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Microplastics are present in marine habitats worldwide and may be ingested by low trophic organisms such as fish larvae, with uncertain physiological consequences. The present study aims at assessing the impact of polyethylene (PE 10–45 μM) microbeads ingestion in European sea bass ( Dicentrarchus labrax ) larvae. Fish were fed an inert diet including 0, 10 4 and 10 5 fluorescent microbeads per gram from 7 until 43 days post-hatching (dph). Microbeads were detected in the gastrointestinal tract in all fish fed diet incorporating PE. Our data revealed an efficient elimination of PE beads from the gut since no fluorescent was observed in the larvae after 48 h depuration. While the mortality rate increased significantly with the amount of microbeads scored per larvae at 14 and 20 dph, only ingestion of the highest concentration slightly impacted mortality rates. Larval growth and inflammatory response through Interleukine-1-beta ( IL-1β ) gene expression were not found to be affected while cytochrome-P450-1A1 ( cyp1a1 ) expression level was significantly positively correlated with the number of microbeads scored per larva at 20 dph. Overall, these results suggest that ingestion of PE microbeads had limited impact on sea bass larvae possibly due to their high potential of egestion. [ABSTRACT FROM AUTHOR]

Protein hydrolysate is an essential component of dry starter diets for fish larvae, as promoting healthy development. Peptides are also suitable substrates for many intestinal microbes. Five experimental diets were compared to a control diet ( CONT) supplemented with a commercial fish protein hydrolysate. Each diet contained one marine protein hydrolysate, which differed by the proportion of di- and tri-peptides, and by raw materials. Two diets ( HYD4 and HYD5) stimulated larval growth compared with CONT. Two other diets ( HYD1 and HYD2) yielded inferior growth. HYD1 was detrimental for survival, which was associated with an up-regulation of genes involved in inflammation and antioxidative responses, while the gene coding for osteocalcin was down-regulated in this group. The relative activity of enzymes in the brush border membrane of enterocytes was significantly stimulated with diets HYD3 and HYD4. Gut microbiota were influenced by the diet, but the bacterial community profiles observed with HYD3 and HYD4 were the only ones that were not significantly dissimilar. Groups HYD1 and HYD2 showed the most dissimilar microbiota. It was concluded that the nature of the marine protein hydrolysate is important for larval development and health, but a high proportion of small peptides is not a sufficient criterion to assess dietary value. [ABSTRACT FROM AUTHOR]

Abstract: The main goal of this work was to determine the effect of dietary live yeast Debaryomyces hansenii on the enzymatic antioxidative status of sea bass Dicentrarchus labrax larvae. Growth, activity and expression of the main antioxidative enzymes: catalase (CAT), glutathione peroxidase (GPX) and superoxide dismutase (SOD), and heat shock protein (HSP70) were measured in sea bass larvae at 23 and 48days after hatching. Larvae were fed on two microdiets: group one, fed microdiet containing live yeast and the control group fed microdiet without yeast. Heat shock protein 70 showed the same expression levels in both fish larvae fed yeast and the control diet. The group fed D. hansenii showed highest growth and lower activity and expression levels of GPX and SOD compared to fish fed control diet. In our work the differences in activity and gene expression patterns could only be attributed to the presence of yeast, assuming a possible involvement of superoxide anion retention in fish larvae, which could represent importance to the host to increase cell or tissue responsiveness to growth- and/or differentiation-enhancing factors. [Copyright &y& Elsevier]

The influence of dietary vitamins on growth, survival, and morphogenesis was evaluated until day 38 of posthatching life in European sea bass larvae (Dicentrarchus labrax). A standard vitamin mix (VM), at double the concentration of the U.S. National Research Council's recommendations, was incorporated into larval feeds at 0.5%, I .5%, 2.5%, 4.0%, and 8.0% to give treatments VM 0.5, VM 1.5, VM 2.5, VM 4.0, and VM 8.0, respectively. The group fed the VM 0.5 diet all died before day 30. At day 38, the larvae group fed VM 1.5 had 33% survival, while the other groups, with higher vitamin levels, showed at least 50% survival. The higher the percentage VM in the diet, the lower the percentage of column deformities. High dietary vitamin levels positively influenced the formation of mineralized bone in larvae: the higher the dietary vitamin level, the higher the ossification status. In the larvae group fed at the highest vitamin levels, we observed a temporal sequence of coordinated growth factor expression, in which the expression of bone morphometric protein (BMP-4) preceded the expression of IGF-l, which stimulated the maturation of osteoblasts (revealed by high osteocalcin expression levels). In groups fed lower proportions of vitamins, elevated proliferator peroxisome- activated receptors (PPAR-γ) expression coincided with low BMP-4 expression. Our results suggest that high levels of PPAR-γ transcripts in larvae-fed diets with a low VM content converted some osteoblasts into adipocytes during the first two weeks of life. This loss of osteoblasts is likely to have caused skeletal deformities. [ABSTRACT FROM AUTHOR]

