The aquaculture industry depends upon the development of sustainable protein sources to replace fishmeal (FM) in aquafeeds and the products derived from soybeans are some of the most studied plant feedstuffs. A key area of investigation for continuing to improve modern aquafeeds includes the evaluation of varying proportions and combinations of plant ingredients to identify mixtures that are more efficiently utilized by the fish. This study investigated the effects of increasing soybean meal (SBM) by replacing a mix of plant ingredients in low FM (20%) diets on growth, blood biochemistry profile and gut histology on European sea bass. Five isonitrogenous and isolipidic experimental diets were formulated: four diets containing increasing SBM levels (0, 10, 20 and 30%; 0SBM, 10SBM, 20SBM and 30SBM, respectively) with a low content of FM (20%) and one control diet (0% SBM; 35% FM). Diets containing SBM brought to comparable performance and protein utilization, while 0SBM had negative impact on feed conversion rate and protein utilization. Blood parameters suggested an optimal nutritional status under all feeding treatments, even though slightly decreased values were reported at increasing dietary SBM. Histology examination did not show any changes indicative of soy-induced enteritis. We can conclude that for European sea bass: (i) different blends of plant protein did not affect feed intake despite the 20% FM dietary level; (ii) the inclusion of SBM maintains optimal growth and feed utilization in low FM diets; (iii) blood biochemistry profile showed a good nutritional status under all feeding regimes; (iv) no evidence of soy-induced enteritis was reported in any group fed low FM diets. For formulation of practical diets in on-growing of European sea bass, SBM up to 30% can be successfully incorporated into feeds containing low FM inclusion.

The effects of short-chain fructo-oligosaccharides (scFOS) and xylo-oligosaccharides (XOS) on gut morphology and hepatic oxidative status were studied in European sea bass juveniles weighing 60 g. Fish were fed diets including fishmeal (FM diets) or plant feedstuffs (PF diets; 30 FM:70 PF) as main protein sources (control diets). Four other diets were formulated similar to the control diets but including 1 % scFOS or 1 % XOS. At the end of the trial, fish fed PF-based diets presented histomorphological alterations in the distal intestine, whereas only transient alterations were observed in the pyloric caeca. Comparatively to fish fed FM-based diets, fish fed PF diets had higher liver lipid peroxidation (LPO), superoxide dismutase (SOD) and catalase (CAT) activities, and lower glutathione peroxidase, glutathione reductase and glucose 6-phosphate dehydrogenase activities. In fish fed the PF diets, prebiotic supplementation decreased SOD activity and XOS supplementation further decreased CAT activity. In fish fed the FM diets, XOS supplementation promoted a reduction of all antioxidant enzyme activities. Overall, dietary XOS and scFOS supplementation had only minor effects on gut morphology or LPO levels. However, dietary XOS reduced antioxidant enzymatic activity in both PF and FM diets, which indicate a positive effect on reduction of hepatic reactive oxygen species production.

The completion of genomic sequences of physiologically important genes frequently revealsnon-coding genetic elements such as tandem repeats (micro- and minisatellites) that areoften more polymorphic than nearby coding sequences. We obtained the complete genomicsequences of three hormone genes in sea bass Dicentrarchus labrax: growthhormone (dlGH), somatolactin (dlSL) and insulin-likegrowth factor-1 (dlIGF-1), including 5′- and 3′-untranslated regions.Mini- and microsatellites were discovered in both flanking and intron regions. Some werepartially conserved across Perciformes. To assess the usefulness and relevance of thesegene-associated markers for understanding population structure, an investigation was madeon genetic diversity and differentiation at four of them in (i) five wildpopulations from the North Sea, the Bay of Biscay and the Western Mediterranean, and(ii) two samples of hatchery-bred individuals from afreshwater-acclimation experiment. Gene and allelic diversities were lower in culturedindividuals than in wild ones. Significant genetic differentiation was demonstratedbetween Bay of Biscay + North Sea and Mediterranean populations(F st > 0.06, p < 0.001),primarily due to dlGH-associated markers. Significant geneticdifferentiation was also detected among the Atlantic and North Sea samples, but restrictedto the locus associated with dlSL. Significant genetic differentiationwas also found among experimental individuals before and after a salinity challenge(F st ≈ 0.05, p < 0.001), but was dueto dlSL and dlIGF-1 loci. Gene-associated markers provedto be more efficient than formerly used anonymous microsatellite markers in providing aclear picture of genetic differentiation.

A method of geometric morphometrics was used to characterize body shape variation inmeiotic gynogenetic and triploid sea bass in comparison with diploid controls. A total of13 coordinate landmark data were recorded on the profile of 34-month-old control(n = 81), gynogenetic (n = 117) and triploid(n = 131) siblings generated from two females (A and B). Three mainaxes of morphometric variation were consistent, and these accounted for 60.8 and 57.6% ofthe total variability in females A and B, respectively. There were significant shapedeviations of triploid and gynogenetic fish relative to the controls, and differences wereparticularly evident in the progeny of one female. Overall, triploids displayed a moreslender shape than diploids, whereas gynogenetic fish were deeper bodied and had flexedcaudal peduncles and cranial features. The results are discussed especially in relation tothe characterization of triploid fish for commercial purposes.

