Representatives of a total of twenty fish species, most of them marine, from the Black Sea coast in Rumania were investigated. Of these, ten species were found to harbour ectoparasitic trichodinids on their skin and gills. Three of them, Trichodina rectuncinata Raabe, 1959, from Gaidropsis mediterranaeus and Crenilabrus griseus, T. caspialosae (Dogiel, 1940) mihi from Alosa braschnikowi meotica and T. d. f. latispina from Gasterosteus aculeatus, were already known.
Three species could be established as new ones: T. puytoraci sp.nov. from Mugil auratus, M. cephalus and M. saliens, T. raabei sp.nov. from Pleuronectes flesus and T. lepsii sp.nov. from M. auratus. They are clearly differentiated from other species.
The following trichodinids were provisionally classified as forms (including one new one) of T. domerguei, thus enlarging this most complicated Trichodina species: T. domerguei, cf. latispina from Gobius syrman, T. domerguei f.n. maris-negri from Gaidropsis mediterranaeus, and T. domerguei f. partidisci from Mugil cephalus. Other populations of T. domerguei could not be properly classified because of lack of material.
The description of the new species of Tripartiella which have been mentioned in the introduction, will be given in a separate paper.
A short survey on marine trichodinids recorded up to the present is given.