What are the reasons for mass mortality of marine crabs during molting?

Mortality of marine crabs during the molting period manifests as large numbers of marine crabs dying before molting (failed molting), and many marine crabs also die after completing the molt (excessive physical depletion after molting, soft shells that do not harden, etc.). The reasons for mortality of marine crabs during the molting period are:

(1) The water body is polluted, dissolved oxygen is low, affecting molting, leading to death;

(2) Nutritional imbalance in marine crabs (deficiency of calcium, phosphorus, magnesium, zinc, iron, vitamins, etc., weak constitution);

(3) Irritating drugs used during the molting period, causing some deaths;

(4) pH value too low or too high, not within the suitable pH range (suitable pH range is 7.8-8.4);

(5) The molting hormone content in the bodies of marine crabs cannot reach the level required for normal molting;

(6) When marine crabs are sick, molting activity will be hindered;

(7) Marine crabs parasitized by ciliates sometimes also suffer from failed molting;

(8) During the molting period, water temperature, water level, salinity and other factors fluctuate too greatly.

Treatment methods: different treatments for the above causes:

(1) Pay attention to changes in water quality, improve water quality or splash granular oxygen to increase dissolved oxygen in the pond, so as to provide the dissolved oxygen needed by marine crabs during molting.

(2) Add crab multivitamins to the bait to balance the nutrition in their bodies, splash Hard Shell Treasure over the whole pond to increase the content of trace elements, enhance disease resistance, and at the same time promote molting;

(3) During the peak molting period, avoid splashing irritating drugs into the water (such as: quicklime, trichloroisocyanuric acid disinfectants, algicides, drugs for removing blue-green algae and mud moss, copper sulfate, etc.); at the same time, reduce the number of operations in the pond to prevent marine crabs from being startled;

(4) Adjust the seawater to a suitable pH range;

(5) When ciliates are found, promptly use Shrimp and Crab Ciliate Clear, Ciliate Net, or Crab Clear and Safe to eliminate the ciliates;

(6) In the early stage of the molting peak (3-5 days), fresh seawater can be exchanged, and Dr. Sea Super Microorganisms can be used to adjust the water quality well;

2. What foods do marine crabs eat?

Marine crab bait varieties are mostly natural baits, such as small shellfish, small miscellaneous fish and shrimp, small crabs, barnacles, snails, spiral shells, frozen fish, etc. In addition, animal offal can also be fed, and artificial compound feed is also being tried.

3. What does g/1000L mean?

In many materials we see the wording of a certain number of grams/1000L. It indicates the concentration of a certain substance in water. The concentration of 1 gram of a substance dissolved in 1 ton of water is 1 g/1000L, that is to say, the concentration of 1 gram per cubic meter of water body is 1 g/1000L. Similarly, a concentration of 5 g/1000L is 5 g per cubic meter of water body. Then calculated at this concentration, the dosage for 1 mu at 1 m water depth: 5 g per cubic meter of water body x 666 sq m x 1 m water depth = 3330 grams.

4. What factors are related to the occurrence of diseases in marine crabs?

During the aquaculture process, marine crabs always suffer from many diseases. Mild cases affect the growth of marine crabs, and severe cases can lead to mass mortality, causing serious losses to aquaculture production. So how exactly do these diseases arise? Through long-term investigation and research, it has been found that the occurrence of all these diseases is related to the following factors: the quality of the water environment, the health status of the marine crabs, and the pathogenic organisms in the water (or pond bottom). The occurrence of all diseases is related to these three factors, and their combined action causes various problems in marine crabs during the aquaculture process. At the same time, these three are also mutually reinforcing, that is to say, when the water environment deteriorates, the pathogenic organisms in the water will inevitably increase greatly, and at this time the constitution of the shrimp and crabs weakens due to poor water quality, and thus diseases arise. In actual production, we can analyze the emergence of problems from the above three aspects.

5. What is the relationship between marine crab illness and pathogenic organisms in the water environment?

Except for nutritional diseases (diseases caused by malnutrition), the occurrence of almost all diseases is related to pathogenic organisms in the water. Pathogenic organisms include: bacteria, fungi, parasites, viruses, etc. In ordinary aquaculture water bodies there are various pathogenic organisms, and three points need attention:

(1) In good water bodies, the number of these pathogenic organisms is very small and does not cause marine crabs to become ill, so disease usually does not occur;

(2) When water quality is poor, pathogenic organisms in the water (bacteria, viruses) will multiply in large numbers, and the pathogenic organisms that have multiplied in large numbers will attack healthy marine crabs, thereby causing marine crabs to become ill;

(3) Healthy marine crabs are generally not easily infected and do not become ill even when there are relatively many pathogenic organisms in the water. The key point is: when disease occurs, the constitution of most marine crabs is not very good.

