Chronic effects of ammonia were studied in juvenile seabass, Dicentrarchus labrax (mean WEIGHT=11 g), exposed for 63 days to eight stable ammonia concentrations, ranging from 0.24 to 0.90 mg l−1 unionised ammonia nitrogen (UIA-N), respectively, from 6.1 to 22.3 mg l−1 total ammonia nitrogen (TA-N). Temperature (21.8 °C), pH (8.0), salinity (37.0 ppt), and oxygen concentration (over 80% saturation at the outlet) were maintained constant. Fish were fed using a self-feeder device, and they were starved during the last 8 days. Mortality of 28.9 and 42.6% occurred within the first 8 days at the two highest UIA-N concentrations, respectively, 0.90 and 0.88 mg l−1. From days 0 to 55, a 1.8fold increase in weight gain was observed under the 0.90-mg l−1 UIA-N condition, compared to a 3.4fold increase in the control. Weight gains were negatively correlated to ambient ammonia concentrations. Weight loss, or a transient period of growth stagnation, was observed from the onset of ammonia exposure to day 13 in seabass exposed to concentrations above 0.43 mg l−1 UIA-N. After day 13, weight gains were observed in all groups, indicating that the fish were able to adapt to increased ambient ammonia concentrations over time. By the end of the experiment, plasma ammonia levels were positively related to ambient ammonia concentrations, and oxygen consumption recorded in fasting fish was significantly dependent on ammonia concentrations. In seabass juveniles, the 0.26mg l−1 UIA-N concentration, under an average pH of 8.0, can be considered as a safe long-term limit conditions in seawater.

Sea bass (Dicentrarchus labrax) (135 ± 4 g) were reared under tank-based recirculating aquaculture system for a 63-day period at four densities: 10, 40, 70, 100 kg m −3. Fish performance, stress indicators (plasma cortisol, proteonemia plus other blood parameters-Na + , K + , glucose, pH, total CO 2 −) and water quality were monitored. At the end of the 63-day period, resistance to infection was also studied by a nodavirus challenge. A 25-day test was performed on fish from two extreme densities (10 and 100 kg m 3) and one intermediate density (40 kg m 3). With regards to the different density treatments, there was no significant difference between the daily feed intake (DFI) and the specific growth rate (SGR) up to a density of 70 kg m −3. No significant difference was found between treatments concerning the feed conversion ratio (FCR) and the mortality rate. No density effect was observed on the fish stress level (plasma cortisol) or on sensitivity to the nodavirus challenge. Under these experimental rearing conditions, the density above 70 kg m −3 has an impact on growth performance (DFI and SGR) indicators and also some blood parameters (CO 2) at the highest density tested (100 kg m −3). This study suggests that a density up to 70 kg m −3 has no influence on sea bass performance and welfare. At 100 kg m −3 , average specific growth rate was decreased by 14% without welfare deterioration according to the welfare indicators monitored.

A study on nitrogenous and phosphorous waste production in European seabass (Dicentrarchus labrax) was carried out in a flow-through land-based farm. The main objectives were (i) to calculate nitrogenous (N) and phosphorous (P) waste production (particulate and dissolved) from in situ measurements for different rearing ponds with specific fish biomasses, fish sizes and flow rates, (ii) to establish nitrogenous and phosphorous waste production budgets, ratios and equations, and (iii) to compare, for the whole farm, in situ measurements to estimate N and P waste production from waste equations. Waste production was manifest by an increase in concentrations of total ammonia nitrogen, total Kjeldhal nitrogen, particulate nitrogen, dissolved phosphorus and total phosphorus concentrations in the outlet water compared to the inlet water for both batches and whole farm. However, no production of nitrite or nitrate was observed. In our budgets, the N and P amounts from biomass gains and wastes were explained by the N and P derived from feed over the range 83.9-105.2 % and 66.5-104.6 % respectively, depending on the fish batch. Values were respectively 103.4 and 87.5 % for the same calculations in the farm. When the whole-farm waste production was calculated from previous equations derived from batches, and then compared with the measured data, the percentages of recovery (estimated by the ratio predicted data/measured data) were 88 and 94 % for total-N and total-P respectively. 0 Ifremer/Elsevier, Paris Fish farm waste I excretion I nitrogenous budget I phosphorous budget ! Dicentrarchus labrax R&urn6-Quantification des rejets azot&s et phosphor&s d'une ferme d'klevage en bassins de bars Dicentrarchus labrax. L'Ctude de la production des dkchets (azote et phosphore) d'une ferme de production de bars (Dicentrarchus labrax) est rkaliske. Cette Ctude k pour objectif (i) de mesurer in situ la production des dkchets azotCs et phosphor& sous forme particulaire et soluble, pour diffkrents bassins d'klevage prksentant des caractkistiques variables en terme de biomasse de Poisson, de taille des poissons, de d&bit de l'eau de renouvellement, (ii) d'ktablir des Cquations de production de dkhets B park des donnees pr&Cdemment acquises, (iii) de comparer, pour l'ensemble des rejets au niveau de la ferme, les rksultats obtenus par des mesures in situ, d'une part, et B l'aide des Cquations, d'autre part. La production de dtchets se traduit par une augmentation des concentrations de l'azote particulaire, de l'azote ammoniacal, de I'azote organique dissous, ainsi que du phosphore particulaire et dissous. Aucune augmentation des nitrates et nitrites n'est observke. L'Ctablissement des budgets d'azote et de phosphore permettent de rendre compte, selon les bassins, du devenir de 88,2 B 105,2 % de I'azote et de 66,2 k 104,6 % du phosphore introduits dans les bassins sous forme de nourriture en granulks. L'Ctude des budgets rCalisCe par les deux mkthodes (mesures in situ et utilisation des kquations) montre que les budgets Ctablis g l'aide des...

