【Common problems】 Fry breeding is the first link in aquaculture production, but also a key link, a little carelessness may make the survival rate of fry low, or even the entire army is destroyed.
【Cause analysis】The fry are small, the body is tender, the swimming is slow, the ability to avoid the enemy is poor, and it is very easy to be invaded by predatory organisms, which brings major losses to production.
【Solution】The common predators in fish fry ponds and their control methods are introduced as follows:
(1) Tadpoles tadpoles in fry breeding ponds have two main hazards: First, tadpoles can swallow fry that have just fallen into the pond;
The second is that tadpoles compete with fry in ponds, affecting the growth of fry. During fry rearing, it is often also the season when frogs spawn in large numbers, and a large number of tadpoles hatch in ponds can seriously affect the growth and survival of fry.
In addition, too many tadpoles in ponds can also cause problems for the sale of summer flower fry. Once the eggs hatch in the pond, the tadpoles quickly disperse into the pond, making it nearly impossible to remove them.
Therefore, a "precaution-based" strategy is usually adopted, that is, to prevent tadpoles from hatching in ponds. Specifically, during the fry rearing period, the pond patrol is strengthened, and the frog eggs or toad eggs are fished out of the pond in time and put on the shore.
This method is simple and effective, if the pond patrol is timely, it can basically solve the harm of tadpoles to fish fry.
(2) Branches and horns Branches are usually suitable feed for fry, and a sufficient number of branches, especially bare-bellied fleas, can greatly improve the growth rate and survival rate of fry.
However, when the fry has just fallen into the pond, if the branches in the pond, especially the large branches and horns such as the flea and the large fleas, multiply in large quantities, it will greatly reduce the survival rate of the fry, and even cause the fry to be extinct.
The main reasons are: on the one hand, the fry cannot feed on large branches, and the large number of large branches will suppress the reproduction of a round of insect populations in the suitable feed of the fry, thus indirectly forming a phenomenon of competing with the fry for food.
On the other hand, the large amount of filtered phytoplankton and its own oxygen consumption will cause the pond to be deprived of oxygen, and in severe cases, the whole pond can die.
Prevention and control methods:
(1) Try to go down to the pond at the right time. That is, according to the hatching time of the fry, the dormant egg density of the pond rotifer and the water temperature, the water injection time of the pond is determined, so that the fry can be lowered in the pond during the peak period of rotifers.
(2) If there is already a considerable number of small branches in the pond (such as naked-bellied fleas) in the pond when the fry enters the pond, it should be avoided as much as possible.
Because they will become the palatable feed for the fry after a few days, the method of feeding soy milk can be adopted to ensure that the initial feed of the fry in the pond is sufficient, otherwise the fry will grow slowly and the survival rate will decrease due to insufficient bait in the later stage.
(3) If the large-scale or large-scale reproduction of the branches causes the lack of oxygen in the pond water (the branches are clumps and the color is red), it should be resolutely killed.
Generally, the whole pond of 0.5 g/m³ water body of crystalline insects is sprinkled, and the method of filling new water is adopted to prevent the lack of oxygen in the pond.
(3) Wild miscellaneous fish After repeated clearing of the pond, there are fewer types of wild miscellaneous fish, mainly loach, wheat ear fish, white fish (meal fish) and so on.
The main reason is, on the one hand, due to incomplete clearance of the pond and, on the other hand, to the introduction of fry or fertilized eggs of wild trash fish when the pond enters the water.
The main hazard of wild trash fish is to compete with farmed fish fry for feed, resulting in waste of feed resources, which can reduce the growth rate of fish fry when serious, in addition, wild trash fish may also carry certain pathogenic factors, resulting in the incidence of farmed fish fry.
(1) Thoroughly clear the pond. It is best to use the dried quicklime method to clear the pond, and the amount of quicklime is 75 to -100 kg/mu. If possible, the fry pond water can be drained before wintering, so that the bottom of the pond is frozen.
(2) When the pond is filled with water, a 150 mesh sieve silk is set at the pump or inlet. If possible, a shaft can be established in the reservoir, and there is a sand and gravel layer of 2 to 3 meters between the shaft and the reservoir, so that the water of the reservoir can pass through the sand and gravel layer and seep into the shaft.
