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.

Feeding motivation is one major indicator of fish welfare and an investigation on the link between feed demand, growth and physiological variables in sea bass juveniles was developed. A computerized on-demand feeding system coupled with a PIT tag monitoring device was used to continuously record for 219 days the triggering activity of 150 individuals (initial average body weight 131.6 +/- 1.80 g and coefficient of variation 16.8%). Each group was held in 400 1 tanks at 22.2 +/- 1.5 degrees C and light regime was 16:8 LD. In all the tanks, 89% of the fish actuated the trigger, but only two or three fish accounted for 45% of the total triggering activity. These few high-triggering individuals had a transient higher growth i.e. at the time an individual was the high-triggering fish in the tank, its Specific Growth Rate (SGR) increased and was higher than that of the other fish. However, high-triggering fish did not exhibit a higher initial and final body weight nor a higher average SGR than low- and zero-triggering fish. Fish of different triggering categories did not show differences in physiological variables (muscle composition, blood and tissues biochemistry). This study also revealed that when an imbalance between apparent daily feed tank consumption and feed demand was observed (i.e. wastage), it was mostly due to an increasing demand rather than a decreasing consumption; such wastage could often be linked to particular stressors (measuring day, population sampling or social interactions) and therefore, feeding motivation disturbances could be a relevant operational fish welfare indicator. (C) 2007 Elsevier B.V. All rights reserved.

The purpose of this study was to determine whether diploid and triploid sea bass differed in terms of main haematological and physiological characteristics. Diploid and triploid fish were produced by sub-optimal pressure treatments and held in communal environments under standard rearing conditions. Total red blood cell count (RBCC), haemoglobin concentration (Hb), hematocrit (Hct), mean cell volume (MCV), mean cellular haemoglobin content (MCH), mean cell haemoglobin concentration (MCHC), plasma metabolites, osmotic pressure, gill Na+/K+-ATPase activity, electrolytes, cortisol, and 3,5,3′-triiodo-l-thyronine (T3), were measured and compared. Triploidisation in sea bass led to an increase in erythrocyte size (32% in cytoplasm surface area, and 50% in nucleus) and a decrease in erythrocyte number (∼34%). Haemoglobin and basal plasma cortisol levels were significantly lower in triploid sea bass than in diploids. There were also differences between ploidies in the plasma concentrations of some electrolytes, with triploids showing lower concentrations of K, Fe, Zn, S, and Cu than their diploid counterparts.

Turbot juveniles were exposed to four ammonia concentrations [0·17 (L), 0·34 (M), 0·73 (MH) and 0·88 (H) mg l−1 NH3‐N] for different exposure durations (28 days minimum to 84 days). Their physiological status and growth performances were compared to a control group [0·004 (C) mg l−1 NH3‐N]. No growth was observed in the H group, and by day 57, mass increase in the MH group was only 15% of that in group C. During the first month growth in the L group was similar to that in control group while it was lower (33%) in the M group; afterwards the L and M groups had a similar growth (half that of controls). Accumulation of total ammonia nitrogen (TA‐N) in plasma was dependent on ambient ammonia concentrations. Plasma urea levels in ammonia‐exposed fish were lower, similar or greater than in controls (depending on ammonia concentration or exposure duration). Osmolarity, Cl– and Na+ plasma concentrations were stable in the L and M groups. The increases in Na+, Cl–, K+ and total Ca concentrations observed by the end of the experiment in the H and MH groups suggest that fish failed to adapt. There was an initial rise in plasma cortisol in all ammonia‐exposed groups followed by a return to basal level (1·7–4 ng ml−1) in the L and M groups. In group MH, plasma cortisol peaked at 42 ng ml−1 by day 14, and after a decline at c. 1 month (14 ng ml−1), it rose again.

