ALBERT

Notes: The role of flow rate in large-volume production units (2800 L silos) for Atlantic halibut, Hippoglossus hippoglossus L., larvae was studied. Correlations between flow rate, bacterial numbers (a measure of water quality), the larval growth and development rates, and mortality were assessed. The experiment included a total of six silos, two each at three different flow rates. Flow rate and mortality were positively correlated: the number of dead larvae on day 30 was highest (i.e. 2200 and 2000) in the silos with highest flow rate (8L min−1) and lowest (i.e. 1300 and 1200) in the silos with the lowest flow rate (2L min−l). Larval weight was negatively correlated with flow rate: on day 30, the mean dry weight was 968 μg in the silo with the lowest flow rate and 820 μg in the silo with highest flow rate. Yolk sac utilization efficiency was 92% in the silo with the lowest flow rate and 72% in the silo with the highest flow rate. The number of bacteria were highest (2.7-106mL−1) in the incubators with the lowest flow rate.

Notes: Atlantic halibut larvae show an increase in activity, together with a decrease in swimming speed during active periods, occurring from day 26 onwards, which corresponds approximately to 50% yolk absorption.

Notes: Timing of development in halibut eggs and larvae from one female was monitored at 3°, 6°, and 9°C. Total and viable count of free-living bacteria in the incubators was monitored from hatching until termination of the experiment and water quality was recorded. Differences in development rates were apparent from the first cell divisions. At 9 °C there were significantly more Kupper's vesicles in embryos and RNA content was lowest. At 3° embryos had the highest RNA content but often showed incomplete development of the caudal fin. At 6°C egg mortality was lowest, and larval rowth was intermediate. DNA was significantly different between all temperature groups. At 9°C, larvae grew faster, but developed abnormalities associated with sublethal stressors. A rise in larval mortaities occurred at the same stage of development at 6° and 9°C. Significantly more jaw deformities occurred at 9°C than at 6°C. There was no significant difference in bacterial numbers between groups. An increase in larval mortalities leads to an increased amount of bacteria which preceded an increase in ammonia levels. Optimal temperatures for egg and larval development probably lie between 3° and 6°C, although there may be different optima for different stages. The experiment was terminated due to uncontrolled temperature fluctuations.〈section xml:id="abs1-2"〉〈title type="main"〉Zusammenfassung Entwicklung von Eiern und Dottersack-Larven des Heilbutts (Hippoglossus hippoglossus L.)Die Entwicklungsgeschwindigkeit von Heilbutteiern und-latven eines Weibchens wurde bei 3°C, 6°C und 9°C verfolgt. Die Gesamtkeimzahl und die Zahl freilebender Bakterien im Inkubator wurde vom Schlupfzeitpunkt an bis zum Versuchsende erfaißt und die Wasserqualität bestimmt. Unterschiede in den Entwicklungsraten waren von der ersten Zellteilung an offensichtlich. Bei 9°C konnten wesentlich mehr Kuppfer'sche Blasen festgestellt werden und die Embryonen hatten den geringsten RNA-Gehalt. Bei einer Inkubationstemperatur von 3°C hatten die Embryonen den hochsten RNA-Gehalt, zeigten jedoch häufig unvollständige Entwicklung der Schwanzflosse. Bei 6°C war die Sterblichkeit am geringsten und das Wachstum der Larven lag zwischen den Werten der beiden anderen Temperaturen. Der DNA-Gehalt war in allen 3 Gruppen unterschiedlich. Bei 9°C wuchsen die Larven am schnellsten, zeigten jedoch Anomalien, die auf subletale Stressoren zurückzuführen sind. Eine Zunahme der Larvensterblichkeit wurde bei 6°C und 9°C auf den selben Entwicklungstadium festestellt. Erheblich mehr Kieferdeformation traten bei 9°C als bei 6°C auf. Die Keimzahlen waren in alfen Versuchsgruppen nicht signifikant verschieden voneinander. Bei steigender Larvenmortalit#ät nahm auch die Bakterienzahl zu. Diese ging der Erhöhung der Ammoniumkonzentration voraus. Die optimale Inkubationstemperatur für die Eier und Larven des Heilbutts liegen wahrscheinlich zwischen 3°C und 6°C; es mögen jedoch unterschiedliche Optima für einzelne Entwicklungstadien existieren. Das Experiment wurde aufgrund unkontrollierter Temperaturfluktuationen beendet.〈section xml:id="abs1-3"〉〈title type="main"〉RésuméDéveloppement des oeufs et des larves sà sac vitellan du flétan (Hippogtossus hippoglossus L.)Le temps de développement des oeufs et des larves d'une seule femelle a été observé sà 3°, 6° et 9°C. De l'éclosion jusqu'sà la fin de l' expérience, on a compté le nombre de bactéries, total et viabilité, qui vivaient librement dans les incubateurs et la qualité de l'eau a été mesurée. Des differences dans le taux de développement sont apparues sà partir de la première division des cellules. A 9°C, il y avait significativement plus de vésicules de Kuppfer dans les embryons et le taux en RNA était plus bas. A 3°C, les embryons avaient le faux en RNA le plus élevé, mais très souvent, le développement de la nageoire caudale était incomplet. A 6°C, la mortalité des oeufs était la plus basse et la croissance larvaire était intermédiaire. Le taux en DNA était significativement différente encre les groupes de température. A 9°C, les lanres grandissaient plus vite, mais développaient des anomalies associées sà des facteurs de stress sublétaux. Une augmentation ade la mortalité larvaire aparait au même stade de développement sà 6° et 9°C. Il y avait significativement plus de déformations de E machoire sà 9°C par rapport sà 6°C. Il n' avait pas de difference significative dans le nombre de bactéries entre les groupes. L'augmentation de la mortalité larvaire conduisait sà un taux de bactéries plus élevé qui précedait l'augmentation de la teneur en ammoniaque. La température optimale pour le développement des ouefs et des larves se trouve probablement entre 3° et 6°C, même s'il peut exister des optima différents pour les differents stades. L'expérience a été terminée lorsque des fluctuations de température non-controllées sont apparues.

