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Plankton in water bodies, here is the meaning of the word "plankton", it refers to a type of micro-organisms in the water itself is very small, the plankton is very weak, plankton has two main categories: phytoplankton and zooplankton. People have a strong understanding of phytoplankton, all kinds of algae in the water are also phytoplankton, in the water by the water color to express what is the phytoplankton, water color is our common and special caution to look at it, algae and water color associated, what algae it shows what color to come, some unfavorable algae (such as cyanobacteria) We can "warn" through the observation of water color. And zooplankton we rarely pay attention to it, because it is not good or bad, and the usual performance is looming, in people's minds has become a dispensable thing. In fact, in aquaculture, the role of zooplankton and phytoplankton are equivalent, and we should not despise or underestimate its existence.
(Phytoplankton)
1. Zooplankton and their classification
Zooplankton refers to the group of animals that live in the water, they either have no swimming ability at all, or their swimming ability is weak, they cannot move long distances, nor are they enough to resist the flow of water, and they cannot produce organic matter.
(Zooplankton)
Zooplankton are divided from small to large, and are composed of four groups: protozoa, rotifers, branches, and copepods. Their size is, in order: protozoa less than 02 mm, rotifers 0.2-0.6 mm, twigs 0.3-3 mm and copepods 5-5 mm, and brachiopods and copepods are generally called large zooplankton. In the biomass composition of zooplankton, rotifers are absolutely dominant, followed by protozoa, and branches and copepods are insignificant.
(Rotifers: Lycamorecerciasis)
Second, the habits of zooplankton
Because the moderate temperature of zooplankton survival is mostly between 18 ° C and 28 ° C, the number of often late spring and early summer increases significantly, which is easy to form an advantage, followed by more autumn numbers; while summer high temperature and winter low temperature are not suitable for zooplankton growth and reproduction, so their biomass is relatively small. Copepods are present all year round in fish ponds, can overwinter under ice in winter, and first dominate zooplankton in spring. Phyllopods overwinter with dormant eggs, and more adults appear after spring and summer, but the generations are shorter, the filter feeding ability is strong, and they quickly replace copepods or rotifers. Protozoa and rotifers have shorter generation times and reproduce faster, and their populations often fluctuate with changes in nutritional conditions.
(Grenade Worm)
3. Species of zooplankton
1. Protozoa
Protozoa, single-celled miniature species (<0.2 mm), a variety of species, its generation time is less than a day, the main species are: barrel shell worms, bouncing worms, rogue insects, trumpet worms, grenade worms and bell worms, etc., the main food is bacteria and other tiniest particles, and requires a high food concentration of 20-60 mg / l or more, so it is not easy to maintain a high density in fish ponds for a long time.
(Calyx-calyx)
2. Rotifers
Rotifers are 0.2–0.6 mm (mm) long and have an age time of 1.25–7 days. There are many species and existing quantities, and it is the best open and palatable food for the lower pond water flower seedlings. The main species are: Calyx, Horned Arm-tailed Rotifer, Kettle-shaped Arm-Tail Rotifer, Tyrannosaurus sylvestris, Wartycephalus, Chakra schipodum, Rotifers, Rotunda, Three-limbed Rotifer, Needle Cluster Multi-Limbed Rotifer, Bulbocarpus and Tortoise Beetles. Rotifers usually eat less than 12 microns (um), and larger species can eat 20-30 microns (um) of food.
(Branch: Bare-bellied)
3. Branches and horns
Phyllonorycters, also referred to as "lumps", water fleas or water fleas, commonly known as red worms, are invertebrates, crustaceans, gill-foot suborder, and bulbous horns. The body is short, generally 0.3-3 mm (mm) in length, depending on the specific species, such as large lumps can reach about 4.2 mm (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 1st pair of antennae is smaller, and the 2nd pair is particularly developed, can be divided into inner and outer branches, and 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.
(Water fleas)
The generation time of the branches is 5.5-24 days, the species are small but the stock is often very large, and it is the main food in the middle and late stages of fry breeding (melon seed seedlings to inch seedlings). The main species are: long line, large, bare-bellied and show body. The size of the grain is similar to that of rotifers, but the feeding ability is much stronger, and the required food density is also 4.5-15 mg/L, so rotifers are often inhibited or died by angular species due to food competition.
4. Copepods
Copepods belong to the phylum arthropods, crustaceans, and copepod subclasses. It is a small crustacean, generally 0.5–5 mm (mm) long, camp floating and parasitic life, rapid activity, relatively long generation cycle, less important in bait than rotifers and twigs. 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 and develop metamorphosis, i.e., have arthropods and copepod larvae.
Copepod generation cycles range from 7 to 32 days. Its arthropods are the main food in the early stages of fry. The main species are: large dart water fleas, right-sided new dart water fleas, close neighboring sword fleas, widely spread medium sword water fleas and Taiwan Wenjian water fleas. There are many carnivorous species of copepods, which can eat rotifers, branches, etc., due to high nutritional requirements, it is not easy to achieve a lot of density.
Fifth, the growth law of zooplankton populations
1. After the fish pond is filled with water after the pond is cleared, the eggs remaining in the sediment and the seed source brought by the water are borrowed, and the order of ciliates and filter-feeding rotifers - carnivorous rotifers - small rotifers - large rotifers - copepods grow and reproduce.
