Bernardo Basurco

Good knowledge on the disease situation and its impact on production is a base mechanism for designing health surveillance, risk analysis and biosecurity systems. Mediterranean marine fish farming, as any aquaculture production, is affected by various infectious diseases. However, seabass and seabream, the main produced species, are not listed as susceptible host species for the notifiable pathogens listed in the current EU legislation, which generates a lack of systematic reporting. The results presented in this study come from a survey directly to fish farms (50 hatchery and on-growing units from 10 Mediterranean countries), with data from 2015 to 2017, conducted by the H2020 project MedAID. Seabass showed a higher survival rate (85%) through a production cycle than seabream (80%) in spite of equal mortality due to pathogen infections (10%). The differences in survival may be explained by mortality 'of other causes'. Seabream and seabass have different disease profiles, and the profile is slightly different between geographical regions. Among the most important diseases, tenacibaculosis and vibriosis were identified in seabass and Sparicotyle chrysophrii (a gill fluke) and nodavirus in seabream. Correlating mortality data to management variables showed that increasing density, buying fingerlings from external sources and treatments due to disease are factors that negatively influence mortality rate. Most of the surveyed farms did not keep sufficient quality data to implement good health status reports and perform detailed impact studies, which shows the necessity of updating the current legislative framework to provide the basis for better reporting of relevant pathogens in the Mediterranean basin.

To evaluate the genetic diversity of viral haemorrhagic septicaemia virus (VHSV), the sequence of the glycoprotein genes (G) of 11 North American and European isolates were determined. Comparison with the G protein of representative members of the family Rhabdoviridae suggested that VHSV was a different virus species from infectious haemorrhagic necrosis virus (IHNV) and Hirame rhabdovirus (HIRRV). At a higher taxonomic level, VHSV, IHNV and HIRRV formed a group which was genetically closest to the genus Lyssavirus. Compared with each other, the G genes of VHSV displayed a dissimilar overall genetic diversity which correlated with differences in geographical origin. The multiple sequence alignment of the complete G protein, showed that the divergent positions were not uniformly distributed along the sequence. A central region (amino acid position 245-300) accumulated substitutions and appeared to be highly variable. The genetic heterogeneity within a single isolate was high, with an apparent internal mutation frequency of 1.2 x 10(-3) per nucleotide site, attesting the quasispecies nature of the viral population. The phylogeny separated VHSV strains according to the major geographical area of isolation: genotype I for continental Europe, genotype II for the British Isles, and genotype III for North America. Isolates from continental Europe exhibited the highest genetic variability, with sub-groups correlated partially with the serological classification. Neither neutralizing polyclonal sera, nor monoclonal antibodies, were able to discriminate between the genotypes. The overall structure of the phylogenetic tree suggests that VHSV genetic diversity and evolution fit within the model of random change and positive selection operating on quasispecies.

The Sparidae, commonly called breams and porgies, is a family of the order Perciformes and includes about 115 species, mainly marine coastal fish, of high economic value, exploited and farmed for human consumption, as well as for recreational purposes. In terms of aquaculture, the Sparidae production in 2006 accounted for 244,153 mtn, and represented 6.8% of the volume and 14.5% of the value of the production of Percoidei fishes (a suborder including the tilapias, breams, seabasses, groupers, etc.). Although the UN Food and Agriculture Organization (FAO) aquaculture statistics compiles data for about 20 Sparidae species—some of them with discontinued records of production—more than 75% of the production is referred to just two species, the gilthead sea bream (Sparus aurata, 107,620 mtn) cultured mainly in the Mediterranean Sea, and the red sea bream (Pagrus major, 75,754 mtn) cultured in the Asia-Pacific region. The present chapter is an updated review of the characteristics of the main aquacultured species, the production cycle, and the production volume of all species with FAO statistics records. A special emphasis is given in the gilthead sea bream farming sector, because it is the Sparid that has shown the fastest and most significant growth during the last two decades. A comparative economic analysis on the ongrowing of several Atlantic-Mediterranean species is also presented.