This paper makes a brief description of the identification, characteristics, transmission, routes of invasion of fish bodies, epidemiology, lesions caused by fish bodies and prevention methods, in order to hope that fish farmers can correctly diagnose fish parasitic diseases, formulate reasonable measures and alternative treatment options, and reduce the losses caused by parasitic diseases in the process of fish farming.
Of course, the occurrence or absence of fish parasitic diseases, the presence of pathogens is only one of the important factors, and the daily management, pool bottom, water quality, tool use and bait feeding are also directly related to it. The spread of many fish parasitic diseases is clearly associated with epidemics and human activities. Experience has pointed out that parasitic diseases are preventable and that it is entirely possible to minimize losses if the work is done well in advance. This is one of the main purposes for which the thematic website was developed.
(Cupworm)
<b>First, the identification of fish parasite species</b>
The diversity of organisms and lifestyles in nature is gradually formed in the long-term evolution of organisms. If there are two organisms living together, and only one of them benefits and the other suffers damage, it is called "parasitism".
Animals that live parasitically are called parasites, and the damaged animals and plants are the hosts. Life history refers to the growth and development of the parasite and the conditions required.
Depending on their species, parasites have different requirements for their hosts. Some require only one host, and do not change the host in the course of life history (such as monozoan trematodes), and some require one host or more (such as trematodes, echinococcus), that is, there are intermediate hosts and terminal hosts. The former refers to the host that is parasitized by the larvae, the asexual stage (life); the latter is parasitic in the stage of sexual maturity (adults) or in the stage of sexual reproduction. The source of infection of the parasite is called the host of the parasite.
(Anchorhead)
According to the difference in its parasitic site, there are in vivo and in vitro parasites. The former is like schistosomiasis (the pathogen of gill swelling), and the latter is like anchorhead bream. Contact with the host is only when food is needed, called transient parasites, such as vampire worms. If a certain stage of life can not leave the host, once left can not survive, called long-term parasites, such as parasitic worms of adult worms.
(Adult schistosomiasis)
According to the nature of parasitism, it can be distinguished into obligatory and facultative parasitism. Obligate parasites are parasites that must live parasitically or fail to survive. Species that can live freely and parasitize are facultative parasites.
The origin of the parasite is a more complex issue. There are two ways to speculate:
One is to change from a symbiotic life to a parasitic life;
The other is to live freely through facultative parasitism to true parasitism.
In the long process of changing from free life to parasitic life, the parasite has produced a series of morphological and physiological changes due to adapting to the new living environment and maintaining the reproduction of the race. For example, the body shape tends to be flattened and shortened; the body segmentation, the body segmentation decreases or becomes soft and elastic; the disappearance and degeneration of motor, digestive and sensory organs; the high development of the reproductive system, and hermaphrodites.
Physiologically, it has the ability to resist digestive juices; adopts new methods of obtaining oxygen and obtains energy; enhances fertility to compensate for losses in the host or during the conversion of the host; and forms various special tropisms to adapt to the external adverse environment.
(Flat mouth fluke)
<b>Second, the impact and harm of fish parasites on fish</b>
Mechanical irritation and tissue damage
Mechanical irritation and tissue damage are a common feature of parasitic diseases.
(Anchovy)
For example, a mackerel parasitizes, with its mouthparts and barbs on the ventral surface of the dorsal carapace, it stabs and tears the skin of the host, making the host very uneasy, and the sick fish swim wildly and jump away from the water.
The parasitism of the Greater Chinese gill can cause inflammatory edema and cell hyperplasia of gill tissue, and the appearance of the gill filament end is enlarged and whitish.
(Chinese bream)
Mechanical stimulation and damage can directly cause death or other lesions, bringing adverse consequences.
Squeezing and blocking
Some parasites that parasites in fish can often cause pressure on host tissues and organs, causing atrophy, necrosis and loss of physiological functions. This lesion is more common in the parenchymal organs.
(Fish Monster)
For example, the parasitism of fish monsters affects the development of the host reproductive glands, resulting in sterility of diseased fish.
(Taenia reticulata)
In addition to affecting the development of the gonads, taenia can also make the body cavity of the diseased fish bulge and bulge, affect swimming, and even abdominal distention, resulting in death.
The large parasitism of lateral trematodes can cause the intestines of small fish to block and cause death.
Blockage can also occur in blood vessels, such as schistosomiasis is a typical case, the triangular egg blocked the renal blood vessels, gill blood vessels, causing edema and gill necrosis.
Plunder the host's nutrients
The nutrients of the parasite are taken from the host, and the result must be some kind of harm to the host to a greater or lesser extent, the light manifestation is malnutrition, the growth and development are affected, and the heavy is even death.
For example, if it parasitizes the gills of sturgeon, each insect body draws 0.5ml of blood from the gills every day, and each sturgeon can parasitize 300 to 400 insects when it is serious, so that the host can lose up to 150 to 200ml of blood per day, so the diseased fish will quickly lose weight.
The effect of toxins
Parasites in the parasite process, its metabolites are excreted in the host. Some parasites can also secrete unique toxic substances, which have a certain impact on the host.
Glandular cells at the base of the crire mouth can secrete toxins.
Greater Chinese loach can secrete enzymes for parenteral digestion when feeding.
<b>Third, the host's resistance to the parasite</b>
Host resistance to the parasite manifests itself as a response (mainly an immune response) that affects the parasite.
Parasite invasion stimulates the host, causing the host's tissue response, manifested by the formation of connective tissue sacs or tissue hyperplasia and inflammation at the parasite site, in order to limit the growth of the parasite, weaken the firmness of the parasite attachment, and thus weaken the harm of the parasite to fish.
Fish reservoirs are sometimes more resistant. The antibodies they produce can inhibit the growth of insects, reduce their fecundity, shorten their lifespan, and even kill them.
But the host's resistance to the parasite is often incompletely immune, often in some equilibrium state, retaining a certain number of insect bodies in the body.
As the host ages, its parasite changes accordingly. Some increase with the age of the host; some decline in number; and some are independent of age. This change is often associated with a change in diet and an increase in food intake.