Crayfish farming is developing rapidly, but these problems need attention
At present, crayfish farming is developing rapidly, the farming area is constantly expanding, and the number of farmers is growing day by day. During the farming process, many unexpected problems will arise. If they are not correctly handled in time, they will cause disease or death of crayfish and restrict the development of the crayfish industry.
I. In the early stage of crayfish farming, when doing pond preparation work, some problems are often encountered. If they are not handled well, they will bring losses to crayfish farming.
1. Fertilizing water at low temperatures
Fertilizing the water for farming is a must during the overwintering process of crayfish farming. Water that appears emerald green or tea-colored is best. At present, commonly used fertilizers include compound fertilizer and biological fertilizer, each with its own characteristics. Generally, in winter and spring, the commonly used water fertilization method is to use biological fertilizer after detoxification. There is no need to deliberately pursue green algae water or diatom water; it is enough for the water to have high dissolved oxygen, good aquatic plants, and clear water that does not grow moss and remains stable.
2. Inoculating bacterial strains
After the spring water temperature reaches above 10°C, microbial activity strengthens. At this time, beneficial bacteria such as Bacillus subtilis, lactic acid bacteria, and yeast should be inoculated to become dominant strains. This can purify water quality, prevent moss, and reduce disease outbreaks.
3. Removing moss
If the water body is too shallow or the water is clear and lean, moss is relatively likely to grow. Generally, deepening the water level and treating it with some moss-removal medicine is enough; after clearing the moss, just fertilize the water. However, it must be discovered early and handled promptly. If there is already too much moss in the water body, treatment becomes relatively difficult.
II. During the crayfish farming period, some diseases will occur. Starting in mid-April, many farmers continuously harvest crayfish every day in order to sell more shrimp. Therefore, undersized small shrimp are easily injured during harvesting and releasing, which then leads to bacterial infection causing disease and death.
1. Hepatobiliary syndrome. In May, as temperatures rise, the food intake of crayfish also increases. In order to bring crayfish to market as soon as possible, farmers blindly increase the feeding amount and feed high-protein feed, causing a heavy load on the shrimp's liver, which easily induces hepatobiliary syndrome and leads to large numbers of deaths when crayfish become diseased.
2. Lack of dissolved oxygen. In May, the Elodea in some shrimp ponds grows too densely, even growing out of the water surface, but farmers do not timely separate rows and cut the grass tops. If Elodea grows out of the water surface and the grass tops are not cut in time, it easily dies and rots, thereby deteriorating water quality. Too much grass will also compete with crayfish for space and dissolved oxygen. There are also some farmers whose shrimp ponds have no grass planted. When temperatures are high, the shrimp have no place to shade themselves and molt, making it easy to form red shrimp, which is also unfavorable for molting. Therefore, the size of the crayfish is relatively small.
3. During the farming process, molting is the most critical part for crayfish. Only after molting can the shrimp grow. Farmers often see crayfish fail to molt smoothly, or die after molting, or be eaten by larger shrimp. Many beginners in crayfish farming do not know how many seedlings to release. Some farmers also stock at relatively high density in pursuit of high yield. In the early stage, when temperatures are low and the seedlings are small, this is not a big problem, but later as the shrimp gradually grow, temperatures rise, and food intake increases, it is easy to make the water body muddy, cause serious grass clipping, and also easily lead to oxygen deficiency.
Some diseases occurring during the crayfish farming process and their prevention and control measures:
1White spot disease
White spot disease is a viral disease. Its outbreak is directly related to water temperature, water quality, and the shrimp's physique. It generally breaks out in May and June. It can be prevented by frequently adding fresh water to lower water temperature, using water quality improvers to regulate water quality, and enhancing physique through oral trace elements or reducing farming density. At present, there is no good treatment plan.
2Soft shell disease
Cause: Calcium deficiency in the body. In addition, insufficient light, long-term low pH, excessively thick pond bottom silt, excessive shrimp seedling density, and long-term feeding of a single bait can also cause this disease.
Symptoms: The shrimp shell is soft and thin, the body color is not red, activity is poor, feeding is not vigorous, growth is slow, and coordination ability is poor.
