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Hypoxia episodes have been generally studied over the last decade for their lethal consequences in coastal areas, which are nurseries for several fish species. The possible long-lasting effects of non-lethal hypoxia exposures at larval stage are, however, poorly documented. We investigated the long-lasting phenotypic impact of an experimental exposure to moderate hypoxia (40% air saturation) between 30 and 38 days post-hatching in European sea bass (Dicentrarchus labrax). At the juvenile stage, our data indicate that this early hypoxia exposure impacted on juvenile growth rate but not on hypoxia tolerance. Growth depression was associated with a regulation of metabolism as suggested by a decrease in blood glycaemia, a decreased hepatic expression of the glucose transporter glut2 and of acaca involved in fatty acid synthesis as well as an increased hepatic expression of glycolytic ldh-a, which is a target gene of hypoxia inducible factors (HIFs). Interestingly, while fish were not exposed to hypoxia, the cellular oxygen sensor egln3 gene, which is also a target of HIFs, exhibited higher expression level in the hepatic tissue of juveniles that have experienced hypoxia at larval stage. Even if further studies are needed to evaluate the functional significance of such effects and to decipher the underlying molecular mechanisms, the present data evidence that early life exposure to a hypoxia event has long-lasting impact on sea bass juvenile physiology., Introduction Over the past 50 years, global warming and anthropogenic activities have greatly influenced coastal marine ecosystems with profound and diverse consequences on water temperature, pH and dissolved oxygen. The [...]

Global climate changes have led to a depletion in omega-3 polyunsaturated fatty acids (n-3 PUFA) in marine phytoplankton that-with food web transfers-could negatively impact fish performance. The aim of this study was to assess the effect of a reduction in the dietary availability of n-3 PUFA on growth performance, organ allometry, and fatty acid composition in juvenile European sea bass (Dicentrarchus labrax) raised at two different temperatures: 15 °C (natural conditions) and 20 °C (global warming scenario). Fish were fed for 5 months with two isoenergetic and isoproteic diets: a reference diet (RD; 1.65% n-3 PUFA on a dry matter basis, DM) used as a proxy of trophic networks where n-3 PUFA were plentiful, and a lower n-3 PUFA diet (LD; 0.73% n-3 PUFA on DM) designed to mimic the expected decrease in n-3 PUFA sources resulting from global climate changes. Results showed decreasing growth rates and slight changes in the muscle polar lipid profile in LD-fed sea bass juveniles, whereas neutral lipids were more affected over the long term. The relative masses of the heart and gastrointestinal system were higher at 20 °C, while liver mass was higher at 15 °C in LD-fed juveniles. However, the mesenteric fat of RD-fed juveniles was higher at 15 °C. Altogether the results suggest that sea bass juveniles are able to implement physiological mechanisms to cope with a decrease in dietary n-3 PUFA and are able to improve growth at the higher temperature, even with a decreased availability of n-3 PUFA. The temperature-driven increase in growth is also observed under the restricted n-3 PUFA diet, and this is accompanied by significant effects on organ allometry and FA profiles. This may indicate the presence of some metabolic costs that remain to be evaluated, but which illustrate that the combination of warming temperatures and n-3 PUFA depletion has significant effects on life history traits., Author(s): Clémence Gourtay [sup.1] [sup.2] , Denis Chabot [sup.3] , Céline Audet [sup.1] , Hervé Le Delliou [sup.2] , Patrick Quazuguel [sup.2] , Guy Claireaux [sup.4] , José-Luis Zambonino-Infante [sup.2] [...]