Feeding algae can keep most of the original nutrition of shrimp in the process of culture. Phytoplankton (hereinafter referred to as microalgae, which is the main component of water color) is the direct or indirect bait for fish, shrimp, crab, shellfish and so on. Microalgae can degrade toxic substances such as ammonia nitrogen in aquaculture water, maintain microecological balance and promote fish, shrimp, crab and shellfish to achieve the purpose of ecological disease prevention. Therefore, microalgae can play a very important role if aquaculture is to be ecological, efficient and pollution-free. According to different fertilization varieties, inoculation methods and breeding needs, microalgae culture methods are divided into the following categories. 1. Cultivating microalgae with different fertilizers 1. Types of fertilizers At present, in aquaculture, fertilizers are commonly used to cultivate microalgae, including organic fertilizers, inorganic fertilizers and newly developed compound fertilizers. (1) Organic fertilizers are manure, green manure and mixed compost. Organic fertilizer has a long-lasting effect, but it consumes a lot of organic oxygen and has a high content of conditionally pathogenic microorganisms, so it must be fermented and decomposed before use. In order to propagate microalgae, it is generally necessary to apply enough base fertilizer, and then topdressing according to water quality, growth activities of cultured organisms and weather conditions. (1) manure: fully ferment and decompose animal manure, and according to the needs of breeding, pile a certain amount of fermented manure in the four corners of the pond 15 days before seedling raising or stocking, or spill the fermented manure with its juice after filtering the residue. (2) Green manure: according to the needs of breeding, a certain amount of new, fresh and tender grass which is non-toxic, non-irritating and perishable is piled up in the four corners of the pond 15 days before raising seedlings or stocking animal seeds, all of which are soaked in water and compacted with soil. ③ Mixed composting: In the fermentor, young grass and animal manure are alternately stacked layer by layer, and lime with composting amount of 65,438+00% ~ 65,438+05% is sprinkled between layers and sealed with soil. Its fermented juice is used as base fertilizer or topdressing. (2) Inorganic fertilizers include nitrogen fertilizer, phosphorus fertilizer and calcium fertilizer. Nitrogen fertilizer is ammonium sulfate, ammonium chloride, urea, etc. ; Phosphate fertilizer is calcium superphosphate, sodium dihydrogen phosphate, etc. The calcium fertilizer is quicklime, etc. There are also compound fertilizers containing trace elements such as iron, manganese, zinc, copper and cobalt. Silicon fertilizer (sodium silicate, etc. ) and iron fertilizer (iron citrate, etc. ) is often used in the closed or semi-closed culture of marine microalgae. (3) There are many varieties of new compound fertilizers, such as "Feishuisu" and "Feishuiwang". 2. Use of fertilizers In aquaculture, fertilizers are sometimes used alone, but most of the time they are mixed. It is common to use organic fertilizer and inorganic fertilizer together. Organic fertilizer is mostly used as base fertilizer, and inorganic fertilizer is mostly used as topdressing; Organic fertilizer is commonly used in ponds, and inorganic fertilizer is commonly used to cultivate microalgae during the breeding period of aquatic animals. Secondly, microalgae 1 were cultured by different inoculation methods. Culture microalgae directly in natural water. At present, in most ponds and some fish, shrimp, crab, shellfish and other breeding processes, microalgae are directly cultivated by using natural fresh water or seawater. There are various microalgae such as diatoms and green algae in the filtered seawater or fresh water: there are various zooplankton such as rotifers, copepods and hornworts; There are many kinds of small benthic organisms. It is a common method to cultivate basic bait by cultivating microalgae in natural water to promote the growth and reproduction of basic bait such as zooplankton and benthos. The natural propagation time of microalgae depends on the production needs. The standard is that after the breeding of fish, shrimp, crab, shellfish and other animals begins, or after their larvae are put into the pond, the larvae raised or put into the pond should have a suitable growth and development environment and sufficient biological bait for eating. Culture shrimp, crab, fish and shellfish in ponds. Generally, fertilization is started to propagate microalgae half a month before stocking fry, and the amount and times of fertilization are adjusted according to water color and transparency, and the water color is generally adjusted to yellow or yellowish brown with transparency of 30-50 cm. The species composition and density of microalgae are different with different water color and transparency. Different cultured varieties and different development stages of the same variety have different requirements for water color and transparency. Processing shrimp, crab, fish, shellfish, etc. We should always keep the water quality fat, fresh, tender and cold so that aquatic animals such as shrimp, crab, fish and shellfish can survive in a good ecological environment. 