Effects of algal-produced neurotoxins on metabolic activity in telencephalon, optic tectum and cerebellum of Atlantic salmon (Salmo salar)

Neurotoxins from algal blooms have been reported to cause mortality in a variety of species, including sea birds, sea mammals and fish. Farmed fish cannot escape harmful algal blooms and their potential toxins, thus they are more vulnerable for exposure than wild stocks. Sublethal doses of the toxins are likely to affect fish behaviour and may impair cognitive abilities. In the present study, changes in the metabolic activity in different parts of the Atlantic salmon (Salmo salar) brain involved in central integration and cognition were investigated after exposure to sublethal doses of three algal-produced neurotoxins; saxitoxin (STX), brevetoxin (BTX) and domoic acid (DA). Fish were randomly selected to four groups for i.p. injection of saline (control) or one of the neurotoxins STX (10 microg STX/kg bw), BTX (68 microg BTX/kg bw) or DA (6 mg DA/kg bw). In addition, 14C-2-deoxyglucose was i.m. injected to measure brain metabolic activity by autoradiography. The three regions investigated were telencephalon (Tel), optic tectum (OT) and cerebellum (Ce). There were no differences in the metabolic activity after STX and BTX exposure compared to the control in these regions. However, a clear increase was observed after DA exposure. When the subregions with the highest metabolic rate were pseudocoloured in the three brain regions, the three toxins caused distinct differences in the respective patterns of metabolic activation. Fish exposed to STX displayed similar patterns as the control fish, whereas fish exposed to BTX and DA showed highest metabolic activity in subregions different from the control group. All three neurotoxins affected subregions that are believed to be involved in cognitive abilities in fish.

Monooxygenase mediated pyrethroid detoxification in sea lice (Lepeophtheirus salmonis)

The role of monooxygenases in detoxification of the pyrethroids cypermethrin and deltamethrin was examined. Four strains of sea lice (Lepeophtheirus salmonis Krøyer) with normal or moderately reduced sensitivity towards the pyrethroids were tested in bioassays by exposure to the pyrethroid alone and in combination with an oxygenase inhibitor, piperonyl butoxide (PBO). The normal (baseline) sensitivity was considered as the sensitivity range for the two most sensitive strains. Pre-treatment with PBO elevated the sensitivity (P < 0.01) compared with groups exposed to the pyrethroid only. A positive, but not statistically significant, correlation between the activity of haem peroxidases and the pyrethroid concentration immobilizing 50% of the parasites was demonstrated (rho = 0.500 for deltamethrin and rho = 0.310 for cypermethrin). The results indicate that cytochrome P450 monooxygenases are involved in detoxification of pyrethroids in sea lice. 14C-Deltamethrin was absorbed in a lesser amount in a group of sea lice exposed to a mixture of the compound and PBO than in a group exposed to 14C-deltamethrin alone. A significant difference could be demonstrated both immediately after exposure (P < 0.01) and 24 h after exposure (P < 0.05). No significant differences were found between groups pre-treated with PBO and groups exposed to 14C-deltamethrin only. 14C-Deltamethrin was taken up mainly through the cuticle, especially the cuticle on the extremities of the ventral surface, and subsequently distributed throughout the body of the parasite.

Novel point mutation in the sodium channel gene of pyrethroid-resistant sea lice Lepeophtheirus salmonis (Crustacea: Copepoda)

Knockdown resistance (kdr) to pyrethroid insecticides is caused by point mutations in the pyrethroid target site, the para-type sodium channel of nerve membranes. This most commonly involves alterations within the domain II (S4-S6) region of the channel protein, where several different mutation sites have been identified across a range of insect species. To investigate the possibility that a kdr-type mechanism is responsible for pyrethroid resistance in sea lice, a domain II region of the Lepeophtheirus salmonis sodium channel gene was PCR amplified and sequenced. To our knowledge, this is the first published sodium channel sequence from a crustacean. Comparison of sequences from a range of samples, including several individuals from areas in which control failures had been reported, failed to identify any of the mutations within this region that have previously been linked with resistance. Instead, a novel glutamine to arginine mutation, Q945R, in transmembrane segment IIS5 was consistently found in the samples from areas of control failure and may therefore be associated with resistance to pyrethroids in this species.

