Prevalence, intensity and abundance of Rhadinorhynchus pristis (Acanthocephala, Rhadinorhynchidae) in chub mackerel, Scomber japonicus (Pisces, Scombridae) from Madeira Island

Males and females of the acanthocephalan Rhadinorhynchus pristis Rudolphi, 1802, were found in the intestine of several chub mackerels, Scomber japonicus Houttuyn, 1782, caught at Madeira, Atlantic Ocean. Prevalence of infection was 50.6% in 1999 (n = 154) and 60.0% in 2001 (n = 30) and intensity of infection was 3.19 +/- 3.84 and 3.056 +/- 2.92, respectively. R. pristis showed an aggregated distribution as indicated by the aggregation and discrepancy indices 0.72 and 0.627, respectively. Comparisons of prevalences by Fisher's exact test showed no significant differences between the two samples and no significant relationship between abundance of infection and fish length. The presence of R. pristis in S. japonicus from Madeiran waters provides further evidence of relationships between the Madeiran parasite fauna and those of the western tropical Atlantic and the Mediterranean-Atlantic regions.