How Are Crayfish Harvested? A Detailed Guide to Common Harvesting Methods

Crayfish farming currently has relatively good development prospects in the aquaculture industry. As people's living standards have continued to rise in recent years, crayfish are not only popular in the late-night snack scene; they have gradually become a fairly common dish on everyday dinner tables as well. Now let's take a look at some information about crayfish together.

Harvesting Methods for Crayfish

Crayfish grow relatively quickly. When crayfish are raised in ponds, after 3 to 5 months of rearing, once the adult shrimp reach a size of more than 30 grams, they can be harvested for market. Juvenile shrimp stocked in March to April can begin to be harvested at the end of May and early June, with concentrated harvesting at the end of July, and all harvesting completed by August; for juvenile shrimp stocked in September to October, harvesting can begin in March of the following year, and can be completed by the end of May.

There are many methods for harvesting crayfish. They can be caught with tools such as shrimp cages, ground cages, hand nets, and shrimp lift nets, or caught with fishing rods or by seine netting, and finally by draining the pond to catch them. From mid-March to mid-July, using shrimp cages and ground cages to catch them gives better results. Shrimp cages and ground cages come in various styles; common ones include soft ground cages made from netting and small shrimp cages made from bamboo. It should be noted that before harvesting crayfish, medications should be used with caution for disease prevention and treatment in ponds and rice fields, otherwise it will affect the recapture rate of crayfish, and drug residues will also affect the quality of commercial shrimp, leading to obstacles in market sales and affecting farming benefits.

Living Habits of Crayfish  

Crayfish are nocturnal animals that live a benthic, crawling lifestyle. They inhabit lakes, rivers, reservoirs, swamps, ponds, and ditches, and are sometimes also found in rice fields. However, they are more abundant in still-water ditches, ponds, and shallow lakes with relatively abundant food. Their habitat is mostly soil-based, with relatively many aquatic plants, tree roots, or stones and other shelters. During the day they often hide in darker corners at the bottom of the water body, beside stones, in grass, or in burrows, and come out at night to feed. Under natural conditions, because of lack of bait and low water transparency, they can also be seen foraging during the day. This shrimp has a relatively strong climbing ability and burrowing ability.  

When the water body is low in oxygen, lacking bait, polluted, or when other biological, physical, and chemical factors change drastically and become unsuitable, they often climb out of the water and enter another water body. For example, when it rains, especially during heavy rain, this shrimp often climbs out of the water body to move around. During the growth period, crayfish basically do not dig burrows. The longest crayfish burrow can reach 100 cm, and the diameter can reach 9.2 cm. Crayfish can use artificial burrows and existing burrows and other shelters in the water body, and their burrowing behavior mostly occurs during the breeding season. Therefore, appropriately adding artificial nests in farming ponds, together with technical measures, can greatly reduce the destructive effect of this shrimp on pond embankments and dikes.

Introduction to the Biological Characteristics of Crayfish  

1. Classification and distribution. In animal taxonomy, crayfish belong to the phylum Arthropoda, class Crustacea, order Decapoda, family Cambaridae, genus Procambarus, and are called red swamp crayfish or red swamp crawfish. Among freshwater crayfish, they are small to medium-sized individuals. They originated in North America and are now widely distributed in more than 20 countries and regions across five continents. The main production area of crayfish in China is the middle and lower reaches of the Yangtze River.  

2. Morphological characteristics. The entire body of a crayfish consists of the cephalothorax and abdomen, with a total of 20 segments. Apart from the telson, which has no appendages, there are 19 pairs of appendages in total, and the body surface has a hard carapace. Sexually mature individuals are dark red or deep red, while immature individuals vary from light brown, yellow-brown, to red-brown, and sometimes blue is also seen. Common individuals are 4 to 16 cm long.  

3. Feeding habits. Crayfish are omnivorous animals, mainly feeding on organic debris. They can feed on various grains, cakes, vegetables, terrestrial forage grasses, aquatic plants in water bodies, attached algae, zooplankton, aquatic insects, small benthic animals, and animal carcasses, and they also like artificial compound feed. At 20 to 25°C, crayfish can consume potamogeton amounting to 3.2% of their own body weight per day and night, bamboo leaf vegetable up to 2.6%, alligator weed up to 1.1%, soybean cake up to 1.2%, artificial compound feed up to 2.8%, fish meat up to 4.9%, and earthworms up to 14.8%. It can be seen that crayfish prefer animal-based substances.  

