Monofoliosis in freshwater farmed fish is mostly caused by parasites of the family Ringworm, The Family Of Anchor worms and the Family Trinidae, and the common monozoan trematode species, infected fish and parasitic sites are shown in the following table:
There are many species of monocultural trematodes that parasitize freshwater farmed fish, but all have a common feature, that is, the insect body has a chitin structure of a fixator, which is inserted into the host tissue.
1. Morphological characteristics
Ringworm Three generations of insects
Parasites of the family Ringworm have 1-3 pairs of headparts and two pairs of black eye spots, the posterior sucker has 7 pairs of small edge hooks; the parasites of the family Anchorhead have 2-3 pairs of head glands and tail glands, with the presence or absence of eye spots, and the posterior sucker has 7-8 pairs of edge hooks, sometimes with 1-2 pairs of needle-like structures. Parasites of the trinidae have a pair of heads, no eye spots, and usually a pair of large edge hooks and several small edge hooks.
2. Ecological characteristics
Monozoan flukes are a type of parasite with strong host specificity, and some monocultural fluke hosts are not specific or have no host specificity (such as neobendeniae, etc.). From an individual point of view, monozoan flukes have strong site specificity, and the site specificity of monosormal trematozoans means that parasites only parasitize in specific parts of the host such as gills, fins, body surfaces, etc., and most monozoan trematozoans only parasitize in gills.
Under pond culture conditions, the number of gills parasitic on silver carp gradually increased from February to March and reached a peak in April; the number of phylloids parasitic on grass carp gills gradually increased from November to March and reached a peak in April; the three generations of gills parasitized on gills were mostly parasitic on the first and second gills of silver carp, and the number of fingerworms parasitic on the 2nd and 3rd gills (Yao Weijian et al., 2004).
Populations of sphingular ringworms that parasitize gills begin to appear in November and peak in infection and abundance in late spring and April. (Xia Xiaoqin et al., 1999)
Eel pseudo-ringworms prefer to parasitize on the left gills and mostly on the 3rd and 4th gills, while short hook pseudo-ringworms prefer to parasitize on the right gills and parasitize on the 1st and 2nd gills (Buchman, 1990).
Monophytic trematodes (yellow-jawed four-anchorworm, yellow-jawed pseudo-plate worm, moonax pseudo-anchor plate worm) on the gills of the yellow-jawed fish are mostly parasitic on the 1st, 2nd and 3rd gills, and the number of parasites in the gill area is the largest (Yao Weijian; 2003).
Many studies have shown that the size or age of the host is positively correlated with the population abundance, infection rate, infection intensity, number of parasites, etc. of monozoan trema. For most third-generation insects, the rate, number, and intensity of infection increase with increased water temperature, which is certainly not unlimited. For other monozoan trematodes, high temperatures become limiting factors, and their infection rates, numbers, and infection intensities peak at lower temperatures (Liu Jifang et al., 2002).
3. Life history
Except for some species of the trigeneridae, most monozoans are oviparous.
Ringworms that are ovulating Ringworms and eggs
After the fertilized egg is excreted from the worm body, the attachment structure on the egg makes it easy to float on the surface of the water or attach to other objects or host gills and skin, generally it takes 7 days to hatch the larvae, but under other stimulating conditions (such as drugs), it only takes 3 to 5 days. Hatched larvae survive for about 1 to 75 hours, and will die on their own without a suitable host. After the host dies, the parasitic ringworm dies in a short period of time (24 hours).
The hatching rate and incubation time of monofocal trematosus eggs are significantly affected by temperature, and the effect of temperature on monofocal tremalar larvae decreases with the increase of temperature.
Monozoan trematodes that parasitize the surface of the body feed on the epidermis, and monosozoans that parasitize gills feed on blood or mucus.
4. Symptoms and pathological changes
Monozoan flukes exhibit obvious "social" phenomena when they parasitize the gills of fish, and there are no obvious symptoms in farmed fish when a small number of monozoans are infected, which are mostly manifested by decreased food intake or dark floating head phenomenon. In large parasites, the diseased fish have difficulty breathing, swim slowly, the gills are significantly puffy (the bighead is more pronounced), and the gill lid is open. Increased mucus on the gills, swelling or adhesions of the gills, degeneration or necrosis in severe cases, pale or gills (carp) due to anemia.
Microscopy is the only diagnostic method, and special attention should be paid to the fact that under the condition of conventional fish culture in ponds, in order to prevent missed diagnosis of monofocal trematodiasis, when using a microscope to quickly check parasites such as grass carp gills, crucian carp and bighead carp must be examined for reference for judgment.
5. Prevalence
Ringworms are transmitted by eggs or larvae. It is endemic in late spring and early summer, with a suitable temperature of 20 to 25 °C, and fish such as tilapia and freshwater pomfret can also occur when fish species overwinter. It mainly endangers silver carp, bighead carp, grass carp, crucian carp, bream, mandarin, eel, yellow jaw, salamander and so on.
The three-generation worm is mainly infected by direct contact between hosts. The three generations of insects have a strong specificity of the host and the middle class and parasitic site, parasitizing the surface and gills of fish. It is easy to catch in late spring and early summer or indoor overwintering. It harms a variety of light and seawater fish, mainly carp, silver carp, grass carp and so on.
Monosozoans are more harmful to fry and fingerlings, and a large number of parasites often cause a large number of seed deaths. Parasitic large-sized fish species or adult fish often cause secondary bacterial infection of farmed fish and cause outbreaks of bacterial diseases (such as gill rot, fulminant hemorrhagic disease, borer fins, etc.) and produce a large number of deaths, in the process of grass carp, crucian carp and other fish breeding process, monoculoskesasis is often associated with protozoan parasites such as wheelworms, and monocultural trematodiasis is also often secondary or complicated by mandarin infected spleen and kidney necrosis in the process of mandarin fish farming.
6, control methods: monofoliary trematodes parasites are very easy to form resistance, the vast majority of conventional insecticides such as "enemy insects" or "enemy insects + face alkali" is currently unable to control the disease. The usual control methods are: (1) ponds or small lakes and reservoirs for the cultivation of grass carp, silver carp, bighead carp, carp, crucian carp, bream, eel, eel, etc. are sprinkled with "car finger double killing" or "car finger double killing + increased copper ;(" ;(3) the whole pond of the reservoir or lake when the large water surface is cultured, the whole pond is sprinkled with "mixed special an" or "mixed security + septic stop" 。
7. Special tips: (1) The amount of the above drugs in the treatment of seed monoculture trematode disease is halved, and the above drugs are prohibited from the treatment of splash monoculture trematode disease of various farmed fish; (2) when using ferrous sulfate to increase efficiency, ferrous sulfate must be sprinkled first, and then sprinkled with "ring special killing" ;(3) Saline ponds or ponds with large alkalinity should appropriately increase the amount of "ring killing"; (4) breeding ponds with high organic matter content should appropriately increase the amount of drugs or first splash "double-effect water Lijing" ;(5) Breeding ponds using groundwater as water sources should be sprinkled first" Use the above drugs after the "fresh water detoxification tablets" or "detoxifying living water treasure"; (6) when secondary bacterial diseases are developed, the sterilization and disinfectant drugs and oral antibacterial drugs should be sprinkled after the use of the above methods.