One article tells you: How to regulate the algae phase in Rudong small-shed shrimp farming?
In small-shed aquaculture, the beneficial algae phase is mainly composed of diatoms and green algae, but it is relatively difficult to cultivate purely beneficial algae species during farming. Generally, the water body in small-shed aquaculture is accompanied by harmful flagellate algae such as dinoflagellates, cryptomonads, and euglenoids. Therefore, regulating the algae phase is a major challenge. Small-shed aquaculture has high water temperature, high density, and small farming space. The direct problem this brings to water quality is: the aquaculture water body has many organic suspended solids, and these organic suspended solids are exactly the indispensable nutrients for flagellate algae.
The growth of algae is regulated according to changes in the nutrients they themselves require, so we must first understand the nutrients required by various algae, and then adjust them appropriately, so that we can regulate the direction of algae phase growth in small-shed water quality.
Required nutrients In aquaculture, we often hear the saying: "To farm shrimp, first cultivate water; to cultivate water, first cultivate the bottom." "To cultivate water, first cultivate the bottom" means: if you want good water quality, you must first cultivate the bottom well. So what is this bottom?
The bottom mainly refers to the source of bottom sediment pollution. When the bottom sediment is good, the water body has few suspended solids, and the water quality is bright and clear. This is what is called good water. In fact, there is another meaning, which is the bottom sediment nutrient reservoir. When the pond bottom nutrient reservoir is rich, algae grow well, and the water quality is bright and clear. The nutrient sources required for algae growth in small sheds come partly from water exchange and artificial fertilization, obtaining nutrients such as nitrogen and phosphorus. The other part comes from feed residues at the pond bottom and organic matter produced by algae phase turnover, which, under the participation and decomposition of bacterial communities, is absorbed and used by algae as nutrients. "To cultivate water, first cultivate the bottom" refers to cultivating the bottom, which means less bottom sediment pollution and a rich pond bottom nutrient reservoir. Therefore, the bottom sediment nutrient reservoir is related to the direction of the water body's algae phase.
Nutrients required for the growth of various algae:
(1) Growth nutrients for green algae: nitrogen-to-phosphorus ratio, with phosphorus more abundant than nitrogen
The freshwater used in small-shed aquaculture is all added from river channels used for domestic water. The river channels contain domestic sewage, and domestic water has high phosphorus content. In this way, when river water directly enters small sheds, it is very easy to cultivate green algae water bodies. This solves a puzzle: "When small sheds directly exchange river water, why does the water become more fertile and greener the more it is exchanged?" It is because the nitrogen-to-phosphorus ratio in river water leans toward phosphorus, so it just suits the growth nutrients of green algae, and the more water is exchanged, the greener it becomes!
(2) Growth nutrients for diatoms: nitrogen-to-phosphorus ratio, with nitrogen more abundant than phosphorus
The underground well water used in small-shed aquaculture has, in some well water, a relatively high ammonia nitrogen content. When small sheds are filled with water and shrimp are stocked, they mainly rely on continuously adding underground well water. Farmers who have raised shrimp in small sheds will observe a common phenomenon: in the early stage after stocking, the water is all somewhat pale yellow and tea-brown, and when checked under a microscope, the water body is mainly diatoms.
At this time, some farmers may not understand why, when farming reaches the middle stage, the water in some sheds turns oily green, and when large amounts of well water are exchanged, the water instead becomes greener and greener. In fact, there is another factor here: when farming reaches the middle stage, the nutrient supplementation brought by large amounts of feed causes the nitrogen-to-phosphorus ratio of the nutrients at the pond bottom to shift, and the total nutrients in the water body turn toward phosphorus, so green algae begin to gradually appear. Also, because diatoms have a short life cycle and their growth density is not as high as that of green algae, diatoms cannot compete with green algae, and green algae grow in large amounts in the water body. At this time, even continuously exchanging nitrogen fertilizer in well water is of no avail, because green algae have become the dominant population, and adding nitrogen fertilizer can no longer change the current growth trend of green algae. Farmer friends must understand a principle: green algae prefer phosphorus-leaning fertilizer, but that does not mean they do not absorb nitrogen fertilizer!
