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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.

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Greater amberjack (Seriola dumerili) is a very promising candidate for the diversification of the Mediterranean aquaculture due to its high demand, excellent flesh quality and high market prices. Its production expansion has, however, failed so far, due to several bottlenecks mainly related to pathology. This review addresses the major pathogens, which hinder the culture of greater amberjack with special focus in the Mediterranean region, and highlights possible treatment solutions. Among the important recorded pathogens of caged greater amberjack in the Mediterranean, the gill monogenean Zeuxapta seriolae seems to be the most problematic, causing significant losses. While formalin immersions are inefficient to combat this parasite, baths with hydrogen peroxide are extremely effective and praziquantel administration could be a more practical in-feed treatment solution. The digenean blood flukes, Paradeontacylix spp., also account for important losses in greater amberjack farms in the same region. Dietary administration of praziquantel constitutes an effective therapeutic measure against those infections. Vibrio harveyi is also a bacterial pathogen severely affecting fish maintained both in land-based facilities and in cages, whereas Epitheliocystis is a disease reported frequently that can be fatal when it occurs at early stages. Skin flukes such as Benedenia seriolae and Neobenedenia girellae as well as other parasites bacteria and viruses mentioned herein, which have caused substantial losses in Asian enterprises, but have not been identified yet in greater amberjack farmed in the Mediterranean, should be considered as potential threats.

Abstract: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.

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The aim of this study was to evaluate the efficacy of dietary praziquantel (PZQ), a promising fish anthelminthic, against Zeuxapta seriolae, a lethal ectoparasite of greater amberjack (Seriola dumerili Risso) farmed in the Mediterranean and elsewhere. The trial was carried out in small cages (3 m3) in situ, harbouring fish (125 ± 14 g) naturally infected with Z. seriolae, at 25 ± 1 °C water temperature. Praziquantel-medicated diet (150 mg PZQ/kg fish) was delivered for three days against a control group. Measurement of both adults and oncomiracidia of Z. seriolae in sampled gill arches revealed significant differences between the tested groups (PZQ: 19.3 ± 9.8 vs. Control: 3.8 ± 6.3). Considering an estimated efficacy of 80.4% in the medicated fish, the present study indicates that oral PZQ treatments can confront Z. seriolae infections considerably in farmed greater amberjack and, perhaps, replace the commonly used hydrogen peroxidase baths.