What are the protozoa that can cause disease in crayfish?

What are the protozoa that can cause disease in crayfish?

The results of the study have confirmed that some protozoa are pathogens of crayfish. For example, microsporidiosis (Microsporidiosis), psorospermiasis (Psorospermiasis), tetrahymeniasis (Tetrahymeniasis), Apostomes disease (Apostomes) of crayfish are caused by protozoa.

It may be that microsporidium and gumspora can be studied using very basic instrumentation even if they do not have particularly sophisticated instrumentation. Therefore, the most research has been done on these two parasitic diseases that can cause crayfish death, although our knowledge of the pathogens associated with these diseases is still quite limited. The spores of Gumsporidium parasitizing crayfish were described more than 100 years ago, but their taxonomic status was not clarified until the late 1990s.

Whether the crayfish that are parasitized with various parasites has parasitic diseases is related to the environment in which the crayfish are located, that is to say, these parasitic diseases can also be effectively prevented through environmental control. Infections such as tetramembranous worms and mouth worms can be effectively controlled through environmental improvement measures such as water exchange or reducing the load of organic matter in aquaculture water bodies. However, due to the lack of in-depth understanding of the basic biological characteristics of parasites such as microsporidium and gelosporidium, there is no particularly effective control measure for these parasitic diseases of crayfish.

(1) Microsporidiosis. Microsporidiosis is a disease that occurs frequently in crayfish because after this disease occurs, the clinical symptoms of the muscles of the diseased shrimp showing significant bleaching can be easily identified.

The infection rate of microsporidiosis in wild crayfish populations is usually less than 1%. However, there are few reports that this parasitic disease spreads quickly. Because microsporidiosis has been reported in wild crayfish populations, it has been suggested that microsporidiosis be used as an important prevention object in crayfish farming to design culture management measures. However, this is not the case observed in semi-intensive captive freshwater crawfish, where microsporidosis is rare in captive crayfish. According to the epidemiological survey results of microsporidium on captive crayfish, crayfish collected from the wild and reared in the first and second years are more or less affected by microsporangia, while microsporidium-infected crayfish are not found in subsequent feeding processes. Although the reason for this phenomenon is unclear, it is speculated that it may be because microsporidium has a relatively complex life history, and the completion of its life history requires other hosts in addition to crayfish as hosts, and these hosts may be fish or other organisms excluded by semi-intensive crayfish farming.

Of course, the above speculation also needs to be supported by the results of the trial, and there have been no successful trial reports so far. By feeding microspores infected with freshwater crawfish tissue to the same species of healthy crayfish, it has been demonstrated that microspores can spread infection successfully, especially diseases belonging to microsporidia, especially Thelohania and the likes of Thelohania. In Europe, the microsporidium commonly found in freshwater crawfish is mainly some species of Thelohania and Pleistophora, while Thelohaniacontejeani is the most common microsporidium. (2) Gumsporidiosis. Recently, the analysis of parasite genes using molecular biology techniques has shown that gelosporidium is a relatively primitive protozoa, which is more closely related to other protozoa that are more studied in aquatic animal pathology, such as Dermocystidium, Ichthyophonus and osetteagent. Psorospermiumhaeckeli, which is infected in European crayfish, is significantly different from the species infected with Australian crayfish and American crayfish. Although gumsporidium is not highly pathogenic to crayfish, large numbers of gumsporidiums can often be detected in dead shrimp cultures. In a large number of dead crayfish, individuals who can detect gumsporidium parasitism are mostly present in the tactile glands with eye necrosis.

(3) Tetrahymosis . Pear-shaped tetrahymosis

( Tetrahymena pyriformis ) is an opportunistic pathogenic organism for crayfish. Crayfish may also be infected when conditions are right. Ciliates may invade the crayfish blood cavities through epidermal wounds and live on crayfish blood cells and their tissues. Histological observations have shown that a surprising number of ciliates is often present in the blood cavities of crayfish infected with tetramembrane pears, and this phenomenon can also be found in gill tissues. In fresh gill tissue, the parasite can also be observed to move rapidly by relying on cilia, and with the circular movement of its cilia, the gill tissue of the crayfish is damaged.

(4) Mouthworm infection. Infection with anchovy worms on crayfish gills has been reported in the United States, but the parasite is less harmful to crayfish than other species.