Chondrichthyes occupy a key position in the phylogeny of vertebrates. The complete sequence of the mitochondrial genome (mitogenome) of four species of sharks and five species of rays was obtained by whole genome sequencing (DNA-seq) in the Illumina HiSeq2500 platform. The arrangement and features of the genes in the assembled mitogenomes were identical to those found in vertebrates. Both Maximum Likelihood (ML) and Bayesian Inference (BI) analyses were used to reconstruct the phylogenetic relationships among 172 species (including 163 mitogenomes retrieved from GenBank) based on the concatenated dataset of 13 individual protein coding genes. Both ML and BI analyses did not support the “Hypnosqualea” hypothesis and confirmed the monophyly of sharks and rays. The broad notion in shark phylogeny, namely the division of sharks into Galeomorphii and Squalomorphii and the monophyly of the eight shark orders, was also supported. The phylogenetic placement of all nine species sequenced in this study produced high statistical support values. The present study expands our knowledge on the systematics, genetic differentiation, and conservation genetics of the species studied, and contributes to our understanding of the evolutionary history of Chondrichthyes.

The diet of the small-spotted catshark Scyliorhinus canicula, captured in the Aegean Sea by bottom-trawl from 2006 to 2012, was investigated with respect to sex, maturity condition, sampling location and season. The stomach contents of 432 specimens, measuring from 144 to 517 mm in total length, were analysed. The cumulative prey curve showed that the sample size was adequate to describe the species’ diet, which was quantified using the percentage gravimetric composition (%W). The identified prey items belonged to eight major groups: Teleostei, Chondrichthyes, Crustacea, Cephalopoda, Annelida, Echinodermata, phanerogams and macroalgae, with Teleostei, Crustacea and Cephalopoda being the most consumed in both females (%W = 48.1, 16.0 and 31.4, respectively) and males (%W = 33.9, 31.6 and 29.8, respectively). Higher diet diversity was observed in males than females, in immature individuals than mature ones, regardless of sex, as well as in spring in comparison to autumn and winter. Feeding intensity seemed to be influenced mainly by sex and maturity condition. No significant dietary overlap was observed for all possible combinations of the factors examined. Gut indices were compared between the two sexes with females showing statistically significantly higher median relative gut length, as well as a longer gut than males of the same length. Based on the diet composition, S. canicula can be considered a generalist predator consuming, with geographical differentiation, a wide variety of benthic taxa. The estimated fractional trophic level (τ = 4.22) classified the species as a carnivore with a preference for Teleostei and Cephalopoda, thus confirming its key role in the food web.

A total of 325 small-spotted catsharks, Scyliorhinus canicula, ranging from 263 to 488 mm in total length (TL) and from 62 to 395 g in round weight (RW), were sampled from trawl catches in the Aegean Sea during the two-year period 2005–2007. The overall ratio of males to females was 1.06:1, and of the specimens almost 60% were mature. The size of mature males and females ranged between 371–488 mm and 364–467 mm in total length, respectively, while total length at 50% maturity was estimated at 396 mm for males and 399 mm for females. Ovary weight varied from 0.1 to 25.4 g and maximum oocyte diameter was 18 mm. Gonadosomatic indices ranged from 0.13 to 9.77 in female fish and from 0.25 to 6.36 in male fish, showing significant seasonal changes only in females (p-value < 0.05). Ovarian fecundity reached a maximum of 18 ripe oocytes in the ovary of a 460 mm TL female. Only one pair of egg cases was found in each one of the 30 adult females examined.