Harry Björklund

Residues of oxytetracycline in wild fish and sediments from fish farms.

Abstract The residues and persistence of oxytetracycline were studied in wild fish and sediments on two fish farms after chemotherapy of the farmed fish. In wild fish, residues of oxytetracycline were detected up to 13 days after the medication. The half-life of oxytetracycline in fish farm sediments was 9 days and 419 days on the two farms, respectively. The results indicate that oxytetracycline may, under stagnant anoxic conditions, be very persistent in fish farm sediments. It is suggested that leakage from sediments, not decomposition, may be the main factor reducing the oxytetracycline levels in sediments. Bacteria, resistant to oxytetracycline, were isolated from the intestines of wild fish.

Residues of oxolinic acid and oxytetracycline in fish and sediments from fish farms

Abstract The residues of oxolinic acid and oxytetracycline were studied in fish and sediments from five fish farms after chemotherapy of the farmed fish. Compared to oxytetracycline, oxolinic acid was better absorbed and faster excreted from the treated fish. Oxytetracycline was found persistent in concentrations of 0.8–6.3 μg/g in the sediments under the medicated fish pens. Oxolinic acid levels of 0.05–0.2 μg/g were measured in the sediments for 5 days after the treatment of the fish. Compared to oxytetracycline, oxolinic acid showed a faster loss of antibacterial activity in the fish farm sediments. Fish pathogenic bacteria resistant to oxytetracycline were isolated from the treated fish and from the sediments under fish pens. No fish pathogenic bacteria resistant to oxolinic acid were found in this study.

Temperature-related absorption and excretion of oxytetracycline in rainbow trout (Salmo gairdneri R.)

Abstract The absorption and elimination of oxytetracycline in serum, muscles and liver of rainbow trout were studied at 5°, 10° and 16°C after a single oral dose of 75 mg/kg fish. The absorption of the drug was relatively rapid, with maximum concentrations reached in serum within 1 h at 16°C, 12 h at 10°C and 24 h at 5°C. The highest drug levels were measured in bile and liver followed by serum and muscle tissue. The elimination of the drug was markedly temperature-dependent. The half-life of oxytetracycline in rainbow trout serum was 4.8 days at 16°C, 6.1 days at 10°C and 8.9 days at 5°C. The predicted withdrawal times varied from 27 days to 135 days depending on temperature and tissue studied. Results obtained from laboratory experiments are compared with results from field trials.

Temperature-related absorption and excretion of oxolinic acid in rainbow trout (Oncorhynchus mykiss)

Abstract The absorption and elimination of oxolinic acid in serum, bile and tissues of rainbow trout were studied at 5, 10 and 15 °C after a single oral dose of 75 mg/kg. The maximum levels of oxolinic acid were obtained in serum within 1, 4 and 6 days at 16, 10 and 5 °C, respectively. The highest drug concentrations were measured in bile followed by liver, kidney, muscle tissue and serum. The higher levels of oxolinic acid in tissues compared to serum indicate a good distribution of the drug. The elimination half-life in serum was 24 h at 16 °C, 4.0 days at 10 °C and 6.1 days at 5 °C. With the detection limit of 0.01 μg/g for the oxolinic acid HPLC assay, the predicted withdrawal time with 95% confidence for muscle tissue was 28 days at 16 °C, 60 days at 10 °C and 140 days at 5 °C. Results obtained under laboratory conditions were in accordance with results from field trials.

Molecular characterisation of the nucleocapsid protein gene, glycoprotein gene and gene junctions of rhabdovirus 903/87, a novel fish pathogenic rhabdovirus.

The sequences of the nucleocapsid and glycoprotein genes and the gene junctions of the fish pathogenic rhabdovirus 903/87 were determined from cDNA and PCR clones. The mRNA of the nucleocapsid is most likely 1492 nucleotides long and encodes a protein of 426 amino acids, whereas the mRNA of the glycoprotein is likely to be 1682 nucleotides long and the protein 517 amino acids. When the nucleocapsid and glycoprotein genes of virus 903/87 were compared at amino acid level with other rhabdoviruses they showed the highest homology with the Vesiculovirus genus. By sequencing the junctions between the N, P, M, G and L genes it was determined that transcription start and stop codons were conserved between virus 903/87 and the vesiculoviruses. Virus 903/87 has no open reading frame coding for a non-virion gene between the glycoprotein and the polymerase gene. Phylogenetic studies based on rhabdovirus nucleocapsid and glycoprotein genes suggested that virus 903/87 is related to viruses in the Vesiculovirus genus.

A novel fish rhabdovirus from sweden is closely related to the Finnish rhabdovirus 903/87.

A novel rhabdovirus, preliminary designated as the Sea trout rhabdovirus 28/97 (STRV 28/97), was isolated from sea trout (Salmo trutta trutta) in Sweden in 1996. The fish showed central nervous symptoms, and at the autopsy petechial bleedings in the mesenteric fat were visible. STRV 28/97 was shown to be serologically related to the vesiculotype rhabdovirus 903/87 isolated from brown trout (Salmo trutta lacustris) in Finland [1,3]. The sequences for the nucleocapsid protein, phosphoprotein, matrix protein, glycoprotein and beginning of the polymerase protein of STRV 28/97 were determined. At the amino acid level the genes were over 97% similar to virus 903/87. The nucleocapsid proteins, glycoproteins and beginning of the polymerase protein of STRV 28/97 and virus 903/87 were clustered with the vesiculoviruses and the phosphoproteins close to the vesiculoviruses in protein parsimony analysis. The matrix proteins formed a distinct clade in protein parsimony analysis.

Analysis of oxolinic acid in fish by high-performance liquid chromatography.

A simple high-performance liquid chromatographic method for assaying oxolinic acid, a chemotherapeutic agent, in fish tissues has been developed. Nalidixic acid is used as an internal standard. The drugs are separated on an internal surface reversed-phase column. The sample clean-up is minimized. Serum samples are analysed by direct injection on the column; muscle and liver samples are analysed after solid-phase extraction. The recoveries of oxolinic acid from spiked rainbow trout serum, muscle tissue and liver are 99.7, 87.7 and 83.6%, respectively. The lowest measurable amount of the drug is 0.01 microgram/g in all three tissues.