The European flat oyster, Ostrea edulis, is a keystone species suffering major population declines due to overfishing, habitat loss and parasite diseases. Knowledge of its fine-scale population genetic structure and connectivity, needed for effective conservation, restoration and management, is largely lacking. Along the eastern Adriatic Sea, genotyping of 1178 O. edulis individuals at 12 microsatellite loci was conducted, grouping the sampled populations by geographical origin (North, Middle, South Adriatic), shell-farm association (farmed, farm-impacted, wild oysters) and sampling year (2017, 2018), in order to explore spatio-temporal genetic variation and potential footprint of known human-mediated spat translocation events for aquaculture purpose. Short-term temporal genetic structuring of O. edulis populations was less pronounced compared to their spatial variability, which showed genetic discontinuity between O. edulis populations from different geographical regions, with the main boundary separating the North from the Middle and South Adriatic, and the weaker one limiting the flow between the Middle and South Adriatic. While the present culture practise and ongoing spat translocation promotes genetic heterogeneity in the investigated farms, reduced genetic diversity and smallest effective populations size of impacted, i.e., farm-associated O. edulis was consistently recorded in all geographical regions. Taken together, the results reflect regional oceanographic features, ongoing spat translocation and intensive harvesting, which might have reduced the wild O. edulis densities below the critical threshold for reproductive success, compromising settlement and favoring unidirectional gene-flow toward higher density farmed O. edulis. Genetic structure of Adriatic O. edulis populations revealed some concerning demographic changes and farm-wild oyster interactions and hence further investigation and management recommendations are given.

This study presents data on the seasonal changes in population structure, maturation, fecundity and reproduction of the Lepidorhombus boscii from the central-eastern Adriatic Sea. This species is a commercially valuable fish in the Adriatic Sea; still, knowledge about its reproductive biology is very scarce. The analyses are based on the data collected between July 2020 and June 2021 by bottom trawls. In total, 963 individuals were collected out of which 508 were females (47.24%) and 455 were males (52.75%). Throughout the year, oocytes in the previtellogenic and vitellogenic stages were present in the ovaries, and the development of the ovaries followed the values of the gonadosomatic index. L. boscii has asynchronous ovarian development and a prolonged spawning season in the Adriatic Sea with the main spawning season between November and March. The oocyte diameter ranged from 34.01 to 562.72 μm (178.49 ± 129.83 μm). This study presents the first information on the reproductive cycle of L. boscii in the eastern Adriatic Sea and contributes to the understanding of the biology of this species necessary for its sustainable management.

Sagittal otolith morphology and otolith shape of two megrim species, Lepidorhombus boscii and Lepidorhombus whiffiagonis, were compared using descriptive morphological characters and Wavelet shape coefficients. Differences in otolith shape were examined by linear discriminant analysis (LDA). The first discriminant axis explained 66.6% of the variation between the groups, and the second axis 28.5%. Otolith classification based on LDA showed that in 79.5% of cases an otolith can be correctly classified based only on its shape. Relationships between otolith morphometric parameters (length and width) and fish size (total length) were described by fitting simple linear regression models. For L. boscii the highest positive correlation was found between right otolith width and total body length (R² = 0.82), and for L. whiffiagonis between left otolith length and total body length (R² = 0.39).

The age and growth of the blackspot seabream, Pagellus bogaraveo, were determined by examining sagittal otoliths from fish sampled in the eastern Adriatic Sea. A total of 674 specimens (181 males, 90 hermaphrodites, 108 females, and 295 immatures) ranging from 8.80 to 47.27 cm (21.93 ± 9.00 cm) in total length were analyzed. The maximum observed age for the whole sample was 13 years. The sample was dominated by 1-year-old specimens as a consequence of an abundance of juvenile specimens collected by beach seines. Growth was described by the von Bertalanffy growth curve (L_∞ = 52.3 cm, K = 0.15 year⁻¹, t₀ = 0.49 year, R² = 0.97), and the growth performance index (Φ’) was 2.61. The length, width, thickness, and mass of the otoliths were compared with the total length and age of P. bogaraveo from the eastern Adriatic. The analysis showed that the measures were adequate predictors of age. These results can be of value for more effective management measures aimed at the conservation of this species.

Feeding habits of the four-spotted megrim, Lepidorhombus boscii, from the eastern Adriatic Sea were examined. A total of 1070 individuals collected using a bottom trawl net between July 2020 and June 2021 were analyzed. A high percentage of empty stomachs (63.27%) was recorded. The food composition proved that L. boscii is a carnivorous species. The identified prey of L. boscii was divided into seven groups: Teleostei, Bivalvia, Gastropoda, Cephalopoda, Isopoda, Mysida, and Decapoda. Decapods were the most important prey (%IRI = 58.18), followed by cephalopods (%IRI = 10.93). At the species level, the most important prey were the decapods Parapeneus longirostris (%IRI = 11.48) and Goneplax rhomboides (%IRI = 5.92). Statistically significant seasonal variations in diet were recorded; decapods dominated in spring, summer, and winter, whereas cephalopods prevailed in autumn. There were no statistically significant differences in the food composition between the three size categories. Decapods were the most important prey in all size categories (%IRI > 50). The lowest feeding intensity, as well as the highest percentage of empty stomachs, was recorded in winter, which is also the main spawning season of this species in the Adriatic Sea.