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First, the main species and existing quantities in the fish pond
Zooplankton is a general term for heterotrophic invertebrates and chordate larvae that often float in the water and cannot make organic matter by themselves, and operate as a group of zooplanktonic animals in the water. They either have no swimming ability at all, or they have weak swimming ability, cannot move long distances, and are not enough to resist the flow of water.
Zooplankton are economic aquatic animals; It is an important bait for fish and other economic animals in the pelagic waters and has great significance for the development of fisheries. Because the distribution of many species of zooplankton is related to climate, it can also be used as an indicator animal for warm and cold currents. Many species of zooplankton are important sources of food for fish and shellfish, and some species such as hairy shrimp and jellyfish can be used as food for people. In addition, there are many species that can be used as indicator organisms for water pollution. For example, in eutrophicationic water bodies, species such as Moina, Sword Water Flea (Cyclops), Brachionus and other species generally form dominant populations. Some species, such as Tetrahymena phriformis and Daphnia magna, are used as laboratory animals in toxicological tests.
1. Protozoa:
(Protozoa: Ciliates)
Protozoa, single-celled miniature species (<0.2 mm), have an age time of less than a day, are numerous and usually have small expanses. Ciliates are mainly found in Chinese fish ponds, and the main species are: barrel shell worms, bouncing worms, rogue worms, trumpet worms and bell worms.
Existing quantity: mainly eat bacteria and other tiniest particles, and require a high food concentration of 20-60mg/L or more, so it is not easy to maintain a high density in the fish pond for a long time.
2. Rotifers:
(Rotifers: Lycamorecerciasis)
Rotifers are 0.2-0.6 mm long and have an age of 1.25-7 days. There are many species and stocks, and it is a suitable food for fry in the lower pond. The main types of fish ponds in China are: Calyx arm tail rotifer, arm tail rotifer, pot-shaped arm tail rotifer, crystal cyst rotifer, warty rotifer, split foot rotifer, three-limbed rotifer, needle cluster multi-limbed rotifer, bubble rotifer and tortoise beetle.
Availability: The food of rotifers is usually less than 12um, and large species can eat 20-30um of food, and the required food concentration is lower than that of ciliates.
3. Branches and corners:
(Branch: Bare-bellied)
Cladophyllum, also referred to as "lutes", water fleas (water fleas), commonly known as red worms, are invertebrates, crustaceans, gill-foot suborder, and bulbous horns. The body is short, generally 0.3-3mm in length, depending on the specific species, such as large clump can reach about 4.2mm, 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.
The generation time of the branches is 5.5-24 days, and there are not many species but the stock is often large, which is the main food in the middle and late stages of fry breeding. The main species in Chinese fish ponds are: longhair, large, bare-bellied and showy body.
Availability: 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 4.5-15mg/L, so rotifers are often inhibited 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 long, camp floating and parasitic life, distributed in the ocean, fresh water 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.
Copepod generation cycles range from 7 to 32 days. Its arthropods are the main food in the early stages of fry. The main types of fish ponds in the mainland are: large dart water fleas, right-sided new dart water fleas, neighboring sword fleas, widely spread medium sword water fleas and Taiwan Wenjian water fleas.
Existing quantity: Many of them are carnivorous, with rotifers, branches, etc. as the faith, due to the high nutritional level, it is not easy to reach a lot of density.
Second, the occurrence of zooplankton in fish ponds
1. The development law of zooplankton population after the pond is filled with water in the fry pond:
Ciliates and filter-feeding rotifers - carnivorous rotifers - small rotifers - large rotifers - copepods are dominant in order.
2, the water source is almost no zooplankton well water or spring water:
The first dominant species are usually the brachiocarpus that germinates from the dormant eggs at the bottom of the pool, and after a few days the kyllary rotifers appear, followed by the peak of the naked-bellied and sloppy. As the fry grew, the branches were almost eaten up, leaving only copepods and a few rotifers.
Such dominant species are usually prominent, and the vast majority of biomass is concentrated in species such as Brachiopodium, Bare-bellied Rotunda, and Bulbophyllum.
3. The water source is the water of reservoirs, lakes or other zooplankton communities that have formed:
There are more species of zooplankton in the pond, and at the same time as the arm-tailed rotifer and the crystal cystic rotifer, there are also copepods, warty rotifers, giant wrist rotifers, three-limbed rotifers, tortoise beetles and multi-limbed rotifers, etc., and there are more weevils, showgillus and boat eggs in the branches.
The temperature of freshwater aquatic animals common in the northern temperate zone is mostly 18-28 °C, so the zooplankton biomass of Yuchi began to increase significantly in late spring and early summer. Copepods are present all year round in fish ponds, overwintering under ice in winter and first predominating among 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.
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, the feeding of fish in the edible fish pond generally only changes the composition of plankton, often because of the selection of large species and small species are easy to dominate, but the total number of zooplankton has little impact, but the density of fish increases, the proportion of small branches such as elephant trunks and reticulated species increases, and the large species of the genus become smaller.
Most of the zooplankton biomass in high-yield ponds in mainland China is 10-20 mg/L, and the composition of the upper roundworm is absolutely dominant, followed by protozoa, and the branches and copepods are insignificant. According to Li Yonghan's determination, the minimum biomass of rotifers to ensure the good growth of silver carp fry is 3mg/L, and the most appropriate amount is 20-30mg/L; according to foreign reports, the minimum density of silver carp fry when eating elephant trunk is 170/l (3mg/L), the most appropriate density is 800-900/l (18mg/L); the most appropriate amount of fish fry is 50-100mg/L.
Third, the production volume
Protozoa , rotifers , and tyracena have shorter generation times , and all individuals in the population can multiply , with a higher turnover rate ( P/B coefficient ) ; copepods have a longer generation time , with only about half of the females can multiply , with a low P/B coefficient. Therefore, in the case of similar existing quantities, the production of the previous types of dominant zooplankton communities is higher than that of copepods.
| class | P/B值 |
| ciliates | 0.5-3 |
| Rotifers | 0.1-0.8 |
| Arm-tailed rotifers | >1 |
| Branches | 0.02-0.3 |
| Naked Belly Wayi | 0.5-0.6 |
| Copepods | 0.02-0.1 |
| Widely spread in the sword water fleas Bulbous water fleas | 0.1-0.2 or more |
According to the study, the effect of different fish farming methods on the stock of zooplankton in ponds was not obvious, but on production and P/B value.
1) Compared with the untroptilized fish pond, the zooplankton is not large, while the production volume is increased by 78%, and the P/B value is doubled; intensive culture and polyculture also have similar effects.
2) In the pond where the fish is fertilized and baited, due to the reduction in the amount of natural food eaten by the fish, the zooplankton biomass is doubled compared with the single fertilized fish pond, but the production and P/B value are not increased.
3) Bait-only fish pond zooplankton have the lowest number of zooplankton stocks and production.
4) The production of zooplankton in various types of fish ponds is about 8-43% of the production of phytoplankton, with the highest production of fish ponds with only fertilization.
5) The ratio of zooplankton production to its total food production (phytoplankton and bacteria) is 3-24%, with the highest fertilized fish pond, the bait pond is lower than the non-bait pond, and the single culture is slightly lower than the polyculture.
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