Dr. Kassai Tibor - Dr. Murai Éva szerk.: Parasitologia Hungarica 10. (Budapest, 1977)
oocyst wall did not exceed 130 R in thé species studied by LOM (19 71). The thin wall is extremely sensitive to exsiccation as well as mechanical and osmotic effects, and is liable to injury. The sporocyst wall is bilayered, structurally much more stable, and also more resistant; according to LOM(1971) the wall of the E. subepithelialis sporocyst consists of a200Ä > thick outer layer and a 700R thick inner one. The sporocyst wall may also be quite thick in certain fish coccidium species, e.g. in E. siliculiformis. 3. It is remarkable that several known species of fish coccidia (E. gadi, E.metscnnikovi, E. siliculiformis , etc.) establish themselves in organs (air bladder, liver, spleen, serous membranes) from which they cannot pass to the outside unless the host dies. 4. Most fish coccidium species are characterized-by a double-shelled, sutured spore, which had once served as one differentiating feature of the obsolete genus Goussia. However, in several species ( E. moronei, E. salvelini , E. anguillae, E. truttae ) either a typical Stieda body, or a terminal cap has been recognized at the more tapered end of the sporocyst. It follows from the foregoing characteristics that the coccidia of fish generally differ from those of other animal species. However, these differences are neither consistent, nor regular, Fish coccidium species displaying all general features of Eimeriae may exceptionally be found. The main differentiating feature from the coccidia of warm-blooded animals is the extremely thin oocyst wall, which can among others account for the rare detection of such parasites. Procedures employed for the demonstration of mammalian or avian coccidia (flotation, sedimentation, incubation in potassium bichromate solution) are less applicable with fish coccidia, owing to the vulnerability of the thin oocyst wall. Immobile protozoa usually escape the attention of the fish pathologist not versed in coccidiology,large their number may be. The technics of oocysts recovery The technical approach depends on the localization of the parasite. With intestinal Eimeriae the examination of unstained smears of faeces, mucus and mucosal scrapings proved to be the method of choice, whereas with those localizing in tissues, the microscopic examination of impression smears has been most succesful. Examination of the faeces ; Only the experienced examiner can detect oocysts in the faeces, and only in the case of massive infection. Faecal samples taken from different segments of the intestine are transferred to the slide and pressed by a coverslip for microscopic examination. Glossy sporulated oocysts become visible at 400 fold magnification. Examination of intestinal mucus: The intestinal contents of fish are often surrounded by a deposition of mucus along the epithelial surface of the mucosa. This deposition is nearly always found in hosts massively infected by coccidia. With some experience the mucous deposit can easly be removed from the solid intestinal content, even from the passed faeces, and it can be secured without adherent clumps of faeces if the fish have been starved for one or two days. The mucous deposit, colourless or yellowish, can easily be examined for oocysts under a coverslip. The oocysts are frequently embedded in a so-called yellow body, and occur either singly or in groups of 2 to 5. If the intestinal content is covered by too small amount of mucous deposit, mucus can be collected from the surface of the intestinal epithelium by cautious scraping. In this case many epithelial cells become admixed with the sample interfereing with the detection of the oocysts. Examination of mucosal scrapings: This approach is less reliable than the other two, because part of the oocysts localizing in the intestinal mucosa are still in the unsporulated state sendering their detection more difficult. Parallel microscopic examination of the faecal mucous deposit and mucosal scrapings is nevertheless strongly recommended, because Eimerian species establishing themselves in foci or in deeper layers of the propria such as E. sub epithelialis can still be most easily found in this manner. Flotation, filtration and sedimentation: Coccidian oocysts of warm-blooded animals are separated from the faeces chiefly by flotation, occasionally combined with other procedures