Prevention: (1) Remove silt in winter; (2) Clear the pond with quicklime, and after releasing seedlings, splash 25 mg/L quicklime every 20 days; (3) Control stocking density; (4) The area of aquatic plants in the pond should not exceed 30% of the pond area; (5) Diversify bait and appropriately increase calcium-containing bait.
3Rotten shell disease
Cause: Caused by infection with Pseudomonas, Aeromonas, Myxobacteria, Vibrio, or Flavobacterium.
Symptoms: There are obvious ulcerated spots on the shell of diseased shrimp. The spots are grayish white, and when severely ulcerated they turn black. The spots sink inward, forming holes, and finally lead to internal infection, even death.
Prevention: (1) Handle carefully during transportation and seedling release; do not put injured or disabled shrimp into the pond. Before seedlings are put into the pond, disinfect with 3% salt water for 5 minutes; (2) Operate carefully at ordinary times and try not to injure the seedlings; (3) Keep the pond water clean; (4) Provide sufficient bait; (5) Every 15-20 days, splash the whole pond with 25 mg/L quicklime dissolved in water.
4Black gill disease
Cause: Caused by fungal infection of the shrimp gills.
Symptoms: The gills change from flesh color to brown or dark brown, until turning black, and the gill tissue shrinks and necroses. Diseased young shrimp have weak activity, mostly crawling slowly on the pond bottom, and stop feeding. Diseased adult shrimp often float to the water surface or cling to aquatic plants and expose themselves out of the water, do not enter burrows, move slowly, and finally die from breathing difficulty.
Prevention: (1) Replace pond water and promptly remove residual bait and decaying matter in the pond; (2) Use 25 mg/L quicklime to regularly disinfect the water body; (3) Frequently feed green feed; (4) In the middle and late stages of adult shrimp farming, put some toads in the pond.
5Ciliate disease
Cause: Caused by ciliate parasitism. The main parasitic species include Epistylis, Vorticella, Carchesium, and Epistylis-like species.
Symptoms: Dirt attaches to the body surface, appendages, and gills. The shrimp body surface is covered with a layer of white flocculent matter, causing reduced activity and decreased appetite in crayfish.
Prevention: (1) Keep pond water fresh; (2) Remove dirt in the pond; (3) Remove silt in winter.
6Crayfish plague
Cause: Caused by fungi.
Symptoms: The body surface of diseased shrimp has yellow or brown spots, and fungal filaments can be found at the base of the appendages and legs. Diseased shrimp are sluggish, activity weakens or becomes abnormal, and in severe cases it causes large numbers of deaths.
Prevention: (1) Keep the water body fresh and maintain normal water color and transparency; (2) Appropriately control stocking density; (3) Remove silt in winter; (4) Pay attention to disinfection at ordinary times.
7Rotten tail disease
Cause: Crayfish are injured, cannibalize each other, or are infected by chitin-decomposing bacteria.
Symptoms: In the early stage of infection, diseased shrimp have small sores on the tail, and the edges ulcerate, necrose, or become incomplete. As the condition worsens, the ulceration spreads from the edges toward the middle. In severe infection, the entire tail of the diseased shrimp ulcerates and falls off.
Prevention: (1) When transporting and releasing shrimp seedlings and shrimp seed stock, do not stack, press, or damage the shrimp bodies; (2) During the farming period, bait should be fed sufficiently and evenly.
8Hemorrhagic disease
Cause: Caused by Aeromonas.
Symptoms: The body surface of diseased shrimp is covered with bleeding spots of varying sizes, especially obvious on the appendages and abdomen. The anus is red and swollen, and death occurs soon after.
Prevention: (1) Keep the water body fresh and maintain normal water color and transparency; (2) Remove silt in winter; (3) Pay attention to disinfection at ordinary times.
9Water mold disease
Cause: Caused by infection with water mold.
Symptoms: A grayish white, cotton-like mycelium grows on the body surface of diseased shrimp. Diseased shrimp generally move very little, do not feed, and do not enter burrows.
Prevention: (1) When the water temperature rises above 15°C, splash the whole pond with 25 mg/L quicklime dissolved in water every 15 days; (2) Cut away overly vigorous aquatic plants to increase sunlight; (3) Strictly prevent injured or disabled shrimp seedlings from entering the pond; dead fish that have grown water mold cannot be used as feed; (4) For every cubic meter of water, use 2 g of Chinese gallnut decoction, dilute it, and splash the whole pond.
