Hypersaline waters are unique polyextreme habitats, where the salinity limits species richness. There are main patterns of a relationship between salinity and the species richness of free-living aquatic animals, but for parasitic organisms, general regularities have not yet been established. There are quite numerous data on parasites in hypersaline waters worldwide; however, they have not been summarized before. This review tries to fill this gap by summarizing the available data. All parasites, 85 species and forms, found in hypersaline waters belong to five phyla: Platyhelminthes, Nematoda, Acanthocephala, Cnidaria, and Arthropoda. Platyhelminthes are the most diverse phylum with the highest species richness in class Cestoda. Most species were noted in hypersaline waters with a salinity of no more than 100 g·L⁻¹. The total number of parasitic species decreases exponentially with an increase in salinity. The number of free-living animal species inhabiting waters with a salinity from 35 to 210 g·L⁻¹ is approximately 12 times higher than that of parasitic ones in all intervals of this salinity range. Salinity influences parasite richness and composition in two ways—directly and through the availability of hosts. Free-living crustaceans were hosts of most parasite species in hypersaline waters. Artemia spp., the most halotolerant animals, are an intermediate host for 22 species and unidentified forms of parasites.

A total of 357 Syngnathidae fishes (Syngnathus abaster Risso, 1827, S. typhle Linnaeus, 1758 and Hippocampus hippocampus (Linnaeus, 1758) caught in different habitats along Crimean Black Sea shelf were examined for presence of endohelminths and revealed to be hosts of 15 helminth species. The fishes are second intermediate hosts for five “birds’” digenean species and nematodes (larvae of three species and immature adults of one more species) completing life-cycles in waterbirds and fish; for two acanthocephalans and three cestodes larvae ending development in fish. We suggest, basing on data on feeding of the Black Sea predatory fish and waterbirds, that Syngnathid fishes are paratenic hosts in parasitic systems of most cestodes, nematodes and acanthocephalans. All the trematodes found are generalists at metacercarial stage; specialists Timoniella imbutiformis and Aphallus tubarium use Syngnathidae as definitive hosts. Cestodes, nematodes as well as acanthocephalans found are generalists, too. Based on infection indices, S. typhle are main final host and H. hippocampus are main 2nd intermediate hosts for T. imbutiformis; Syngnathids are accidental hosts for other trematodes as well as for all the cestodes, nematodes and acanthocephalans. Cryptocotyle concava and Pygidiopsis genata are important as Syngnathid fishes’ threats, especially in marine protected aquatoria, being potential agents of “black spot disease”.

The genus Grillotia Guiart, 1927 is cosmopolitan in its distribution and the type-species, G. erinaceus (van Beneden, 1858), has been relatively well studied. However, this study provides infection indices of Grillotia erinaceus from southern and northern Black Sea whiting Merlangius merlangus for the first time. The specimens of Grillotia erinaceus were obtained from subserosa of the anterior oesophagus, stomach, pyloric caeca, liver, ovaries and mesenterium of whiting caught by commercial fishing vessels off Sinop, Turkey and off Balaklava, Ukraine. Fish were examined during the period from May 2011 to April 2012. Prevalence and mean intensity values in 268 fish collected off Sinop in the Black Sea were 18.66% and 1.82 ± 0.16 parasites per infected fish, respectively. In Ukrainian 166 whiting samples collected off Balaklava in the Black Sea, however, G. erinaceus plerocercus infection prevalence was 10.24% and mean intensity 1.71 ± 0.75 parasites per infected fish. Infection parameters were also determined at both sampling sites in relation with host length, sex and season.