Notes: The pharmacokinetic properties of the antibacterial agent oxolinic acid and vetoquinol, the carbitol ester of oxolinic acid, were studied after intravenous (i.v.) and oral (p.o.) administration to 100–150 g cod, Gadus morhua L., held in sea water at 8 °C. Following i.v. injection, the plasma drug concentration-time profile showed two distinct phases. The distribution half-life (t1/2α) was estimated at 1.3 h, the elimination half-life (t1/2β) as 84 h and the total body clearance (ClT) as 0.047 L kg−1 h−1. The volume of distribution at steady state, Vd(ss) was calculated to be 5.5 L kg−1, indicating good tissue penetration of oxolinic acid in cod. Following p.o. administration of oxolinic acid or vetoquinol, the peak plasma concentrations (Cmax) of oxolinic acid and the time to peak plasma concentrations (Tmax) were estimated to be 1.2 and 2.5 μg mL−1, and 24 and 12 h, respectively. The bioavailabilities of oxolinic acid following p.o. administration of oxolinic acid and vetoquinol were calculated to be 55 and 72%, respectively. The in vitro minimum inhibitory concentration (MIC) values of oxolinic acid against three strains of Vibrio anguillarum isolated from diseased cod were 0.016 μg mL−1 (HI-610), 0.250 μg mL−1 (HI-618) and 0.250 μg mL−1 (HI-A21). Based on a MIC value of 0.016 μg mL−1 a single p.o. administration of 25 mg kg−1 of oxolinic acid maintains plasma levels in excess of 0.064 μg mL−1, corresponding to four times the MIC-value, for approximately 12 days. The analogous value for a single p.o. dose of 25 mg kg−1 of oxolinic acid administered as vetoquinol was 13 days.