2. Adopt closed or semi-closed method to directionally cultivate microalgae. In recent years, crab culture in earthen ponds has set off an upsurge, and earthen ponds for mariculture of fish, shellfish and shrimp have also begun to rise. The key to cultivating microalgae in soil ponds is to promote the growth and reproduction of zooplankton, benthos and other basic food organisms that feed on microalgae. In order to make the microalgae in the pond high-quality and stable, the best culture method at present is to adopt closed or semi-closed three-stage culture of microalgae. The first stage of culture is carried out in a microalgae preservation room, most microalgae are cultured in 250-5000 ml triangular bottles, the second stage is carried out in plastic barrels and plastic bags, and the third stage is carried out in a soil pool. Commonly used microalgae include Phaeodactylum tricornutum, Chlorella, Platymonas, Microcystis, Skeletonema, etc. 3. The source and species characteristics of pure algae liquid (1) produced by natural seawater screening and culture. When the temperature of natural seawater is lower than 65438 02℃, there are fewer protozoa in natural seawater ponds, and the purity of microalgae is high. Therefore, algae liquid with relatively single species can be selected for screening and culture. The microalgae screened in this way have strong adaptability to the local water environment, anti-pollution and easy to master the culture technology. This culture method is often used to cultivate marine microalgae in the process of shrimp and crab culture in Jiangsu coastal areas. (2) Theoretical basis and methods for screening and culturing high-yield pure algae solution According to the living habits of the cultured microalgae, we tried to form a water environment suitable for the growth and reproduction of marine microalgae, rapidly cultivate microalgae and form a good complex ecological balance system. As a dominant species, marine microalgae inhibit the growth and reproduction of other harmful microorganisms through nutritional competition and spatial competition. When the cultured algae solution reaches a certain concentration, some microorganisms will secrete a certain concentration of antibiotics or bacteriocin, killing some harmful microorganisms such as protozoa. The antagonistic effect of dominant algae is used to inhibit the growth and reproduction of other microalgae in dominant microalgae. By stopping gas, other microalgae, inhibited microalgae and animal carcasses at the bottom of the sedimentation tank are cleaned. Repeated inoculation, expanded culture and cleaning the bottom of the pond for 2-3 times can screen out high-yield pure microalgae solution. According to the conventional microalgae culture method, the productive pure algae solution was inoculated, fertilized and amplified. Thirdly, according to the needs of cultured species, different cultured species and different development stages have different requirements on the species and quantity of microalgae. We should cultivate specific microalgae varieties or microalgae in a certain way according to the different needs of fish, shrimp, crab and shellfish. For example, in the early stage of the cultivation of granola, flat algae, Chaetoceros and Chlorella were used, and Chlorella was used as supplementary feed. The larvae of Stichopus japonicus were fed with dinoflagellate such as Dunaliella salina, Chaetoceros, Chrysophyta tricornutum and Chrysophyta. Chlorella contains more essential amino acids and unsaturated fatty acids than other microalgae, and is often used as intensive feed for rotifers, copepods and cladocera. In the high-yield and efficient cultivation of omnivorous fish such as crucian carp and carp, before the fry enter the pond, the fermented and decomposed livestock manure is used as the base fertilizer for microalgae cultivation. The reason is that these fish are omnivorous, and the fermented livestock manure can not only breed microalgae, but also be eaten by fish as supplementary bait. The larger the specifications, the greater the demand for microalgae. We should take corresponding measures to meet the demand of bighead carp as much as possible.