Exclusive report of Teng's Aquatic Products Business Network:
Author | Live Baoyuan Fish Disease Room Liang Zhiyuan Hu Fei Hu Xiong
Raw fish, also known as blackfish, belongs to the order Perch, Trout family, snakehead genus, with strong vitality, fast growth, high yield, less disease, good meat quality and other advantages, is one of the famous freshwater breeding species in China.
In the Pearl River Delta region, the main farmed raw fish are hybrid snakeheads, with a small number of them (commonly known as Hong Kong species). Because raw fish has a special auxiliary respiratory organ----- gill upper organ, the ability to tolerate low oxygen is very strong, and the mucus on the surface of the body is very rich, the disease resistance is very strong, the adaptability is very wide, and it is generally rare to occur. In recent years, with the increase of culture density, the disease problem of raw fish has gradually become prominent, but it is mainly concentrated in epidemic ulcer syndrome (EUS), nocardiosis, Schubert aeromonas, whitehead and white mouth disease. Regarding the parasites of raw fish, there are not many reports in the industry, and there are few relevant literature, but in practice, we sometimes encounter cases of raw fish infected with a large number of parasites and cause death; on the other hand, some body surface parasites, although they do not directly cause raw fish death, will lead to body surface damage, and it is easy to cause secondary fibrous mold infection and rot disease during the overwintering period.
It is predicted that the probability of cold winter this winter is large, and the prevention and control situation of raw fish epidemic ulcer syndrome (EUS) is more severe. The pathogen of raw fish epidemic ulcer syndrome is filamentous mold, and the invasion of sac mold is premised on body surface damage. Reasonable insecticide before winter, preventing parasitic bites, and avoiding fish body injuries into winter is one of the important measures to prevent epidemic ulcer syndrome in raw fish. So, what are the parasites of raw fish, those that will cause damage to the body surface, how to kill insects reasonably before winter?
I. Overview
According to hundreds of raw fish samples tested since the establishment of the Huobaoyuan Fish Disease Room, a total of 11 species of parasites were detected: gill cryptoflagellus, six-front flagellar, filariae, tailsporum, wheelworm, cupworm, small melon worm, tired branch insect, three-generation insect, nail worm, Taiwan spiny band fluke (tail cyst), etc. Among them, gill cryptoflora, cupworm and Taiwan spiny band fluke (tail cyst), six anterior flagellar parasitize only in the stomach, tired branches and nail worms only parasitize on the body surface, mouth filaria, tail spore, wheel worm, melon worm, three generations of worms, etc. can parasitize both gills and body surfaces. In addition, the industry's reported Emmy worm, quadrupolar worm, oblique tube worm, uterine nematodes, compound flux, etc. have not been detected.
Second, raw fish parasites and their control methods
2.1 Gill crypter whipworm
It belongs to the genus Bo legumes, Cryptocephalus. The insect body is long and narrow, with a willow-like silhouette, 2 flagellar hairs, and often swings irregularly (P01, V01). It is mainly parasitic in gills and occasionally in seed and first-instar fish. When raw fish are infected with a small amount of gill cryptoflagellus, there is no obvious disease, even if the number of infections is large, there is no obvious abnormality in appearance, and there are generally no dead fish, but the feeding will become worse or even appear spitting.
When the number of gill cryptocephalus infections is small, it can be left untreated, and the water can be adjusted and oxygenated to ensure that the dissolved oxygen of the water body is sufficient; if a large number of infections affect feeding, zinc sulfate can be used for expulsion.
P01: Cryptocephalus (40*10)
2.2 Six preflagents
It belongs to the family Hexaphoridae and the genus Hexaphora. The worm body is pear-shaped, has 4 pairs of flagella, and is very active (P02, V02). It is mainly parasitic in the stomach and is only sporadic in the middle and late stages of culture. When hybrids are infected in large numbers with the worm, the fish are emaciated, poorly fed, have significant enteritis, and have a persistent small number of dead fish.
P02: Show six front flagellar (40*10)
Due to the low detection rate of the insect, its epidemiology is unknown, and there is currently no therapeutic drug for the insect in China. However, in our experience, the pure feed hybrid snakehead has not been detected, and it is inferred that it may be related to the feeding of unclean food such as chicken intestines.
2.3 Mouth filariae
Also known as fish and bean worms, it belongs to the family Bo Legume and the genus Officiasis. The worm is ovate or pear-shaped, with 2 (sometimes 4) flagellar hairs at the front end, and is very active (P03, V03). It is mainly parasitic on the surface of the body, followed by gills. When raw fish are infected with filariae in large quantities, the diseased fish float on the surface of the water, have poor vitality, and have a slight redness on the body surface (P04), which can cause a sustained small number of dead fish in severe cases.
