Various Standards and Management Points for Australian Freshwater Crayfish Farming
The Australian freshwater crayfish is one of the more precious kinds of shrimp, one of the world's more valuable shrimp at present. It mainly grows in Australia, so farming it is not as simple as farming crayfish. Precisely because its price is relatively high, the farming cost of the Australian freshwater crayfish is also much higher.
What Is the Australian Freshwater Crayfish
The Australian freshwater crayfish (Cherax quadricarinatus), scientific name Cherax quadricarinatus, also known as the redclaw crayfish, is native to Australia. Its appearance closely resembles that of a marine lobster, and it is one of the world's most valuable freshwater economic shrimp species. The body color of this shrimp is brownish green, and the outer tip of the claw of a mature male shrimp has a membranous bright red band, beautiful to look at, which is why it is also praised as the redclaw crayfish.
The Australian freshwater crayfish, also known as the redclaw crayfish, belongs to the order Decapoda, family Parastacidae. It is a large freshwater crayfish native to Australia. In recent years this shrimp was introduced for trial farming in Guangdong Province, China, and success was achieved successively in artificial breeding of seedlings and in adult shrimp farming, and it is currently being promoted for farming inside and outside the province. Because the Australian freshwater crayfish is relatively large in size, somewhat resembles a marine lobster in appearance, and lives only in freshwater, it is called the freshwater lobster. Its individuals generally weigh 100-200 grams, and the largest individuals in Australia can weigh up to 500 grams. According to research, the Australian freshwater crayfish is one of the world's valuable economic shrimp species at present.
Management Techniques for Farming the Australian Freshwater Crayfish
1. Suitable growth speed. The natural distribution of the Australian lobster is in subtropical and tropical regions. A good growth rate can be achieved between 18°C and 32°C. In the Yangzhou area, the period each year from May to November when the water temperature is above 18°C lasts 6 and a half months. Normal growth can begin once the water temperature reaches above 16°C. To make full use of local thermal energy resources, in the Yangzhou area the seedling release time for the Australian lobster should be arranged for early May, and the harvest time for late November.
2. Water quality requirements.
① Water source: mainly unpolluted surface water from large water bodies such as rivers, lakes and reservoirs. Groundwater can also be used; groundwater has the following advantages: a fixed and independent water source; no wild miscellaneous fish carrying pathogens; no pollution; and a relatively stable temperature year-round.
② The pH value of the water: during the farming process, the lowest value recorded was 6.10 and the highest was 9.33, and the shrimp could survive at both, but 6.5-9.0 is good, and neutral to slightly alkaline is best.
③ Dissolved oxygen in the water: although the Australian lobster tolerates low oxygen and can survive for a short time with dissolved oxygen below 1 mg/L, if it remains in a low dissolved oxygen state for a long time, its growth and survival rate will be affected. Therefore, ponds must be equipped with aerators or other aeration equipment when necessary, so that dissolved oxygen is kept at above 4 mg/L, and pollution by heavy metals, insecticides, herbicides, oil, chlorine, methane, hydrogen sulfide, high iron content and the like should be avoided.
④ Adopting micro-flow water or regularly adding new water for farming can promote the growth of the lobster.
3. Pond conditions.
① The pond should be rectangular, with no limit on area, but 2-5 mu is good, water depth 0.9-1.5 m, and the long axis of the pond should be the same as the summer wind direction.
② The pond bottom should be hard soil with no silt, and the pond walls must have a slope, with the slope greater than 3:1.
③ The pond must have a good drainage and irrigation system, with water entering at the upper part of one end and draining from the bottom of the other end, and both the inlet and outlet must have mesh covers to prevent predators and escape.
④ The pond bottom should have a submerged plant area of about 1/5 of the bottom area, and sufficient artificial hiding places, such as waste tires, mesh sheets, PVC pipes, waste tile jars, bamboo rafts and the like.
⑤ Ponds with the conditions for it may be equipped with aerators.