Effects of O-2 supersaturation on metabolism and growth were studied in juvenile turbot (Scophthalmus maximus L.). When fish were reared for 30 days in water containing O-2 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 O-2 consumption of resting fish were not affected by O-2-concentrations, and there were no significant differences in rates of nitrogenous excretion among fish exposed to the different O-2-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 O-2 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 pCO(2). Plasma CO2 was dose dependent averaging 11.3 and 18.9 mmol l(-1) under 147% and 224% O-2 saturation, respectively, compared to 6.7 mmol l(-1) under notmoxia. 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(-1) 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 x 10(6) mm(-3). respectively) and no signs of stress (plasma cortisol averaged 3.8 ng ml(-1)) related to exposure to O-2-supersaturation for 30 days. (C) 2002 Elsevier Science B.v. All rights reserved.

We studied the circadian variations of the ionic composition ([Na+], [K+], [Cl-]), total CO2 ([tot CO2]), and protein concentration ([protein]) in the plasma and endolymph in the distal and proximal sides of the sacculus in the turbot Psetta maxima. Daily variations in total plasma calcium ([tot Ga]) were also recorded. Significant diurnal fluctuations occurred in most parameters and the spatial heterogeneity of the endolymph composition was maintained throughout a 24 h period. The main parameters implicated in otolith calcification, endolymph [tot CO2] and endolymph [protein], fluctuated diurnally, [tot CO2] was highest and [protein] lowest at night; the relative concentrations were reversed during the day. The inverse, alternating relationship of maximal and minimal [tot CO2] and [protein] implies that calcium carbonate and organic matrix rates of deposition vary in antiphase. We therefore propose that in the turbot P. maxima, in autumn, the incremental zone (L-zone) is formed at night whereas the discontinuous zone (D-zone) is formed during the daytime.

Des turbots d'un poids moyen initial de 32 g ont été exposés pendant 60 jours à 4 photopériodes constantes (8L:160, 12L:120, 16L:80, 24L:0O) et à 2 photophases variables : l'une croissante (de 12 à 16 h) et l'autre décroissante (de 12 à 8 h). Les autres paramètres du milieu ont été maintenus constants pendant les 2 mois de l'expérimentation (température : 17 ± 0,5 °C, salinité : 34,5 ppm, intensité lumineuse : 2 W.m-2 , concentration en oxygène supérieure à 6 mg.l-1). La survie, la croissance pondérale et différents indicateurs alimentaires (taux de conversion apparent, coefficients d'utilisation et d'efficacité protéiques) ont été déterminés. L'excrétion azotée (niveaux journaliers et profils horaires de l'excrétion d'Azote Ammoniacal Total, AAT, et d'azote uréique) et certains paramètres plasmatiques (osmolarité, natrémie, kaliémie, chlorémie, niveaux circulants des hormones thyroïdiennes) ont été mesurés. Au cours de l'expérience, aucune mortalité n'est apparue. Les croissances pondérales et les taux de croissance spécifique ont été identiques pour tous les traitements (poids moyens multipliés par trois en 60 jours). De même, la prise alimentaire (1,5-1,7 % de la biomasse par jour), le taux de conversion alimentaire (0,70-0,75) et les coefficients d'utilisation (36-39 %) et d'efficacité (2,5-2,7) protéiques ne sont pas influencés par la photopériode. La composition corporelle des animaux en protéines, lipides totaux, cendres et eau n'a pas subi de modification au cours de l'expérimentation. Osmolarité et electrolytes plasmatiques sont stables et identiques pour les différentes conditions. La thyroxine est stable quelle que soit la photopériode, les niveaux circulants sont compris entre 2 et 4 ng.ml-1. Les concentrations plasmatiques en T3 apparaissent significativement différentes en fin d'expérience : elles sont plus basses chez les animaux en photophase décroissante et chez ceux maintenus en photophase courte (8 h). Les taux journaliers d'excrétion azotée sous la forme d'AAT (200-230 mg.kg-1.j-1) et d'urée (65-75 mg.kg-1.j-1) sont identiques pour tous les traitements. Les profils d'excrétion azotée ont présenté des différences notables selon la photopériode. L'excrétion d'AAT est caractérisée par un pic post-prandial chez les animaux soumis à une alternance jour/nuit. Par contre, en éclairage continu, les taux horaires d'excrétion d'AAT restent stables tout au long du nycthémère. L'urée présente un pic nocturne dont l'amplitude, l'étalement et l'heure d'apparition dépendent de la photopériode. En éclairage continu, cette augmentation de l'excrétion d'urée est observée à un moment durant lequel les autres poissons sont en phase nocturne. A l'instar d'autres espèces de poissons plats, le turbot est peu sensible à la photopériode du moins lorsque les conditions d'alimentation sont ajustées à la durée de la phase éclairée.