Therefore, after everyone understands the growth form of diatoms, do not make this mistake: "In a water body dominated by green algae, simply adding nitrogen fertilizer can change the growth trend of green algae." In terms of competitiveness, even when fertilizer efficiency is sufficient, as long as there is slightly suitable fertilizer efficiency for green algae growth, green algae can grow rapidly. Because diatoms have a short growth cycle and weak ability to suppress other algae phases, they will ultimately still evolve into a green algae water body. So a phenomenon is often seen: the small-shed water is oily green, and amino acids are continuously splashed to change the fertilizer ratio, but the result is that the more fertile the water, the greener it becomes.
Regarding how diatoms can suppress green algae in small-shed water bodies, the editor has a method. In a water body dominated by green algae, where the water is too fertile and too green, and you want to convert it into diatom water: first, exchange water, disinfect, or apply Bacillus bacteria to suppress a large portion of the vigorously growing green algae. Based on the feeling that the green algae are aging or declining, and a small amount of diatoms appears, at this time you can apply "sodium humate." The purpose is to further suppress green algae by using the light-shading effect of sodium humate. After the water body becomes darker, green algae growth slows down, and diatoms begin to grow in large amounts. After diatoms gain a certain advantage, this is still not the most stable period. Subsequently, nitrogen fertilizer and nitrogen fertilizer containing silicate must be supplemented regularly in small amounts and multiple times for diatoms to absorb, so as to achieve the goal of dominating the water body's algae phase. This is the method for suppressing green algae. Everyone can try it.
(3) Blue-green algae are prone to growing in water bodies with an imbalanced nitrogen-to-phosphorus ratio
Because of the special structure of small-shed aquaculture -- high water temperature, high density, and fertilizer efficiency that is difficult to control -- blue-green algae are very likely to grow. The harm of blue-green algae to small-shed aquaculture is very great. It can be said this way: as long as large blue-green algae appear in a small shed, shrimp are very likely to develop a series of aquaculture diseases such as green liver, liver atrophy, and liver poisoning, followed by a low survival rate of seedlings and no aquaculture yield. Their harm is no less than viral diseases such as red body and white spot. Therefore, the prevention and control of blue-green algae is also crucial!
Blue-green algae obtain fertilizer efficiency for growth. Many farmer friends believe that water bodies with more phosphorus are prone to growing blue-green algae. In fact, regarding this issue, in the book "Looking at Water to Raise Fish" written by teacher Jin Hui of Huazhong Agricultural University, it is clearly stated that blue-green algae are prone to outbreaks in water bodies with an imbalanced nitrogen-to-phosphorus ratio. Interested farmer friends can learn about it. Since water bodies with an imbalanced nitrogen-to-phosphorus ratio are prone to growing blue-green algae, how should we prevent and control blue-green algae?
When regularly supplementing fertilizer during aquaculture, use less single fertilizer and more complete fertilizer to cultivate algae. First, the fertilizer efficiency is not single, the nitrogen-to-phosphorus ratio does not become imbalanced, and blue-green algae are difficult to grow. Second, complete fertilizer has comprehensive nutrition, algae species grow comprehensively, and it can effectively inhibit the growth of blue-green algae.
(4) Harmful flagellate algae such as dinoflagellates, cryptomonads, and euglenoids
They have no special requirements for fertilizer efficiency; they can absorb both nitrogen fertilizer and phosphorus fertilizer. They prefer suspended organic matter and nitrogen fertilizer.
Because of the special structure of small-shed aquaculture, the two major polluting forces of algae turnover and feed residues far exceed the self-purification capacity of algae. The small-shed water body becomes eutrophic. Because organic suspended solids have large particles and belong to macromolecular organic matter, they cannot be directly absorbed by algae. Instead, they must be decomposed into small-molecule organic matter with the participation of bacterial communities before algae can absorb and use them.