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Commercial net-pen mariculture of Seriola dumerili recently started in Mediterranean countries. While the introduction of new species allows for product diversification and strengthens the European seafood market, net-pen farming and escape events can lead to a number of socio-economic and ecological interactions in the coastal zone. To assist in the genetic management of broodstocks and mitigate the effects of escape events, the potential of morphological and genetic traits of wild, farmed and escaped S. dumerili from the Balearic and the Adriatic Sea were examined as a proxy of wild and farmed origin. Body shape, head profile and mouth position allowed correct classification between fish groups (82%). The global FST of 0.053 across all loci showed significant subdivision between wild and farmed fish, and allowed correct assignment of escapees. Integration of both genetic and morphometric data using the R package assignPOP improved the assignment results of the escaped group with unknown origin. Potential ecological and socioeconomic implications of escape events are discussed, along with guidelines promoting sustainable development of coastal net-pen aquaculture in a future to come.

A dramatic decline has been recorded in Croatian shellfish production in recent years. Among the many factors that may have contributed to the decline of mussel production, i.e. EU import barriers and consequently small domestic market, great variability in larval dispersion and settlement, it is suspected that fish predation plays an important role in shellfish sustainability. Following this hypothesis, the abundance and diversity of fish assemblages around the Marina mussel farm, situated along the eastern coast of the Adriatic Sea, was monitored for a two-year period, and the mussel recruitment losses, potentially driven from fish predation, after the ‘early thinning-out’ process was quantitatively evaluated by measuring the percentage of consumed or destroyed ropes of longlines. Overall, a total of sixteen fish taxa were recorded at the mussel farm, as opposed to fifteen taxa registered at all control locations. The asymmetrical design of the multivariate analyses revealed a statistically significant impact of the farm on fish assemblages, with expressed seasonal species variation. At mussel farm, the most abundant species observed were gilthead seabream Sparus aurata, sand smelt Atherina hepsetus and mullet Mugilidae species in summer and autumn; sand smelt A. hepsetus and bogue Boops boops in winter; and the sand smelt A. hepsetus, mullet Mugilidae species and seddled bream Oblada melanura in spring. At control locations, characterised with significantly lower fish assemblage abundances, the most abundant species were sand smelt A. hepsetus and mullet Mugilidae species in summer, sand smelt A. hepsetus and seddled bream O. melanura in autumn, sand smelt A. hepsetus and picarel Spicara flexuosa in winter, sand smelt A. hepsetus and bogue B. boops in spring. Gilthead sea bream was extremely abundant at mussel farm, with 5936 individuals censused in 155 of 192 fish counts (80%), and a maximum abundance of 285 individuals per 5000 m3. Stomach content analysis confirmed the presence of mussel Mytilus galloprovincialis as the dominant prey. During August (2009), monitoring of 423 ropes revealed that 276 m of mussel ropes or approximately 828 kg of mussels with an average shell length of 34.3 ± 2.54 mm were destroyed within the first week of mussel deposition into the sea. The recorded recruitment losses of 54% in only one month of monitoring indicate a strong negative impact on farm management stability.

Gilthead sea bream (Sparus aurata) is considered the most important finfish aquaculture product in the Mediterranean Sea, but inadequate number of domestic hatcheries has reflected in fact that 70% of fingerlings are imported, mainly from Italy and France. In order to assess potential genetic differentiation between wild and cultured sea breams, we screened eight microsatellite loci. Analyses evidenced heterogeneous genotypic distributions for each population, with extensive polymorphism and overall expected heterozygosity levels >71%. Such a high admixture and weak population structuring has previously been reported in the rest of the Mediterranean Sea. Results imply that farmed escapees are involved in genetic pollution of adjacent wild populations showing lower differentiation among themselves. Inference of such a situation strongly encourages strengthening of routine aquaculture practice in the Adriatic through development of genetic-based management for broodstock, fingerlings and farmed fish, as well as better zootechnological protocol related to maintenance of nets and cages.