SUMMARY: 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 (R 2 >0.8). These relationships offer a helpful tool in feeding studies and also provide support to palaeontologists in their research on fish fossils.Keywords: mesopelagic fishes, bathypelagic fishes, otolith, fish-otolith sizes, length-weight relationship, Mediterranean Sea. RESUMEN: Relaciones entre talla del otolito y talla del pez en algunos peces mesopelágicos y batipelá-gicos del Mediterráneo (estrecho de Messina, Italia). -En este trabajo se presentan las relaciones talla-peso y las regresiones entre la talla del otolito (longitud y anchura) y la talla del pez (SL) para algunos peces meso y batipelágicos que viven en el Mediterráneo central. Se incluyen imágenes y descripciones morfológicas de los otolitos (sagittae) de 16 especies de las familias Gonostomatidae (1), Microstomatidae (2), Myctophidae (8), Phosichthyidae (2), Sternoptychidae (2) y Stomiidae (1). La relación talla-peso muestra un crecimiento isométrico en 13 especies. No se encontraron diferencias relevantes (t-test) entre la talla del otolito derecho e izquierdo, por lo que se representó una sola regresión lineal entre la longitud estándar y los siguientes parámetros: longitud de otolite (OL) y la anchura (OW). Los datos se ajustaron bien al modelo de regresión lineal para OL y OW, para todas las especies (R 2 >0.8). Las relaciones obtenidas puede ser utilizadas como instrumento en estudios de alimentación y para sustentar estudios de paleontología sobre peces fósiles.Palabras clave: peces mesopelágicos, peces batipelágicos, otolito, pez-otolito, relación talla-peso, Mediterráneo. 2010, 605-612, Barcelona (Spain) Scientia Marina74(3) September

The study of feeding habits of the Atlantic bluefin tuna was carried out in 123 specimens, ranging from 115 to 222 cm fork length (FL) and collected during spring seasons of 2010 and 2011 in the central Mediterranean Sea (Strait of Messina). The analysis of stomach contents allowed us to identify 91 taxa of prey items, mainly belonging to Teleostea (54), Cephalopoda (20) and Crustacea (13). The percentage of index of relative abundance (IRI) shows the highest values for the myctophid Hygophum benoiti (%IRI = 22.854) and the stomiid Chauliodus sloani (%IRI = 15.124), followed by the oegopsid squid Illex coindetii (%IRI = 14.316). The broad spectrum of prey items could suggest a generalist behavior of this predator, with several species that occasionally occurs in its diet. However, if prey are grouped into food categories, the importance of mesopelagic and benthopelagic fishes can be appreciated (54.41 % of %IRI). The assessment of the hypothetical foraging rhythm of the Atlantic bluefin tuna highlighted that its feeding activity is concentrated on diel migrating fauna during night and on larger preys upon daylight. The predation on the highenergetic food as mesopelagic and bathypelagic fishes during the pre-spawning and the spawning period may bring an energetic advantage in tuna metabolism and gonadal maturation

The shore stranding of mesopelagic fauna is a recurrent phenomenon in the Strait of Messina (Central Mediterranean Sea). The aim of this paper is to test the influence of lunar phases, winds and seasons upon the frequency of occurrence of strandings of mesopelagic fish. Species abundance in relation to these factors was quantified for the first time. Specimens were collected stranded on the shore along the Sicilian coast of the Strait of Messina between 2008 and 2016. Overall 32 species belonging to seven families (Gonostomatidae, Microstomatidae, Myctophidae, Paralepididae, Phosichthyidae, Sternoptychidae, Stomiidae) were found stranded. Myctophidae was the family including the highest number of species (16), whereas Gonostomatidae was the most abundant in terms of total number of individuals (47.2%), mainly thanks to the species Cyclothone braueri. The moon, which influences the strength of currents (highest during full and new moon phases) and irradiance (higher in some lunar phases, such as the full moon), affected the abundance of stranded mesopelagic fish in the study area. The highest number of stranding events was recorded during the new moon: 34.6% of the total relative abundance of stranded mesopelagic fish. Wind blowing from the sea towards the coastline (southeasterly and easterly winds) created the best conditions for strandings. The highest abundance of stranded specimens was recorded during the winter season.

Length-mass relationships and linear regressions are given for otolith size (length and height) and standard length (LS ) of certain mesopelagic fishes (Myctophidae, Paralepididae, Phosichthyidae and Stomiidae) living in the central Mediterranean Sea. The length-mass relationship showed isometric growth in six species, whereas linear regressions of LS and otolith size fit the data well for all species. These equations represent a useful tool for dietary studies on Mediterranean marine predators.

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.