The factory artificial seedling raising of river crab is one of the major production projects in many seawater breeding rooms in the coastal area of ​​our province. It has produced remarkable economic benefits. In this year's report, the author of the Huangpi Xingsheng nursery field guided the crab breeding technology, more than 800 cubic meters of water emerged nearly 400kg, the highest yield of 0.7kg/m3. A few of the techniques taken are briefly described below. 1 The rotifer is used as the main bait for pod-like larvae. The traditional method of pod-like construction is based on feeding, fertilizing and inoculating unicellular algae in the nursery, and is mainly fed with spirulina powder, egg yolk and yeast. The authors fed the above-mentioned baits on the evening of the larvae hatching in the cocooning period this year, and began to feed live rotifers or refrigerated rotifers with better quality in the daytime during the day and the results were good. The main features are as follows: 1.1 When feeding the substitute meal such as spirulina powder during the whole period of the metamorphosis, the time of the cocoon stage is about 3 to 4 days or more, and it is shortened to 2.5 when it is mainly rotifer. ~3.5d. 1.2 Metamorphosis in the completion phase is dominated by substitute bait, because the metamorphosis time is longer and the metamorphosis is obviously different. The cumulative difference in each period is greater, and it is often 2 to 3 days for all metamorphosis of the larvae to be large larvae. Due to the severe fratricide at this stage, the yield of crab seedlings has been greatly reduced, while rotifers have mainly solved this problem. 1.3 The juvenile zoster-based brood larvae are not only large individuals, but also have good vigor and strong disease resistance. For example, there was a serious filamentous bacterial disease in the nursery pool this year. However, after careful treatment and cultivation, it was miraculously metamorphosis to the burrow-shaped larvae, the metamorphosis rate was as high as 90%, and the single water body emerged to more than 500 g. 2 Microscopic quantification of residual bait amount in nursery ponds In the process of crab breeding, proper feeding of bait is one of the key technologies. Usually, it is based on the larval stage, the number of larvae, the feeding conditions of larvae, the type of bait, and the bait situation. The amount of residual bait is the main basis for judging whether the amount of bait is appropriate or not. Live baits, dead baits, feces and larvae are mixed together in actual breeding waters, and it is very difficult to observe directly with the naked eye. The method I used was to use a porcelain bowl to draw water from the seedling pool. After a few minutes of stillness, a dropper was used to collect sediment from the bottom of the bowl. The observation was performed under a low magnification microscope to clearly distinguish the residual bait situation and combine the previous shot. The bait time and quantity can accurately determine whether the feeding amount is appropriate or not, and provide an important basis for timely adjustment of the type and quantity of feeding. (3) The waterlogging of the big-eyed larvae under the higher density conditions of the braided v larvae has the habit of killing the pod-shaped larvae. In the metamorphosis of the larvae of the braid-shaped larvae, the large larval larvae, if the larval density is too large, the bait is insufficient. , it is extremely prone to killing, which greatly reduces the yield of crab seedlings. The author of this year, for the pool with a higher density in the braided stage v larvae, change the amount of water before the metamorphosis, and use the water flow method to change the water in the metamorphosis process. That is, one end of the nursery pond is siphoned and drained with a cage, and the other end is filled with water to keep the seedling pond water level basically stable. Each inflow of water is 1/3 to 1/2 of the water holding capacity of the nursery pond, avoiding the normal water level change. The decrease in the larval density increases the size of the larval larvae. At the same time, the amount of diets such as large Artemias and freshwater turtles has increased. Therefore, this year's cockroach v-period larval body metamorphosis stage lighter, crab production significantly increased. 4 Fresh rotifer ice preservation In the production of crab breeding, the time and number of rotifers purchased is often unstable. Sometimes the number of rotifers acquired is large, and the feed can not be completed within a short time. If no measures are taken, the remaining rotifers will die after several hours, which not only causes great waste, but also seriously affects the normal feeding of crab breeding seedlings. The method I used was to pour the remaining rotifers into a foam plastic box. The number of rotifers in each box was about 1/2 to 2/3 of the volume, and about two to three kilograms of ice cubes were placed in the tank. Store in a cool place. After 24 hours, most rotifers still survived, which solved the problem of preservation and continuous supply of rotifers.
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