Distribution of emamectin benzoate in Atlantic salmon (Salmo salar L.)

The aims of this study were to investigate the content of emamectin in blood, mucus and muscle following field administration of the recommended dose, and correlation with sea lice infection on the same fish (elimination study). The tissue distribution of tritiated emamectin benzoate after a single oral dose in Atlantic salmon was also investigated by means of whole-body autoradiography and scintillation counting (distribution study). In the elimination study, concentrations of emamectin benzoate reached maximum levels of 128, 105 and 68 ng/g (p.p.b.) for blood, mucus and muscle respectively, on day 7, the last day of administration. From day 7, the concentration in the blood declined until concentration was less than the limit of detection on day 77. The concentration was higher in mucus compared with plasma (P < 0.05) except on days 7 and 21. The concentration of emamectin benzoate decreased gradually from the end of treatment (day 7) to day 70 with half-lives of 9.2, 10.0 and 11.3 days in muscle, plasma and mucus respectively. The distribution study demonstrated a high quantity of radioactivity in mucous membranes (gastrointestinal tract, gills) throughout the observation period (56 days). Activity was high in the epiphysis, hypophysis and olfactory rosette throughout the study. The highest activity was observed in the bile, indicating this to be an important route for excretion. The distribution study confirmed the results from the elimination study with respect to concentrations in blood, skin mucous and muscle.

Consumption of drugs for sea lice infestations in Norwegian fish farms: methods for assessment of treatment patterns and treatment rate

Sea lice are a major problem in Norwegian fish farms; however, data on drug treatment patterns or treatment rates of sea lice infestations are not available. Such data are important for analysing resistance patterns against drugs used for such infestations. The main objective of the present study was to develop a method to estimate the treatment patterns and treatment rates for drugs used in the treatment against sea lice (Lepeophtheirus salmonis and Caligus elongatus) in farm salmonids by means of national sales statistics. Annual sales figures, as weight of active substances, were obtained from the drug wholesalers and the feed mills. The weight of active drug substances is not useful as a unit of measurement of drug use in an epidemiological context because it does not correct for dosage differences and number of repeat treatments. To correct for these factors, we introduced approved daily dose (ADD(farm fish)) and treatment course-doses(farm fish) kg(-1) live-weight fish. To express the drug treatment patterns, the biomass (in weight) of farm salmonids treated with 1 course of a drug were estimated. When measured as kg active substance, the quantities of drugs for the treatment of sea lice infestations declined by 98% during the study period (1989 to 2002) but this figure increased 5-fold when it was corrected for differences in dosage. To correct for amounts of farm salmonids liable to require treatment we estimated the annual treatment rate, defined as the number of treatments for sea lice infestations per biomass slaughtered Atlantic salmon Salmo salar and rainbow trout Oncorhynchus mykiss. The annual treatment rate increased gradually during the study period; however, it varied considerably (range 0.45 to 1.34, mean 0.90). Before 1995, organophosphates were the most frequently used drugs against sea lice; since then pyrethroids have become the dominating drug group.

Pharmacokinetic and pharmacodynamic properties of metomidate in turbot (Scophthalmus maximus) and halibut (Hippoglossus hippoglossus)

