Do you know the effects of eight common algae on aquaculture and their control measures?

Common freshwater algae:

Cyanophyta, Chlorophyta, Chrysophyta, Pyrrophyta, Cryptophyta, Bacillariophyta, Chlorophyta, Xanthophyta.

1. Cyanobacteria

Microcystis (more toxic after death, inhibiting the growth of other algae)

Spirulina (indigestible)

Tremor algae (indigestible)

Spirulina platensis

Alternaria alternata

Anabaena

Microcystis bloom

(1) the occurrence of cyanobacteria.

Temperature factor

Cyanobacteria reproduction is sensitive to temperature and does not occur in large numbers or cause harm to fish when the water temperature is below 17 ℃. When the water temperature rises to 28 ℃, cyanobacteria can easily form the dominant population and break out due to the inhibition of the growth of other algae and their digestion by fish (enhanced metabolism of fish with high temperature).

PH value:

Algae prefer alkaline water with high pH (pH8. 0~pH9. 5) it will promote the occurrence of cyanobacteria, so the method of sprinkling lime water alone should be avoided to improve water quality.

Ratio of nitrogen to phosphorus:

Cyanobacteria can not only utilize nitrogen in water, but also have higher ability to utilize phosphorus. Water bodies with low N / P ratio or high phosphorus content may lead to the occurrence of a large number of cyanobacteria. Properly increasing the ratio of nitrogen to phosphorus can inhibit the growth of cyanobacteria to some extent.

Ecological relationship:

Cyanobacteria together with other algae form the producers of the pond ecosystem, providing more than 89% of the dissolved oxygen. Therefore, these producers not only participate in the material cycle of the ecosystem, but also affect the survival of fish.

Assumptions about the cause of bloom:

The key factors vary from stage to stage:

The formation of cyanobacteria bloom can be divided into four stages: dormancy, resuscitation, biomass increase, floating, forming bloom and turning to water.

(2) the harm of cyanobacteria

Because cyanobacteria can change the swelling pressure, it gathers on the surface of the water body in the weather of high temperature and strong light, absorbs most of the sunlight, and inhibits the growth of other algae while reproducing in large numbers. The mass reproduction of cyanobacteria continuously secretes toxic metabolites into the water body, which affects the population succession and reproduction cycle of plankton, and can also cause a large number of deaths of some zooplankton.

With the occurrence of a large number of cyanobacteria, cyanobacteria particles are difficult to be digested by fish, and cyanobacteria gradually become the absolute dominant population. This overreproduction formed by interspecific competition will inevitably lead to intraspecific struggle, and the result of intraspecific struggle will lead to the death of a large number of cyanobacteria.

The death of a large number of cyanobacteria has led to a sharp decrease in the production of water bodies, resulting in a serious shortage of dissolved oxygen supply in the water body. At the same time, the death and decomposition of cyanobacteria will also consume a lot of dissolved oxygen and release a lot of toxic substances such as hydroxylamine and hydrogen sulfide. Under the condition of severe hypoxia and toxic storage, a large number of fish will die, or even all of them will die.

(3) the methods of controlling cyanobacteria:

Thoroughly clean the pond and add fresh water without cyanobacteria. Because cyanobacteria is more competitive than other algae, prevention is more important than control. Thorough pond cleaning and disinfection can effectively kill cyanobacteria, depress the base and reduce the possibility of large-scale occurrence. Avoiding the introduction of cyanobacteria with added water is also of positive significance to control.

Change fresh water regularly: for ponds that contain more cyanobacteria, change fresh water frequently and in large quantities, which can dilute the concentration of cyanobacteria. At the same time, it also dilutes the concentration of poison secreted by cyanobacteria, promotes the growth of other algae and maintains the dynamic balance of the whole ecosystem.

When a large number of blue-green algae occur, local algae-killing drugs can be selected, and the algae can be re-cultured with fish fertilizer three days later. It is proved by practice that it has a good effect on the control of blue-green algae.

