Armelle Severe

Effects of hypoxia on growth and metabolism of juvenile turbot.

The effects of hypoxia on growth, feed efficiency, nitrogen excretion, oxygen consumption and metabolism of juvenile turbot (120 g) were studied in a 45-day experiment carried out in sea water at 17.0±0.5°C and 34.5 ppt salinity. Fish were fed to satiation at O2-concentrations of 3.5±0.3, 5.0±0.3 mg l−1 (hypoxia) and 7.2±0.3 mg l−1 (normoxia). Both feed intake (FI) and growth were significantly lower under hypoxia than under normoxia, with no significant differences being observed between 3.5 and 5.0 mg O2 l−1. During the first 2 weeks of the experiment, FI was halved under hypoxic conditions, and there were large differences among treatments in feed conversion ratio (FCR), i.e., it was 3.2, 1.5, and 0.9 in turbot exposed to 3.5, 5.0, and 7.2 mg O2 l−1, respectively. Thereafter, FCR was not significantly affected by O2-concentration. Nitrogen excretion and oxygen consumption of feeding fish were significantly higher under normoxia than under hypoxia, but following 7 days of feed deprivation oxygen consumption was similar under normoxia and hypoxia. Plasma osmolarity, ionic balance, and acid-base status were not affected by the two hypoxic conditions tested. Overall, our results indicate that turbot have some capacity to adapt to relatively low ambient O2-concentrations.

Effects of O2 supersaturation on metabolism and growth in juvenile turbot (Scophthalmus maximus L.)

Abstract Effects of O2 supersaturation on metabolism and growth were studied in juvenile turbot (Scophthalmus maximus L.). When fish were reared for 30 days in water containing O2 at 147% or 223% air saturation, there were no significant differences in food intake, growth, food conversion or protein utilization compared to fish exposed to normoxia (100% air saturation in water outlet). Exposure to hyperoxia resulted in increased body fat deposition. Daily rates of O2 consumption of resting fish were not affected by O2-concentrations, and there were no significant differences in rates of nitrogenous excretion among fish exposed to the different O2-concentrations. Turbot tolerated severe hyperoxia, 350% air saturation, for 10 days. There were changes in acid–base balance that compensated for the respiratory acidosis resulting from O2 supersaturation. Blood pH was regulated within 24 h (it averaged 7.69 over the 30-day experiment) by significant increases in plasma CO2 content and pCO2. Plasma CO2 was dose dependent averaging 11.3 and 18.9 mmol l−l under 147% and 224% O2 saturation, respectively, compared to 6.7 mmol l−l under normoxia. Over the 30-day experiment, the only change in hydromineral balance was a slight, but non-significant decrease in plasma chloride content in fish exposed to hyperoxia (137 mmol l−l compared to 139 under normoxia). There were no changes in haematocrit, haemoglobin and red blood cell counts (they averaged 18.3%, 3.7 g dl−1 and 1.37×106 mm−3, respectively) and no signs of stress (plasma cortisol averaged 3.8 ng ml−1) related to exposure to O2-supersaturation for 30 days.

Evaluation of the impact of polyethylene microbeads ingestion in European sea bass (Dicentrarchus labrax) larvae

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.

Hypoxia tolerance of common sole juveniles depends on dietary regime and temperature at the larval stage: evidence for environmental conditioning

An individuals environmental history may have delayed effects on its physiology and life history at later stages in life because of irreversible plastic responses of early ontogenesis to environmental conditions. We chose a marine fish, the common sole, as a model species to study these effects, because it inhabits shallow marine areas highly exposed to environmental changes. We tested whether temperature and trophic conditions experienced during the larval stage had delayed effects on life-history traits and resistance to hypoxia at the juvenile stage. We thus examined the combined effect of global warming and hypoxia in coastal waters, which are potential stressors to many estuarine and coastal marine fishes. Elevated temperature and better trophic conditions had a positive effect on larval growth and developmental rates; warmer larval temperature had a delayed positive effect on body mass and resistance to hypoxia at the juvenile stage. The latter suggests a lower oxygen demand of individuals that had experienced elevated temperatures during larval stages. We hypothesize that an irreversible plastic response to temperature occurred during early ontogeny that allowed adaptive regulation of metabolic rates and/or oxygen demand with long-lasting effects. These results could deeply affect predictions about impacts of global warming and eutrophication on marine organisms.

Identification of Hypoxia-Regulated Genes in the Liver of Common Sole (Solea solea ) Fed Different Dietary Lipid Contents

Coastal systems could be affected by hypoxic events brought about by global change. These areas are essential nursery habitats for several fish species including the common sole (Solea solea L.). Tolerance of fish to hypoxia depends on species and also on their physiological condition and nutritional status. Indeed, high dietary lipid content has been recently shown to negatively impact the resistance of sole to a severe hypoxic challenge. In order to study the molecular mechanisms involved in the early response to hypoxic stress, the present work examined the hepatic transcriptome in common sole fed diets with low and high lipid content, exposed to severe hypoxia. The activity of AMP-activated protein kinase (AMPK) was also investigated through the quantification of threonine-172 phosphorylation in the alpha subunit. The results show that hypoxia consistently regulates several actors involved in energy metabolism pathways and particularly AMPKα, as well as some involved in cell growth and maintenance or unfolded protein response. Our findings reveal that (1) the expression of genes involved in biological processes with high energy cost or implicated in aerobic ATP synthesis was down-regulated by hypoxia, contrary to genes involved in neoglucogenesis or in angiogenesis, (2) the consumption of high lipid induced regulation of metabolic pathways going against this energy saving, and (3) this control was fine-tuned by the regulation of several transcriptomic factors. These results provide insight into the biological processes involved in the hepatic response to hypoxic stress and underline the negative impact of high lipid consumption on the tolerance of common sole to hypoxia.