A study of myxosporea SPP in Rutilus rutilus L. (roach) with particular reference to Myxidium rhodei Leger, 1905 in the renal tissue

Abstract

The myxosporean parasites of roach (R. rutilus L) were studied in three different water bodies, two in Britain and one in Northern Greece. Two Myxobolus species (M. pseudodispar Gorbunova, 1936 and M. ellipsoides Thelohan, 1892) and two Myxidium species (M. rhodei Leger, 1905 and M. pfeifferi Auerbach, 1902) were found. M. pseudodispar and M. ellipsoides were found in the kidneys and spleen, whereas M. ellipsoides was found in the kidneys, spleen, gill, gill arch and cartilage. M. rhodei was found in the kidneys, liver, spleen and muscle, whereas M. pfeifferi was found exclusively in the gall bladder and bile ducts. The seasonality of the two Myxobolus and two Myxidintn species was investigated in the present study, and showed that in each of the different habitats all the parasites had at least one peak in prevalence in Springtime. In addition to this, the two myxobolid species found in the Greek lake as well as Myxidium rhodei in all three locations, show another peak during the Winter months (December to February). Myxidium pfeifferi showed only one peak in Spring (April to May) in all three lakes. The two Myxobolus species studied in the present project were considered well adapted kidney parasites provoking no host response to this tissue. In contrast, M. pseudodispar in the muscles and M. ellipsoides in the gills were found to be very pathogenic. The spore morphology and variability study of these two species showed that M. pseudodispar has a distinct variability in the spore dimensions between the organs of fish, although M. ellipsoides showed only slight differences. From the study of the two Myxldlum species, evidence was produced that M. rhodei is synonymous with M. pfeifferi. This evidence was produced from the morphological investigation and the experimental infections carried out in two fish hosts and was supported by the seasonal data. Through three different experimental infections in carp and roach, the life cycle of M, rhodei and its development in the hosts was proposed. No intermediate hosts could be detected in the life cycle of the parasite and the Exposure Method was considered the most effective, and the Intraperitoneal Injection Method the second most successful one. Two cycles of development of M. rhodei infection were detected in roach. The first, occurring in the bile ducts, had a fast process resulting in the production of mature and maturing spores. The second started with the infection of glomeruli and had a slow progress with the final production of cysts containing mature spores. Lesions due to degenerating trophozoites were also detected in the interstitial tissue of the kidney, where they were usually calcified and in the heart. Large mature cysts were also found in the muscles of the fish. In the liver, disturbance of the metabolism of the body was assumed from the extent of the lesions in heavy infections with M. rhodei. The pathogenicity of the parasite was thought to be serious in both renal tissue and liver/bile ducts. In the kidneys, the pathology concerned both the glomeruli and interstitial tissue. The pathology was assessed for the first time in terms of area of lesions and volume of affected tissues, as well as in relation to the environmental conditions of the habitats. Other concurrent infections and conditions in fish with M, rhodei were considered to enhance the pathology of M. rhodei in the hosts. Finally, the infection of M. rhodei was considered important in terms of both Greek economy and fish health monitoring.