Common algae in freshwater aquaculture are roughly divided into: cyanobacteria, bare algae, golden algae, dinoflagellate, cryptoalgae, diatom, green algae, yellow algae, etc. Cyanobacteria, microcystis (more toxins produced after death, inhibiting the growth of other algae); spirulina (indigestible), fibrillary algae (not easy to digest), flat crack algae, collared algae, fishy algae, microcystic algae (easy to produce blooms). Some of them are beneficial algae, and some are harmful algae.
Cyanobacteria
Habits of cyanobacteria
The occurrence of cyanobacteria depends largely on temperature. Cyanobacteria are sensitive to temperature when they reproduce, and when the water temperature is below 17 ° C, they do not occur in large quantities or do not pose a hazard to fish. When the water temperature rises to 28 ° C, due to the inhibition of the growth of other algae, and at the same time a large number of fish ingestion (high temperature fish feeding metabolism is enhanced), cyanobacteria are prone to form a dominant population and a large number of outbreaks.
1.ph values:
Algae prefer alkaline water bodies, high pH (ph8.0 ~ ph9.5) will promote the occurrence of cyanobacteria, so the use of lime water sprinkling alone should be avoided to improve water quality.
2. Nitrogen and phosphorus ratio:
Cyanobacteria can use both nitrogen in water and have a higher ability to use phosphorus, and low nitrogen-to-phosphorus ratios or water bodies with higher phosphorus-rich enrichment can lead to the occurrence of cyanobacteria in large quantities. Appropriately increasing the nitrogen-phosphorus ratio can inhibit the growth of cyanobacteria to a certain extent.
3. Ecological relationship:
Cyanobacteria, along with other algae, form producers of pond ecosystems, providing more than 89% of dissolved oxygen. Therefore, in addition to participating in the material cycle of the ecosystem, these producers also affect the survival of fish.
4. Causes of cyanobacterial blooms:
The key factors at different stages are different, and the formation of cyanobacterial blooms can generally be divided into four stages: dormancy, recovery, biomass increase, and floating. After floating, cyanobacterial blooms are formed, and then the water transfer begins to appear.
5. Hazards of cyanobacteria:
Cyanobacteria can change the expansion pressure, in the case of high temperature and strong light weather conditions, gather on the surface of the water body, absorb most of the sunlight, in their own large numbers while inhibiting the growth of other algae. The large number of cyanobacteria continues to secrete toxic metabolic substances to the water body, which affects the population succession and reproductive cycle of plankton, and can also cause a large number of deaths of some zooplankton.
Hazards of cyanobacteria in large numbers
Cyanobacterial particles are difficult to digest by fish and soon become an absolute dominant population after large numbers. This overbreeding, formed through spatial competition for species, will inevitably lead to intraspecific struggles, and the result of this infighting will lead to the death of a large number of cyanobacteria. The mass death of cyanobacteria has led to a sharp decline in the producer of water bodies, resulting in a serious shortage of dissolved oxygen supply in water bodies. At the same time, the death and decomposition of cyanobacteria will also consume a large amount of dissolved oxygen, releasing a large number of toxic substances such as hydroxylamine and hydrogen sulfide. Under severe hypoxia and toxic substance storage conditions, fish, shrimp and crabs will die in large quantities, or even all of them.
Methods of controlling cyanobacteria
1. Thoroughly clear the pond and disinfect it, and fill it with fresh water without cyanobacteria:
Because cyanobacteria are more competitive than other algae, control measures focus on prevention and prevention over treatment. Thorough pond disinfection can effectively kill cyanobacteria, reduce the cardinality, and reduce the possibility of large-scale occurrence. At the same time, care should be taken to avoid bringing cyanobacteria with water, which also has positive significance for the control of cyanobacteria.
2. Change the fresh water regularly:
For ponds containing more cyanobacteria, it is often necessary to change the fresh water in large quantities, which can dilute the concentration of cyanobacteria. It also dilutes the concentration of poisons secreted by cyanobacteria, promotes the growth of other algae and maintains the dynamic balance of the entire ecosystem. When cyanobacteria occur in large quantities, it is optional to use a scramble algae killer drug to kill algae locally, and re-cultivate the algae after three days.
