In April this year, shortly after the early production of white shrimp seedlings in Leizhou and Xuwen high salinity areas in western Guangdong, there was a large number of stealing deaths of large-scale ponds and shed shrimp, and the success rate of early planting and release of seedlings was less than 30%, which directly led to the wait-and-see mentality of the farmers who subsequently released seedlings, which is also an important reason for the delay in the release of seedlings by white shrimp farmers this year for one month. In these cases, 60-70% are related to dinoflagellates, and about 40% of the shrimp ponds are still related to dinoflagellates in May. Do you really understand dinoflagellates?
First, biological characteristics
The vast majority are single-celled swimming species with flagella, especially seafood, and are among the original producers in the food chain of aquatic organisms; Some species, such as the knee groove algae in the order Polydiformes, form a "red tide" when they overbreed, making the water red, reddish brown and emitting a fishy odor, reducing the dissolved oxygen amount of the water, and secreting toxins - stone clam toxins and their derivatives, which can cause the death of other aquatic organisms and cause harm to aquatic products.
Due to the eutrophication of offshore waters, it leads to the explosive growth and reproduction of dinoflagellates (such as luminous algae, marine protodiformes, etc.), forming blooms, changing the color of the water, emitting a fishy odor, and forming a red tide. After the density is too large, it causes the dead algae to breed saprophytic bacteria, which makes the dissolved oxygen in the water drop sharply and produces dinoflagellate toxins, which are more harmful to fish, shrimp and shellfish.
Figure 1 (Some small black spots that swim fast can be observed under a 40x microscope)
The characteristics of the fish and shrimp pond are: the water color is dark brown, the green is dark, the soy sauce water is dull and dull, the algae phase is not clear, and the pH value varies greater than 0.8 between day and night (Figure 2).
Figure 2
Second, the area of frequent occurrence
High salinity offshore aquaculture areas are more common, and estuarine and freshwater aquaculture areas are less common.
3. Hazards
1. Swim in the pond at the seedling stage, and die of white body. For 3-10 days, the shrimp pond appears dinoflagellate, shrimp fry often appear to swim wildly along the pond wall for several consecutive days, when not treated in time, about 4 days the shrimp fry muscles are white, and a large number of deaths occur.
2. In the middle of breeding, the white body does not eat and dies. In the middle of breeding, the shrimp pond appears to be dominant, and the white shrimp often appears first to reduce the material, do not eat the material, and finally the liver and pancreas are seriously damaged, the muscles are white, swimming on the water surface or lying on the grass wall of the pond to die (Figure 3), and the shrimp pond with 200,000 seedlings can die 10,000-20,000 in 1 day (close to 10% daily mortality rate)
Figure 3
Fourth, governance
Since dinoflagellates secrete toxins, especially dead dinoflagellates, it is a very helpless choice to solve the problem by killing it in the breeding pond by drugs. In the long run, this method can only treat the symptoms, not the root causes. I have used the following schemes to deal with a lot of dinoflagellate problems, if the shrimp pond conditions are suitable, you can also refer to it:
1, the water color is not thick dinoflagellate problem. This situation often occurs in the early stage of breeding, the algae concentration is not high, the yellow-brown color is dark water, you can consider transferring water from the next door to the thicker green water to the pond, adjusting the concentration of nitrate in the nutrient ratio of the pond (that is, adding urea, etc.), increasing the magnesium content of the water body to improve the green algae component of the water body, so that it forms a dominant population to suppress dinoflagellates, degrade dinoflagellate toxins, achieve dynamic balance, and ultimately harmless.
2, the water color is not thick dinoflagellate problem. Areas rich in freshwater resources are addressed by adding fresh water.
3, the water color is very strong dinoflagellate problem. This situation often occurs in the middle and late stages of aquaculture, which can be solved by a large amount of drainage, reducing the total amount of dinoflagellates in the pond (to achieve more than 60% of the water exchange), and then mobilizing the thick green water next door to the pond (10-20 cm water) and foreign new water, but in the process of use, the ph buffer system (add carbonate) and the osmolality of the shrimp body must be protected before adding water, this method can solve the problem caused by dinoflagellates in one day, but the damaged liver and pancreas of the shrimp body need to be restored by feeding about 5 days of wall-breaking yeast + oligosaccharides.
4, the water color is very strong algae, but there is no green algae shrimp pond nearby. If you have the conditions, you can also use the way of relocating the whole pond, and you can't change the water to move (haha). Of course, it is also possible to take the way of replacing the whole pond with new water, but as in plan 3, it is necessary to do a good job of ph buffer system, shrimp body osmotic pressure protection, damaged liver and pancreas need to be restored by feeding about 5 days of broken wall yeast + oligosaccharides.
