How can freshwater crayfish farming avoid pitfalls and improve economic returns in 2018?
Freshwater crayfish in the farming process require a rational analysis of many aspects, including their living habits, variety sources, farming environment setup, reasonable feed combinations, disease prevention and treatment, and scientific estimation of yield, so as to formulate a corresponding farming plan, reduce the chance of falling into farming pitfalls, and obtain higher economic returns.
In recent years, as market demand has continued to increase, the “farming craze” for freshwater crayfish has heated up year by year, one wave after another, and many aquaculture farmers have set their investment sights on crayfish farming. However, many farmers have not fully mastered the correct farming techniques, thereby neglecting normal management during the farming process in areas such as the stocking of crayfish seedlings, water quality environment, feed feeding, and disease prevention and treatment, ultimately making it difficult to improve the economic returns of farming. Through visits and surveys, it is believed that freshwater crayfish farming mainly has the following six pitfalls:
1. Insufficient understanding of the living habits of crayfish
From the first autumn (September to October), crayfish that have reached sexual maturity begin to mate, dig holes, and carry eggs. The growth, development, and overwintering process of the larval shrimp are attached to the mother's abdomen. By the following spring (February to March), when the seedlings reach more than 2 to 3 cm, they leave the mother and live independently. After more than 2 to 3 months of growth, they become egg-bearing adult shrimp. Therefore, the scientific time period for stocking crayfish seedlings and breeders is the two seasons of spring and autumn. For spring stocking, seedlings can be put into the pond at the end of March and the beginning of April; for autumn stocking, breeder shrimp should be put into the pond at the end of September and the beginning of October. After they rest and adapt on their own, let them reproduce naturally in the pond, which can not only provide seedlings for one's own pond but also allow part of them to be sold. Because crayfish have the habit of digging holes and escaping, the farming pond for crayfish should use mesh, wooden stakes, thick plastic sheeting, or other sheet-like materials to build good escape prevention along the pond ridge. Crayfish generally dig holes 30 to 40 cm deep, and some reach about 1 m, so the width of the pond ridge is best kept above 3 m to prevent crayfish from digging holes and escaping.
2. On the issue of freshwater crayfish varieties
What we currently call freshwater crayfish is scientifically named Procambarus clarkii, belonging to the class Crustacea, order Decapoda, family Cambaridae, genus Procambarus. It originated in northern Mexico and the southern United States. In the early 20th century, Japan introduced it from the United States, and not long afterward it was introduced into Nanjing, China, via Japan. Its distribution range now exceeds 20 provinces and cities, and it has become one of the important resources among freshwater shrimps in China. At present, the crayfish farmed in Jiangsu, Anhui, Hubei, and other areas along the middle and lower reaches of the Yangtze River are all one variety. There is also a “hybrid” crayfish variety, which is an object of research by professional aquaculture departments and is basically still in the experimental stage, with its technical level still needing to mature and improve. Artificially domesticated seedlings and naturally reproduced seedlings are different. Due to the high cost of artificial breeding of seedlings, coupled with the large output and low prices of wild seedlings in ditches, ponds, rivers, and lakes at present, it is difficult to promote this technical variety on a large scale. Of course, the survival rate of artificially bred seedlings is very high, reaching about 85%, while wild seedlings generally reach only about 70%, and there are also limitations of water body geographical location. Generally speaking, the selection and stocking of crayfish seedlings for pond farming is only one important part of farming. More important is what kind of effective scientific management methods are adopted in daily farming. If management can reach a relatively high level, the probability of successful farming is greater; otherwise, it fails.
3. Over-idealizing the yield of freshwater crayfish
The farming yield of crayfish is extremely closely related to the stocking of shrimp seedlings, control of the water environment, the combination of meat and plant feed, daily scientific and systematic management, and timely prevention and treatment of common diseases. Generally, in April and May, about 50 to 70 kg per mu of seedlings with a specification of 130 to 150 tails/kg are stocked. After about 70 days of rapid growth, in June one can begin adopting the method of selling the large and keeping the small, until it basically ends at the end of October. In total, each mu of pond can capture 150 to 180 kg of crayfish. Depending on the farming level, the average specification is generally 20 to 30 tails/kg. Where farming techniques and pond conditions are good, the stocking number of shrimp seedlings can be slightly increased and feeding increased, and the yield per mu will increase to a certain extent. As for those unrealistic exaggerations and boasts that even higher yields can be achieved, there is no scientific basis at all; at most they are isolated cases.
