The head region of 72 bullet tunaAuxis rocheifrom the western MediterraneanSea (south-east Spain and the Strait of Gibraltar) was examined for parasites.Seven metazoan species were found in the fish from south-east Spain: threemonogeneans, two trematodes and two copepods, whereas only three specieswere isolated in the fish from the Strait of Gibraltar. A comparison of the levelsof infection of the parasites according to fish size in south-east Spain showed thatthe prevalence ofDidymozoon auxisand the mean abundance ofAllopseudaxinemacrovawere higher in the larger hosts (range of fork length1⁄438 – 44 cm) than inthe smaller ones (33 – 37 cm). A comparison of the parasite infections according togeographical region showed that the mean abundances of Nematobothriinaegen. sp. andCaligus bonitowere higher in fish from south-east Spain than in thosefrom the Strait of Gibraltar. A comparison of the parasite fauna ofA. rocheifromthe Mediterranean Sea with the published data onAuxisspp. from the Atlantic,Indian and Pacific Oceans revealed the closest similarity between theMediterraneanA. rocheiand the AtlanticA. thazard
