Ragnar Salte

Genetic variation in susceptibility of Atlantic salmon to furunculosis.

The purpose of this experiment was to study the magnitude of genetic variation in mortality due to experimental furunculosis; furunculosis is the most serious salmon disease in Norway at present. Fifty fulisib- and 25 paternal halfsib groups of Atlantic salmon, in total 5000 fish, were infected with Aeromonas salmonicida ssp. salmonicida at Vikan AkvaVet, Namsos. Infection was by means of cohabitation, and all fish were marked and kept in the same tank during the experiment. The death rate averaged 68% with large variation between family groups. Heritability of mortality was high, h2 = 0.48 ± 0.17 for the sire component and h2 = 0.32 ± 0.10 for the dam component estimates. It is concluded that resistance to furunculosis can be effectively improved by selective breeding.

Absorption, distribution and elimination of oxolinic acid in Atlantic salmon (Salmo salar L.) after various routes of administration.

Abstract Elimination half-life ( t 1 2 ,τ) of oxolinic acid (OA) in Atlantic salmon was estimated to be 60.3 h after a single rapid intravascular (i.v.) injection of 20 mg OA kg−1 body weight through a cannula into the dorsal aorta. Apparent volume of distribution (Vd(ss)) was estimated to be 1.8 l kg−1 and total clearance (ClT) was 0.7 l 24 h−1 kg−1. Peak serum concentration (Cmax) was achieved within 1 h and the mean bioavailability of OA was 47% after injection of 20 mg OA kg−1 body weight into the peritoneal cavity. After oral administration of 10 mg OA kg−1 body weight, Cmax was achieved after 3.9 h while mean bioavailability was 25%. All the fish were kept in seawater at 9.0°C. Repeated blood samples were taken via the cannula and serum was analysed by reversed-phase high-performance liquid chromatography.

Does oral administration of oxolinic acid or oxytetracycline affect feed intake of rainbow trout

Abstract Short-term oral drug intake was measured in rainbow trout ( Oncorhynchus mykiss ) using radioactively labelled diets. In Experiment 1, duplicate groups of trout were fed either a control diet without antibiotic addition, or diets containing either 10 g oxolinic acid (OA) or 10 g oxytetracycline (OTC) per kg. In Experiment 2, triplicate groups of trout were fed diets containing either 1 or 10 g OA per kg. The trout, weighing 200–900 g, were kept in freshwater at 10°C. The fish were accustomed to feeding to satiation every 20 min, 20 h/day; the drugs were fed over a 6-h period. The amount of radioactive feed ingested by the fish was measured directly on anaestherized fish with a portable gamma scintillation counter. The results showed that OA in the diet tended to reduce mean feed intake (mean reduction 17%) compared to controls. This reduction was, however, not significant ( P =0.09). Addition of OTC led to a 61% reduction in feed intake ( P

Distribution and elimination of oxolinic acid in rainbow trout (Oncorhynchus mykiss Walbaum) after a single rapid intravascular injection

Abstract Pharmacokinetic studies are important tools in improving the dosage regimens for antibiotics curently in use. In this study elimination half-life, apparent volume of distribution and total clearance of oxolinic acid (OA) were estimated after a single intravascular injection of OA in rainbow trout kept in freshwater and in seawater at 8.5°C. The drug was given as a rapid injection through a cannula into the dorsal aorta. Repeated blood samples were taken via the cannula and serum was analysed by reversed-phase high-performance liquid chromatography. The terminal elimination half-life for OA in rainbow trout was estimated to be 52.6 h in freshwater ( t 1 2 ,β ) and 29.1 h in seawater ( t 1 2 ,τ ). This considerable difference in elimination half-lives was mainly due to the increase in total clearance; total clearance (Cl T ) values were 1.2 and 2.0 l kg −1 24 h −1 . The apparent volume of distribution ( V d(ss) ) was estimated to be 2.9 and 2.6 l kg −1 in freshwater and seawater, respectively.

A practical evaluation of metomidate and MS-222 as anaesthetics for Atlantic halibut (Hippoglossus hippoglossus L.)