4. Insufficient control of the farming water body environment
Usually crayfish have a very strong ability to adapt to the farming water body environment, which has caused some people to mistakenly believe that crayfish like to live in blackened, stinking water bodies and that water quality does not matter. The fact, however, is that crayfish living in dirty water bodies are dirty and black, with hard and thick shells, small bodies and large heads, and they are neither attractive for sale nor appetizing. The correct understanding should be that clear water quality, abundant aquatic plants, high dissolved oxygen, and no pollution are the keys to raising crayfish well. In water bodies lacking aquatic plants, first, dissolved oxygen is insufficient; second, during molting crayfish have no better area to hide from enemies, and they will be attacked by the same species or other carnivorous aquatic animals, thereby producing an animal stress response. Many crayfish will show slow growth, and the occurrence of “old man shrimp” will be very obvious.
5. Inadequate feed feeding
For intensive crayfish ponds, the feeding of bait must be increased, which can reduce crayfish killing each other due to lack of bait and improve the survival rate of crayfish. In the selection of feed varieties, attention should be paid to a scientific and reasonable combination of coarse and fine, meat and plant feeds, adopting a meat-plant-meat method, namely: animal feed accounts for 70% in the early and late periods, and plant feed accounts for 70% in the middle period. When conditions permit, try not to feed animal materials such as poultry internal organs. For daily animal feed, one can choose unpasteurized small wild miscellaneous fish, snail meat, and so on as the main items; plant feed is mainly corn, soybean cake, small pumpkin, and aquatic plants such as Elodea. The feeding amount of bait should be adjusted in a timely manner according to the timely temperature, changes in cloudy and clear weather, the activity and appetite of crayfish, and the existing stock in the pond. Generally, the feeding ratio is that bait accounts for 3% to 5% of the total weight of crayfish stored in the pond, and it is best to finish eating within 2 to 3 hours after feeding. Close observation is required to strictly prevent residual bait from polluting the pond water body.
6. Insufficient attention to the prevention and treatment of crayfish diseases
Because crayfish have a relatively strong resistance to diseases, they generally do not get sick, but after being intensively cultivated by humans, many uncertain factors easily cause disease. For example, in previous years, in crayfish farming ponds in townships along the Huai River area of Xuyi County, a contiguous white spot disease situation appeared across nearly 1,000 mu, and many farmers ultimately ended up with only a pond of empty water. The reason is that crayfish farming must do a good job in disease prevention and treatment. First, from the beginning, do a good job in pond clearing and disinfection, spreading 80 to 160 kg of quicklime per mu over the whole pond to thoroughly kill various enemies and pathogenic microorganisms. Second, during the farming process from May to September, spread quicklime or chlorine preparations over the whole pond every 10 to 15 days, which can effectively kill many pathogens. Third, during the high temperatures of July to August, appropriately raise the water level to about 1.2 m to lower the temperature of the farming water body environment, so that crayfish maintain a certain growth rate in a suitable ecological environment. Fourth, by the middle and late stages of farming, excessive organic matter accumulated in the pond cannot be fully oxidized and decomposed due to lack of oxygen. Anaerobic decomposition replaces oxidative decomposition, producing large amounts of harmful substances such as ammonia nitrogen, hydrogen sulfide, and nitrite, causing chronic poisoning of crayfish, and various pathogens multiply in large numbers, causing crayfish to become sick or die. At this time, biological preparations and EM bacteria should be used to regulate water quality and improve the substrate, inhibiting the production of pathogenic microorganisms through biological antagonism and creating a good ecological environment. Fifth, do a good job in daily pond inspections. When abnormal phenomena appear in crayfish, quickly investigate and diagnose, find out whether it is a problem in the water environment or whether the shrimp itself is sick, prescribe the right medicine, and promptly take remedial measures. At the same time, dead shrimp should be taken out of the pond water and buried away from the pond to cut off further spread of the disease.