Objective: To provide a current survey of parasitic infections in the Mediterranean needlefish Tylosurus acus imperialis (T. acus imperialis). The impact of host's size and sex on some characteristics of the infection was also examined. Methods: Between 2004 and 2009, 126 specimens of T. acus imperialis were necropsied to study their parasites. Results: Fifteen species of metazoan parasites were collected including 3 monogeneans (Aspinatrium gallieni, Nudaciraxine imperium and Axinoides sp.), 4

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... digeneans (Lecithostaphylus tylosuri, Tetrochetus coryphaenae, Oesophagotrema mediterranea and Sclerodistomoides pacificus), 1 cestode (Ptychobothrium sp.), 3 copepods (Lernanthropus tylosuri, Caligodes laciniatus and Caligus sp.), 1 isopod (Irona nana), 1 acanthocephalan (Rhadinorhynchus sp.), 1 nematode (anisakid larvae) and 1 annelid (piscicolid). Cestoda Ptychobothrium sp. was the most frequent species (72%). Prevalence and abundance of infection with Ptychobothrium sp. and Rhadinorhynchus sp. were positively correlated with the total length of the host. Host's sex did not seem to affect the infection parameters of parasites in T. acus imperialis. Conclusions: This study provides first information on parasitic infections in the Mediterranean needlefish T. acus imperialis off Tunisia. Parasites can be used to understand phylogeny, biology and ecology of fish host and also as bioindicators of water quality.