Spotted snakeheads are very susceptible to filariasis, hybrids are often detected, and can be infected in various sizes, with diseases occurring almost all year round. If diagnosed, zinc sulfate, etc. can be used for exorcism. However, the worm is prone to recurrence, and it needs to be re-examined after medication and re-administered if necessary.
2.4 Ceratophyllus
It belongs to the family Iodophyllaceae and the genus Tailspora. The worm body is spindle-shaped, with 2 polar sacs, and the shell extends from the posterior part to two caudal processes, which are generally stationary (P05). It is mainly parasitic on the surface of the body and gills, and when the number of parasites is small, the disease is not obvious; even if there is a large number of infections, it is only manifested as a dark body color, dullness, mild ulceration at the lesion (P06), and generally no dead fish or only sporadic dead fish.
Left: P05, show the sporangia and body of the tail sporangia (40 *10), right: P06, show the tail sporangia foci
The worm is more common in autumn, and because its sporangia can cause damage to the surface and gills of diseased fish, it may be secondary to infection with filament mold during the overwintering period and cause raw fish to rot. Therefore, it is recommended to properly mix with special drugs for sporangia such as chlorphenidine hydrochloride or dichloruli in autumn for prevention; if confirmed, targeted drugs should be used in time for exorcism.
2.5 Wheelworm
It belongs to the genus Officinalis and Rotifers. The insect body is disc-shaped on the reverse side, felt-like on the side, and more lively when moving like a rotating wheel (P07). Raw fish are very common in the seedling stage, mainly parasitic gills and body surfaces, resulting in poor feeding, fish body wasting (P08), easy to induce columnar xanthobacterium infection or bullet virus disease, which can directly lead to a large number of seed deaths in severe cases; in the middle adult stage, it is mainly parasitic gills, but generally the number is not large, and the harm is not large.
Left: P07, show gill wheel worm (10 * 10), right: P08, show wheel worm disease fish body emaciation
The insect is endemic from April to October and mainly endangers seedlings. In the seedling stage, bacillus, photosynthetic bacteria and other beneficial bacteria should be flexibly used to improve the stability of the water body, maintain the appropriate fertilizer of the water body, and regularly test the fry (2-3 days to detect once), once the infection is confirmed, timely use of copper sulfate and other broad-spectrum insecticides or other special drugs for wheel insects for exorcism.
2.6 cupworms
It belongs to the family P. reedidae, the genus Cupworm, and is an epiphytic ciliate. The worm body is cup-shaped, thick at the anterior end, cilia, narrowed backwards, and has an attachment disc (P09, P10) at the back of the body. Cupworms only parasitize gills, all sizes of raw fish can be infected, most common in ponds with poor water quality, often in the form of secondary pathogens, generally do not cause disease alone, but when they are infected in large quantities, it will affect breathing and worsen the condition.
P09, P10: Cupworm
Cupworms can infect raw fish of all sizes and are detected almost all year round. However, even if cupworms are detected from diseased raw fish, special attention should be paid to the presence of other pathogenic infections, and priority should be given to the treatment of major pathogens. If the number of cupworms is particularly high, zinc sulfate can be used for expulsion.
2.7 small melon worms
It belongs to the family Notchidae and the genus Melon. The worm body is ovoid, cilia, and has a large horseshoe or sausage-shaped nucleus (P10) in the middle of the adult body. Small melon worms mainly parasitize the body surface and gills, only seen in the seed stage; when parasitizing in large quantities, the body color of the diseased fish is black, the response is sluggish, and the body surface is covered with white spots (P11), and as the disease worsens, the diseased fish will die in large numbers or even completely cover the pond.
Left: P11, show small melon worm (10 * 10), right: P12, show small melon worm disease fish (body white point)
Raw fish melon worm disease is more common in factory nurseries, and if diagnosed, it can be controlled by raising the water temperature to about 32 °C. Raw fish fry cultured in ponds under natural conditions generally do not become infected with disease, and seed quarantine can be effectively prevented.
2.8 Tired branches
It belongs to the family P. idae and the genus P. phylloscopus. The worm body is cup-shaped, thick and fibrous at the front, retractable, attaches to the fish body with the help of a muscle stalk, mostly lives in groups, and the group branches are equally bifurcated (P12). The worm mainly parasitizes the surface of the body, early infection, redness, bleeding at the lesion, there is a small amount of hair (P13), as the disease progresses, often due to the large number of insects or secondary infection with water mold and a large number of hairy (P14, P15), and there are a small number of persistent dead fish.
Left: P13, showing mycoccystium (10*10), right: P14, showing mycoccal infection with foci of the lesion
P15, P16: shows trichomes at the lesion after infection with a large number of mycobacteria
P. repertoire infects raw fish almost all year round, but is most prevalent in October and November. The parasitism of the insect has a great relationship with water quality, and the incidence is high during the period of water quality fluctuations. In autumn, appropriate diligence to change the bottom, and the rational use of bacillus, lactic acid bacteria and other beneficial bacteria, maintain appropriate fertilizer, improve the stability of water, is an important means to prevent the insect. If it is diagnosed, it can be exorcised with special drugs for ciliates such as zinc sulfate, and an appropriate amount of enrofloxacin and multi-dimensional drugs can be taken internally to promote wound healing.