Fifth, prevention
Although it is important to use the right method to control the disease, it is the key to the success of breeding before the onset of white shrimp and early prevention. Usually do every detail, prevention is a smart move, I have the following experience to share with you:
1. The turn of spring and summer and the turn of autumn and winter is the season of high red tide in the sea area, and the direct use of external seawater is minimized during this period;
2. The high-level pond in the densely cultivated area uses a certain proportion of the reservoir (4-6:1 reservoir of the breeding pond), and the harmful algae are treated with copper sulfate, zinc sulfate and ferrous sulfate in advance in the reservoir, and then the tea bran conducive to the growth of beneficial algae is used to cultivate yellow and green water in a targeted manner to reduce the impact of exogenous algae on the aquaculture water body;
3. The earthen pond can use part of the pond to breed fish, and the shrimp pond can be taken from the fish pond with water;
4. Conditional shrimp ponds should try to add fresh water to the proportion of 1.005-1.008 in the middle of breeding.
The harm of dinoflagellates is enough to make farmers lose their money. In short, early prevention is to prevent problems before they occur, and timely governance is to prevent micro-graduals. Although prevention and treatment methods can emerge in an endless stream, in the final analysis, it still depends on the farmers' own attention to shrimp pond management and their understanding of the harm of dinoflagellates.
The quarterly killer of Penaeus vannamei culture in South America (II): Cyanobacteria
South American white shrimp farming with the increase in water temperature, sunlight enhancement, aquaculture pond water body eutrophication intensified, in early May in western Guangdong began to appear new breeding problems - cyanobacteria, to mid-May reached a small peak, at this time, there are 6-70% of the problem shrimp pond and cyanobacteria-related, to late May west Of Guangdong to rainy days, sunlight decreased, cyanobacteria hazards began to decrease, but from the breeding process and normal weather changes, June to July will still be the high incidence of cyanobacteria season, shrimp farming to prevent cyanobacteria work has a long way to go.
First, the characteristics of cyanobacteria
Biological characteristics: Cyanobacteria are single-celled prokaryotes, also known as cyanobacteria, blue-green bacteria, cyanobacteria or blue-green algae; Common cyanobacteria are cyanococcus (crobococcus), candida, fibrillation, hair and so on. Cyanobacteria are single-celled organisms that are easy to see when they appear in the form of cell populations, which is the "bloom" we usually see.
In nutrient-rich water bodies, cyanobacteria often multiply in large quantities in the summer, and form a layer of blue-green cyanobacteria blooms and fishy odorous foam on the water surface, called "blooms", causing water quality to deteriorate, and when severe, exhausting oxygen in the water and causing the death of fish, shrimp and crabs. More seriously, some species of cyanobacteria (such as microcystis) also produce microcystins (mcs for short), and about 50% of green tides contain a lot of mcs. In addition to directly toxic to fish, humans and animals, mcs are also an important cause of liver cancer.
In the fish and shrimp pond, the characteristics are blue and blue-green, and in severe cases, "water blooms" appear (Figures 1 and 2).
Figure 1
2. Endemic areas
There have been outbreaks in all aquaculture areas offshore, estuaries and freshwater aquaculture areas, especially freshwater aquaculture areas.
Third, the harm of cyanobacteria
1. A large number of trace elements in water are used to reduce the hardness of the water body, causing soft shells and carapace ulcers of crustaceans.
2. The purification ability of cyanobacteria is poor, and long-term cyanobacteria often cause the substrate to turn black and the water to stink.
3. Cyanobacteria is easy to cause enteritis of breeding objects and damage the liver and pancreas of farmed shrimp (Figure 3).
Fig. 3 Liver and pancreas dissolve as soon as the shrimp dies, resulting in the phenomenon of "blackheads"
4. When severe, the oxygen in the water is exhausted and the death of fish and shrimp is caused. In the middle of May this year, a new situation appeared, continuous north wind followed by rain and then high temperature, shrimp body infection (yellow body, yellow legs, lying side), if the parallel outbreak of cyanobacteria, there will be 3,000 pounds of shrimp shrimp pond on the first day of death of 30 pounds, the second day of death of more than 100 pounds, the third day of hundreds of pounds of shrimp explosive death, to the treatment of great difficulties (Figure 3, Figure 4).