Usually diseases such as rotten gills, black gills, rotten limbs, enteritis, and rotten shell (crustacean ulcer) are all caused by bacteria; ciliate disease is caused by parasites; mold disease is caused by fungi; yellow water disease and white water disease are caused by comprehensive factors.

6. What should be done when marine crabs contract yellow water disease or white water disease?

Because yellow water disease and white water disease of marine crabs are caused by comprehensive factors such as bacteria and viruses, treatment is relatively difficult, but in the early stage of the disease when the internal organs are still intact, it is not incurable. At this time, promptly adopting the method of oral administration plus external application can still recover certain losses, that is, adding Crab Disease Cure and antibacterial and antiviral Chinese herbal medicines Jun Du Sha Xing or San Huang Powder to the feed to enhance their antibacterial and antiviral ability, while externally using Jun Du Qing, double-chain quaternary ammonium salt iodine, etc. to thoroughly disinfect and sterilize the whole pond. But once this disease reaches the late stage after the internal organs have ulcerated, there is no way to save it, so the key to this disease is prevention. Frequently use Jun Du Qing or bromochloro hydantoin for aquaculture, etc. for disinfection, and frequently add crab multivitamins and Crab Disease Cure, San Huang Powder, or Jun Du Sha Xing to the fed bait to enhance the disease resistance of marine crabs to this disease.

Yellow water disease and white water disease of marine crabs are often caused by changes in aquaculture water quality, especially by the massive appearance of Noctiluca in the sea area. Such ponds often have water quality and pond bottom that turn black and stink, and are prone to occur in the high-temperature summer season. Therefore, to prevent and treat these diseases, we first need to start with improving water quality or using Jun Du Qing to kill Noctiluca. We can splash microorganisms over the whole pond to purify the pond water quality, rapidly degrade the organic matter and humus in the deteriorated pond water, and convert toxic and harmful factors such as ammonia nitrogen and nitrite nitrogen in the pond water. At the same time, the main mechanism of increasing oxygen throughout the pond is to rapidly increase the dissolved oxygen at the bottom of the pond, which has already become severely oxygen-deficient due to water quality deterioration, and to rapidly oxidize toxic substances such as hydrogen sulfide, ammonia nitrogen, and nitrite nitrogen accumulated in the pond bottom, reducing the toxicity of these harmful factors to the benthic marine crabs. Through these measures, the condition of ponds with deteriorated water quality can be rapidly improved, thus eliminating the occurrence of diseases.

7. I am a marine crab farmer. I would like to ask why, after using some disinfectants and oral medicines available on the market, my marine crabs still frequently and severely develop diseases?

There are many types of medicines popular on the market now, and many are products from informal manufacturers with no quality guarantee. In addition, some current oral medicines and disinfectants are products developed by manufacturers for freshwater aquaculture. Because seawater has a strong buffering capacity for medicines, the situation of no effect occurs. At this time, one should choose disinfectants, oral medicines, and water quality improvers produced by formal manufacturers to purchase. At the same time, on the instructions of these products, one should clearly see the indicated target of use. The key is that when disease occurs, one must also prescribe the right medicine for the illness, avoiding indiscriminate use of medicines. Otherwise, not only is money wasted, but treatment of the condition is also delayed, thereby causing unnecessary losses.

8. What are white crab, thin crab, flower crab, and red roe crab?

White crab: an unmated female crab, with an individual size of 150-200 grams. The main feature is that the abdominal flap is grayish-black. Under relatively strong light, it can be observed that the two sides of the carapace from the base of the eye to the 9th lateral tooth have no clear outline of the gonads. If white crabs are to be raised into roe crabs, they need to be stocked together with male crabs at a ratio of 3:1 or 4:1 (female/male) so that they mate. After one reproductive molt, with sufficient bait feeding for 40-50 days, they can be raised into roe crabs.

Thin crab: a female crab that has just mated, with an individual size of more than 250 grams. Under strong light, it can be observed that from the base of the eyestalk to the ninth lateral tooth on both sides of the carapace there is a crescent-shaped ovarian outline, transparent above and below, which is the expanded range of ovarian maturation. After 30-40 days of rearing, this kind of crab can become a green crab with plump ovaries.

Flower crab: a female crab that mated nearly 1 month ago. The ovaries have begun to develop and mature and expand, but have not yet extended to the edge of the carapace. Under light, some transparent areas can be seen, like a crescent-shaped curve. The round spot above the abdominal flap has changed from milky white to yellow. After another 15-20 days of intensive rearing, it can be raised into a red roe crab.

Red roe crab: the ovaries have already matured, body weight is more than 250 grams, both sides of the carapace are filled with red roe, the body is firm, and under light no transparent area is observed. The round spot above the abdominal flap has turned red, and some carapaces already show a bright red color.