Water quality regulation technology of crab

At present, "raising crabs in clear water" is an unchanging truth in the minds of most farmers. It seems that the clearer the water in the crab ponds, the thinner the better. Once the water in the crab ponds becomes fat, they are busy changing water in case of accidents. As everyone knows, it is very beneficial for crab culture to maintain a certain degree of fatness in the water of crab ponds. According to the preliminary investigation, the survival rate, specification and yield of crabs raised in medium-fat ponds are higher than those in ordinary clear-water ponds, especially the incidence of trembling disease prevalent in recent two years is also much lower than that in other ponds. The reason is that moderate fertilizer and water can make the pond water have enough dissolved oxygen, and oxygen is the decisive factor for the growth and development of river crab. The main source of oxygen in crab ponds is the photosynthesis of aquatic plants, while in ponds with more verticillium, the intensity of photosynthesis is much weaker than that of green aquatic plants, and the oxygen released is much less. Then the main source of oxygen in this pond depends on the photosynthesis of phytoplankton. Ponds with moderate fertile water have a large amount of phytoplankton and a lot of oxygen produced by photosynthesis. in sunny days with high water temperature, the dissolved oxygen in the pond water can often reach a state of saturation. When the oxygen is insufficient, the bottom gas-disrelenting bacteria decompose to produce a large number of organic acids and toxic substances, reducing the pH value of the pond water. If the river crab lives in this water for a long time, it will lose appetite, molt abnormality, easy to form lazy crab, and also easy to get sick; when oxygen is sufficient, the river crab has exuberant appetite, agile activities, increased molting times, high bait utilization rate, strong disease resistance and rapid growth.

The fat and thin of the water is often judged by the transparency of the pool water.

Clear water refers to light water color, less phytoplankton in water, transparency is generally above 35cm, fat water refers to strong water color, more phytoplankton in water, low transparency, generally below 15cm, moderate fat water is between the two, water color is fat and tender.

So how to adjust the fat and thin of crab pond water?

At present, many crab farmers generally use the method of intake and drainage to adjust the fertility of pond water, the author thinks that this is not the best way. Because excessive water intake and drainage is a waste of financial resources, the second is the loss of effective ingredients in the water, bringing in harmful substances, the third is the uncertain water level, the frequent changes in river crab caves, and some river crabs do not eat above the surface of the water, do not molt, and form lazy crabs. fourth, stimulate the river crab to form precocious puberty. Generally speaking, the pond with thin water color can be regulated by fertilization. 200 kg of fermented manure is applied per mu 15 days before planting. If the water quality is still thin, urea can be used once per mu. If there is more silt at the bottom of the pond, the fertility in the water is sufficient, you can put in some silver carp, bighead carp or green shrimp fry, or plant some aquatic plants, such as bitter grass.