Abstract Metomidate and MS-222 were tested as anaesthetics for Atlantic halibut (Hippoglossus hippoglossus L.) at temperatures of 9.5±0.3°C and 10.5±0.3°C. An effective concentration of the drug was defined as one giving a sure state of anaesthesia for 75% of the fish after an exposure time of less than 5 min. The lowest effective concentration of metomidate was 10 mg l−1; with MS-222, concentrations of 250 mg l−1 were required. Doses should further be kept below 60 mg metomidate l−1 or 480 mg MS-222 l−1. There was interaction between anaesthetic and dose for both drugs with respect to the required exposure time, which focuses on the necessity of testing several doses when a new anaesthetic is to be used on a given species. It is concluded that metomidate gives a broader safe anaesthetic range with a lower effective dose than MS-222.

Genetic variation in red cell membrane fragility in Atlantic salmon and rainbow trout

Abstract The strength and flexibility of cell membranes are of particular importance for fish which routinely experience changes in the surrounding temperature. 496 fingerlings of Atlantic salmon from 50 full-and 25 halfsib groups and 133 fingerlings of rainbow trout from 14 fullsib groups were used to study the total as well as the genetic variation in cell membrane Strength, measured as red cell membrane fragility. Fragility is defined as the salinity at which 50% of the red cells are hemolyzed, and gradient as the regression coefficient of the fragility curve at the turning point. Both parameters showed significant differences between Atlantic salmon and rainbow trout. The mean fragility curve for rainbow trout was similar to the fragility curve for the family of Atlantic salmon which had the strongest cell membranes. Heritability was high for fragility and medium for gradient. There was no significant genetic correlation between red cell fragility and susceptibility to experimental infection with furunculosis.

Fluctuating asymmetry in farmed Atlantic salmon (Salmo salar) juveniles: also a maternal matter?

Developmental stability reflects the degree to which phenotypic expression is unaffected by random accidents or developmental noise. Developmental stability may be measured by phenodeviance or fluctuating asymmetry (FA), and estimation of developmental stability has attracted substantial interest because it appears to represent a relatively simple method to identify sub lethal stress exposure and to assess animal welfare. As a part of a long-term study, the work presented here primarily aimed to investigate impacts on developmental instability in farmed salmon offspring ten months post hatch attributable to maternal cortisol administration prior to spawning and mild hyperthermia exerted during incubation. Main results show that maternal cortisol enhancement increased the level of FA in pectoral and pelvic fins, but did not affect the frequency of malformations in offspring. Mild hyperthermia during incubation increased weight and fork length and also increased pelvic fin FA. Malformed fish were heavier and longer than the normal ones, and pelvic fin asymmetry was positively related to condition factor. These results illustrate plausible lasting impacts on offspring development due to the maternal endocrinological state at spawning and indicate that developmental instability in farmed salmon juveniles may mirror aspects of the broodstock’s housing conditions.

Combatting cold-water vibriosis in Atlantic salmon (Salmo salar L.) with oxolinic acid: a case report

Abstract Mean serum oxolinic acid (OA) concentration was above 1.2 μg per ml for more than 10 days during treatments of Atlantic salmon suffering from infection with Vibrio salmonicida , the causative agent of cold-water vibriosis. The therapeutic schedule was based on estimates of pharmacokinetic parameters from individual resting fish, and OA was incorporated into the feed to attain 15 mg per kg body weight per day. A total dose of 75 mg OA per kg fish was given at seawater temperatures between 2 °C and 4 °C (site 1), while a total dose of 90 mg per kg fish was given at seawater temperatures between 13 °C and 15 °C (site 2). Mortalities ceased between 3 and 4 days after initiation of treatment in both cases. Based on serum concentrations of OA post-treatment, withdrawal periods of 38 days at 4–6 °C and 31 days at 13–15 °C were necessary to ensure (with a probability of 95%) that the drug levels would remain below 1 ng per ml serum.

151. Gene delivery in larger animals

Intramuscular injection of plasmid DNA followed by electrical stimulation (electroporation) is an efficient mean for non viral delivery of DNA in vivo in smaller animals like mice and rats. In animals with increased body mass however, transfection is less efficient, often caused by the difficulty of DNA distribution relative to the electric field. We have developed a new device for the combined DNA injection and electroporation in which the injection needles also serve as electrodes. DNA is injected through two needles during insertion into the muscle and is thus distributed along the entire needle path enabling a perfect match between the DNA and the electric field. Using this device we have aimed to optimize electroporation conditions such as injection volume, DNA concentration, and field strength for use in larger animals.