Cryptonuclear stimulating insects, commonly known as seawater melon worms or seawater fish white spot disease, are a lethal parasitic disease of marine teleost fish. It is characterized by a large number of small white spots in the gills, eyes and skin of diseased fish. It is a serious hazard to marine aquaculture fish. In 2008 the Ministry of Agriculture No. 1125 listed it as a Class II animal disease.
Cryptonuclear stimulating insect is a common parasite in marine fish, can infect almost all kinds of marine cultured fish, in the south of China, mainly endanger grouper, yellow croaker, oval pomfret, cobia and other marine fish. The rate of transmission is fast, the mortality rate is high, and all farmed fish can die within 1-2 days. Its popular season is generally from May to October of each year, and it is high in late summer and early autumn. The optimal water temperature to stimulate cryptonuclear worms is around 25 ° C, and its reproduction rate will increase at this temperature. Especially after the typhoon, the environment in the sea area changes greatly, and it is easy for the fish body to erupt and stimulate cryptonuclear worm disease when the resistance of the fish body is poor.
Stimulation of cryptonuclear worms is caused by larvae swimming in the water to find a host, resulting in fish body disease can be divided into three periods:
Initial stage of disease: after contacting the host, the larvae will quickly burrow into the epithelium of the host's body surface in a rotating manner, forming a trophoblast, which will stimulate the host to secrete a large amount of mucus to envelop the insect body, resulting in the gradual appearance of "white spots" visible to the naked eye on the surface of the sick fish.
In the middle of the disease: many white spots will appear on the surface of the fish body, gills and even the eyes, accompanied by symptoms such as increased mucus, body surface congestion and gill ischemia. Irritating cryptonuclear infection usually leads to secondary infection of other causative factors such as bacteria. If there is no secondary infection of the bacteria, the infected damaged tissue can recover within a week.
Late onset: severe secondary infection, the physical function of the diseased fish is significantly reduced, and the eating is stopped until it weakens and dies. The trophozoites under the skin of the host fish develop into cystic precursors, detach from the host, reproduce asexually, and produce new larvae to infect other fish bodies.
Because of the open nature of mariculture waters, it is almost impossible to eliminate the possibility of contact between cultured organisms and the source of infection during the breeding process. Coupled with the increasing density of aquaculture, this also makes the outbreak of disease more and more frequent, and the harm caused by high death is becoming more and more serious. In order to solve the small melon worm, people have also exhausted all kinds of thoughts, using traditional drugs such as formaldehyde, hydrogen peroxide, quicklime, etc., and have also tried Chinese herbal medicines, but there is no obvious effect. Therefore, the treatment is difficult, and we can only take precautions in advance!
1. Improve the water environment:
Good water quality can reduce the stress response of fish, improve immunity and disease resistance. Marine cage culture should be selected in the waters with smooth flow and strong water exchange force. In the sea area with better water flow, the erosion of water can wash away the insect body on the surface of the fish body, and because of the flow of seawater, it is not easy to stimulate cryptonuclear worms to have the opportunity to attach, even if a small number of fish bodies still have pathogens that have not completely fallen off, it is not easy to infect other fish.
2. Reasonably control the breeding density, strengthen nutrition and enhance resistance:
Can not blindly pursue the yield and increase the density of breeding, stocking density is too high, it is easy to lead to poor breeding environment. It can be fed with liver-protecting bile acids to protect the liver of fish and enhance its own immunity and disease resistance.
3. Prevention and control of the use of safe drugs:
When parasites appear, a large number of chemical insecticides are often used, which will not only weaken the resistance of the fish itself, but also open a gap to the invasion of parasites, which is more likely to erupt in large quantities of parasites, and will also make parasites resistant. However, Lechang Eucalyptus essential oil has no negative impact in this regard.
Longchang Lechang is made of eucalyptus essential oil imported from Victoria, Australia, which has obvious avoidance effect on a variety of parasites, it has strong penetration and permeability, and can destroy the cell membrane structure of parasites to achieve the effect of killing parasites. Because it is plant extract, it is safe and green without toxic side effects, will not affect the fish feeding and its own health, and will not affect the water quality.
For stimulating cryptonuclear worms, there is no good way to treat them as far as the current means are concerned, and the use of some insecticides is often "injuring the enemy with a thousand self-damage eight hundred", so in the case of treatment conditions are not allowed, we must do a good job of management prevention and control to reduce the occurrence of parasites.