4. Growth and molting. Like other crustaceans, crayfish must molt the carapace on their body surface to complete their sudden growth. In the Jingmen area, juvenile shrimp that leave the mother in mid-September have an average total length of about 1.0 cm and an average weight of 0.04 g. When raised in net cages until the end of November, the average total length is 5.19 cm, the average weight is 4.50 g, and the maximum total length reaches 7.4 cm, with a weight of 12.24 g. When raised in ponds until July of the following year, the average total length reaches 10.2 cm, and the average weight reaches 34.51 g. In ponds with good conditions, juvenile shrimp that have just left the mother can reach market size after growing for 2 to 3 months.  

5. Reproductive habits. Sex ratio: in crayfish, in both size groups of body length 3.0 to 8.0 cm and 8.1 to 13.5 cm, females outnumber males. In the small size group, females account for 51.5% of the total and males account for 48.5%, with a female-to-male ratio of 1.06:1. In the large size group, females account for 55.9% of the total and males account for 44.1%, with a female-to-male ratio of 1.17:1. The reason females are clearly more numerous than males in the large size group is that males tend to die after mating, and the larger the male individual, the higher the mortality rate. 

Notes on Crayfish Farming  

First, people. In the process of farming crayfish, it can be said that people who farm crayfish "succeed because of Xiao He and fail because of Xiao He"; success lies in human management, and failure also lies in human management. For example, with seedling release, aquatic plant management, and water quality issues, when releasing seedlings one should handle them gently and scatter the shrimp seedlings so that they slowly crawl away on their own. However, because some people release a relatively large number of shrimp seedlings at one time, they directly pour the shrimp seedlings onto the edge of the pond. The shrimp seedlings all pile together, ultimately leading to death from lack of oxygen, and more than half of the seedlings are lost. In the high-temperature season, aquatic plants grow rapidly. If they are not "topped," they will soon spread across the entire pond, resulting in poor water flow, and once the aquatic plants rot they will also cause the water to turn black and smell foul. If not dealt with in time, crayfish will show black bottoms and death.  

Second, climate. In the end, outdoor pond crayfish farming still depends on "living off the sky." Climate determines how fast crayfish grow and affects the incidence of disease in crayfish. Therefore, it can be said that crayfish farming is "planning lies with man, success lies with heaven." For example, the continuous rainy days in June and July this year and the relatively low temperatures caused crayfish to grow slowly, while after August there were more than 40 consecutive days of high-temperature weather, and more than half of the crayfish climbed onto slopes and grass. Some cases that were discovered late and not handled in time resulted in large numbers of deaths.  

Third, pests, diseases, and natural enemies. In March, April, July, and August this year, pest outbreaks were especially severe. In seriously affected ponds, the leaves of all the aquatic plants in the entire pond were eaten bare in two or three days. With crayfish losing the shelter of aquatic plants, they killed each other during molting, resulting in an excessively high mortality rate during molting. Natural enemies such as rats, snakes, and frogs will swallow crayfish seedlings.  

Fourth, feed quality. The quality of the feed determines whether crayfish eat and how much feed they eat. With high-quality feed, crayfish eat vigorously, grow quickly, have fewer disease outbreaks, and have a lower feed conversion ratio, which can reduce feed costs.  

Fifth, market fluctuations. Market fluctuations can be divided into two parts: one is the price of seedlings, and the other is the price of commercial shrimp. In early March and April, the price of shrimp seedlings was between 18 and 22 yuan per jin. After this batch of seedlings is released, they can only be marketed after May Day. Those stocked at a larger size and rushed to market before May Day could still sell for a good price, around 28 yuan per jin. After May Day, the price of commercial shrimp fell all the way, and some people sold at 13 yuan per jin. Buying seedlings at a high price and selling shrimp at a low price means that the profits of crayfish farming will again be eaten away by more than half. 

Although the demand market for crayfish is currently relatively large, its price fluctuations are still relatively large. Therefore, the crayfish farming industry cannot achieve success overnight. Only through continuous learning and continuous development of new farming techniques can higher-quality crayfish be produced.