Macrobrachium rosenbergii has been introduced into China since 1976 in Japan. After many years of promotion and breeding, it has now become the main breeding object for economic shrimp. The ecological habit of the shrimp is different from that of ordinary shrimps. The larval stage needs to be spent in seawater. The production of seedlings must be carried out by production units with specialized production facilities and technologies. It is an important part of the production of Macrobrachium rosenbergii to purchase high quality Macrobrachium prawn seedlings (referred to as shrimp seedlings hereinafter) and to increase the survival rate of shrimp slaughter. From 1990 to 1997, we transported a total of 37.40 million desalinated shrimps, of which 22.85 million were purchased and shipped 14.55 million. The survival rate was 75 to 95%, and the purchases and sales are spread throughout the country's major shrimp farming areas.
1 buy shrimp
The larvae hatched from fertilized eggs undergo metamorphosis into shrimp seedlings after eleven times of molting, which takes 25 to 30 days. Shrimp production units are subject to production conditions such as broodstock, water quality and other technical constraints, the shrimp produced by the larger differences, when choosing to buy good quality shrimp must be transported. Good health of shrimp: normal body, neat specifications, transparent body, strong activity; poor quality shrimp: uneven size, weak ability to climb, the naked eye can see obvious deformities. At the same time, we must pay attention to the desalination of shrimp seedlings, Macrobrachium rosenbergii metamorphosis as postlarvae, the need for timely desalination, ecological conditions will change drastically, and some poor health of shrimp, due to poor adaptability, over time Over time, they will die one after another, or be eaten by physically robust shrimp. Therefore, they should purchase the shrimp thoroughly and dilute the shrimps that are a bit longer. Generally prepared to package shipped shrimp, desalination time can not be less than 24 hours. Therefore, before the purchase of seedlings, we should also understand the desalination situation of shrimps at the production site. If there is no instrument, we can taste the water in the shrimp seedlings pool with experience, and feel no saltiness, indicating that the shrimp seedlings in the pool have been basically reduced. complete.
The date of purchase (or stocking) of shrimp seedlings is also very important for shrimp farmers. In addition to routine breeding requirements, Qingchi disinfection, water injection, preparation of shrimp ponds, but also based on the location of shrimp breeding sites, climate change, determine the appropriate date for the purchase of shrimp. If it is too early, the outside temperature is not stable, and in case of cold wave, the water temperature drops below 18°C, which threatens the growth of shrimp seedlings. It will bring about a low survival rate of the shrimp seedlings in the lower pool; if it is too late, it will affect the feeding time, resulting in a growing period too Short, shrimp does not reach the market specifications, and the group's output is also low. In areas suitable for the development of Macrobrachium praecox, the pond water temperature is stable at more than 20 °C, and the effect of releasing the seedlings is good. In recent years, the earliest time for the direct release of shrimp ponds in Wuhan was May 11th and the latest was July 10th. The variation of adult shrimp production was 75-150kg/mu, and the body weight was above 12g, which met the market requirements. . Appropriate restocking time is from late May to early June, the growth period is about 135 days, and the output will generally reach 100 kg/mu.
2 Transportation Methods and Effects
The Macrobrachium rosenbergii seedlings are mostly concentrated production. In order to get the shrimp seedlings needed in a timely manner in the shrimp farming area, from April to June every year, we have to carry out a lot of shrimp and seedling transportation. Tools include plastic bags, canvas baskets, iron buckets, etc. The shipping density depends on the size of the shrimp, the water temperature, and the length of the transportation route. At present, the use of oxygen-sealing plastic bags is more convenient and the effect is very good. The bag contains about 6 kg of water (20 kg of water). After the shrimp is filled with enough oxygen, it is placed in a carton and wrapped with external packaging tape. The total weight is 7-8 kg and you can get on the train (car, train ) Or aircraft transport. Because shrimps are young and their asphyxiation point is 0.96mg/L (dissolved oxygen in water), which is obviously higher than that of the main cultured fish, and they have the habit of mutual-residual food, so the shipping density of shrimps is much higher than that of fish seedlings. low. Over the years, in a large number of long-distance transportation, the water temperature is 22 ~ 26 °C, the general plastic bag seedlings 3000 ~ 5000, the survival rate of about 90%, shrimp swimming after swimming normal.
The length of transportation time directly affects the number of seedlings per bag. The shipment time is about 10 hours, the density is 4500 to 5000/bag; the shipment time is 20 to 30 hours, and the density is 2500 to 3000/bag. In the case of similar density, the survival rate of shrimp seedlings was inversely related to the shipping time. In production, our largest transportation volume is 450 boxes (bags), 2.25 million, and the longest transportation time is 32 hours. The highest survival rate is 98%. All this shows that this method of transportation is feasible and fully meets the transportation technology level of the main farmed fish.
3 Precautions
In order to ensure the safety of transportation and improve the survival rate of transportation, various preparations for transportation equipment, oxygenation, packaging equipment, and freight plans for trains and airplanes must be made before transportation, and the time of the journey should be accurately calculated and the appropriate loading density should be selected. If necessary, a gradient test of the density of the bagged shrimp should be done, especially when transporting large quantities of goods over long distances.
The water for transport is best taken from the larval rearing tank or holding pond. The water temperature should be the same as the nursery pond. In order to avoid the killing of the shrimp seedlings, a steamed egg or duck egg that has been filtered through a 40-mesh plastic mesh cloth should be fed prior to packaging and transportation. The shrimp should be fully fed, and then the bait in the larvae box should be completely removed. Dirt, to ensure the accurate count of shrimp seedlings and the cleanliness of the transport of water quality.
After the shrimps are transported to their destinations, they should be stocked with plastic bags for 15-30 minutes on the surface of the shrimp ponds. After the water temperatures inside and outside the bags are basically the same, they are opened in the windward bank to increase the survival rate of the shrimp seedlings.
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