Metomidate was administered to halibut (Hippoglossus hippoglossus) and turbot (Scophthalmus maximus) intravenously at a dose of 3 mg/kg bodyweight, as a bath treatment at a dose of 9 mg/L water for 5 min to study the disposition of metomidate, and as bath treatment (9 mg/L) for 10 min to study the absorption and effect of metomidate on respiration and balance/motor control. Additionally, turbot were given metomidate orally at a dose of 7 mg/kg. The studies were performed in seawater at a temperature of 10.3 +/- 0.4 degrees C (halibut) and 18.0 +/- 0.3 degrees C (turbot). Pharmacokinetic modeling of the data showed that metomidate had shorter elimination half-life and higher plasma concentrations in turbot compared with halibut, both species displaying a rapid uptake, distribution and excretion. Following intravenous administration, the volumes of distribution at steady state (Vd(ss)) were 0.21 L/kg (halibut) and 0.44 L/kg (turbot). Plasma clearances (Cl) were 0.099 L/h.kg in halibut and 0.26 L/h.kg in turbot and the elimination half-lives (t(1/2)lambdaz) were calculated to be 5.8 h and 2.2 h in halibut and turbot, respectively. Mean residence times (MRT) were 2.2 h in halibut and 1.7 h in turbot. Following oral administration, the t(1/2)lambdaz was 3.5 h in turbot. The maximum plasma concentration (Cmax) was 7.8 mg/L in turbot 1 h after administration. The oral bioavailability (F) was calculated to 100% in turbot. Following 5 min bath the maximum plasma concentrations (Cmax), which were observed immediately after end of the bath, were 9.5 mg/L and 13.3 mg/L in halibut and turbot, respectively. Metomidate rapidly immobilized the fish, with respiratory depression, reduced heart rate, and loss of balance/motor control within 1 min (mean). Recovery was slow, with resumed balance/motor control after 26.4 min. Opercular respiration movements were resumed more rapidly with a recorded mean of 1.7 min. Oral administration was demonstrated to be a way of immobilizing fish, for example in large aquariums, without exposing them to unwanted stress.

Flumequine in Atlantic salmon Salmo salar: disposition in fish held in sea water versus fresh water

14C-labeled flumequine was administered as a single oral (5 mg kg(-1), 86 microCi kg(-1)) or intravenous (5 mg kg(-1), 82 microCi kg(-1)) dose to Atlantic salmon Salmo salar held in sea water or in fresh water. The absorption, tissue distribution and elimination were determined by means of liquid scintillation counting and whole-body autoradiography. The drug was rapidly absorbed and extensively distributed in all groups of fish. Radiolabeled compound was present in blood and muscle for more than 8 wk in the freshwater groups. In the seawater groups, however, no radioactivity was detected in the blood and muscle after 4 d and 2 wk, respectively. It was concluded that flumequine was eliminated at a substantially higher rate from Atlantic salmon in sea water than in fresh water.

Disposition of 14C-flumequine in eel Anguilla anguilla, turbot Scophthalmus maximus and halibut Hippoglossus hippoglossus after oral and intravenous administration

The absorption, distribution and elimination of 14C-labelled flumequine were studied using whole body autoradiography and liquid scintillation counting. Flumequine was administered to eel Anguilla anguilla, turbot Scophthalmus maximus and halibut Hippoglossus hippoglossus intravenously and orally as a single dose of 5 mg kg(-1), corresponding to 0.1 mCi kg(-1). The turbot and halibut studies were performed in salt water (salinity of 32%) at temperatures of 16 +/- 1 degrees C (turbot) and 9.5 +/- 0.5 degrees C (halibut). The eel study was conducted in fresh water at 23 +/- 1 degrees C. In the intravenously administered groups flumequine was rapidly distributed to all major tissues and organs. After oral administration flumequine also appeared to have rapid and extensive absorption and distribution in all 3 species. After the distribution phase, the level of flumequine was higher in most organs and tissues than in the blood, except in muscle and brain. The most noticeable difference between the species was the slow elimination of flumequine from eel compared to turbot and halibut. In orally administered eels, substantial amounts of flumequine remained in all major organs/tissues for 7 d. At 28 d significant levels of flumequine were present in liver, kidney and skin (with traces in muscle), and at the last sampling point (56 d) in eye, bone, bile and posterior intestine. In orally administered turbot significant levels of flumequine were observed over 96 h in bile, urine, bone, skin, intestine and eye, and traces were detected over 28 d in bone and eye in addition to a significant level in bile. In orally administered halibut, significant levels of flumequine were observed in bile, skin, intestine and eye over 96 h. Traces were present in skin and eye over 7 d. The maximal flumequine concentrations in blood were calculated to be 2.5 mg equivalents l(-1) (eel at 12 h), 0.8 mg l(-1) (turbot at 6 h) and 0.6 mg l(-1) (halibut at 6 h) after oral administration.