Self-feeding systems allow fish to freely express feeding activity. A simple rod at the water surface can act as a trigger and provide fish with a way of obtaining pellets from a feeder. Such a rod presented to experienced European seabass, Dicentrurchus Zubran, may lead to feed wastage, probably as a result of unintentional fish contacts with the trigger. Trigger protection screens have been designed to prevent fish contacting the trigger by chance, and the efficacy of such screens was tested. Nocturnal and diurnal feed delivery and feed wasted were compared under conditions where the rod was unprotected or protected by semi-cylindrical or cylindrical screens. Tests were conducted using an unrestricted self-feeding regime (reward: 0.2 g pellet per kg of body weight and per fish contact) in juvenile seabass (57 g body weight) fed for 28 days at 21.3 "C. Fish were subjected to a 4-h L:20-h D (1ight:dark) photoperiod. The daily feed demand pattern and the nocturnal and diurnal feed wastage were recorded. Fish activated the trigger predominantly at night, except in the case of one group exposed to a trigger protected by a semi-cylindrical screen. In the latter, triggering activity was progressively distributed throughout the 1ight:dark cycle. The cylindrical screens markedly reduced feed wastage and seabass were able to locate and activate the trigger (even in total darkness) to obtain a reward. 0 IfremerMsevier, Paris Fish culture / self-feeding / feed wastage / feeding behaviour R&m15-Une facon simple d'bliminer le gaspillage d'aliment chez le loup europken, Dicentrarchus labrax, en condition d'auto-alimentation. Les syst&mes d'alimentation en libre-service laissent les animaux exprimer librement leur rythme alimentaire. Une simple tige immergee a la surface du bassin set? de levier clue les poissons apprennent rapidement & utiliser pour obtenir leur nourriture. Cependant, ce levier proposC 5. des loups europ&ns expCriment&, Dicentrarchus lubrax, peut provoquer un nombre tlev6 de contacts et un gaspillage d'aliment probablement dil 2 des contacts involontaires. Des &ram de protection ont &t mis au point pour Cviter ces contacts au hasard et le gaspillage d'aliment. L'efficacitk d'un levier simple a &d compar6e B celle d'un levier prottg8, soit par un &ran semi-cylindrique, soit par un Ccran cylindrique dans des conditions d'auto-alimentation continue (r&ompense : 0,2 g de gram.& par kg de poissons et par contact) de juve'niles de loup (poids moyen 57 g) pendant 28 jours & 21.3 "C. Le profil d'activitC alimentaire journalier sous une photop&iode de 4-h de jour et de 20-h de nuit (obscurid totale ou non) a Ct6 enregistrk ainsi que la part de gaspillage nocturne et diurne. Tous les poissons ont p&sent& une activitLS alimentaire nocturne zi l'exception d'un groupe placC en pr&ence d'un &ran semi-cylindrique oti cette activid s'est bquilibrke progressivement entre le jour et la nuit. Seuls les leviers CquipCs d'un Ccran cylindrique ont permis une rbduction notoire du gaspillage. Dam cette situation, les poissons furent...

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