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.

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The incorporation of various bulk agents by substitution of an equivalent amount of the basal mixture was studied in terms of protein digestibility, growth performance and body composition in European seabass (Dicentrarchus labrax) juveniles. During the growth trial, triplicate groups of 40 seabass (mean initial weight: 7.0 g) were grown in seawater (salinity: 35; temperature: 18 "C) over 60 days. Fish were hand-fed, three times a day, one of seven experimental diets. Bulk agents tested at 10 or 20 % level of incorporation were silica, cellulose and a natural zeolite (chabamin). Feeding rates were adjusted in proportion to the percent dilution of the control diet without bulk incorporation. The incorporation of the bulk agents, at a 10 and 20 % level, did not affect protein digestibility or growth performance. Dietary bulk incorporation reduced feed efficiency values, particularly at the 20 % incorporation level. However, this reduction was mostly caused by the dietary nutrient dilution of the bulk-incorporated diets, rather than by a negative effect of the bulk agents as dietary ingredients. In comparison to the control treatment, bulk incorporation at 10 and 20 % level did not affect protein retention values. When compared with the control diet, 20 % bulk agent incorporation changed the evacuation profile of faeces and increased faecal egestion time. 0 Ifremer/Elsevier, Paris Fish nutrition I inert fillers / digestibility / Dicentrarchus labrax R&urn6-Influence des agents liants alimentaires (silice, cellulose et une zkolithe naturelle) sur la digestibilitk des protkines, la croissance, I'ingestion alimentaire et le transit digestif chez le juvCnile du bar (Dicentrarchus labrax). L'effet de l'incorporation de divers agents liants alimentaires sur la digestibilitk proteique, les performances de croissance et la composition corporelle sont Ctudi& chez le juvCnile du bar (Dicentrarchus lubrcu-). La croissance pond&ale est suivie pendant 60 jours, durant lesquels des lots de 40 poissons (poids moyen initial : 7,0 g) sont ClevCs en eau de mer (salinitC : 35 ; temperature : 18 "C). Les poissons sont nourris & la main, trois fois par jour. Des agents liants sont test& selon deux taux diffkrents d'incorporation dans l'aliment (10 et 20 %) : la silice, la cellulose et une zColithe naturelle (chabamin). Les taux de rationnement ont Ct.5 ajust& en proportion au pourcentage de dilution du rCgime tCmoin, saris incorporation de liants. L'incorporation 2 10 et 20 % des divers liants n'a pas affect6 la digestibilitk des protCines ou les performances de croissance. L'utilisation des agents liants a entrain6 une diminution de 1'effcacitC alimentaire, notamment avec les regimes comprenant 20 % de liants. Cependant, cette rCduction est surtout due B la dilution des nutriments des aliments avec les liants et non 5. un effet nCgatif des liants proprement dits. La composition corporelle des poissons entiers. & la fin de la pCriode exp&imentale, n'est pas significativement affectCe par les differents regimes alimentaires. Par rapport ...

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%, 1.5%, 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-1, 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-gamma) expression coincided with low BMP-4 expression. Our results suggest that high levels of PPAR-gamma 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.

The influence of dietary vitamin D 3 (VD 3) on survival, growth and morphogenesis during the larval development of European sea bass (Dicentrarchus labrax) was evaluated until 45 days post hatching. Diets contained 4% of the standard vitamin mix (VM) recommended by the National Research Council (NRC) and incorporated 0, 19.2, 38.4, or 140 IU of VD 3 per gram of diet to give VD-0, VD-1, VD-2 and VD-3 dietary treatments, respectively. The present study revealed for the first time an impact of dietary VD 3 on the sea bass digestive system ontogenesis that consequently conditioned the ossification process and morphogenesis. All dietary VD 3 levels were in the "adequate range" based on larval survival. Nevertheless, growth, intestinal maturation and ossification at the end of the larval stage were harmed by the minimum dose of VD 3 tested and resulted in the appearance of malformations. VD-2 and VD-3 groups showed satisfactory growth and ossification levels at the end of the larval period. However, results of enzymatic activity and expression of genes involved in the VD 3 pathway (bone morphogenetic protein 4, osteocalcin, vitamin D receptors and transient receptor potential cation channel-subfamily V, member 6-) gave evidence of complications during the ossification process as revealed by the high percentage of deformed larvae. A VD 3 level of 19.2 IU/g diet appeared necessary to obtain harmonious larval morphogenesis.

International audienceThe aim of this work was to investigate the catabolic process of three kinds of dietary carbohydrates in the gut of sea bass juveniles, with the possible contribution of the intestinal microbiota to the nutrition of the host, and the subsequent effects on intermediary metabolism. A first diet contained waxy maize (99% amylopectin), a highly digestible form of starch. A second diet was less quickly digestible due to its high amylose content of resistant starch. Two other diets contained fibre instead of starch, either only cellulose as control, or also other non-starch polysaccharides brought by lupin meal. The effect of the diets on the host confirmed previous results, with the stimulation of glucose storage in the liver in sea bass fed the starchy diets, which caused a significant increase in liver weight, while lupin meal caused an increase in visceral mass. Glycaemia was higher 7 ± 1 h after the last meal in the group fed resistant starch, compared to the other dietary groups, while the fast digestion of waxy maize resulted already in hypertriglyceridemia, possibly due to hepatic neolipogenesis. At the same sampling time, the activity of free amylase was reduced in the intestine of sea bass fed resistant starch, but maltase activity was stimulated in the brush border membranes of enterocytes in the same group, confirming thus the timely digestion of resistant starch. Hepatic mRNA transcripts indicated that glucose metabolism was oriented towards neoglucogenesis by the high-fibre diets, and towards glucose storage by the starchy diets, especially with waxy maize. The diet influenced both faecal and mucosal microbiota, though in different ways, likely due to the interaction with the host. Lupin meal seemed potentially interesting as a source of prebiotic polysaccharides, by modifying the balance between Vibrio spp. and Clostridium sp. Both forms of starch were also partly metabolised by microbiota, resulting in an increased concentration of acetate in the faeces