ is unscientific.” Huang Cheng said that crayfish grown in clean water are vigorous and very hard to catch without tools, while crayfish in polluted environments have very poor vitality and struggle to reproduce.
Shu Xinya, a senior engineer at the Hubei Provincial Fisheries Science Research Institute, believes that because crayfish are highly tolerant, they can survive in sewage, but during growth crayfish must molt seven or eight times; if the environment is poor, crayfish will not molt and will not grow well. Many farmers previously paid no attention to the water environment and used shallow, dirty water for farming, resulting in very low crayfish yields; later they paid attention to using deep, good water, and yields increased.
Create a good growth environment for crayfish. Crayfish are crustaceans, similar to crabs, with a pair of especially well-developed claws, and have the habit of digging burrows to live in, generally digging burrows near the water's edge. Crayfish prefer shade and fear light; when the light is weak or dark they crawl out of their burrows, and when the light is strong they sink to the bottom or hide in their burrows. According to the habits of crayfish, a 50 cm high anti-escape net can be added along the edges of rivers and ponds to prevent crayfish from escaping. At the same time, the river or pond should simulate the ecological environment of crayfish under natural conditions, with 10-15% aquatic plants and hiding objects planted in the shallow areas at the pond edges, creating an environment for crayfish to inhabit and molt and reducing mutual killing.
The impact of water quality on crayfish yield also cannot be ignored. Water quality directly affects the healthy growth and development of crayfish. During farming, the pH value of the pond water should be kept between 7.5-8.5, and the transparency at 30-40 cm. New water should be added frequently, and quicklime solution should be sprinkled regularly to regulate water quality and prevent disease outbreaks and incomplete molting.
What is the origin of crayfish
Crayfish are a world-class invasive alien species, native to Central and South America and northeastern Mexico. They were introduced to Japan in 1918 as bait for raising bullfrogs, and then spread from Japan to China. They have now become an important resource among China's freshwater shrimp species, widely distributed across the provinces and cities of the middle and lower reaches of the Yangtze River. In May 2013, rumors spread online that crayfish were introduced to China by the Japanese biological and chemical warfare units during the Japanese invasion of China specifically to dispose of corpses; this claim is purely false.
Crayfish are a lobster-like crustacean that lives in freshwater, with the scientific name Procambarus clarkii, also called red swamp crayfish, freshwater crayfish, and fighting shrimp. Crayfish are the most widely distributed invasive alien species among crustaceans. Because of their omnivorous diet, fast growth speed, and strong adaptability, crayfish form an absolute competitive advantage in local ecological environments. Their feeding range includes aquatic plants, algae, aquatic insects, animal carcasses, and so on, and when food is scarce they even kill each other.
During World War II, crayfish spread from Japan to China and began to reproduce in Nanjing, Jiangsu Province, and its suburban counties. After a long period of expansion, the population continued to increase and their living space continued to expand. At present, crayfish have spread to Anhui, Shanghai, Jiangsu, Hong Kong, China, Taiwan, China, and other places, forming a huge natural population and becoming an important resource among China's freshwater shrimp species.
What are the advantages of farming crayfish
1. Large market potential: The market demand for crayfish is very large. This tight market supply-demand relationship gives the crayfish industry relatively high economic benefits and broad development prospects, and sales are not a problem.
2. Low farming difficulty: Crayfish have strong adaptability to the environment, few diseases, and tolerance to low oxygen. They can be farmed at high density in small water bodies in ponds, and can also reproduce naturally in various water bodies such as ditches, lakes, rice fields, and swamps, with simple farming techniques.
3. Low farming cost: Crayfish are omnivorous, and their feed is easy to obtain. At low farming density there is no need to feed special feed. They grow quickly, have high yields, high energy conversion rates, low farming costs, and good benefits.
4. Short farming cycle: Crayfish can generally be marketed after about 2 months of growth. Through the technical plan of catching the large and keeping the small, a cycle farming method can be adopted; this is a farming model of one-time stocking and year-round benefits.
Crayfish feeding and management techniques
1. Choosing a pond: Crayfish farming requires a water source with fresh water quality, sufficient dissolved oxygen, and no pollution. The pond embankment should be more than 3 m wide, and the pond area should not be too large, generally 3-8 mu is suitable. It is worth noting that crayfish have a strong ability to escape, so anti-escape facilities must be built well.
2. Pond clearing and disinfection: Pond clearing and disinfection can effectively kill harmful organisms in the pond (catfish, loach, snakehead, snakes, rats, etc.), wild miscellaneous fish that compete for food (carp, crucian carp, etc.), and pathogens. Quicklime and bleaching powder can be used; they are economical, affordable, and safe.
3. Planting aquatic plants: Aquatic plants play a decisive role in crayfish farming, generally occupying about half of the pond area. Low-stem reeds, wild rice stem, Elodea, and Hydrilla verticillata can be chosen, and if conditions permit, some empty cans, bamboo tubes, and tree roots can also be placed at the bottom.
4. Fertilizing the shrimp pond: Before stocking crayfish, apply an appropriate amount of organic fertilizer to the shrimp pond to cultivate feed organisms, which can directly provide natural feed after the shrimp enter the pond. However, the amount and timing of fertilization should depend on whether the water is rich or lean, and at the same time the pond water transparency should be kept at about 35 cm.
5. Stocking crayfish: Crayfish seedling stocking is divided into spring stocking and autumn stocking. It requires uniform size, complete appendages, no disease or injury, and sufficient stocking in one go. Before stocking, bathe them in 5% salt water for 5-10 minutes to kill parasites and pathogenic bacteria.
6. Feed selection: Crayfish are omnivorous. Animal feed mainly includes small fish pieces, dried fish meal, snail and mussel meat, and various animal internal organ scraps, while plant feed mainly includes rapeseed cake, soybean meal, bran, wheat, corn, pumpkin, and various vegetables and aquatic and terrestrial grasses.
7. Feeding: Crayfish mostly move and forage at night. Feed once each at 10 a.m. and 4 p.m. every day, with the afternoon feeding amount accounting for about 70% of the whole day's feeding amount. The daily feeding amount can be appropriately increased or decreased according to weather, water quality conditions, and the shrimp's activity and foraging conditions.
8. Daily management: Crayfish farming requires patrolling the pond every day, paying attention to changes in water color and crayfish activity. If shrimp are found going ashore or climbing on aquatic plants and refusing to enter the water when driven away, check whether the water body is short of oxygen or the water quality has deteriorated, and take corresponding measures such as increasing oxygen or changing the water.
From the above analysis we can see that crayfish are not, as everyone imagines, fond of living in dirty environments. Facts prove that in dirty environments crayfish have poor vitality and are difficult to reproduce, while crayfish in clean water are more active and very hard to catch without tools. Therefore, crayfish do not like living in dirty environments.