Fish Farm Sediments Research Articles

Organic matter mineralization in an organic-rich sediment: Experimental stimulation of sulfate reduction by fish food pellets

The combined effects of organic matter additions and temperature on short chain fatty acid (SCFA) turnover, sulfate reduction and nutrient accumulation were examined in an organic-rich fish farm sediment. Fish food pellets, which contribute significantly to the organic matter loss from fish farms, were added to surface sediment at three loadings (2.8; 14.0; 28.0 mg ww g−1 ww sediment; equivalent to organic matter loadings measured during fish farming) and incubated for 30 days in anaerobic bags at 5°C and 15°C. SCFA accumulated to high levels (acetate up to 85 mM, propionate up to 17 mM, butyrate up to 25 mM) in sediments amended with food pellets, and sulfate reduction was stimulated up to 30 times relative to unamended sediments. Sulfate reducers appeared saturated with substrates (SCFA) even in the lowest additions. A low C/N ratio (0.4–1.8) of the major mineralization products (TCO2 and NH4+) indicated preferential nitrogen mineralization in amended sediment compared with the total particulate pool (C/N = 8.8–11.9) and added food pellets (C/N = 8.4).

Organic matter mineralization in an organic-rich sediment: Experimental stimulation of sulfate reduction by fish food pellets

The combined effects of organic matter additions and temperature on short chain fatty acid (SCFA) turnover, sulfate reduction and nutrient accumulation were examined in an organic-rich fish farm sediment. Fish food pellets, which contribute significantly to the organic matter loss from fish farms, were added to surface sediment at three loadings (2.8; 14.0; 28.0 mg ww g−1 ww sediment; equivalent to organic matter loadings measured during fish farming) and incubated for 30 days in anaerobic bags at 5°C and 15°C. SCFA accumulated to high levels (acetate up to 85 mM, propionate up to 17 mM, butyrate up to 25 mM) in sediments amended with food pellets, and sulfate reduction was stimulated up to 30 times relative to unamended sediments. Sulfate reducers appeared saturated with substrates (SCFA) even in the lowest additions. A low C/N ratio (0.4–1.8) of the major mineralization products (TCO2 and NH4+) indicated preferential nitrogen mineralization in amended sediment compared with the total particulate pool (C/N = 8.8–11.9) and added food pellets (C/N = 8.4).

Environmental distribution of organic waste from a marine fish farm

Organic components in marine sediments were determined along a transect away from a salmon farm in western Norway. Dry weight, ash-free dry weight and total bacterial numbers gave a basic description of the sediments. Pristane, elemental sulphur and fatty acids resulting from organic enrichment from the farm were detected. The method used was solvent extraction of the sediments and subsequent silica gel fractionation into aliphatic and aromatic hydrocarbons and polar components. The polar components were subjected to methanolysis followed by gas chromatography (GC) of the resulting fatty-acid methyl esters. The hydrocarbon fractions were analysed by GC directly. Amounts and composition were found to depend mainly on the distance from the farm site. Principal component analysis was carried out on 20 representative fatty acids in fish farm sediments, clean sediments, feed and fish faeces. A multivariate correlation between the fatty acids and pristane indicated that these components may be used as chemical markers of disposal from an aquaculture site.

Erratum: Effects of oxytetracycline, oxolinic acid, and flumequine on bacteria in an artificial marine fish farm sediment

Oxytetracycline, oxolinic acid, and flumequine are at present the most frequently used antibacterial agents in the treatment of marine farmed fish in Norway. These substances are supplied with the food pellets and a substantial amount ends up in the sediment under the net pens. The effects of these antibacterial agents on the microbial community in a sediment were experimentally examined in tanks containing sediment to which was added either oxytetracycline, oxolinic acid, or flumequine, and supplied with a constant water flow. During the first 20 days of the experiment, approximately one-third of the antibacterial agents disappeared from the sediments. During the next 165 days another 25% vanished. There were elevated numbers of bacteria resistant to oxytetracycline and oxolinic acid a few days after the start of the experiment. The resistance that developed to oxytetracycline was higher and longer lasting than that to oxolinic acid and flumequine. Of the quinolones, flumequine seemed least disposed to induce resistance. The number of bacteria in all treated sediments decreased to 50–67% of the numbers in the control sediment 2 days after medication. Seven days after medication the sulfate reduction rates in the treated sediments were reduced to less than 10% of the rates found in the control. This effect lasted at least 29 days, but after 70 days the inhibition of the sulfate reduction in the treated sediments had disappeared.Key words: antibacterial agents, sediment, bacterial resistance, sulfate reduction.

