First molecular identification, biological diversity, and infection features of myxozoan parasites in Whiting Merlangius merlangus along the Turkish coast of the Black Sea.

Objective: Myxosporean parasites are worldwide-distributed cnidarians that infect the organs and tissues of marine and freshwater organisms, primarily fish. Based on morphological peculiarities, two myxosporean species, Myxidium gadi and Ceratomyxa merlangi, from the gallbladder content of Whiting Merlangius merlangus inhabiting four sampling localities (Kocaeli, Sinop, Ordu, and Trabzon) along the Black Sea coast of Türkiye have been identified.

Methods: Concordant with the morphological data, the first phylogenetic analyses on the nucleotide sequences of 18S ribosomal DNA confirmed our Myxidium specimens to be M. gadi. This study also provided the first molecular data on C. merlangi, which appeared to be the closest species to C. cretensis and C. arcuata on the phylogenetic trees. The infection prevalence (%) and density values of each parasite species were calculated according to season and sampling localities of Whiting.

Results: Ceratomyxa merlangi had a higher overall prevalence value (39.6%) than M. gadi (25.7%). The density values of both parasite species ranged between 2+ and 3+ in all fish samples. When the infection indices in sampling localities were compared for both parasite species, C. merlangi and M. gadi had the highest infection prevalence values in Sinop samples (66.3%); the highest density of infection (3+) was recorded in Sinop samples for C. merlangi and in Ordu samples for M. gadi.

Conclusions: This study provides the first molecular data on M. gadi and C. merlangi, revealing their phylogenetic positions. In addition, seasonal and regional infection data for these species in the southern Black Sea region are reported for the first time, and it has been determined that both species can occur together.