4. Stocking techniques and daily management.
① Density: stock 600 juvenile shrimp of 2-3 cm per mu, and appropriately polyculture 100 silver carp, 50 bighead carp and 50 grass carp.
② Micro-flow water farming or adding new water 2-3 times per week.
③ Feeding should adopt fixed-point, fixed-time, fixed-quality and fixed-quantity feeding, and the types of feed should be as diverse as possible: aquatic plants such as water hyacinth, water lettuce and floating celery, cow dung, pig dung and artificial pellet feed. Animal bait such as river snails, earthworms and river mussels may also be appropriately fed. Feed fermented cow dung once a week, 100 kg per mu, placed in the four corners of the pond, fully submerged in water; feed pellet feed once a day, at 6 p.m., at an amount equal to 20% of the shrimp body weight.
④ During the high-temperature period in summer, attention should be paid to increasing the flow rate or the amount of water added, and the number of water additions; at night the aerator can be turned on for aeration.
The Growth Environment of the Australian Freshwater Crayfish
1. Water temperature: the Australian freshwater crayfish has a habit of adapting to the tropics and can withstand high temperatures; the suitable growth temperature range is 24-42°C. Below 21°C feeding declines and growth speed decreases. Below 10°C adult shrimp stop growing. If the time below 9°C is too long, adult shrimp will also die, so in regions with lower winter temperatures, overwintering management is needed for farming.
2. Dissolved oxygen: besides tolerating high temperatures, the Australian freshwater crayfish also tolerates low oxygen. Under normal circumstances, dissolved oxygen in the pond is kept between 4-5 mg/L, and growth is normal. Adult shrimp can even endure a dissolved oxygen level of 1 mg/L, and can briefly climb out of the water to breathe air. Juvenile shrimp are relatively more sensitive to low dissolved oxygen; shrimp seedlings cannot survive in water with 1.2 mg/L.
3. pH value: the suitable pH value is 6.5-9. During the incubation period it should be above 7, because acidic water quality is not conducive to molting and growth, and will increase death during molting or prolong the molting time.
4. Salinity: the Australian freshwater crayfish does not have high requirements for salinity, so it can grow smoothly in freshwater ponds. At the same time, larvae can still adapt in water with a salinity of 3 g/L, and adult shrimp in water with a concentration of 5 g/L. Therefore, juvenile shrimp can be soaked for a short time in 1% salt water and adult shrimp in 3% salt water to kill parasites on the body surface.
The Reproductive Habits of the Australian Freshwater Crayfish
The Australian freshwater crayfish is native to the tropical regions of Australia and has a relatively fast growth speed; within 6 months it can reach 50-80 g. The Australian freshwater crayfish generally reaches sexual maturity at 6-12 months of age. The large claws of the sexually mature male shrimp have an obvious red or orange-yellow stripe on the outer extension, and there is a pair of papilla-like genital spines at the base of the fifth pair of walking legs; the claws of the male shrimp exceed the body length. The female shrimp has a pair of genital pores at the base of the third pair of walking legs; the claws of the male shrimp are blue and shorter than the body length. Sexually mature Australian freshwater crayfish will reproduce naturally in ponds when the water temperature reaches above 21°C.
The reproduction time of the Australian freshwater crayfish is relatively long, beginning in April and extending to the end of October. The suitable reproduction temperature is 22-33°C, and the optimum water temperature is 28-30°C. A mature female shrimp must undergo one pre-mating molt before it can mate. Generally, after mating the female shrimp ovulates within 24 hours, and then the eggs combine with sperm and are fertilized; the fertilized eggs are orange-yellow. After spawning and fertilization, the eggs are carried by the mother and incubated; generally at a water temperature of 28-29°C the incubation period is 30-31 days. The Australian freshwater crayfish can spawn 2-3 times a year.
As people now constantly pursue a higher quality of life, many years ago what everyone pursued was solving the problem of having enough food and clothing; now most people pursue attention to taste, and a small number of people pursue things that are usually hard to eat and rare in variety. For such people, when it comes to eating shrimp, this editor absolutely recommends the Australian freshwater crayfish.