When the seedlings are released one year later, the choice of seedlings determines the quality of the cultivation. This article describes the methods and techniques for selecting some fish, crabs, and shrimps, and helps the farmers to purchase high-quality seed for the harvest of the whole year. basis.

Identification of fry and fingerling quality

Identification of fry quality: fry due to the quality of fish eggs and environmental conditions in the incubation process, physical strength is strong and weak, which has a great impact on the growth and survival of fry. Production can be based on the color of the fish, swimming conditions and the ability to struggle to distinguish the pros and cons (discrimination method in Table 1).

Summer flower species quality identification: The quality of summer fish species can be based on the size of the outlet pond, body color, fish activity and physical strength to determine (see Table 2).

Number of fry methods: In order to count the number of fry production, or to calculate the survival rate of fry, the number of ponds and the number of sales, the total number of fry must be correctly calculated. There are currently four methods of fry production in production:

(1) The division method (or the opening method, the division method). Firstly, the fish seedlings are densely packed at one end of the bundle box. The bundle box is divided into several compartments with a small bamboo basket, and the fish fry is picked out with a fish dish and placed into several aliquots in order. Extract 1 part from it, and then divide it into several equal parts according to the above operation. According to this method, continue to divide until each fry is less, so that it is convenient to count one by one. Then take a small portion and use a small clam shell (or other container) to calculate the number of mandarin fish fry. Based on the calculated number of this part, calculate the number of fry.

(2) cup method (also known as sampling method, point water method, barrel keg method, cup method). This method is a commonly used method. When it is used specifically, it has the following two forms.

Direct sampling method: This method can be used when the total number of fry is small. The fish fry is densely packed at one end, and then the fish is directly mashed in a container of known capacity (previously used for fry storage and counting test) (a variety of sizes can be configured), the total number of cups of the container is recorded, and then calculated according to the pre-calculated The total number of manuscripts is calculated from the number of holdings of a single container.

When using the above method, it should be noted that the water content in the cup should be appropriate and uniform, otherwise the error is large. Second, pay attention to the size of the fry, otherwise it will produce errors. Different fish fry have individual differences even at the same age and should be noted when counting.

The saucer set saucer method: This method can be used when there are a large number of fry. For specific operation, first use a large basin (or album) to count, then use a known small container to measure the capacity of the large basin, and then seek total.

(3) volume method (also known as measuring cylinder method). Before the calculation, the number of fry per milliliter (or every 10 milliliters or 100 milliliters) was measured, and then the total number of milliliters (also in the case of dense fry) was measured, and the total number of fry was calculated. The accuracy of this method is worse than that of the sampling method because of the large influence of water content.

(4) Direct counting of fish gills. This method is used in the Hunan area. Before the count, it first determines how much water a fish can hold, and how many fish dishes can be filled with a bucket. Then the fish is put into the fry with a known capacity and slowly stirs. The fish fry were evenly distributed, and a number of fish dishes were counted to find the average number of fish dishes. Then the number of whole fish fry was calculated.

Identification of fish quality: High-quality fish species must meet the following conditions: 1 the same species of fish of the same species with the same specifications; 2 strong physique, muscular muscles on the back, fleshy fleshy triceps, 3 body surface smooth, disease-free, Scales, fins intact; 4 bright and shiny body color; 5 lively swimming, strong retrogression, in the dense, the head down to the tail, fins continue to fan; 6 with the body length and body weight ratio to determine the quality is good Bad. The specific approach is: Weigh 500 grams of fish species with similar specifications to calculate the number of tails, and then compare the quality table with the specifications of quality fish species. The weight of each kilogram of fish is said to be equal to or less than the standard tail number for high-quality species; otherwise, it is for inferior species. .

Identification of crab species

Identification of species of crabs: There are more than 500 species of crabs in China, but only a few are suitable for freshwater aquaculture. Now it is the Chinese mitten crab which is popularized for breeding. It grows faster and has bigger individuals. It has high nutritional value and good breeding efficiency. The body color of Chinese mitten crabs is gray-gray, abdomen is silver-white, body shape is irregular oval, four forehead teeth are sharper, and the fourth tooth on the anterior edge is obvious. Please read the above characteristics when you purchase.