The effects of constant temperatures on growth, food efficiency, and physiological status were studied in four different batches of juvenile turbot. The growth responses were studied in three experiments lasting 70–85 days under 8–20° C thermal conditions. There was a positive correlation between growth and temperature from 8 to 17° C and a plateau was observed from 17 to 20° C. In fish fed to satiety, specific growth rate was positively correlated to the food intake, which was double at 20° C, compared with 8° C. Minor changes were observed in food efficiency. Body fat deposition decreased as temperature increased (25% lower at 20° C, compared with 8° C). Apparent food conversion, PER (protein efficiency ratio) and PUC (protein utilization coefficient) ranges were 0.8–0.9, 2.1–2.3 and 33–38% respectively. In 70–300 g fish, routine MO2 increased (2.5–6.5 μmol O2 h−1 g bw−1) with temperature up to 20° C, while larger turbot (500–600 g) appeared relatively thermo‐independent, with a lower oxygen consumption (1.5 ìmol h−1 g−1). The average daily total ammonia nitrogen (TAN) and urea‐N excretion per fish biomass was positively related to temperature. TAN was 30% lower at 8° C, compared with 20° C. Ingested nitrogen was mainly excreted under the final form of TAN, urea‐N representing 26% of the total amount. A post‐prandial peak in TAN and a delayed peak in urea‐N nitrogen were observed. The hydromineral status [osmolarity, sodium, chloride and potassium blood plasma, gill (Na+‐K+)‐ATPase activity] of turbot was not affected by progressive changes in temperature during the acclimation period. Juvenile turbots show remarkable homeostatic capacities and so they have a relatively thermo‐independent physiology within the range of temperature studied.

The effects of salinity changes (27, 19 and 10‰) on seawater‐adapted juvenile turbot were studied on their plasma osmolarity and ion concentrations, on oxygen consumption, on gill Na+,K+‐ATPase activity after 3 months and on growth parameters. All plasma concentrations (except chloride) were unchanged, suggesting that fish were well adapted to their environment. Oxygen consumption was significantly decreased in the 19 and 10‰ groups, where fish weighed significantly more 105 days after transfer than fish maintained in sea water. These results, and the fact that apparent food conversion rates were lower in a diluted environment, suggest that on a long term schedule growth conditions could be improved by adaptation to brackish waters (salinities between 10 and 19‰). The effects of transfer from sea water to 27, 19, 10 and 5‰ were also followed during the first 3 weeks. With salinity 10‰ a steady state was reached on day 21 with all plasma values within the same range. The significant differences observed in osmolarity, plasma ion concentrations and Na+,K+‐ATPase activity 3 weeks after transfer of juveniles to 5‰ salinity, compared with transfers in higher salinities, suggest that there is a threshold of acclimation of turbot to a hypotonic environment.

The influence of autumnal progressive and direct seawater transfers on ionic parameters, plasma growth hormone (GH) and thyroid hormones (TH) and also on the non–specific immune traits phagocytic activity, lysozyme and non–specific cytotoxicity were examined in 45–55 g brown trout (Salmo trutta). In both experiments, the seawater transfer induced the same pattern of endogeneous modifications but they were more pronounced and more lasting after the direct seawater transfer than after the progressive one. In seawater–transferred trout, there was a significant transitory increase of the plasma osmolarity, chloride concentration, GH levels and a transient decrease of the TH. The phagocytic activity of the pronephric leucocytes and the lysozyme concentrations were significantly higher in seawater–transferred trout than in controls. Nevertheless, the non–specific cytotoxicity should not be modified after the seawater exposure. Moreover significant positive correlations were observed between plasma GH and chemiluminescence or lysozyme increases. These data support the hypothesis that GH is involved in the salmonids’ non–specific immune potential, especially by stimulating the macrophage functions.