The length-weight relationships and the regressions between otolith size (length and width) and fish length of some mesopelagic and bathypelagic fishes living in the central Mediterranean Sea were provided. Images and morphological description of otoliths (sagittae) from 16 species belonging to the families of Gonostomatidae (1), Microstomatidae (2), Myctophidae (8), Phosichthyidae (2), Sternoptychidae (2) and Stomiidae (1) were given. The length-weight relationship showed an isometric growth in 13 species. No differences between right and left otolith sizes were detected by t-test, so a single linear regression was plotted against standard length (SL) for otolith length (OL) and otolith width (OW). Data fitted well to the regression model for both OL and OW to SL, for each species (R2 > 0.8). These relationships offer a helpful tool in feeding studies and also provide support to palaeontologists in their research on fish fossils.

This study aims to assess the litter ingestion in some demersal elasmobranchs, combining a classical gastro-intestinal tract (GIT) analysis with a procedure methodology to reduce airborne fibers contamination. In order to prevent the overestimation of litter ingestion, we applied severe mitigation measures to avoid airborne contamination during the analyses, integrating a new approach for the correction of estimates of fibers abundance using control procedure. In this study, we assessed the anthropogenic litter ingestion in four elasmobranch species from the southern Tyrrhenian Sea: Scyliorhinus canicula (n = 27), Etmopterus spinax (n = 16), Galeus melastomus (n = 12), and Raja clavata (n = 6). The GIT of each specimen was analyzed by visual sorting and the polymers identified by Fourier transform infrared spectroscopy technique. Overall, 19 litter particles were found in the GIT of 13 demersal elasmobranchs (%O = 21) and for the first time, evidence of litter ingestion by R. clavata in Mediterranean waters was also reported. In G. melastomus and R. clavata all anthropogenic particles were plastics, whereas in S. canicula other litter categories were also found. No litter ingestion was instead observed in E. spinax. More than 50% of litter particles belonged to microlitter category (<5 mm). Polyamide was the only polymer typology found in all examined species. We described the procedures to control the airborne contamination applied at each step of laboratory analysis and, thanks to the application of our control method, it was possible to exclude the 95% of fibers found in samples from the assessment. Moreover, we compared fibers abundances observed in samples and controls. This study, combining an approach for minimizing the bias associated to airborne fiber contamination, provided a reliable assessment of marine litter ingestion in demersal elasmobranchs.

The feeding habits of the bathypelagic, non-migratory myctophid Diaphus metopoclampus from a shrimp fishing ground area in the Strait of Sicily were analyzed. Overall, 296 adult specimens ranging from 50.8 to 92.8 mm standard length (SL) (mean SL = 72.9 ± 8.0 mm) were collected during two trawl surveys (October 2010 and May 2011) and their stomach contents were examined in order to provide new information on prey composition and feeding strategy of this poorly known lanternfish. Differences in diet depending on fish size and time (daylight and night) were also checked by statistical analysis. D. metopoclampus is a zooplanktivorous predator, consuming mainly Crustacea, but also Mollusca, Polychaeta, Chaetognatha, Taliacea and Actinopterygii, and showing a moderate opportunistic feeding strategy. D. metopoclampus can be ascribed to the group of acyclic predators, since it seems to be a non-migrator myctophid that feeds when prey are available. Statistical analysis indicated a size-related shift in the diet of D. metopoclampus from smaller prey organisms (e.g, Metridinidae) to larger ones (e.g, Euphausiidae and Myctophidae). Some differences in prey composition between daylight and night were highlighted: euphausiids and myctophids were more abundant during night, Metridinidae during daylight.