Synthesium Tursionis (Marchi, 1873) Stunkard & Alvey, 1930 (Trematoda: Brachycladiidae) in tursiops truncatus (Montagu, 1821) (Cetacea: Delphinidae) in the state of Santa Catarina, southern Brazil

Abstract

The common bottlenose dolphin (Tursiops truncatus Montagu, 1821) is widely distributed worldwide. In Brazil, parasitological studies on cetaceans remain scarce and are mostly based on stranded individuals, which limits our understanding of their parasitic fauna. This study aimed to report the occurrence of the trematode Synthesium tursionis (Marchi, 1873) Stunkard & Alvey, 1930 in T. truncatus along the southern coast of Santa Catarina, Brazil. Between 2020 and 2024, 36 dead dolphins were examined, of which only four were in suitable condition for parasitological analysis. A total of 494 parasites were recovered, 472 of which were identified as S. tursionis, found exclusively in the subspecies T. t. truncatus. Identification was based on morphological and morphometric analyses, complemented by molecular characterization using the 18S and 28S rDNA genes. Molecular analyses revealed a single haplotype with 100% identity to sequences available in GenBank, confirming species identification and suggesting low genetic variability in the studied population. These findings expand the known distribution of S. tursionis in the South Atlantic and reinforce its potential as an ecological indicator associated with cetacean diet and migratory patterns. Despite the limitations imposed by the advanced decomposition of the specimens, this study highlights the importance of stranding monitoring and parasitological investigations for understanding the ecology, health, and epidemiology of cetaceans in Brazilian waters.