Background: Digenean trematodes of the family Didymozoidae are tissue parasites that are particularly common in scombrid fish. These parasites can reduce the commercial value of fish, especially the ones occurring in the muscle.
Purpose: In the present study and for the first time, we report the occurrence of didymozoids in muscle tissue of Atlantic chub mackerel (Scomber colias) collected in northeast Atlantic (Portuguese coast).
Methods: The entire musculature of 64 Scomber colias was removed and examined macroscopically and under a stereomicroscope to search for parasites.
Results: The prevalence (3.1%) and abundance (0.03) of infection detected were quite low, but the parasites cause muscle softening decreasing the quality of the infected fish. If the infection levels increase, this may constitute a cause of concern for the fisheries and canning industry.
Conclusion: Didymozoids identified in this study are closely related to muscle parasites detected in other fish species of the genus Scomber, most probably the same species. Phylogenetic analysis also corroborates the hypothesis that muscle-parasitizing didymozoids are distinct from the ones parasitizing other fish organs.
Keywords: Atlantic chub mackerel; Didymozoidae; Northeast Atlantic (Portuguese coast); Scomber colias; Scombridae.