Antibacterial therapy is still in many cases the only way to control bacterial disease outbreaks, with relevant economic issues. Nevertheless, this necessity should also be well balanced with other relevant aspects such as suitability, efficacy and refinement of the treatments but also with consumer and environmental welfare. With this aim, the literature pertaining to the use of antibacterials (i.e. oxytetracycline, oxolinic acid, flumequine and potentiated sulphonamides) in Mediterranean farmed European seabass (Dicentrarchus labrax) and gilthead seabream (Sparus aurata) was reviewed and addressed. Knowledge of drug pharmacokinetics along with the related legislation is also presented. The main criteria, technical aspects and constraints affecting the design of an appropriate antibacterial therapy are also discussed. An evaluation of available bibliography revealed the existence of considerable information on several registered antibacterials, while it is limited for others. Typically, minimum inhibitory concentrations (MIC) have been used as a reference for antibacterial selection. However, the methodologies used for MIC assessment require refinement and more sophisticated data such as epidemiological cut‐off breakpoint values. Due to the characteristics of farming systems, antibacterials are mostly delivered through medicated feeds. The large number of production units and number of fish per unit, together with a limited timeframe margin for efficient therapy, makes Mediterranean gilthead seabream and European seabass, one of the best examples where the metaphylactic concept has to be considered in aquatic medicine. The information presented in this review should guide future action taken to fulfil research gaps and promote effective and prudent antibacterial practices.

Parasitic infections can be occasionally severe in the European marine aquaculture industry, including the Mediterranean region, as they can incur considerable financial losses. Due to the lack of commercial vaccines, therapeutic approaches seem the only measure to battle parasitic outbreaks. Integrated strategies and increased resilience of the hosts, may limit to some degree the level of infestation. Ectoparasitic therapy is traditionally based on baths, with few exceptions. Several antiparasitic compounds have been registered in European aquatic medicine to combat mainly salmon sea lice; however, few of them are readily used against Mediterranean fish parasites. Formalin and less commonly hydrogen peroxide baths are applied against ectoparasites in the Mediterranean region. Most of the registered anti‐lice antiparasitics have limited potential perhaps due to their adverse environmental impact. Future therapies against fish parasites will rely mainly on effective substances ensuring consumer, animal, and environmental welfare. Ideally, dietary antiparasitics such as praziquantel exhibiting mild environmental impact and high efficacy against a wide range of pathogens should be adopted. Moreover, combined strategies such as integrated pest management, involving various management practices with limited use of chemicals, should be a priority for specific parasitic outbreaks. The information presented in this review can guide future research and promote effective and prudent parasite control practices for Mediterranean‐farmed fish.

Following the intensification of the Mediterranean aquaculture over the years, Sparicotyle (syn. Microcotyle) chrysophrii (van Beneden and Hesse, 1863; Microcotylidae, Monogenea) became one of the most pathogenic ectoparasites for the gilthead seabream (Sparus aurata L.) aquaculture. It has demonstrated a remarkable versatility to expand over its known host range, accomplish an efficient transfer between the wild and farmed sparid populations over wide geographic areas, and establish itself as the most detrimental gilthead seabream pathogen. Even though the incidence of S. chrysophrii is closely monitored in marine aquaculture system throughout the Mediterranean, there is a general lack of recent and publicly available data on its epidemiology. Being considered as a parasite whose proliferation is expected to increase under global warming conditions, such lack of data additionally humpers the implementation of integrated pest management strategy at national and Mediterranean level. While EU scientific initiatives greatly contributed to our understanding of S. chrysophrii biology, ecology and sparicotylosis treatment and pathogenesis, there is more ahead to elucidate about the mitigation of the diseases, particularly towards the development of genomic selection breeding programs of parasite‐resilient gilthead seabream, omic‐based screening of novel drug targets and reversed vaccinology.

We have evaluated the therapeutic effect of a compound mixture of caprylic acid (200 mg/kg fish), organic iron (0.2% of diet) and mannan oligosaccharide (0.4% of diet) in gilthead sea bream, Sparus aurata Linnaeus, infected with Sparicotyle chrysophrii Beneden et Hesse, 1863 in controlled conditions. One hundred and ten reared and S. chrysophrii-free fish (197 g) located in a cement tank were infected by the parasite two weeks following the addition of 150 S. chrysophrii-infected fish (70 g). Growth parameters and gill parasitic load were measured in treated against control fish after a ten-week-period. Differences in final weight, feed conversion ratio, specific growth rate and feed efficiency were not statistically significant between the experimental groups, suggesting no evident effect with respect to fish growth during the study period. Although the prevalence of S. chrysophrii was not affected by the mixture at the end of the experiment, the number of adults and larvae was significantly lower. The mean intensity encompassing the number of adults and larvae was 8.1 in treated vs 17.7 in control fish. Individual comparisons of gill arches showed that the preferred parasitism site for S. chrysophrii it the outermost or fourth gill arch, consistently apparent in fish fed the modified diet and in control fish. In conclusion, the combined application of caprylic acid, organic iron and mannan oligosaccharide can significantly affect the evolution of infection with S. chrysophrii in gilthead sea bream, being capable of reducing adult and larval stages of the monogenean. However, no difference in growth improvement was observed after the trial period, potentially leaving space for further optimisation of the added dietary compounds.

The pharmacokinetic properties and residue elimination of florfenicol (FLO) and its amine were investigated in European seabass Dicentrarchus labrax at 24°C. The trial mainly included analysis of FLO in plasma after a single dose dietary administration of 10 mg/kg and in muscle plus skin following a multiple dosing (10 mg kg⁻¹ day⁻¹ for 7 days) to estimate pharmacokinetics and residue depletion, respectively. The maximum plasma concentration of FLO was measured to be 1.64 μg/ml, 4 hr post administration. The elimination half‐life (t_1/2b) and the area under the concentration‐time curve extrapolated to infinity (AUC_0‐∞) were calculated to be 13.0 hr and 34.7 μg h⁻¹ ml⁻¹, respectively. Withdrawal times of FLO and its amine were calculated to be 46.3 degree‐days, indicating a fast removal from the edible tissues of treated European seabass. Overall, FLO can be considered as a potentially efficient antibacterial agent for farmed European seabass provided that additional efforts will be devoted towards its in vitro and clinical efficacy.