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Zooplankton is a general term for heterotrophic invertebrates and chordate larvae that often float in water and cannot make organic matter by themselves. There are many types of zooplankton in the water, from low-level micro-protozoa, coelenterates, ctenophores, rotifers, crustaceans, gastropods, etc., to higher tails, almost every category has permanent representatives, of which a wide variety, a large number, and a wide distribution of copepods are the most prominent. Copepods have a relatively long generation cycle and are less significant in aquaculture than rotifers and phylums.
Most aquatic zooplankton are natural food for fish, and we often call rotifers, fleas (fleas and "dipteras", non-"algae", the same below) and micro-aquatic organisms such as rotunda and copepods are zooplankton. Rotifers are invisible to the naked eye, and phylloscopes and copepods (such as fleas) are visible to the naked eye, and they are all high-quality natural food for fish. Aquatic zooplankton are commonly found in freshwater water bodies, as long as there is a certain degree of fertility in the water, there are widespread species of zooplankton such as rotifers and water fleas.
Zooplankton can be roughly divided into: rotifers, branches, copepods, and so on. These three are particularly prominent in the waters. Cladophylla and copepods, both belonging to the arthropod phylum Crustaceans, are a small crustacean like shrimp and crabs. Most of them live in freshwater water bodies, only a few are marine life, generally camp pelagic life, they are the main components of freshwater water body plankton. It has wide adaptability, strong fertility, rapid growth, high nutritional value, and is also a suitable bait for the larval stage of aquaculture. Rotifers are the most suitable for the opening bait (note that it is "opening") in the early stage of the pond under the water splash seedlings), and the water fleas are the suitable bait for the late stage of the splash seedlings, but in the adult stage, if the zooplankton, especially the water fleas, etc., if the breeding is too large, it will cause an oxygen-dehydrobic pond accident.
Fertile water pond
In the production of aquatic fry, the so-called "fat water pond" is the core of which is to prepare for the delicious bait after the fry are lowered. Fertilization and water should be mastered in good timing, too early or too late, the biomass of the open bait rotifer has not reached the peak or the peak has passed, these are the two links that need to be properly fertilized and cultivated at the right time, and the two links of timely water splashing down the pond should be appropriate.
After fertilization in the fish pond:
The law of the peak formation of various types of zooplankton is: the first to form the peak is the protozoa, followed by rotifers, then the branches, and finally the copepods.
This is the same as the requirements for food size changes in the whole growth process from the pond to the summer flower (inch seedling) of the water flower fry: protozoa and rotifers → small branches→ large branch → copepods, which is consistent with the order in which the fish pond zooplankton form peaks.
The consistency of the two can be well utilized by timely fertilization and water cultivation in the fish pond, so that the peak period of rotifers just occurs after the splash fry go down the pond, not only the splash fry that has just entered the pond has sufficient palatable bait, but also has a wealth of palatable bait at all stages of development in the future. Therefore, timely fertilization and timely release of splash fry into the pond are the keys to raising fry.
(Microscopic --- rotifers, picture from the Internet)
Rotifers
Rotifers are a group of small multicellular animals in the phylum Rotunda. Widely distributed, most live freely, there are parasitic, some individuals and some group habits. General body length 100-300 μm. The body is long,Most rotifer bodies are composed of three parts: head, trunk and foot, some without feet, cilia at the front end, and the head has a 1-2 circles of fibers, shaped like a wheel and named, so it is called rotifer. The roulette wheel is the modal and feeding organ of rotifers, with a chitin chewer in the pharynx. The trunk is cylindrical, with a broad dorsal abdomen, thorns or spines, and a transparent carapace on the outside. At the end of the tail, there are forked toes, and glands inside secrete mucus, which is fixed to other objects. dioecism. Oviparous, mostly parthenogenesis.
(Microscopic branches and horns--- water fleas, picture from the Internet)
Branches
Cladocera (Cladocera) is also referred to as "water fleas", water fleas (water fleas), commonly known as red worms, is an invertebrate, crustacean, gill foot suborder, mycopoda. The body is short (body length 0.2 to 1 mm, depending on the specific species, such as large lump can reach about 4.2 mm, oblong, divided into head and torso, the lateral flat body segment is not obvious. Except for the bare head, the rest of the body is enclosed in a transparent mesoform shell flap. The head has 2 pairs of obvious antennae, the first pair of antennae is small, and the second pair is particularly developed, can be divided into inner branches and outer branches, can be paddled in water, as a motor organ. 4 to 6 pairs of thoraxes, which can produce water flow when swinging, and have long bristles on them, which can filter food and send it to the mouth.
(Copepods under the microscope, picture from the network)
Copepods
Copepods belong to the phylum arthropods, crustaceans, and copepod subclasses. It is a small crustacean with a body length of <3 mm, camp planktonic and parasitic life, distributed in the ocean, freshwater or brackish water. Copepods are rapidly active and have relatively long generation cycles, and are less important in aquaculture than rotifers and phylloids. The body is longitudinal and segmented, with no more than 11 segments of the body segment, 1 section of the head, 5 segments of the thorax, and 5 segments of the abdomen. The head has a point of sight, two pairs of antennae, and three pairs of mouthpieces. The thorax has 5 pairs of pectoral feet, the first four pairs are of the same structure, the limb type, the fifth pair is often degenerate, and the sexes are different. The abdomen is unincorporated and has a pair of tail forks at the end and several pinnate bristles behind it. Females often have oocysts in their abdomen. Metamorphosis. i.e., there are arthropods and copepod larvae.