Effects of oxytetracycline, oxolinic acid, and flumequine on bacteria in an artificial marine fish farm sediment

Oxytetracycline, oxolinic acid, and flumequine are at present the most frequently used antibacterial agents in the treatment of marine farmed fish in Norway. These substances are supplied with the food pellets and a substantial amount ends up in the sediment under the net pens. The effects of these antibacterial agents on the microbial community in a sediment were experimentally examined in tanks containing sediment to which was added either oxytetracycline, oxolinic acid, or flumequine, and supplied with a constant water flow. During the first 20 days of the experiment, approximately one-third of the antibacterial agents disappeared from the sediments. During the next 165 days another 25% vanished. There were elevated numbers of bacteria resistant to oxytetracycline and oxolinic acid a few days after the start of the experiment. The resistance that developed to oxytetracycline was higher and longer lasting than that to oxolinic acid and flumequine. Of the quinolones, flumequine seemed least disposed to induce resistance. The number of bacteria in all treated sediments decreased to 50–67% of the numbers in the control sediment 2 days after medication. Seven days after medication the sulfate reduction rates in the treated sediments were reduced to less than 10% of the rates found in the control. This effect lasted at least 29 days, but after 70 days the inhibition of the sulfate reduction in the treated sediments had disappeared. Key words: antibacterial agents, sediment, bacterial resistance, sulfate reduction.

Transferable drug resistance in bacteria from fish-farm sediments

Antibiotic-resistant bacteria were isolated from sediment samples collected beneath two fish farms west of Bergen (Norway). The samples were collected just after the fish had been treated with oxytetracycline. Eighty-four bacterial isolates were tested for susceptibility to antibacterial agents. Most of the isolates were resistant to oxytetracycline, kanamycin, and sulfamethoxazole. Transferable plasmid-related resistance was shown by direct cell transfer and agarose gel electrophoresis. Among 34 multiple-resistant isolates, 7 isolates were able to transfer resistance to Escherichia coli HB101. Phenotypical characterization indicated that these seven isolates belonged to the genera Vibrio and Pseudomonas. The results indicate that sediments beneath fish farms may serve as a reservoir for transferable antimicrobial resistance genes. Key words: drug resistance, gene transfer, marine sediment bacteria.

Long-range changes in oxytetracycline concentration and bacterial resistance towards oxytetracycline in a fish farm sediment after medication

Following 10 days medication with oxytetracycline, marine sediment was sampled beneath three selected cages (cages 1, 2 and 3) at a fish farm over a period of 18 mnd., in order to detect any change in the sediment oxytetracycline concentration, bacterial number and bacterial resistance towards the drug. The bulk of oxytetracycline disappeared during the first weeks, but it persisted in the sediment at lower concentrations for quite some time after the medication. Half-life ( f 1 2 ) of oxytetracycline in the sediment was measured as: 125, 144 and 87 days under cages 1, 2 and 3, respectively. At the end of the medication, all three sediments had > 100% oxytetracycline-resistant bacteria. This value dropped to 20% after 72 days and stabilised at levels of between 10 and 50%. The change in bacterial numbers, described as total and plate counts, was due to seasonal variations rather than to the medication.

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

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.

Residues of oxytetracycline in wild fish and sediments from fish farms

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.

Presence of the fish pathogen Vibrio salmonicida in fish farm sediments

The persistence of the fish pathogen Vibrio salmonicida in fish farm sediments was studied by use of fluorescent-antibody techniques. The specificities of the monoclonal antibodies and polyclonal rabbit serum used in the study were tested against a number of Vibrio strains, including 4 isolates from intestinal tracts of healthy fish and 98 isolates from sediments. V. salmonicida was detected in sediment samples from diseased farms several months after an outbreak of the disease. The bacterium was also detected in a sediment sample from a disease-free fish farm. No V. salmonicida could be detected in sediments not influenced by fish farming. The number of positive samples was generally higher with application of rabbit serum as opposed to use of monoclonal antibodies, indicating that the rabbit serum may cross-react with other bacteria.