Notes: Three different concentrations (107, 105 and 103 TCID50 ml−1) of infectious pancreatic necrosis virus (IPNV) serotype Sp isolated from Atlantic halibut, Hippoglossus hippoglossus L., were used to bath-challenge Atlantic halibut yolk-sac larvae. The larvae challenged with 107 TCID50 ml−1 suffered significantly higher cumulative mortality than the other challenged groups and the control group, and affected individuals displayed necrosis of the intestine, liver and kidney. In larvae from the groups challenged with 107 and 105 TCID50 ml−1, IPNV was detected by immunohistochemistry and in situ RNA/DNA hybridization in the intestine, liver and kidney. In addition, some individuals stained IPNV-positive in the heart and eye/ brain region. Detection by in situ hybridization did not appear to be more sensitive than immunohistochemistry. However, background staining was virtually absent in comparison with immunohistochemistry, and the staining seemed to be more distinctly localized to the cytoplasm of infected cells. The results show that farmed halibut yolk-sac larvae can be infected by IPNV immediately after hatching, with resulting high mortality. As the larvae are not immunologically mature at this stage of development, vaccination is not recommended.

Notes: Abstract Bacteria capable of inhibiting growth of a pathogenic Vibrio sp. were isolated from the gastrointestinal tract of cultured halibut larvae during the first feeding and weaning stages. No such bacteria were found among isolates from the surface of eggs or the gastrointestinal tract of yolk sac larvae. The fraction of pathogen-inhibitors among the total number of isolates ranged between 0–100% (first feeding) and 0–66% (weaning). All pathogen-inhibitors were Gram-negative rods, and 95% were oxidase and catalase positive fermentative isolates, capable of producing acid aerobically from a varying range of carbohydrates. These isolates possessed the characteristics of the Vibrio/Aeromonas-group, but only 19% were sensitive to the vibriostatic agent 0/129. Isolates from eggs and yolk sac larvae were dominated by bacteria belonging to the Cytophaga/Flexibacter/Flavobacterium- group. The high fraction of isolates with the ability to inhibit growth of the pathogenic Vibrio sp. among the total number of isolates indicates that pathogen inhibition may be an important mutualistic role of the intestinal flora of early life stages of halibut.

Notes: Abstract Scanning electron micrographs of halibut eggs with an epiflora dominated by Flexibacter sp., showed ulcerations colonized by large numbers of bacteria. The chorion was dissolved in most ulcerations and the zona radiata was severely damaged. Infection experiments showed that exposure to these bacteria caused high mortalities at the late egg stage, hatching and the early yolk sac stage. Eggs exposed to three different Vibrio spp. showed different mortality patterns, with low mortality at hatching, followed by a continuous high mortality throughout the yolk sac stage. Mortality in the uninfected control group was low throughout the experiment. Transmission electron microscopy of the Vibrio-infected larvae showed bacteria present in the gill, heart and frontal yolk sac regions.

Notes: Three different concentrations (107, 105 and 103 TCID50 ml-1) of infectious pancreatic necrosis virus (IPNV) serotype Sp isolated from Atlantic halibut, Hippoglossus hippoglossus L., were used to bath-challenge Atlantic halibut yolk-sac larvae. The larvae challenged with 107 TCID50 ml-1 suffered significantly higher cumulative mortality than the other challenged groups and the control group, and affected individuals displayed necrosis of the intestine, liver and kidney. In larvae from the groups challenged with 107 and 105 TCID50 ml-1, IPNV was detected by immunohistochemistry and in situ RNA/DNA hybridization in the intestine, liver and kidney. In addition, some individuals stained IPNV-positive in the heart and eye/brain region. Detection by in situ hybridization did not appear to be more sensitive than immunohistochemistry. However, background staining was virtually absent in comparison with immunohistochemistry, and the staining seemed to be more distinctly localized to the cytoplasm of infected cells. The results show that farmed halibut yolk-sac larvae can be infected by IPNV immediately after hatching, with resulting high mortality. As the larvae are not immunologically mature at this stage of development, vaccination is not recommended.