Effects of nasal parasite species in the small-spotted catshark Scyliorhinus canicula (Scyliorhinidae; Carcharhiniformes)

Abstract. The presence of the parasitic copepod Neoalbionella globosa in the olfactory chamber of a specimen of the catshark Scyliorhinus canicula has been already reported in the literature, but this is the first record from the north-western Mediterranean Sea. Besides confirming this host-parasite association in the Ligurian Sea, the present study aims to describe some effects of the copepod's presence on the olfactory system of S. canicula, thus inferring potential effects of nasal parasites on olfaction. The copepod was accidentally found during a sampling campaign. The copepod, a mature female with well-developed egg sacs, parasitized the right olfactory rosette; the rosette presented visible swelling in some of the olfactory lamellae while, histologically, restricted edema was detectable close to the zone of attachment. The ipsilateral olfactory bulb, which receives the primary olfactory afferences, had a smaller number of cells and smaller neuron density compared to the contralateral bulb and to the average values for non-parasitized specimens of the same size. The results suggest that, although the olfactory rosette does not seem severely damaged, the presence of the parasite could deeply affect the highly efficient water flow within the nasal chamber, potentially causing partial olfactory impairment.