Fig. 4 Yellow-bodied jejunum shrimp appear in cyanobacterial water
Fig. 5 Liver and pancreas atrophy of some dead shrimp
Fourth, cyanobacteria treatment
If the conditions of the shrimp pond are suitable, I have also dealt with a lot of cyanobacteria problems through the following programs, providing them for your reference:
1. Freshwater areas. Algae such as cyanobacteria are the food of silver carp and bighead carp, and they can be treated by releasing them to prevent cyanobacteria outbreaks.
2. High-level ponds and factory areas. Microcystin can be absorbed by activated carbon, so activated carbon can be used to absorb microcystins in water, and then excreted from the pond to reduce the poisoning of cyanobacteria to farmed shrimp.
3, just emerging cyanobacteria problem. It can be solved by reducing the total amount of cyanobacteria in the pond (to achieve more than 30% of the water turnover) through a large amount of drainage, and then mobilizing the thick green water next door, the brown water crossing the pond (10-20 cm water) and the new water from outside. Adjust the np ratio of the breeding pond (put in highly active photosynthetic bacteria / denitrifying bacteria to use most of the nitrate in the water body, put a small amount of inorganic phosphorus to raise the np ratio, so that it can achieve a nutritional structure that is conducive to the growth of other beneficial algae and not conducive to the growth of cyanobacteria), but during the use of water, the ph buffer system (adding carbonate) must be done before adding water, this method can solve the cyanobacteria within two days, but the damaged liver and pancreas of the shrimp body need to be restored by feeding about 5 days of broken wall yeast + oligosaccharides. However, it should be noted that this method has high weather requirements (not in rainy days), photosynthetic bacteria/denitrifying bacteria (only a few brands on the market can achieve).
4, the water color is very strong cyanobacteria. If you have the conditions, you can also use the way of relocating the whole pond, and you can't change the water to move (haha); Of course, it is also possible to replace the whole pond with new water (do not be afraid of "stress", no matter how to say it will not be more influential than shrimp fry from the nursery to the breeding pond). However, as in scenario 3, a ph buffer system must be done, and the damaged liver and pancreas need to be recovered by feeding the wall-breaking yeast + oligosaccharides for about 5 days.
5, the water color is very strong cyanobacteria. Sodium humate + high concentration of highly active photosynthetic bacteria/ denitrifying bacteria were used to treat, and then adsorbed dead algae particles on the 2nd day, and excreted/aspirated out of the pool. The principle is to use sodium humate to shade the light, photosynthetic bacteria / denitrifying bacteria to use excess nitrate in the water body to adjust the nutritional structure of the water body, weather requirements, strain requirements, shrimp body conditioning the same method 3.
6. Complicated infection with yellow shrimp pond, after processing the cyanobacteria, you can use five yellow + povidone iodine for continuous disinfection for 2 days (6 pm), and add a persulfide on the morning of the second day, shrimp body conditioning as scheme 4.
5. Prevention of cyanobacteria
1. The use of shading nets to reduce sunlight during the high temperature season of conditional breeding ponds has a certain effect on preventing cyanobacterial outbreaks.
2. Under the condition of high temperature and strong light, the appropriate use of sodium humate products also has a certain preventive effect.
3. The high-level pond in the dense area of breeding uses a certain proportion of the reservoir (4-6:1 reservoir of the breeding pond), and the harmful algae are treated with copper sulfate, zinc sulfate and ferrous sulfate in advance in the reservoir, and then the tea bran that is conducive to the growth of beneficial algae is used to cultivate yellow and green water in a targeted manner to reduce the impact of exogenous algae on the aquaculture water body.
4. Bottom salinity earthen ponds can be polycultured to breed fish (silver carp, bighead carp) to prevent the outbreak of cyanobacteria.
5. Eutrophicationic water bodies regularly use photosynthetic bacteria /denitrifying bacteria to use excess nitrates in some water bodies, and even regularly add inorganic phosphorus to adjust the nutritional structure of water bodies, and find ways to discharge the water bodies and substrate organic matter from the pond.
6, the most important. The breeding process is to do a good job in the conditioning of the shrimp liver and pancreas, the above figure 2 breeding pond cyanobacteria for more than 1 week, in the early May cyanobacteria small peak period is unharmed, and the nearby farmers are dead shrimp, ponds, shrimp catch...
Cyanobacteria control methods are diverse, all roads lead to Rome, welcome the majority of farmers, experts to participate in online exchanges, June-July will be the high incidence of cyanobacteria season, are you ready to meet the challenge of cyanobacteria?