How to Raise Mud Crabs in Freshwater? A Detailed Explanation of New Farming Techniques
In fact, many delicacies are produced in autumn, such as crabs among seafood. Surely everyone is fairly familiar with the mud crab, as it often appears in our daily lives. At present, the mud crab has also become a hot trend in the farming industry, but if raising mud crabs is to bring certain economic benefits, then one must certainly master certain farming techniques.
New Mud Crab Farming Techniques
1. Crab seedling selection: At present, the sources of mud crab seedlings for farming mainly fall into two categories: natural seedlings from sea areas and factory-based artificially bred seedlings (the technology for factory-based seedling production has not yet been fully popularized, and seedling sources are still very few). One should choose healthy seedlings that are strong-bodied with hard shells, have a dark green carapace, are uniform in size, have complete bodies without damage, have all ten legs complete (especially a pair of chelipeds and swimming legs, of which not one may be missing or damaged), respond sensitively, are full of vitality, crawl quickly, and show no signs of disease.
2. Site selection: Mud crab farming ponds (pools) should be built in areas in the upper-middle tidal zone where there is no industrial or agricultural production wastewater, no toxic substances, no pesticide or domestic sewage pollution in the surroundings, where the seawater is fresh, the water body has a strong self-purification capacity for exchange, the physical and chemical factors are stable, the tidal range is large, the inner bay is calm with gentle winds and waves, and a certain amount of land-derived freshwater flows in.
3. Anti-escape facilities: Anti-escape fencing must be installed along the inner side of the entire perimeter of the pond embankment (it can be made from materials such as thin cement boards, bamboo fences, and hard plastic sheets), and the height of these facilities should exceed the highest water level in the pond by more than 50 cm. The upper ends of the facility boards and fence pieces should tilt slightly toward the inside of the pond, and the installation must be tight and firm to effectively prevent mud crabs from escaping.
4. Feeding ratio: The feeding amount during the farming period should be flexibly controlled according to water temperature, tides, water quality, and the activity of the mud crabs. For example, mud crabs feed vigorously when the water temperature is above 15°C, reaching their peak at 26°C, but when the water temperature is above 30°C or below 13°C, their food intake decreases noticeably.
5. Regulating salinity: When the seawater salinity in the pond is too low or too high, water should be exchanged promptly to adjust it. Especially during the rainy season when freshwater surges in, or during typhoon and heavy rainstorm days, when the specific gravity of the seawater in the pond becomes too low, the upper gate board should be opened promptly to first discharge the lower-specific-gravity water in the upper layer of the pond, and then take in higher-specific-gravity seawater from the middle and lower layers at high tide. For ponds built on high shoals where natural water intake is difficult, a lift pump can be used to draw seawater from the middle and lower layers for adjustment.
How to Raise Mud Crabs in Freshwater
The mud crab is a marine crab. Because it has long lived by the sea, its gills have adapted to high-salinity seawater and are not suited to low-osmotic-pressure freshwater. It is not suitable for farming in freshwater, and it is recommended that everyone still farm it in seawater according to its growth habits. However, if you are only keeping it for a few days, you can directly use freshwater, or buy the special seawater-mixing salt from an aquarium shop in a flower-and-bird market, and the shop owner will teach you how to mix seawater.
What Food Do Mud Crabs Eat
The mud crab has a very omnivorous diet, mainly feeding on animal-based food. Its food composition is dominated by mollusks and small crustaceans. In its stomach contents, there are often shell edges and hinge fragments of bivalves, opercula of gastropods, broken spiral axes, and fragments of limbs and carapaces of grapsid crabs. It also often feeds on tidal-flat worms, and also eats small fish and small shrimp; sometimes fragments of plant stems and leaves are also found in its stomach. Farmed mud crabs are not strict in their choice of bait; trash fish, shrimp, small shellfish (blue clams, Musculus senhousei, river clams, river snails, etc.), soybean cake, and peanut cake can all be eaten. It has the habit of cannibalism, often preying on soft-shelled crabs that have just molted.
Mud Crab Polyculture Techniques
1. Shrimp. Such as Chinese white shrimp, long-haired prawn, black tiger shrimp, Japanese shrimp, Metapenaeus ensis, and ridge-tailed white shrimp self-propagated in the pond. The stocking size for shrimp seedlings is required to be over 3 cm after temporary holding, and the stocking amount is generally about 1000-2000 tails/mu. Their growth rate is faster than in shrimp ponds in the upper tidal zone, and when the water temperature is suitable, harvesting can begin 1 month after stocking.
2. Fish. The main species include: mullet, grey mullet, black sea bream, mudskipper, etc. The organic matter accumulated in the pond is excellent bait for these fish, and the general stocking amount ranges from 20-500 tails/mu.
3. Algae. In Taiwan, China, the polyculture of mud crabs with gracilaria (called dragon beard vegetable in Taiwan, China) is relatively common. Polyculturing an appropriate amount of algae can absorb and consume a large amount of dissolved organic matter in the water body and can increase the dissolved oxygen in the water body, which is more conducive to the growth of mud crabs and other economic animals in the pond.
At present, the market prospects for mud crabs are still quite good, and successful farming can naturally bring people relatively optimistic economic benefits. However, the mud crab is a marine crab, so everyone should master its key farming points well when farming it.