3. Stocking a certain number of filter-feeding fish:
Although cyanobacteria is not easy to digest, due to its large particle size, it is easier to be ingested into the body by filter-feeding fish, which delays and hinders the growth of cyanobacteria to a certain extent. Fish to choose from include silver carp, silver carp, white crucian carp and so on. Practice has shown that when stocking a certain number of filter-feeding fish, there is basically no outbreak of cyanobacteria.
Naked algae
1. The occurrence of nude bath produces the water environment of naked algae blooms:
Naked algae like to grow in small water bodies rich in organic matter, stationary and waterless, and multiply in large quantities to form blooms when nutrients are sufficient, becoming the dominant species in water bodies and quickly occupying the entire water surface.
2. The suitable temperature and season for bloom formation:
The temperature range suitable for naked algae is wide. The suitable temperature for bloom formation is 20 to 35 °C, and the growth period spans spring, summer and autumn, especially in June, July, August and September.
3. The harm of naked algae:
Naked algae is difficult to digest, the utilization rate is low, fish do not like to eat; naked algae is easy to corrupt the water quality when a large number of deaths, and the secreted substances also have a toxic effect on fish, shrimp and crabs.
4. Prevention and control of naked algae
A large number of water changes, so that the water body forms micro-flowing water. Since naked algae prefer to live in small water bodies rich in organic matter and stationary and without flowing water, a large amount of water change can change this environment, making it difficult for naked algae to multiply in flowing water or new water. It is also possible to use algae killing drugs for local algae killing, and after three days, it is fertilized with fishing fertilizer, which has a good effect.
Golden algae, golden algae
1. Occurrence of Golden Algae:
It occurs mainly in ponds with high salinity in coastal saline areas. The water quality of the pathogenic pond is thin, there is no other algae in the water, and the water color is pale yellow.
2. Symptoms of golden algae poisoning:
The surface of the pond is full of fish, most of which stay at the four corners and the edge of the shallow pool, head to the shore, neatly arranged, stationary under the water, not floating, and there is no reaction to disturbance. Random fishing of dying silver carp and crucian carp can be observed, and it can be found that the base of the body fin is congested and the color of the back of the fish body becomes lighter; the gill cover is opened to find a large amount of mucus in the gills, and the gills are mildly decayed; the fish body is dissected, the intestine is inedible, and there is no obvious lesion.
3. Control of golden algae:
Symptoms of poisoning can be temporarily alleviated by injecting fatter river water into the pond or from adjacent ponds. The whole tank is sprinkled with 20g/m3 ammonium sulfate to make the ammonia ions in the water reach 0.06~0.10g/m3 to inhibit or kill the golden algae.
Dinoflagellates, thyatophylla, dinoflagellates
Dinoflagellates prefer to grow in water bodies with a lot of organic matter, high hardness and slight alkalineity. When they breed in Dali, the water is reddish brown and commonly known as "red water".
The harm of dinoflagellates: dinoflagellates is a general term for a large class of flagella, the body is oval, when multiplying, often can change the color of its living waters, some dinoflagellates can be used as bait for some aquatic larvae, but some of them, in the reproductive process, can produce a variety of toxins, causing nerve numbness, metabolic disorders and breathing disorders of fish, and finally lead to death. Odophyllum can also be attached to the fish, live a parasitic life, absorb fish nutrients, stimulate the growth of mucus in the fish body, so that the fish body is like a layer of rice flour, so it is called "powder disease", the prevention and control of dinoflagellates is the same as cyanobacteria.
Cryptoalgae
Advantages of Hidden Baths Cryptoalgae is one of the most important flagella in natural waters, and ponds rich in cryptoalgae are highly productive. Cryptoalgae have a higher protein content (50% to 70%), and some species, such as cryptom onas ovata, are also rich in unsaturated fatty acids, especially gla (octadecatrienoic acid) and epa (eicosataenoic acid) with high nutritional value, which account for 20%, 16% and 4% of the total fatty acid content, respectively. Cryptoalgae have high nutritional value, and their fiber-free cell walls are easily digested and absorbed. As a result, it is one of the high-quality baits for fish and some precious aquaculture animals.