The dietary methionine (Met) and total sulfur amino acid (TSAA) requirements of European sea bass (Dicentrarchus labrax) (initial body weight 13·4 (sd 0·2) g) were estimated in a 12-week dose–response experiment. Seven isonitrogenous (7·6 % DM) and isoenergetic (gross energy, 21·2 MJ/kg DM) diets, based on soya protein and crystalline l-amino acids containing graded levels of l-Met (1·6–16·2 g/kg) at a constant cysteine (4 g/kg) level and a fish meal-based diet, were fed each to triplicate groups of fifty fish kept in 250 litre tanks in a thermoregulated (23 ± 0·5°C) seawater system. The Met and TSAA-deficient diet resulted in higher mortality, impaired feed intake and growth relative to the other treatments (P < 0·01). No signs of lens opacity due to limiting Met intake were observed and no feed intake or growth depression occurred at the highest level of dietary TSAA. Met and TSAA requirements for optimal N deposition or weight gain as fitted with the broken-line model resulted in estimated values of 8·0 and 12·0 g/kg diet (for example, 1·8 and 2·7 % dietary protein) and 9·1 and 13·1 g/kg diet (for example, 2·0 and 3·0 % dietary protein), respectively. Plasma levels of Met, homocysteine and cysteine increased in response to excess dietary TSAA, corroborating requirement estimates from growth data. N gain resulted in a linear function of TSAA consumption at marginal Met (TSAA) intake. The TSAA intake needed to maintain N balance resulted in a value of 20·0 mg TSAA/kg average body weight0·75 per d, which represents 23 % of the total (maintenance+accretion) requirement.

Despite extensive knowledge of the genetic structure of sea bass (Dicentrarchus labrax) populations, no studies have investigated genetic structure within early life stages, or compared such structure between such stages and (sub)adults. Using nine newly developed microsatellite loci, we investigated patterns of genetic variation and relatedness among juveniles that settled in two NW Mediterranean nursery grounds in close geographical proximity. There was no evidence for differentiation among samples at settlement (θ = -0.0010), and no significant genetic relatedness. Nevertheless, significant departures from Hardy-Weinberg equilibrium were detected in each sample, which could not be attributed exclusively to the presence of null alleles and to Wahlund effect. These results are compared with and discussed in relation to the genetic structure of adults described in the same area 10 years ago.

Within a decade or so insufficient fish oil (FO) will be available to meet the requirements for aquaculture growth. Consequently, alternative sources are being investigated to reduce reliance on wild fish as a source of FO. Vegetable oils (VO) are a feasible alternative to FO. However, it is important to establish that alternative dietary lipids are not only supplied in the correct quantities and balance for optimal growth, but can maintain immune function and prevent infection, since it is known that the nutritional state of the fish can influence their immune function and disease resistance. A way of maintaining immune function, while replacing dietary FO, is by using a blend of VO rather than a single oil. In this study, juvenile European sea bass (Dicentrarchus labrax) were fed diets with a 60 % substitution of FO with a blend of rapeseed, linseed and palm oils. Two oil blends were used to achieve a fatty acid composition similar to FO, in terms of energy content, and provide a similar balance of SFA, MUFA and PUFA. Fish were fed the diets for 64 weeks, after which time growth and fatty acid compositions of liver and blood leucocytes were monitored. The impact of the dietary blends on selected innate immune responses and histopathology were also assessed, together with levels of plasma prostaglandin E2. The results suggest that potential exists for replacing FO with a VO blend in farmed sea bass feeds without compromising growth, non-specific immune function or histology.

European sea bass larvae were fed different dietary vitamin A levels. Growth, skeletal development and the expression of genes involved in larval morphogenesis were evaluated. From 7 to 42 d post-hatching, larvae were fed five isoproteic and isolipidic compound diets with graded levels of retinyl acetate (RA; RA0, RA10, RA50, RA250 and RA1000, containing 0, 10, 50, 250 and 1000 mg RA/kg DM, respectively), resulting in an incorporation of 12, 13, 31, 62 and 196 mg all-trans retinol/kg DM. Larvae fed extreme levels of RA had weights 19 % and 27 % lower than those of the RA50 group. The RA1000 diet induced a fall in growth with an increase of circulating and storage retinol forms in larvae, revealing hypervitaminosis. High levels of RA affected maturation of the pancreas and intestine. These data indicated that the optimal RA level was close to 31 mg/kg DM. Inappropriate levels of dietary RA resulted in an alteration of head organisation characterised by the abnormal development of the splanchnocranium and neurocranium, and scoliotic fish. Of the larvae fed RA1000, 78·8 % exhibited skeletal abnormalities, whereas the RA50 group presented with 25 % malformations. A linear correlation between vitamin A level and malformation percentage was observed and mainly associated with an upregulation of retinoic acid receptor-γ expression in the RA1000 group during the 2 first weeks after hatching. The expression of retinoid X receptor-α decreased during normal larval development when that of the retinoic acid receptors increased. This work highlights the involvement of retinoid pathways in the appearance of dietary-induced skeletal malformations during post-hatching development in sea bass.

The immune response of European sea bass after intracaelomic immunization with Sphaerospora dicentrarchi was studied. Fish were injected with S. dicentrarchi spores (DIC), with spores plus adjuvant (DIC+FCA), with adjuvant alone (FCA) or with PBS. Several parameters of the immune response were measured. Serum lysozyme increased significantly in DIC fish 1 week after immunization (p.i.) and it remained significantly higher in DIC+FCA fish 4 weeks p.i., and in DIC fish 8 weeks p.i. than in PBS-injected fish. The number of nitroblue tetrazolium-positive blood cells was significantly higher in DIC+FCA fish 1, 4 and 8 weeks p.i, but the highest values were detected 1 week p.i. The highest stimulation index was detected in phagocytes from DIC+FCA fish. The number of S. dicentrarchi antibody-secreting cells was significantly higher in DIC+FCA fish than in DIC fish. Serum from DIC and DIC+FCA fish, stained the polar capsules and the valves of S. dicentrarchi spores in immunohistochemistry. Serum antibodies could not be detected using immunoblot assay. All these results show that immunization with S. dicentrarchi resulted in the activation of the non-specific immune response, mainly 7 days p.i. A specific humoral response against the parasite was also demonstrated but it had a low magnitude.