Are Australian freshwater crayfish juveniles expensive? A detailed guide to farming methods
The Australian freshwater crayfish is native to Australia. Because it is relatively large, closely resembles a marine lobster in appearance, and lives only in freshwater, it is called a freshwater crayfish. Individuals generally weigh 100 g—200 g, and the largest individuals can reach 500 g. As early as the 1990s, the Australian freshwater crayfish set off a farming wave around the world. However, due to problems such as insufficient promotion, low investment, and low juvenile survival rates, especially limited juvenile supply, Australian freshwater crayfish farming has still not become large-scale in China. Are Australian freshwater crayfish juveniles expensive? How are they farmed?
1. Are Australian freshwater crayfish juveniles expensive?
In recent years, because the farming situation for Thai prawns has been relatively unstable, many farmers have turned to farming Australian crayfish as an edible shrimp species for shrimp fishing ponds and restaurant tables. In the Pingtung area, operators have successively stocked them on a large scale. The pond-side price is about NT$300-350 per Taiwan catty (600 g) (equivalent to about 60-70 yuan RMB), and juvenile prices range from NT$4-15 (equivalent to about 0.8-3 yuan RMB), depending on the size grade.
2. How are Australian freshwater crayfish farmed?
1. Pond conditions. Freshwater crayfish prefer water environments with fresh water quality and abundant dissolved oxygen. Choose a place with sufficient water sources, no pollution sources, and convenient water intake and drainage. An area of 2000--3300 sq m is suitable. The bottom is best sandy or hard soil, and there should not be too much silt. The pond bottom should have submerged plants covering no less than 1/5 of the area. The pond should be equipped with good water inlet and drainage facilities, and both the inlet and outlet should be fitted with mesh covers to prevent escape and predators. Around the pond, plant aquatic plants such as water grass, water hyacinth, and water lettuce, with coverage of about 1/3 of the water surface. Arrange sufficient hiding places on the pond bottom, such as artificial burrows, stones, and tiles, for the crayfish to hide and rest. This should occupy about 1/5 of the pond area.
2. Juvenile stocking. Be sure to dry and disinfect the pond. In addition to splashing quicklime, thoroughly remove predators in the pond, such as catfish, loach, snakes, and rats. Juvenile stocking time is suitable from March to May, chosen on sunny mornings or evenings. Juvenile size is 2--4 cm, and density is 800--1000 individuals per mu.
3. Feed feeding. This crayfish has a wide diet and likes small trash fish, snails, and soybeans, and also likes formulated prawn feed. Within 3 days after stocking, feed mainly minced small trash fish and minced meat; within the following month, feed small trash fish, leftover meat, or artificial formulated feed; when they grow to 6--7 cm, all can be fed crushed snails, river mussels, and an appropriate amount of plant-based feed. Feed once each morning and evening. The feeding amount is about 4%--7% of body weight, and the specific amount should be increased or decreased according to their feeding situation. Most feeding occurs at dusk and at night, and the nighttime feeding amount should account for more than 70% of the whole day.
4. Daily management. Pond water quality should always remain fresh. Generally, change water to a depth of 15--20 cm each week, and ensure sufficient dissolved oxygen. Check frequently and patrol the pond frequently, and remove moss from the pond in time; often check the filter nets at the water inlet and outlet, and also pay attention to observing the crayfish's various activities and feeding conditions, and take care to prevent and remove predators.
5. Disease control. Since this crayfish was introduced to China, no explosive or epidemic diseases have been found, but when farming density is relatively high, attention should also be paid to disease control. First, brown spot disease. Diseased crayfish have speckled dark brown ulcers on the surface shell and often lie at the pond edge in a dying state. The control method is mainly to maintain good pond water quality, regularly change water or apply quicklime, and carry out pond dredging every year; during capture, transport, and stocking, operate carefully to prevent damaging the shell; when disease is found, 1 mg/kg furacilin can be splashed for treatment. At the same time, 10--15 mg/kg tea seed cake liquid can be splashed to promote molting and repair damaged shells. Second, black gill disease. This disease is mainly caused by water pollution and mold infection. Its symptoms are that the gills change from red to brown or light brown, until they completely turn white, causing gill shrinkage. The control method is: use 2--3 mg/kg furazolidone or bleaching powder to kill the pathogens, or splash malachite green or methylene blue at 2 mg/kg over the whole pond. Third, ciliate disease. This disease is mainly caused by ciliates such as Carchesium and Vorticella attaching to the crayfish's body surface, appendages, eyes, and gills. In severe cases, it can make the crayfish restless, frequently swimming at the pond edge, hindering feeding, molting, and growth. It can even cause the crayfish to suffocate and die from lack of oxygen. Generally, injecting new water and keeping the pond water clean can be adopted for prevention. For treatment, soak diseased crayfish in 0.40 mg/kg copper sulfate solution for 5--6 hours, for 3--5 consecutive days per treatment course.
6. Harvesting. Freshwater crayfish stocked in the same year can be harvested from October to November. One-time harvesting can be carried out in the evening by drying the pond or using surrounding nets. If listing in stages and batches is desired, cast-net harvesting can be used.