This paper reports on parasitism in the marine fish Atlantic bumper Chloroscombrus chrysurus (Osteichthyes: Carangidae) by the cymothoid isopod Cymothoa spinipalpa as well as information pertaining to biological aspects. The fish samples were netted in the coastal waters of the Rio Grande do Norte, Brazil, and examined on a monthly basis from January to December 2006. A total of 30 adults of C. spinipalpa were found in 26 of the 204 Atlantic bumpers sampled. A prevalence of 12.8% and mean intensity of 1.15 parasites per fish were registered. The isopods were found in the branchial chamber and buccal cavity of the host. However, the parasitized and non-parasitized fish did not show any significant differences in their mean body mass, body length and condition factor. A positive correlation was found between the total length of female isopods and total body length of the hosts. The parasitic isopod females were larger than the males. Occurrence of males in the branchial chamber and the buccal cavity did not show any significant differences statistically, whereas the females showed a preference for the buccal cavity.

Description of the first specimen of Chloroscombrus chrysurus, caught in the Spanish waters of the Gulf of Cadiz, a rare species in north-east Atlantic waters. The nearest zone of frequent occurrence for this species is the Mauritanian coast, about 11 degrees south. Different hypotheses to account for the increase in reports are discussed.