(3) Pull the net empty before the fry go down to the pond. The purpose of this is to check whether there are wild trash fish in the pond before the fry are stocked, and if wild trash fish are found, the trash fish should be used to kill the hemoglobin animals. (4) Aquatic insects The main species of aquatic insects are water centipedes, water nymphs, field turtles, red maidens, water axe insects, pine algae insects and so on.
The water centipede, also known as the water clip, is the larva of the dragon lice, the body is long, with a pair of pincer-shaped jaws, much like the centipede's poisonous claws, so it is called the water centipede. When hunting, the fry is clamped to death with large tongs, and it is the most harmful to the fry among all aquatic insects. It has been observed that a water centipede can eat more than 10 fry at night, especially in May and June of each year, the large number of water centipedes is more harmful to the fry.
The body of the pine algae worm is boat-shaped, yellow-brown, and when swimming, the abdomen is facing upwards, and it stabs into the body of the fry with its mouth, causing the fry to die and then eat it.
It is worth mentioning that when fishing fry, pine algae insects will emit a foul odor if they gather in large quantities, causing the fry to be comatose or even dead, and the ponds that have appeared in large quantities before will occur frequently for several consecutive years.
Prevention and control methods:
(1) Thoroughly clear the pond. It is best to clear the pond with quicklime to eliminate adult insects and eggs of aquatic insects. The dosage of quicklime is 25 to 100 kg/mu.
(2) Sprinkle kerosene on the whole pool. The dosage is 2 to 3 liters / mu, this method can form a layer of oil film on the surface of the water, and when the insect breathes on the surface of the water, it will block the stomata of the insect, so that it will suffocate to death.
(3) Booby trap by light. Specifically, a triangular frame of bamboo and wood is placed in the corner of the pond, and a small amount of kerosene is placed in the rack.
When it is dark, an electric lamp is set up above the frame, and the insect's phototropism is used to attract it to the frame to kill, which has a good effect on killing the water centipede.
(4) The whole pool of wine crystal enemy insects. The dosage is 0.5 g/m³ water body, and the whole pool is sprinkled. It also has a definite effect on killing aquatic insects.
(5) Aquatic grass The large reproduction of aquatic grasses (such as eye vegetables) in ponds will inhibit the reproduction of plankton, resulting in lack of food for fry and reducing the growth rate and survival rate of fry.
Aquatic weeds can also seriously hamper netting operations when fishing fry. Incomplete fry harvesting.
(1) The quicklime is completely cleared, and the dosage of quicklime is 25 to 100 kg per mu.
(2) Organize personnel to go into the water to cut grass.
(3) Drug clearance. Some fish medicine manufacturers' drugs can cause aquatic plants to die and rot, and the effect is better, but after the use of drugs, the reproduction of phytoplankton in the pond will be inhibited for a long time, so it should be used with caution during fry breeding.
(6) Moss and water mesh moss Moss is some filamentous algae, which reproduces in large quantities in the summer, which can make the water quality "thinner" and affect the growth of fish.
Moreover, fry and fingerlings are easy to swim into the mud moss, and cannot swim out and cause death. Water mesh algae is a kind of green algae that grows in fertilizer water with abundant organic matter.
In the spring and summer of mass breeding, both consume a lot of nutrients, but also often like a fishing net in the water, more than the mud moss can trap the fish, so the harm to the fry is greater.
(1) The quicklime is completely cleared, and the dosage of quicklime is 25 to 100 kg/mu.
(2) When the mud moss and water mesh algae multiply in large quantities, use moss to kill quickly and sprinkle the whole pond with sodium humate.
(3) Ponds that are not stocked with fish, each acre of pond is covered with 50 kg of grass and wood ash on the moss, so that it can not get sunlight and die.
(4) For ponds where mud moss and reticulites often occur, organic fertilizer can be applied after water injection in the pond to maintain the transparency of the pond water at 25 to 30 cm.
Poor underwater light conditions can inhibit its large number of reproduction, combined with regular salvage, can prevent the occurrence of large quantities of mud moss and water mesh algae.
For the problem of birds, the method of expulsion is generally adopted, that is, the continuous expulsion of birds after a period of continuous driving can achieve better results. There are also some diseases, and the cause should be found in time.
