The in vivo and in vitro toxicity of bacterial cells and their extracellular products (ECPs) from 16 strains of Photobacterium damselae subsp. damselae isolated from 7 epizootic outbreaks were evaluated. On the basis of their 50% lethal dose (LD 50 ) values (about 1 × 10 5 CFU), these strains may be considered as moderately virulent. However, their ECPs were strongly lethal for redbanded seabream Pagrus auriga causing fish death within 2 h post-inoculation (protein concentration ranged between 2.1 and 6.41 µg g -1 fish). The bacterial ECPs tested exhibited several enzymatic activities, such as amylase, lipase, phospholipase, alkaline phosphatase, esterase-lipase, acid phosphatase, and β-glucosaminidase. These ECPs displayed a strong cytotoxic effect on 4 fish and 2 mammalian cell lines, although this activity disappeared when ECPs were heated at 100°C. The virulence of the strains tested could not be related to the hemolytic activity or to the production of the toxin damselysin. Therefore, another unknown type of toxin could play an important role in the virulence mechanisms of this bacterial pathogen.KEY WORDS: Toxicity · ECP · Photobacterium damselae subsp. damselae · Cultured marine fish Resale or republication not permitted without written consent of the publisherDis Aquat Org 92: [31][32][33][34][35][36][37][38][39][40] 2010 brane, has been described (Kreger 1984, Kothary & Kreger 1985, Kreger et al. 1987. In addition, a relationship between the degree of virulence and the hemolytic activity has been demonstrated in P. damselae subsp. damselae strains isolated from fish (Fouz et al. 1993). However, Cutter & Kreger (1990) found that not all the P. damselae subsp. damselae strains presented the damselysin gene (dly), but only those strains showing intense hemolytic activity. A further study demonstrated that the presence of this gene was not correlated to the virulence in mice and fish of 17 P. damselae subsp. damselae strains isolated from different sources (Osorio et al. 2000).The extracellular products (ECPs) are produced by bacterial pathogens to facilitate the uptake of nutrients from the surrounding environment, and/or for the successful penetration and survival of pathogens inside the host (Bakopoulos et al. 2003). However, the role of ECPs in the pathogenesis of Photobacterium damselae subsp. damselae in fish is poorly known, which is a considerable disadvantage for the development of vaccines and vaccine strategies, since it has been suggested that the ECP components are major antigenic compounds of several vaccine formulations (Collado et al. 2000, Bakopoulos et al. 2004.The aim of this study was to determine the toxicity of different Photobacterium damselae subsp. damselae strains isolated from cultured diseased fish. For this purpose, we performed in vivo and in vitro assays using bacterial cultures and their ECPs. In addition, the enzymatic activities of the ECPs and their cytotoxicity in fish and mammalian cell lines were compared. MATERIALS AND METHODSBacterial strains. In this...

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The high number of multiplex PCRs developed for gilthead seabream (Sparus aurata L.) from many different microsatellite markers does not allow comparison among populations. This highlights the need for developing a reproducible panel of markers, which can be used with safety and reliability by all users. In this study, the first standardised panel of two new microsatellite multiplex PCRs was developed for this species. Primers of 138 specific microsatellites from the genetic linkage map were redesigned and evaluated according to their genetic variability, allele size range and genotyping reliability. A protocol to identify and classify genotyping errors or potential errors was proposed to assess the reliability of each marker. Two new multiplex PCRs from the best assessed markers were designed with 11 markers in each, named SMsa1 and SMsa2 (SuperMultiplex Sparus aurata). Three broodstocks (59, 47 and 98 breeders) from different Spanish companies, and a sample of 80 offspring from each one, were analysed to validate the usefulness of these multiplexes in the parental assignation. It was possible to assign each offspring to a single parent pair (100% success) using the exclusion method with SMsa1 and/or SMsa2. In each genotyped a reference sample (Ref-sa) was used, and its DNA is available on request similar to the kits of bin set to genotype by genemapper (v.3.7) software (kit-SMsa1 and kit-SMsa2). This will be a robust and effective tool for pedigree analysis or characterisation of populations and will be proposed as an international panel for this species.

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The integration of physical and high-density genetic maps is a very useful approach to achieve chromosome-level genome assemblies. Here, the genome of a male Senegalese sole (Solea senegalensis) was de novo assembled and the contigs were anchored to a high-quality genetic map for chromosome-level scaffolding. Hybrid assembled genome was 609.3 Mb long and contained 3403 contigs with a N50 of 513 kb. The linkage map was constructed using 16,287 informative SNPs derived from ddRAD sequencing in 327 sole individuals from five families. Markers were assigned to 21 linkage groups with an average number of 21.9 markers per megabase. The anchoring of the physical to the genetic map positioned 1563 contigs into 21 pseudo-chromosomes covering 548.6 Mb. Comparison of genetic and physical distances indicated that the average genome-wide recombination rate was 0.23 cM/Mb and the female-to-male ratio 1.49 (female map length: 2,698.4 cM, male: 2,036.6 cM). Genomic recombination landscapes were different between sexes with crossovers mainly concentrated toward the telomeres in males while they were more uniformly distributed in females. A GWAS analysis using seven families identified 30 significant sex-associated SNP markers located in linkage group 18. The follicle-stimulating hormone receptor appeared as the most promising locus associated with sex within a region with very low recombination rates. An incomplete penetrance of sex markers with males as the heterogametic sex was determined. An interspecific comparison with other Pleuronectiformes genomes identified a high sequence similarity between homologous chromosomes, and several chromosomal rearrangements including a lineage-specific Robertsonian fusion in S. senegalensis.

One of the most important problems of fish aquaculture is the high incidence of fish deformities, which are mainly skeletal. In this study, genetic parameters on gilthead seabream (Sparus aurata L.) for skeleton deformities at different ages (179, 269, 389, 539 and 689 days) and their correlations with growth traits were estimated, as were as their genotype × environment interactions (G × E) at harvesting age. A total of 4093 offspring from the mass spawning of three industrial broodstocks belonging to the PROGENSA(®) breeding programme were mixed and on-grown by different production systems in four Spanish regions: Canary Islands (tanks and cage), Andalusia (estuary), Catalonia (cage) and Murcia (cage). Parental assignment was inferred using the standardized SMsa1 microsatellite multiplex PCR. From three broodstocks, 139 breeders contributed to the spawn and a total of 297 full-sibling families (52 paternal and 53 maternal half-sibling families) were represented. Heritabilities at different ages were medium for growth traits (0.16-0.48) and vertebral deformities (0.16-0.41), and low for any type of deformity (0.07-0.26), head deformities (0.00-0.05) and lack of operculum (0.06-0.11). The genetic correlations between growth and deformity traits were medium and positive, suggesting that to avoid increasing deformities they should be taken into account in breeding programmes when growth is selected. The G × E interactions among the different facilities were weak for length and deformity and strong for growth rate during this period. These results highlight the potential for the gilthead seabream industry to reduce the prevalence of deformities by genetic improvement tools.

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