The mechanisms behind the beneficial effects of dietary peptides on fish skeletal development remain unrevealed. In the present study, we evaluated the effect of 0% (C, Control), 6% (P6) and 12% (P12) levels of small peptide incorporation on European sea bass (Dicentrarchus labrax) early larval skeletal development and post-larval skeletal integrity against a swimming challenge test. Survival was not affected by the peptide diets, whereas P6 presented the lowest growth rate. Larval quality control underlined the advantageous effect of P12 on reducing the frequency of cephalic deformities (e.g., branchiostegal rays, operculum and cross-bite), pre-haemal lordosis and vertebrae bone loss. Simultaneously, individuals from P12 group exhibited an earlier mineralization of the vertebral column and were less prone to develop swimming-induced haemal lordosis (16.0 ± 0.1%) and scoliosis (3.3 ± 0.6%). Expression analysis of genes involved in digestive function, protein transport, muscle ontogeny and bone mineralization revealed a peptide-enhanced larvae development of the P12 group. An early nutritional programming of the post-larval musculoskeletal system is proposed. Limitations induced by the differential free amino-acid profiles are discussed. A potential developmental-stage-specific incorporation of peptide diets in European sea bass rearing is suggested. • Small dietary di- and tri-peptides reduce the skeletal deformities in sea bass larvae • Sea bass larval nutrition with small peptides increases the resistance against swimming-induced lordosis in later stages • The total sea bass larvae maturation is enhanced by a 12% incorporation of small peptides during the early stages [ABSTRACT FROM AUTHOR]

Abstract: Supplies of marine fish oils are limited, and continued growth in aquaculture production dictates that lipid substitutes in fish diets must be used without compromising fish health and product quality. In this study, the total substitution of a fish meal and fish oil by a blend of vegetable meals (corn, soybean, wheat and lupin) and linseed oil in the diet of European sea bass (Dicentrachus labrax) was investigated. Two groups of European sea bass were fed with fish diet (FD) or vegetable diet (VD) for 9months. VD, totally deprived of eicosapentaenoate (EPA; 20:5n-3) and docosahexaenoate (DHA; 22:6n-3), revealed a nutritional deficiency and affected growth performance. Whilst VD induced a significant increase in fatty acid desaturase 2 (FADS2) and sterol binding regulatory element-binding protein 1 (SREBP-1) mRNA levels, the desaturation rate of [1-14C]18:3n-3 into [1-14C]18:4n-3, analysed in microsomal preparations using HPLC method, did not show an upregulation of FADS2 activities in liver and intestine of fish fed VD. Moreover Western-blot analysis did not revealed any significant difference of FADS2 protein amount between the two dietary groups. These data demonstrate that sea bass exhibits a desaturase (FADS2) activity whatever their diet, but a post-transcriptional regulation of fads2 RNA prevents an increase of enzyme in fish fed a HUFA-free diet. This led to a lower fish growth and poor muscle HUFA content. [Copyright &y& Elsevier]

Abstract: It is known in vertebrates that endothelin-1 (ET-1) plays a key role in morphogenesis whose expression level greatly influences the development of craniofacial malformations. In the present study, the complete cDNA fragment encoding a precursor of endothelin-1, the preproendothelin-1 (PPET1), was cloned by RACE-PCR from European sea bass. The cDNA encoded a 199 amino acid polypeptide that was composed of the “mature” and “big” ET-1. Relative ET-1 expression levels were investigated in European sea bass larvae fed microparticulate diets containing the standard amount (0.08 g retinol/kg diet: group N) or an excess of retinoic acid which induces skeletal malformations (0.5 g retinol/kg diet: group RA). Real-time reverse transcription polymerase chain reaction analysis revealed that PPET1 mRNA levels were sensitively reduced in the RA group during early development (days 10 and 15 post hatching). Regulation of ET-1 gene expression in larvae fed the teratogenic level of vitamin A confirmed the involvement of ET-1 in the molecular mechanism involved in craniofacial deformities. These results suggest that the expression level of ET-1 may be used as a precocious molecular marker to predict malformations during European sea bass development. [Copyright &y& Elsevier]