Physical quality is good or bad identification: good quality crab seedlings have strong support and activity. When the crabs are piled together, they are in a granular structure. If they are put into the seedling box, the seedlings are fluffy and the individuals keep certain gaps. When the crabs are picked up by hand and then released, the crabs can quickly climb away. Or the abdomen can be rapidly turned over to the sky, or buried with water droplets, they can quickly get rid of water viscosity and escape from the water, both supportive, active ability and anti-viscosity of high-quality crab.

Identification of maturity level: When purchasing crab species, mature young crabs should be selected; precocious mature crabs have a very low survival rate and are easy to die, so they cannot be purchased. Precocious female crabs are covered with navels. There are many side hairs on the four sides of the navel, and the color is dark. The male crabs are thick, long, dense and have long external genitalia. The juvenile crab body is thin, body color is blue-gray, female crab abdomen is a pagoda-shaped, behind the reproductive part of the gray rather than purple; male step foot bristly sparse, external genitalia thick.

Evenness and specification identification: good crab species are uniform, tender and old, and specifications meet quality standards. Insufficient or poor quality crabs, individuals are small. Before the official purchase of seedlings, a certain number of crab species should be randomly selected from the nursery ponds. Weigh the crabs on an ordinary balance or torque balance with a quantity of 0.1g to 0.01g, and count only the number of crabs. Calculate the number of crabs per gram. The number or the average weight of each crab, and finally determine whether the crab's specifications meet the quality indicators.

Identification of shrimp quality

Observe the vitality of shrimp: to determine whether it is healthy shrimp, should at least meet three conditions: First, shrimp without specific pathogens; Second, shrimp immunity is strong, able to resist the invasion of foreign bacterial viruses; third is able to Survival in harsh environments.

To determine how viable the surviving ability of shrimp is in a hostile environment, the approach is simple: use the "temperature difference method" to test, that is, when selecting seedlings, use container A to take a certain number of shrimp seedlings and a small amount of water, and then use containers. Take a small amount of this pool water and put a certain amount of ice, so that the water temperature dropped to about 3 °C, put A shrimp in B for 10 seconds, and then put back A, observe the recovery of shrimp. After such a severe test of environmental changes, if the survival rate is high, it indicates that the viability of the shrimp is very good. On the contrary, the vigor is poor (this method can only judge the vigor of the shrimp seedlings, and cannot judge whether it has a virus).

Observe the transparency of the shrimp body: If the shrimp seedlings have good transparency, there is no phenomenon of muscle turbidity, and there is no attachment on the body surface, the shrimp seedlings are relatively healthy, otherwise, they should be observed further.

Observe if there are any remaining shells on the head of the shrimp. If there is any residue, it indicates that the shrimp has a weak constitution. If not, it indicates that the shrimp has a good constitution.

Observe the hepatopancreas and intestines of the shrimp: if it is full, the color is darker and it is about the same as the color of the food (red for red shrimp, black for black shrimp), and more than 1/2 full in the intestine. It indicated that the feeding condition of the shrimp seedlings was very good. If the color of the hepatopancreas is shallow and the intestinal tract is empty, it means that the feeding condition is poor and the shrimp seedlings may have problems. It should be noted that when the shrimp has just finished its shell, there is no food in the intestine, but the hepatopancreas is still full, which is normal.

To see the “fat lean” of the shrimp seedlings, that is, the ratio of muscular bowel in professional jargon: the more “fat” the shrimp seedlings, the better the nutrition of the shrimp seedlings, and vice versa. It should be noted that the gut of the shrimp muscle is often related to the traits of the shrimp and cannot be generalized.

When the shrimp seedlings are finished and before putting the seedlings into the pond, observe a cup with a transparent glass. If a lot of oyster shells are found, it indicates that the shrimps have poor anti-stress ability, otherwise the instructions are stronger.

When buying shrimp seedlings at the shrimp farm, the farmer will be used to picking up dense shrimps from the bottom of the nursery ponds in a small hand-sweeping net and then picking them in white or transparent containers. At this point, we see shrimps with uniform and uniform specifications. However, when the final count was packaged, the size of the shrimp was found to be inconsistent, and the proportion of the small size was still quite large. Experienced shrimp peasants will avoid this problem by using a container to remove some of the shrimp and water from the sample when observing the shrimp seedlings, and then carefully remove the shrimp larvae from the sample. Repeated several times, you can find out what proportion of the small-scale shrimp.

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