Myxosporeans of the genus Kudoa (localization in the fish body, the form of spores and ways of their entry into the environment and into new hosts)

Abstract

The purpose of the research is to study the localization of myxosporeans of the genus Kudoa Meglitsch, 1947 in body fish and possible ways for them to master organs and tissues in the process of evolution, the form of spores associated with localization, as well as the ways of their release into the environment and getting into new hosts.Materials and methods. The work is based on our own materials on fish myxosporeans from the Black, Azov and Mediterranean seas, as well as the Atlantic, Indian and Pacific oceans, collected in 1987–2021. In total, we have studied more than 12,000 sp. more than 100 species of fish. We also analyzed descriptions of 126 species of myxosporeans of the genus Kudoa, known in the world scientific literature until 2021 inclusive. For this, 450 domestic and foreign works have been worked out. The material was collected by the method of incomplete parasitological dissections. Smears made from tissues were processed according to the generally accepted method with the manufacture of permanent preparations. All measurements were made according to the standard method. To assess the number of parasites, standard indicators were used: the extensiveness and intensity of infection.Results and discussion. In total, we studied 19 species of myxosporeans of the genus Kudoa and 8 species of Kudoa spp. Six species (K. stellula, K. niluferi, K. anatolica from the Black Sea, K. unicapsula from the Mediterranean Sea, K. borimiri and K. igori from the South China (or East) Sea) were new to science. We have established 24 places of parasitism of myxosporeans of this genus in the body of fish. 83 species (66%, or 2/3 species) are found in muscles, sometimes affecting (8 species) other tissues and organs of the host. 43 species (34%, or 1/3 species) of representatives of the genus Kudoa are never found in muscle tissue. The primary sites of parasitism of myxosporeans of the genus Kudoa were probably the intestinal wall and gallbladder, then the parasites mastered other internal organs of fish and, ultimately, brain and muscle. The hypothetical ways of getting spores into the external environment and into new hosts are indicated. It is assumed that the most ancient forms are bivalve Kudoa, parasitizing in the gallbladder, four-valve Kudoa of an unusual shape, resembling representatives of other genera and parasitizing mainly in internal organs, as well as four-valve Kudoa with a classical square spore shape, rounded valve tops, with four equal polar capsules and the smallest sizes. Spores with a pointed stellate shape (only muscular forms) and spores with five or more valves and polar capsules (occurring in muscle and brain and having a larger size) should be considered to have arisen at a later time. The ways of getting spores into the environment and into new hosts are highlighted.