Stocking a certain number of filter-feeding fish:

Although cyanobacteria are not easy to digest, because of their larger particles, they are more easily ingested by filter-feeding fish, delaying and hindering the growth of cyanobacteria to some extent. The fish to choose from are silver carp, flower silver carp, crucian carp and so on. Practice shows that cyanobacteria basically do not break out when a certain number of filter-feeding fish are released.

two。 Naked algae

(1) the occurrence of gymnoalgae.

The water environment that produces naked algae bloom: naked algae like to grow in a small water body with rich organic matter and no running water, and multiply to form a water bloom when its nutrition is sufficient, and become the dominant species in the water body to quickly occupy the whole water surface.

The suitable temperature and season for the formation of water bloom: the suitable temperature range for naked algae is wide, and the suitable temperature for the formation of water bloom is 20-35, which spans the three seasons of spring, summer and autumn, especially in June, July, August and September.

(2) the harm of naked algae.

Naked algae is difficult to digest, the utilization rate is low, fish do not like to eat; when a large number of naked algae die, it is easy to damage the water quality, and the secreted substances may also have a toxic effect on fish.

(3) Control of gymnoalgae.

A large number of water changes to form micro-running water: because naked algae like to live in small water bodies with rich organic matter and still no running water, a large amount of water exchange can change this environment, making it difficult for naked algae to reproduce in running water or new water. We can use algicidal drugs to kill local algae for three days and then use fish fertilizer to fertilize and water, which has a good effect.

3. Chrysophyta

Chrysophyta trichaeoides

The main results are as follows: (1) the occurrence of trichaeophyta: it mainly occurs in ponds with high salinity in coastal saline-alkali areas. The water quality of the sick pond is thin, there are no other algae in the water, and the water color is light yellow.

(2) symptoms of tricorphylla poisoning:

The surface of the pond is covered with fish, mostly staying at the four corners and the edge of the shallow water, facing the shore, neatly arranged, motionless under the water surface, no floating head, and no response to disturbance. Four dying silver carp and four crucian carp were randomly selected to observe the hyperemia at the base of the surface fin and the lighter color at the back of the fish body; opening the Gill cover, there was a large amount of mucus in the Gill, and the Gill filament was slightly rotten; dissecting the fish body, there was no food in the intestine and no obvious focus.

(3) Prevention and control of trichaeophyta:

Immediately inject into the pond the river with fatter water or the fertile water near the pond, so that the symptoms of poisoning can be temporarily relieved. The whole pool was sprinkled with ammonium sulfate 20g/m3 to make the ammonia ion in the water reach 0.06~0.10g/m3, so as to inhibit or kill trichaeophyta.

4. Dinoflagellate

Dinoflagellate

Dinoflagellate dinoflagellate

Dinoflagellate

The occurrence of dinoflagellate

Dinoflagellates like to grow in water with a lot of organic matter, high hardness and slightly alkaline. When they breed in Dali, the water is reddish brown, commonly known as "red water".

The harm of dinoflagellate

Dinoflagellate is the general name of a large class of dinoflagellates, which is oval in shape and can often change the color of its living waters when it propagates in large numbers. Some dinoflagellates can be used as bait for some aquatic larvae, but some of them, in the process of reproduction, can produce a variety of toxins, causing nerve numbness, metabolic disorders and respiratory disorders in fish, resulting in death.

Egg dinoflagellate can also be attached to the fish, live a parasitic life, absorb the fish body nutrients, stimulate the fish body proliferation of mucus, so that the fish body like coated with a layer of rice noodles, so it is called "powdery disease". The prevention and control of dinoflagellate is the same as cyanobacteria.

5. Cryptic algae

(1) the advantages of Cryptophyta.