Disadvantages of cryptoalgae: Cryptoalgae have a short growth cycle, are prone to death, and the water color is gray-brown.
Diatoms: small ring algae, boat-shaped algae, straight-chain algae, feathered algae
The advantage of diatoms is that the individual is small and palatable. The speed and distribution of movement are consistent with the activity habits of the larvae, which is convenient for feeding, that is, there are more opportunities for feeding. Rich in nutrients and easy to digest and absorb, it is non-toxic and its metabolites, and does not affect the normal growth of larvae and seedlings. It is conducive to the reproduction of excellent planktonic single-celled algae, ensuring adequate nutrition of fish and shrimp, ensuring that fish and shrimp fry are full and fast, enhancing disease resistance and improving survival rate. Efficient, no residue, protect the breeding environment, stabilize water quality, do not pollute the pond. Effectively reduce the ammonia nitrogen content in water, high dissolved oxygen, good water color.
Green algae:
Green algae: Disc star algae, crescent algae, chlamydia, chycoccus, hollow star algae, solid bulbous algae, water mesh algae (harmful to fish fry), sponge (water body thin filamentous algae), micromanthus.
1. Application of green algae:
Due to its easy culture, thin cell wall and rich nutrition, chlorella is currently mainly used as bait in the aquaculture industry.
2. Advantages and disadvantages of green algae:
Most of the chlorella grown in our pond culture is chlorella, because of its small size and rich nutrition, it is an excellent erbium feed for rotifers. It can produce a large number of rotifers in the water body, which is more suitable for the cultivation of fish, shrimp and crab seedlings. It can be used directly as an open bait for aquatic seedlings, and can also be used to feed seedlings by breeding rotifers; but due to its small individual size, the utilization rate of farmed finished fish is not high, and it can be used as a water transfer product.
Yellow algae, knee-mouth algae
Yellow algae and knee-mouth algae often appear in fertile fish pond water bodies during the warm season. When multiplying, a cloud-like bloom is formed, and the water color is yellow-green. It is a good food for silver carp and bighead carp. Primary productivity is concentrated in temperate or nutrient-rich lakes in winter; in winter, phytoplankton productivity and biomass are generally low in low light, short daylight and low temperatures. When the surface of the water is frozen, if the ice layer is not thick and there is no snow cover, the illumination under the ice is usually much higher than the compensation point of the algae, and photosynthesis can still be carried out to varying degrees. When the ice is made up of thick black ice or long-term snow cover on the ice, net yields turn negative, and biomass is reduced to a minimum due to the easy sinking of non-turbulent algae under the ice.
Subgland phytoplankton are mainly composed of cryptoflaginous algae, dinoflagellates, golden algae and other flagella.
Spring begins with a massive increase in diatom populations. The peak period of diatoms generally does not exceed 3 months, after which due to silicate depletion (<0.5 mg/l) or other reasons (animal filter feeding, fungal parasitism, etc.), the population begins to fade and is replaced by chlorella or some dinoflagellates. During this period, if nutrients at the production level can be replenished in time, productivity remains high.
With the development of green algae in summer and autumn, the nitrogen content in the water drops to a very low point, so after midsummer, nitrogen-fixing cyanobacteria (fishy algae, bundle of silk algae, etc.) replaces green algae and increases sharply. The reasons why cyanobacteria dominate at this time are also related to high temperatures (above 25 ° C), strong light, high pH and less food intake. Cyanobacterial bloom biomass is high, but productivity is generally reduced.
Causes such as the weakening of light and the drop in temperature after autumn can cause the cyanobacterial population to fade suddenly.
Since then, as the water layers are mixed vertically in autumn, the environmental conditions are similar to those in spring, resulting in a second peak of diatoms.