Do Swimming Crabs Eat Fish or Carrion? A Detailed Guide to Farming Precautions
Swimming crab, also known as white crab, is a relatively common crab in China. Because it has plenty of meat and comes to market relatively early, its price is a little high, so many people farm it. So what does a swimming crab eat as it grows? Fish or carrion? What should be noted when farming it?
1. The swimming crab is an omnivorous animal. It likes to feed on shellfish meat, fresh trash fish, small mixed shrimp, and so on, and also feeds on tender algae shoots, carcasses of marine animals and decaying aquatic plants. Moreover, its feeding habits differ at different growth stages. At the juvenile crab stage it tends to be omnivorous, and the larger the individual, the more it tends toward carnivory. It usually feeds little during the day and feeds heavily in the evening and at night. However, when the water temperature is below 10°C or above 32°C, the swimming crab stops feeding.
2. Swimming crabs are dioecious. Their lifespan is generally 2 years, rarely more than 3 years. Their biological minimum size is a carapace length of 5.1 cm; the largest male individual has a carapace length of 11 cm, a width of 22 cm and a body weight of 710 grams; the largest female individual has a carapace length of 10.5 cm, a width of 22 cm and a body weight of 730 grams. The egg-laying and breeding population is mainly composed of parent crabs aged 1—2 years. Females die immediately after spawning and hatching. Males die after mating, which takes 2—3 days. For overwintering three-spot swimming crabs, the mating time is between July and August each year, while for swimming crabs born in the current year, the peak mating period is between September and October.
Farming precautions:
1. Farming water quality
In the past, people generally focused only on pH, oxygen, temperature and salinity, and did not pay enough attention to calcium. In fact, calcium is crucial to the growth of crabs, shrimp and shellfish. If it is slightly insufficient, swimming crabs will grow slowly or have difficulty molting.
The density of calcium-demanding organisms in ponds is far higher than in natural sea areas, and relatively speaking their demand for calcium is also greater. Relying on water changes alone is absolutely not enough to meet demand, especially in the middle and late stages of farming.
Applying quicklime midway is an effective measure. It can both increase the calcium source and adjust the pH value, but if applied too many times or in too large an amount, it will inevitably kill some useful bacteria and microorganisms, causing the ecology in the pond to lose balance.
2. Equip with aeration equipment
Because swimming crabs live on the bottom during the day, when oxygen deficiency begins it is often not easy to notice, but by the time you notice it, the consequences have already occurred. Therefore, in seasons with high temperatures and low air pressure, the equipment must be turned on at any time to increase oxygen.
3. Temperature
The “appetite” of swimming crabs is closely related to water temperature. At 20-30°C they feed vigorously; at other temperatures their “appetite” is not great.
4. Salinity
In farming areas where the pond water salinity is above 1.015, the bottom is sandy or muddy-sandy, and the average water depth is above 1.5 m, adult swimming crabs have good body color and clean appendages, are relatively close to natural swimming crabs, and have higher commercial value.