Cryptophyta is one of the most important flagellates in natural waters. The reservoirs rich in Cryptophyta have high productivity. Cryptosporium is high in protein (50%-70%), and some species, such as Cryptom onas ovata, are also rich in unsaturated fatty acids, especially GLA (octadecatrienoic acid) and EPA (eicosapentaenoic acid), which account for 20%, 16% and 4% of the total fatty acids. Cryptophyta has high nutritional value, and its cellulose-free cell wall is easily digested and absorbed, so it is one of the high quality bait for fish and some precious aquatic animals.

(2) the shortcomings of Cryptophyta.

Cryptoalgae has a short growth cycle, easy to die, and the water color is grayish brown.

6. diatom

Cyclophyta, navicular algae, Alternaria alternata, Alternaria pinnata

The advantages of diatoms

The individual is small and palatable. The movement speed and distribution are consistent with the activity habits of the larvae, which is convenient for feeding, that is, there are more opportunities for feeding. Rich in nutrition, easy to digest and absorb. Itself and its metabolites are non-toxic and do not affect the normal growth of larvae and seedlings.

It is beneficial to the reproduction of excellent planktonic unicellular algae. Ensure the adequate nutrition of fish and shrimp, ensure that fish and shrimp fry eat fast, enhance disease resistance and improve the survival rate. High efficiency, no residue, protect the culture environment, stabilize the water quality, do not pollute the pond. Reduce the content of ammonia nitrogen in water, high dissolved oxygen and good water color.

7. Green algae

Spirulina platensis

Crescent algae

Scenedesmus

Chlamydomonas aeruginosa

Chlorella spp.

Alternaria alternata

Chlorella vulgaris

Water net algae (harmful to fish fry)

Water sponges (thin filamentous algae in water)

Microawn alga

(1) the application of green algae.

Because Chlorella has the characteristics of easy culture, thin cell wall and rich nutrition, it is mainly used as bait in aquaculture.

(2) the disadvantages of green algae.

Chlorella grows in large numbers in our pond culture. Because of its small size and rich nutrition, it is an excellent erbium material for rotifers.

8. Yellow algae

Genostoma

It appears in fertile fish ponds and other water bodies in the warm season. When it propagates in large numbers, it forms a cloud-like bloom, and the water color is yellowish green. It is a good bait for silver carp and bighead carp.

Winter primary productivity

In temperate or eutrophic lakes, the productivity and biomass of phytoplankton are generally low under low light, short day and low temperature in winter. When the water surface is frozen, if the ice is not thick and there is no snow cover, the illuminance under the ice is usually much higher than the compensation point of algae, and photosynthesis can still be carried out to varying degrees. When the ice is composed of thick black ice or covered with snow for a long time, the net output becomes negative, and the biomass decreases to the lowest point because there is no turbulence under the ice. Subglacial phytoplankton are mainly composed of dinoflagellates, dinoflagellates, dinoflagellates and other flagellates.

Spring

The first is the massive growth of diatom population. The peak period of diatoms is generally less than 3 months, and then due to silicate depletion (< 0.5 mg/L) or other reasons (filter feeding of animals, parasitism of fungi, etc.), the population begins to decline and is replaced by Chlorella or some dinoflagellates. During this period, if the nutrients of the production layer can be replenished in time, the productivity is still very high.

Summer and autumn seasons

With the development of green algae, the nitrogen content in water decreased to a very low point, so nitrogen-fixing cyanobacteria (Anabaena, filamentous algae, etc.) replaced green algae and increased rapidly after mid-summer. The dominant reason of cyanobacteria at this time is also related to high temperature (more than 25 ℃), strong light, high pH and less food. The biomass of cyanobacteria in bloom stage is very high, but the productivity usually decreases.

The abrupt decline of cyanobacteria population was caused by the decrease of light and temperature after autumn. Since then, with the vertical mixing of the water layer in autumn, the environmental conditions are similar to those in spring, resulting in the second peak of diatoms.

Article Source: aquatic products Portal

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