The effects of medetomidine and its reversal with atipamezole on plasma glucose, cortisol and noradrenaline in cattle and sheep

In the present study, we report the effect of medetomidine followed by atipamezole on plasma glucose, cortisol and noradrenaline in calves, cows and sheep. Eight calves, eight lactating dairy cows and eight adult female sheep were included in a crossover trial. The animals were injected i.v. with medetomidine (40 microg/kg), followed 60 min later by atipamezole i.v. (200 microg/kg) or saline. The wash-out period between experiments was 1 or 2 weeks. In every animal, medetomidine induced a marked hyperglycaemia, which was reversed by atipamezole. Cortisol levels increased significantly in cows and sheep, reaching levels 4-8-fold higher than the baseline levels 25-45 min after injection of medetomidine. Atipamezole did not affect the cortisol levels, except in sheep where an increase was observed. Plasma levels of noradrenaline decreased in cows and sheep after medetomidine injection, reflecting the inhibition of sympathetic activity by the drug. After injection of the antagonist, there was a large increase in noradrenaline levels. In conclusion, a high dose of medetomidine does not seem to reduce the overall endocrine stress response in cattle and sheep, which has previously been reported in other species.

Single-dose pharmacokinetics of flumequine in cod (Gadus morhua) and goldsinny wrasse (Ctenolabrus rupestris)

Knowledge of the pharmacokinetic properties of drugs to combat bacterial infections in cod (Gadus morhua) and wrasse (Ctenolabrus rupestris) is limited. One antimicrobial agent likely to be effective is flumequine. The aim of this study was to investigate the pharmacokinetic properties of flumequine in these two species. Flumequine was administered intravenously to cod (G. morhua) at a dose of 5 mg/kg bodyweight and wrasse (C. rupestris) at a dose of 10 mg/kg. Flumequine was also administered orally to both species at a dose of 10 mg/kg body weight, and as a bath treatment at a dose of 10 mg/L water for 2 h. Identical experimental designs were used otherwise. The study was performed in seawater with a salinity of 3.2% and a temperature of 8.0 +/- 0.2 degrees C (cod) and 14.5 +/- 0.4 degrees C (wrasse). Pharmacokinetic modelling of the data showed that flumequine had quite different pharmacokinetic properties in cod and wrasse. Following intravenous administration, the volumes of distribution at steady-state (Vss) were 2.41 L/kg (cod) and 2.15 L/kg (wrasse). Total body clearances (Cl) were 0.024 L/hxkg (cod) and 0.14 L/hxkg (wrasse) and the elimination half-lives (t1/2lambda z) were calculated to be 75 h (cod) and 31 h (wrasse). Mean residence times (MRT) were 99 h (cod) and 16 h (wrasse). Following oral administration, the t1/2 lambda z were 74 h (cod) and 41 h (wrasse). Maximal plasma concentrations (tmax) were 3.5 mg/L (cod) and 1.7 mg/L (wrasse), and were observed 24 h post-administration in cod and 1 h post-administration in wrasse. The oral bioavailabilities (F) were calculated to be 65% (cod) and 41% (wrasse). Following bath administration, maximal plasma concentrations were 0.13 mg/L (cod) and 0.09 mg/L (wrasse), and were observed immediately after the end of the bath.

Single-dose pharmacokinetics of flumequine in the eel (Anguilla anguilla) after intravascular, oral and bath administration

