In this study, we investigated ontogenetic and sexual changes of the brain scaling as well as the scaling and the relative size of six major brain areas in the small-spotted catshark Scyliorhinus canicula from the Mediterranean Sea. The brain somatic index (0.31–1.25%) did not differ significantly between sexes but was significantly affected by size with smaller specimens exhibiting higher values. Brain growth exhibited negative allometry (allometric coefficient 0.634), not affected by sex or maturity status. The brain growth rate was found to be higher compared with a previous study from the Atlantic Ocean. Regarding the scaling of the brain areas, the olfactory bulbs scaled with positive allometry, the telencephalon and the diencephalon scaled with the same rate of negative allometry, the mesencephalon exhibited even higher negative allometry, while the cerebellum and the medulla oblongata both followed a close-to-isometric growth pattern. Immature S. canicula possessed a larger mesencephalon and diencephalon, highlighting the importance of vision in this life period, while mature specimens had enlarged olfactory bulbs, indicating that olfaction may be more important after the animal attains sexual maturity. In respect of sexual dimorphism, males had a larger cerebellum and medulla oblongata, while females had enlarged telencephalon and olfactory bulbs.

This study concerns the cephalopod species that are part of the diet of the small-spotted catshark Scyliorhinus canicula and the longnose spurdog Squalus blainville sampled by commercial trawlers in the Aegean Sea from 2005 to 2012. Based on the examined cephalopod beaks, 15 species were identified belonging in six families of Teuthida, one of Sepiida and two of Octopoda. The diversity of cephalopod prey species was higher for S. canicula (N = 15) than for S. blainville (N = 10). Nektonic cephalopods comprised the majority (>72%) of the preyed species by both sharks, among which about 55% inhabit the demersal zone and 45% the mesopelagic. In the diet of S. canicula, the demersal squid Illex coindetii and the pelagic sepiolid Heteroteuthis dispar were equally represented composing 20% of prey specimens, followed by the small-sized squid Abralia veranyi and the demersal sepiolid Rossia macrosoma. The latter species was substituted in the diet of S. blainville by the demersal medium-sized octopod Scaeurgus unicirrhus, which with the equally represented three other species, composed 50% of the cephalopod prey. Differences observed between S. canicula and S. blainville in the condition of beaks retained in their stomach contents and in the variation of prey species diversity by predator specimen size, may imply differences in their foraging tactics (hunting for prey vs scavenging on the bottom), habitats and stomach evacuation frequency.

The parasitic fauna of the small-spotted catshark, Scyliorhinus canicula in the north-eastern Aegean Sea was investigated. Twenty-one out of the 52 (prevalence 40.4%) specimens collected were found infected with parasites; an arthropod and two nematode genera. Seven specimens (prevalence 13.5%) were infected by a Neoalbionella sp. copepod. Ten and 14 specimens were infected by the nematodes Proleptus obtusus (prevalence 19.2%) and Anisakis sp. (prevalence 26.9%), respectively. Female S. canicula specimens were significantly more heavily infected during autumn and when the whole sampling period is considered. Nematode infection was significantly related to season, becoming progressively heavier from spring to autumn. No correlation was found between TL of specimens and number of parasites for males or females, irrespective of gender. The present study provided a first record of Neoalbionella sp., P. obtusus and Anisakis sp. infections of S. canicula in the north-eastern Mediterranean. The lower prevalence of Proleptus obtusus and the higher prevalence of Anisakis sp. infection recorded in this study may be due to prey availability and parasite populations in this locality.