2.9 Three generations of insects
It belongs to the trinidae and trinidae. The worm body is finger-shaped, with 1 pair of central large hooks and 16 small edge hooks in the posterior suction device; no eye spots; the uterus has an embryonic body with a "fetus" inside, often seen in the central large hook (P16); as a leech-like movement. The worm predominantly parasitizes the surface of the body and is also detected in the gills when it is severely infected. When raw fish are infected with individual three-generation insects, the symptoms are not obvious; when infected in large quantities, raw fish have poor vitality, float on the surface of the water, redness on the body surface, less mucus, sunken eyes (P17), redness of muscles, intestines and so on (P18), and a small number of persistent dead fish.
Left: P17, showing three generations of insects (10 * 10); medium: P18, indicating the redness of the body surface of the diseased fish; right: P19, indicating the redness of the muscles and intestines of the diseased fish
The insect mainly infects first-instar fish and is common in summer and autumn. If confirmed, mebendazole can be used for exorcism, and the effect is very significant.
2.10 Nail worms
That is, anchorhead bream, belongs to the anchorhead bream family, anchorhead bream genus. The body is elongated and needle-shaped, the body of the insect is nearly transparent in childhood (P19), the body of the worm becomes cloudy in the old stage, and the banded oocyst (P20) is often seen in the tail. The nail worm only parasitizes the surface of the body, and in the early stages of parasitism, it is difficult to detect because of the slender body; as the worm grows, there is punctate bleeding and damage at the lesion (P21); the worm body will fall off on its own after aging. The worm does not directly cause dead fish, but it can cause the fish to be restless, eat poorly, and because it can damage the surface of the diseased fish, it may induce rotting disease during the overwintering period.
P20, P21, P22: Shows nailworms and wounds caused by nailworm infections
The worm can infect raw fish of various sizes, all year round, and is relatively common in autumn. Its life history is more special, which can be divided into four stages: egg, arthropod stage, copepod larval stage, adult stage, etc., while fishery insecticides are only effective for arthropods and copepod larvae. Therefore, it is recommended to take prophylactic drugs against this insect 1-2 times in the autumn; if confirmed, it is possible to use cypermethrin, octylthion, etc. for exorcism, every 3-5 days, 2-3 times continuously.
2.11 Taiwan spiny band fluke (cysticercosis)
It belongs to the family Trematodes, The Order Polypodidae, and the Family Heterogeneous. The worm (Cysticercus caudatus) can parasitize the gills of raw fish. The worm body is ovate and the excretory sac is "worker" or "X" shaped (P22, P23). It only parasitizes gills, which can destroy gill filaments and hinder breathing; the general number of infections is not much, the harm is not large; and it is also occasionally seen that a large number of raw fish seed infections, although it does not cause dead fish, but the long speed is very slow, which seriously affects the efficiency of breeding.
P23, P24: Gills of the oseulin infected with the Taiwan spiny fluke cysticers
The insect is a tail cyst of Taiwan spiny fluffworm, and the Taiwan spiny fluffworm uses freshwater snails as the first intermediate host. Therefore, thoroughly clearing the pond before releasing seedlings and killing snails can be effectively prevented.
3. Prevention and control recommendations
Raw fish has a strong resistance to low oxygen, the mucus on the surface of the body is very rich, and the disease resistance is very strong. Although we have detected many species of raw fish parasites, in most cases the parasites infected by raw fish are in a latent state, and the large number of infections has a great relationship with water quality, and cases of death caused by parasite infection alone are not common.
Before releasing seedlings, do a good job of clearing the pond, remove harmful organisms such as snails, and flexibly use beneficial bacteria such as photosynthetic bacteria and bacillus in the breeding process to maintain the appropriate fertilizer of the water body and ensure adequate dissolved oxygen, which is the basic measure to prevent raw fish parasites. If treatment is required, because the species status of these parasites varies greatly, the sensitivity to drugs varies greatly, and it is generally recommended to select and use drugs after diagnosis.
However, it should be noted that the body surface parasites such as nailworms, twigs, three-generation insects, tailspores, and mouthworms, although it is not common for large infections to directly lead to dead fish, even a small number of infections can cause body surface damage, laying a huge risk of outbreak of epidemic ulcer syndrome (rot disease) for infection with filar mold during the wintering period. Therefore, we recommend that in the autumn, special attention should be paid to these surface parasites, strengthen detection, if found, timely targeted drugs; even if not detected, when formulating the insecticidal plan before winter, special attention should be paid to the above-mentioned surface parasites, targeted medication, to ensure that the fish body is healthy in the winter, safely through the wintering period.