According to the impact of zooplankton on the fish and water environment and their living rules, artificial use and regulation can be carried out. For example, in the spring, when the application of green manure and manure and other farm manure (chemical fertilizer is not OK) to cultivate protozoa and rotifers, 5-7 days later can form a peak of rotifers, at this time the water and flower seedlings in the pond at the right time, there is a rich and tasty supply of live bait, the survival rate is generally very good, especially loach, yellow spicy ding and other picky varieties of water and splash seedlings should be so; 10-15 days later, branches and radial feet and other large numbers appear, the same pond with the growth of seedlings or summer flower seedlings (inch seedlings or inch seedlings, mainly melon seed seedlings) at this time at this time at the right time to put down the pond, Seedling cultivation is carried out with extraordinary results.
(Loach splash)
2. If the water source is well water or spring water with almost no zooplankton, also known as oligohydrates, the first dominant population to emerge is usually the arm-tailed rotifer germination from the bottom of the pond, the emergence of kyllary rotifers a few days later, and then the peak of bare-bellied and muddy. As the fry grew, the branches were almost eaten up, leaving only copepods and a few rotifers. Such pond dominant populations are usually prominent, with the bulk of biomass concentrated in species such as Brachiocarpus, Bare-bellied Bulbophyllum and Genus T. chinensis.
3. If the water source is a reservoir, lake or other water that has formed a zooplankton community, there are more species of zooplankton in the pond, and there are also copepods, warty rotifers, giant wrist rotifers, three-limbed rotifers, tortoise beetles and multi-limbed rotifers in the branches, and there are more weevils, show bodies and boat eggs in the branches.
6. Aquaculture and zooplankton
Under fish farming conditions, the influence of fish feeding cannot be ignored, such as the late growth of fish fry ponds, which often eat the branches and horns. However, in the edible finished fish pond, the feeding of fish generally only changes the composition of plankton, and adult fish are often dominant because they choose to eat large species and make small species easy to survive. Zooplankton, like phytoplankton, is an indispensable natural live bait for fish. Among them, bighead carp feed on zooplankton all their lives, and rotifers and protozoa are natural open live bait for a variety of fish fry such as grass carp, silver carp, bighead carp, carp, crucian carp, bream and tuantou bream. The feeding habits of seedlings under 3 cm (inch seedlings) are not differentiated, and the feeding habits at this time are the same, and there is no distinction between zooplankton and plants.
(Fry)
Zooplankton are important food for fish and other economic animals in pelagic waters, and experiments have shown that the minimum biomass of rotifers to ensure good growth of silver carp fry is 3 mg/L, the most appropriate is 20-30 mg/L, and the maximum suitable for carp fry is 50-100 mg/l. Large zooplankton such as branches and copepods are also natural live baits for a variety of predatory fish, such as grass carp, carp, crucian carp, bream and tuantou bream.
However, everything must have a "degree", more algae will form a "bloom", such as too many cyanobacteria outbreaks are very headache. In the same way, if zooplankton form an absolute advantage, eat a large number of phytoplankton, reduce the energy of biological oxygenation (phytoplankton through photosynthesis oxygen), while making the water quality thinner and clearer, and consume a large amount of dissolved oxygen in the water, it is easy to cause fish floating head or serious floating head or even pond. At this time, the shortcomings of zooplankton appeared, they competed with the seedlings for oxygen and food, so that the growth of the seedlings was slow and the survival rate was low or even "completely destroyed".
If large zooplankton such as phylum and copepods enter the incubator with the flow of water, it will also endanger fish eggs and reduce hatching rates. Fish hatching water must be excluded from the harassment of large zooplankton, and can be intercepted and filtered by 60-65 days of ethyl gum cloth (silk) windows. If zooplankton form an excessive advantage in the pond, it can be killed with insecticides, and crystalline insects can be sprinkled at a concentration of 0.5 g/m3, which can kill most of the zooplankton and can remain a small number of zooplankton, so as not to become extinct and control biomass, in addition, increasing the stocking of bighead carp is also a good measure.
(Cyanobacterial outbreak)
7. The ecological role of zooplankton
Zooplankton can not be more but not less, phytoplankton and zooplankton "mutual balance", in the water body of zooplankton is not or too small, phytoplankton will grow sharply, may occur cyanobacteria outbreak or dead algae inverted algae, seriously corrupt water quality, is the most difficult problem for fish farmers. Therefore, in the fish farming water body should try to maintain a certain proportion of zooplankton, let it digest a part of the phytoplankton and control its overcrowding, so as to ensure the biological balance of the aquatic ecosystem, of course, the addition of silver carp is also the same effect.
Biologically, zooplankton feed on food, which also reduces the amount of organic debris and bacteria in the pond. Bacteria are an important source of food for zooplankton, it can eat a lot of germs and even some insect eggs (such as anchorhead loach eggs), has a certain effect on the prevention of fish diseases, and also has a great effect on the cleaning of water bodies.
In summary, water bodies with a large content of zooplankton have a much smaller probability of fish disease, and the water body is not easy to be overly fertile, and the water quality will not be eutrophicated. In the treatment of zooplankton, we should adhere to the principle that zooplankton must have but not more, not more but not less. That is to say, in the presence of a certain moderate proportion of zooplankton in the waters, in addition to the lack of oxygen, fish diseases are rare, and cyanobacterial outbreaks are impossible.
(Note: This article is original, for reference and communication only!) Most of the content and pictures are from online materials, if there is any disagreement, change or delete)
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