Knowledge of the pharmacokinetic properties of drugs to combat bacterial infections in the European eel (Anguilla anguilla) is limited. One antimicrobial agent likely to be effective is flumequine. The aim of this study was to investigate the pharmacokinetic properties of flumequine in European eels in fresh water. Flumequine was administered to eels (Anguilla anguilla) intravenously (i.v.) and orally (p.o.) at a dose of 10 mg/kg body weight, and as a bath treatment at a dose of 10 mg/L water for 2 h. The study was performed in fresh water with a temperature of 23 + 0.3 degrees C, pH 7.15. Identical experimental designs were used. Two additional bath treatments were also performed, one in which the pH in the water was lowered by approximately 1 unit to 6.07 (dose: 10 mg/L) and one at a dose of 40 mg/L for 2 h in a full-scale treatment. Following i.v. administration, the volume of distribution at steady state was 3.4 L/kg. Total body clearance was 0.012 L/h per kg and the elimination half-life (t1/2lambda z) was calculated to be 314 h. Mean residence time was 283 h. Following oral administration, the t1/2lambda z was 208 h. Maximal plasma concentration (Cmax) was 9.3 mg/L, at 7 h after administration (Cmax). The oral bioavailability (F) was calculated to be 85%. Following bath administration in 10 mg/L for 2 h, maximal plasma concentration was 2.1 mg/L, observed immediately after the end of the bath. The 'bioavailability' in eel following a 2-h bath treatment was 19.8%. Reducing the pH in the bath to 6.07 produced a maximal plasma concentration of 5.5 mg/L, observed immediately after the end of the bath. The 'bioavailability' was increased to 41% by the lowering of the pH. A similar effect was observed in a full-scale treatment (1 kg eels/L water). The CO2 produced by the eel lowered the pH and increased 'bioavailability' to 35%.

A pharmacokinetic study including some relevant clinical effect of medetomidine and atipamezole in lactating dairy cows

Medetomidine is the most potent and selective alpha2-agonist used in veterinary medicine and its effects can be antagonized by the alpha2-antagonist atipamezole. The pharmacokinetics of medetomidine and atipamezole were studied in a cross-over trial in eight lactating dairy cows. The animals were injected intravenously (i.v.) with medetomidine (40 microg/kg) followed by atipamezole i.v. (200 microg/kg) or saline i.v. after 60 min. Drug concentrations in plasma were measured by HPLC. After the injection of atipamezole, the concentration of medetomidine in plasma increased slightly, the mean increment being 2.7 ng/mL and the mean duration 12.1 min. However, atipamezole did not alter the pharmacokinetics of medetomidine. It is likely that the increase in medetomidine concentration is caused by displacement of medetomidine by atipamezole in highly perfused tissues. The volume of distribution at steady state (Vss) for medetomidine followed by saline and medetomidine followed by atipamezole was 1.21 and 1.32 L/kg, respectively, whereas the total clearance (Cl) values were 24.2 and 25.8 mL/min x kg. Vss and Cl values for atipamezole were 1.77 mL/kg and 48.1 mL/min x kg, respectively. Clinically, medetomidine significantly reduced heart rate and increased rectal temperature for 45 min. Atipamezole reversed the sedative effects of medetomidine. However, all the animals, except one, relapsed into sedation at an average of 80 min after injection of the antagonist.

Single-dose pharmacokinetics of flumequine in halibut (Hippoglossus hippoglossus) and turbot (Scophthalmus maximus)

Flumequine was administered to halibut (Hippoglossus hippoglossus) and turbot (Scophthalmus maximus) intravenously (i.v.) and orally (p.o.) at a dose of 10 mg/ kg bodyweight, and as a bath-treatment at a dose of 10 mg/L water for 2 h, using identical experimental designs. The study was performed in seawater with a salinity of 3% and a temperature of 10.3+/-0.4 degrees C (halibut) and 18.0+/-0.3 degrees C (turbot). Pharmacokinetic modelling of the data showed that flumequine had quite similar pharmacokinetic properties in halibut and turbot. Following intravenous administration, the volumes of distribution at steady state (Vss) were 2.99 L/kg (halibut) and 3.75 L/kg (turbot). Plasma clearances (Cl) were 0.12 L/kg (halibut) and 0.17 L/h x kg (turbot) and the elimination half-lives (t(1/2lambdaz)) were calculated to be 32 h (halibut) and 34 h (turbot). Mean residence times (MRT) were 25.1 h (halibut) and 22.2 h (turbot). Following oral administration, the t(1/2lambdaz) were 43 h (halibut) and 42 h (turbot). Maximal plasma concentrations (tmax) were 1.4 mg/L (halibut) and 1.9 mg/L (turbot), and were observed 7 h post administration in both species. The oral bioavailabilities (F) were calculated to 56% (halibut) and 59% (turbot). Following bath administration maximal plasma concentrations were 0.08 mg/L (halibut) and 0.14 mg/ L (turbot), and were observed 0 h (halibut) and 3 h (turbot) after the end of the bath. The bioavailability in halibut following a 2-h bath treatment was 5%.

