Ecological Specialization Within a Carnivorous Fish Family Is Supported by a Herbivorous Microbiome Shaped by a Combination of Gut Traits and Specific Diet

Animals have been developing key associations with micro-organisms through evolutionary processes and ecological diversification. Hence, in some host clades, phylogenetic distance between hosts is correlated to dissimilarity in microbiomes, a pattern called phylosymbiosis. Teleost fishes, despite being the most diverse and ancient group of vertebrates, have received little attention from the microbiome perspective and our understanding of its determinants is currently limited. In this study, we assessed the gut microbiome of 12 co-occurring species of teleost representing a large breadth of ecological diversity and originating from a single family (i.e., the Sparidae). We tested how host evolutionary history, diet composition and morphological traits are related to fish gut microbiome. Despite fish species having different microbiomes, there is no phylosymbiosis signal in this fish family, but gut length and diet had a strong influence on the microbiome. We revealed that the only species with a specialized herbivorous diet, Sarpa salpa had a 3.3 times longer gut than carnivorous species and such a long gut favor the presence of anaerobic bacteria typical of herbivorous gut microbiomes. Hence, dietary uniqueness is paired with both unique gut anatomy and unique microbiome.

Toxic Metals (Al, Cd, Pb) and Trace Element (B, Ba, Co, Cu, Cr, Fe, Li, Mn, Mo, Ni, Sr, V, Zn) Levels in Sarpa Salpa from the North-Eastern Atlantic Ocean Region

Sarpa salpa is a fish belonging to the Sparidae family and is usually found in local markets. Toxic metals such as aluminum (Al), cadmium (Cd), lead (Pb) and trace elements such as boron (B), barium (Ba), cobalt (Co), copper (Cu), chromium (Cr), iron (Fe), lithium (Li), manganese (Mn), molybdenum (Mo), nickel (Ni), strontium (Sr), vanadium (V) and zinc (Zn) are incorporated into fish tissues and remain there. The liver has the highest concentrations of all the analyzed toxic metals and almost all the analyzed trace elements. The consumption of 100 g/day of S. salpa muscle tissue does not pose a health risk. However, 100 g/day of liver consumption may pose a serious health risk due to the intake of Cd (572% of the tolerable weekly intake for adults with a body weight of 68.48 kg) and Pb (117% of the tolerable daily intake for adults weighing 68.48 kg). The consumption of liver of this species is not recommended due to its possible harmful effects on health.

Feeding preferences of amphipod crustaceans Ampithoe ramondi and Gammarella fucicola for Posidonia oceanica seeds and leaves

The functional importance of herbivory in seagrass beds is highly variable among systems. In Mediterranean seagrass meadows, macroherbivores, such as the fish Sarpa salpa and the sea urchin Paracentrotus lividus, have received most research attention, so published evidence highlights their importance in seagrass consumption. The role of small crustaceans in seagrass consumption remains less studied in the region. Herbivory on Posidonia oceanica seeds has not previously been reported. In turn, crustacean herbivory on P. oceanica leaves is broadly recognized, although the species feeding on the seagrass are mostly unknown (except for Idotea baltica). This work evaluates P. oceanica consumption by two species of amphipod crustaceans commonly found in seagrass meadows. Ampithoe ramondi and Gammarella fucicola actively feed on P. oceanica leaves and seeds. Both species preferred seeds to leaves only when the seed coat was damaged. This study provides the first direct evidence of consumption of P. oceanica seeds by the two named amphipod crustaceans, and confirms that they also consume leaves of this seagrass species.

Variability of Otolith Morphology and Morphometry in Eight Juvenile Fish Species in the Coastal Eastern Adriatic

Sagittae otoliths of eight juvenile species: Boops boops, Diplodus vulgaris, Diplodus puntazzo, Sarpa salpa (family Sparidae), Liza ramada, Liza aurata (family Mugilidae), Atherina boyeri, Atherina hepsetus (family Atherinidae) were analysed and compared using descriptive morphological characters and morphometric indices. The noticeable differences among the otoliths of the investigated species are in their overall shape, margins (i.e. irregular, sinuate or crenate) and anterior region. Otolith shape varied from elliptic to pentagonal in sparids, elliptic to rectangular in mugilids and elliptic in two atherinids. Aspect ratio (OW/OL), ratio of the sulcus length occupied by the cauda length (CL/SL) and ratio of the sulcus length occupied by the ostium length (OSL/SL) were calculated for all species. The otolith contour was described using wavelets. The Canonical Analysis of Principal Coordinates (CAP) gave an overview of the otolith shape differentiation between eight juveniles. Using the Wavelet coefficients, the first principal component (CAP1) explained 58.1% of the variation among species and the second principal component (CAP2) 25.2%.