10Failed molting
Cause: The growing water body lacks a certain element.
Symptoms: Diseased shrimp show cracks at the junction between the cephalothorax and abdomen, and the whole body turns black.
Prevention: (1) Every 15-20 days, splash the whole pond with 25 mg/L quicklime dissolved in water; (2) Every month, splash the whole pond with 1-2 mg/L superphosphate dissolved in water.
Treatment: (1) Mix 1‰-2‰ molting hormone into the feed; (2) Mix bone meal, eggshell meal, etc. into the feed to increase the calcium content in the feed.
11Edema disease
Cause: After the abdomen of crayfish is injured, it is infected with Aeromonas hydrophila.
Symptoms: The cephalothorax of diseased shrimp is edematous and transparent. Diseased shrimp lie prone among the grass at the pond edge, do not eat or move, and finally die on the shallow water beach at the pond edge.
Prevention and control: During production operations, minimize injury to crayfish.
12Cold injury disease
Cause: When the water temperature is below 4°C, the shrimp will suffer cold injury.
Symptoms: When crayfish suffer cold injury, the cephalothorax noticeably swells, and white spots appear on the abdominal muscles. As the condition worsens, the white spots grow from small to large, and finally spread over the entire body. Diseased shrimp initially enter a state of shock, lying flat or on their side in submerged grass. In severe cases, symptoms such as paralysis and rigidity appear, and death occurs soon after.
Prevention and control: (1) In early winter, when the water temperature drops below 10°C, deepen the water level; (2) During the overwintering period, apply organic fertilizer or straw in the pond to promote fermentation of microorganisms at the bottom and raise water temperature; (3) In autumn and winter, pay attention to feeding more fat-containing bait, such as soybean cake, peanut cake, rapeseed cake, etc.
13Spasmodic disease
Cause: In high-temperature seasons, caused by frequent harvesting and fright to adult shrimp.
Symptoms: The main symptom is a bent abdomen in adult shrimp. In severe individuals, the area from below the cephalothorax to the tail is obviously stiff, and they lie on their side at the bottom without moving. After being caught, they cannot return to normal for a long time. Mild cases can paddle briefly, but the body is hunchbacked and cannot stretch out. Some diseased shrimp also have a whitish abdomen, but it is not transparent.
Prevention and control: (1) Try to avoid harvesting in high-temperature seasons; (2) During production, frequently replace with fresh water, raise the water level, and improve water quality; (3) After disease occurs, promptly add fresh water for 5 consecutive days.
14Deformity disease
Cause: Caused by excessive heavy metal salts in pond water and deficiency of a certain nutrient element.
Symptoms: The body of diseased shrimp is bent. Some have bent tails, some have shrunken tails, and some have bent or even incomplete setae on the appendages. Larvae have poor phototaxis and weak activity, mostly sink to the bottom, and molting is very difficult.
Prevention and control: (1) Strengthen feeding management and feed more feed containing calcium, phosphorus, and rich nutrition; (2) When parent shrimp are incubating eggs, controlling the water temperature at 22-25°C is appropriate, and at the same time strictly prohibit heavy metal salts such as zinc, copper, chromium, etc. from entering the pond, and keep the pond water clean and pollution-free.
15Pond-wide suffocation
Cause: Mainly oxygen deficiency in pond water.
Symptoms: When pond shrimp lack oxygen, they become restless and rush about everywhere. Sometimes they crawl in groups into the grass at the pond edge and remain still, and some crawl onto the bank. If they leave the pond water for too long, it leads to death.
Prevention and control: (1) During the winter fallow period, promptly remove excessive silt and freeze-dry the pond bottom; (2) Use already fermented organic fertilizer and control the water from becoming too dense; (3) Control the stocking density of shrimp seed stock; (4) Frequently add fresh water and keep the pond water clear and refreshing.
All diseases of crayfish are related to the substrate and water quality of the farming pond or rice field. Therefore, during the farming process, insist on improving the bottom and treating the water every 10 days, and maintain good substrate and water quality for a long time, creating an excellent ecological environment for crayfish. This can both reduce the occurrence of crayfish diseases and promote crayfish growth.