Prudent use of antibacterial drugs in Norwegian aquaculture? Surveillance by the use of prescription data

Antibacterial drug treatment in aquaculture during 1991-1996 was investigated using prescription data provided by the Norwegian Government Fish Inspection and Quality Control Service (NFCS). The majority of prescriptions (n = 5401) were for Atlantic salmon and rainbow trout (salmonids), while 383 prescriptions were for other species. Of the 13 different single substances or combinations prescribed during the study period, only 5 were approved for or had been subjected to clinical trials in salmonids. Of the prescriptions for the salmonids, 99% were for approved drugs or drugs subjected to clinical trials. The major proportion of the antibacterial drugs prescribed for other fish species were drugs which were approved for or which had been subjected to clinical trials in salmonids. In all fish species, the prescribing of antibacterial drugs which were neither approved for nor had been subjected to clinical trials was mainly for fish far below slaughter weight. The prescription data were validated against the drug statistics from the wholesalers and feed mills. It was concluded that the data indeed represented antibacterial drug prescribing in Norwegian aquaculture. The prescribing of antibacterial drugs proved to be almost completely reported to NFCS, which is responsible for the control of drug residues in farmed fish in Norway.

Pharmacokinetics of medetomidine and atipamezole in dairy calves: an agonist-antagonist interaction

Medetomidine and atipamezole are licensed for use in dogs and cats in several countries and are highly selective and specific alpha2-adrenoceptor agents. The pharmacokinetics of the agonist medetomidine and the antagonist atipamezole were studied in a cross-over trial in eight dairy calves. The animals were injected intravenously (i.v.) with medetomidine (40 microg/kg i.v.), followed by atipamezole (200 microg/kg i.v.) or saline after 60 min. The wash-out period between experiments was 1 week. Drug concentrations in plasma were determined using HPLC. Atipamezole significantly (P < 0.05) increased the AUMC and MRT of medetomidine due to an increase in the medetomidine concentration when atipamezole was injected i.v. The mean increment in medetomidine concentration was 6.4 ng/mL, increased levels having a mean duration of 39.4 min. Other pharmacokinetic parameters of medetomidine were not significantly altered by atipamezole. Sedative effects of the agonist, and the effectiveness of the antagonist were recorded. All the animals relapsed into sedation on average 80 min after reversal with atipamezole. It is likely that the increase in medetomidine concentration after the injection of atipamezole i.v. results from displacement of medetomidine from alpha2-adrenoceptors in highly perfused tissues.

Drugs in salmonid aquaculture--a review

In contrast to mammalian therapeutics, the use of pharmaceutical substances is rather limited in fish. It is basically restricted to anaesthetic agents and anti-infective agents for parasitic and microbial diseases. Anaesthetic agents are used primarily in fish farm and laboratory settings to provide analgesia and immobilization of fish for minor procedures. The anti-infective agents are used for controlling diseases and the choice of drug depends on efficacy, ease of application, human safety, target animal safety including stress to the fish, environmental impact, regulatory approval, costs, and implications for marketing the fish. In this article, the major drugs used in salmonids in North America and Europe will be reviewed and some insight into future directions for drug development and use for the salmonid industry will be introduced. The mechanisms of action, pharmacokinetics, side effects, and uses of the drugs are emphasized.

Reversal of medetomidine-induced sedation in reindeer (Rangifer tarandus tarandus) with atipamezole increases the medetomidine concentration in plasma

The pharmacokinetics of two potent alpha 2-adrenoceptor agents that can be used for immobilization (medetomidine) and reversal (atipamezole) of the sedation in mammals, were studied in three reindeer (Rangifer tarandus tarandus) in winter and again in summer. Medetomidine (60 micrograms/kg) was injected intravenously (i.v.), followed by atipamezole (300 micrograms/kg) intravenously 60 min later. Drug concentrations in plasma were measured by HPLC. The administration of atipamezole resulted in an immediate 2.5-3.5 fold increase in the medetomidine concentration in plasma. Clearance for medetomidine (median 19.3 mL/min.kg) was lower than clearance for atipamezole (median 31.0 mL/min.kg). The median elimination half-lives of medetomidine and atipamezole in plasma were 76.1 and 59.9 min, respectively. The animals became resedated 0.5-1 h after the reversal with atipamezole. Resedation may be explained by the longer elimination half-life of medetomidine compared to atipamezole.