(Branch: Water)
Feeding habits of copepods
Branches and copepods can be divided into phylum filter feeding and phyllonory predators according to the feeding method, and they all feed on fungi and algae. Freshwater phylum mainly filters bacteria, monocytozoals, protozoa and organic detritus in the water, etc., and the photosynthetic bacteria and EM bacteria we usually put in may become bait for zooplankton; predatory brachiopods use their thoracic limbs to catch other aquatic micro-animals for food.
(Copepods)
The breeding pattern of the branch-horned copepods
Propagation of phylloids
Phyllonorycters are hermaphrodites and have a life history of alternating generations of parthenogenesis and sexual reproduction. Generally speaking, when the external water temperature is suitable and food is sufficient (mostly in the spring and summer period), the females produced are called non-mixed females; when the external environment deteriorates, such as water temperature decreases, bait is poor, and water quality deteriorates, the branches and horns change the reproductive mode for sexual reproduction (amphoteric reproduction), at this time, the non-mixed females will produce two different eggs. One hatches as a female egg of both sexes, one hatches as a male egg, and the two mate to produce dormant eggs. Its growth cycle is about 7-10 days.
(Small fish eating faiths)
Water quality conditions suitable for asexual reproduction of branches: water temperature 17-30 °C, PH6.5-8.5, dissolved oxygen 1-5ppm, dissolved oxygen exceeding 5ppm, fecundity will decrease. The optimal growth temperature of the phylum is 18-25 ° C (so it is the outbreak period every April), and as the temperature increases, the sexual maturation time of the phylum will be advanced, shortening the spawning cycle.
Reproduction of copepods
Copepods generally reproduce with both sexes. Many species of copepods can sleep through adverse environments, but species that dormant in copepod larvae and adults are more common. During spring or hibernation, their bodies hide in a sac consisting of a special secretion that sticks to some mud blocks of plants. Some species carry oocysts with mature females, and the oocysts in the sacs also survive unfavorable environmental conditions; others overwinter in the silt at the bottom of the water.
That is to say, when we are in Qingtang, the branch horns copepods exist in the form of dormant eggs, and the Qingtang drugs only play a role in sterilization, disinfection and insecticide, but have no effect on the eggs of the branches and copepods. By the end of March and the beginning of April, the temperature rises, the light is suitable, the water quality conditions such as dissolved oxygen and PH meet the living conditions of the branches and horns of copepods, and the dormant eggs begin to hatch, so the "bugs" begin to multiply in large quantities. This can also explain why every year the pond is dried, the pond is medicated, and the pond is thorough, and in April, the branches and copepods will erupt.
Sequence of zooplankton in the pond
The figure below is the sequence of phytoplankton in a pond after April, which is the only basis for us to judge how long bugs have been in the pond.
According to the law of conservation of energy, it is assumed that fish ponds have high natural productivity and sufficient carbon sources, that is to say, at this time the algae in the water body is sufficient, the branches and copepods eat algae and grow in large quantities because there are no natural enemies, the algae are less and less, the insects are multiplied in large numbers, and then the eggs are reproduced, and then eat and drink, and later the water quality is clear and thin and becomes a "landscape". Therefore, this is a very good thing in seedling breeding, and when things are extremely reversed, it may become another harm! Of course, cyanobacteria will never have a chance to erupt, and cyanobacteria will also be eaten by the pyroclasm of the outbreak.
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(Video: Flea of the branches, note: many people mistakenly think that it is a rotifer)
Treatment and response to outbreaks of branches and copepods
In the early stage of aquatic seedlings, zooplankton is a rare high-quality bait, which has a non-underestimated effect on the increase of seed yield, in addition, silver carp and other fish that filter zooplankton bait are used for life. However, if excessive breeding, or before the splash does not go down the pond, large zooplankton (branches and copepods) are at their peak (splash fry can not be eaten), especially in the adult stage is particularly risky, because the increase in the volume of zooplankton, fish are not consumed enough to eat, is bound to cause an increase in oxygen consumption, the water body is thin and reduces the oxygen-making function of phytoplankton photosynthesis, the water body is more hypoxic, and it is easy to have serious pond dead fish events.
(The water body is thin and transparent at the bottom)
In response to outbreaks of branches and copepods, the following measures can be taken to deal with them:
1. Light trapping. Due to the strong phototropism of the branches and copepods, light trapping can be carried out with this property. The advantage is environmental protection, in line with the concept of ecological breeding, no harm to fish, shrimp and crabs; the disadvantage is that the efficiency is too low.
2. Use insecticides. Generally, a dose of 0.2-0.5 g/m3 of dinoflagellates is used, and this amount does not harm rotifers. However, it should be noted that the dose of insecticide is not easy to control, and a little attention will damage the seedlings. After killing insects, due to the decay of insect corpses, the water will quickly become fat. In addition, you can also choose to sprinkle insecticides along the edge of the pond when the sky is just dawn on a sunny day, with the help of zooplankton having the habit of swimming in groups in the morning.
3. Do not do processing. This method is only suitable for ignoring the situation that does not affect the growth of aquatic animals, but it is necessary to add an aerator to prevent accidents. Because the growth cycle of branches and copepods is generally only 7-10 days, after this period of time, it will die naturally. Or wait for the temperature to get higher until it dies naturally.
(Synthesis of information in this article: Southwest Fishery Network)
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