Evaluation of the dorsal aorta cannulation technique for pharmacokinetic studies in Atlantic salmon (Salmo salar) in sea water

The antimicrobial drug flumequine was given intravascularly and orally to cannulated and non-cannulated Atlantic salmon (Salmo salar) in sea water at 11 degrees C. The cannulated fish were divided into two groups, which were given flumequine (25 mg/kg) intravenously into the caudal vein (n = 8) and orally via a stomach tube down the oesophagus (n = 8). After a washout period of 2 days, the intravenously administered fish were given the drug orally, and the orally administered fish were given the drug intravenously. Blood samples were taken at different time points after drug administration through a cannula inserted into the dorsal aorta. The fish in the non-cannulated group were either given flumequine intravenously or orally, and blood samples were collected by killing five fish at predetermined time points after administration. The haematocrit values were measured in all the fish daily for 4 days after drug administration and thereafter, in all the collected blood samples throughout the whole experiment. The haematocrit values differed significantly between the cannulated and the non-cannulated fish. We found low haematocrit values and slow drug elimination in the cannulated groups, compared with higher haematocrit values and faster drug elimination in the non-cannulated groups, but further investigations are needed to prove any causal relations of this observation. The volume of distribution (Vd(ss)) was twice as large in the cannulated groups compared with the non-cannulated group, in the fish administered the drug intravenously. In the last part of the elimination phase, the half-lives differed considerably between the cannulated and the non-cannulated groups both after oral and intravenous administration. The slower depletion of the drug concentration in the plasma of the cannulated fish is due to the large Vd(ss) as there are only small differences in clearance (ClT) between the groups. In this study the elimination of flumequine in cannulated Atlantic salmon differed from the elimination of flumequine in non-cannulated Atlantic salmon.

Comparative single-dose pharmacokinetics of four quinolones, oxolinic acid, flumequine, sarafloxacin, and enrofloxacin, in Atlantic salmon (Salmo salar) held in seawater at 10 degrees C

Quinolones are currently the most commonly used group of antimicrobial agents in Norwegian aquaculture. The aims of this study were to examine and compare the pharmacokinetic properties of the quinolones oxolinic acid, flumequine, sarafloxacin, and enrofloxacin after intravascular and oral administration to Atlantic salmon (Salmo salar) by using identical experimental designs. The study was performed in seawater at 10.2 +/- 0.2 degree C with Atlantic salmon weighing 240 +/- 50 g (mean +/- standard deviation). The bioavailability varied considerably among the four quinolones. Following oral administration of medicated feed, the bioavailabilities of oxolinic acid, flumequine, sarafloxacin, and enrofloxacin were 30.1, 44.7, 2.2, and 55.5%, respectively. Taking the different dosages (25 mg/kg of body weight for oxolinic acid and flumequine and 10 mg/kg for sarafloxacin and enrofloxacin) into account, enrofloxacin showed the highest maximum concentration in plasma, followed by flumequine, oxolinic acid, and sarafloxacin. Following intravenous administration, the volumes of distribution at steady state of oxolinic acid, flumequine, sarafloxacin, and enrofloxacin were 5.4, 3.5, 2.3, and 6.1 liters/kg, respectively. Hence, all the quinolones showed good tissue penetration in Atlantic salmon. The elimination half-life of three of the quinolones, oxolinic acid, flumequine, and sarafloxacin, was less than or equal to 24 h, with oxolinic acid showing the shortest (18.2 h). On the other hand, the elimination half-life of enrofloxacin was estimated to be 34.2 h, almost twice that of oxolinic acid. This study showed that flumequine and enrofloxacin had better pharmacokinetic properties, compared with those of oxolinic acid, in Atlantic salmon held in seawater.