Farm-raised Fish Research Articles

Variations in the volumes of parenchyma and stroma of the liver and in the cytology of hepatocytes are associated with gonadal stages in female Ohrid trout (Salmo letnica)

Quantitative microscopic studies of season- and breeding-related changes in the liver of farm-raised fish are very scarce, and those of wild fish populations are virtually nonexistent. Moreover, none of the available studies investigated breeding-related changes in hepatic stroma, although it is already known that changes might exist in the parenchyma. To the best of our knowledge, ours is the first study using wild adult Ohrid trout females to evaluate quantitative influences of the breeding cycle on the volumes of the two liver compartments—parenchyma and stroma. Quantitative microscopy (stereology) using light microscopy was supplemented with semi-quantitative and quantitative analyses of hepatocyte cytology to express in numbers the seasonal changes in the extent of vacuolated versus basophilic cytoplasm. The liver volume and that of each compartment changed from that at the time of pre-vitellogenesis to the end of the spawning season. The changes in total volumes of parenchyma and stroma—increasing from pre-vitellogenesis to late vitellogenesis—followed the changes in total liver volume. Despite all the changes in total volumes, no differences existed in the relative proportions between the two major compartments. After spawning, the stromal volume continued to increase while that of the parenchyma reduced despite no detectable statistically significant impacts on the liver volume. Changes in both the liver and parenchyma volumes were correlated with the gonadosomatic index and plasma oestradiol levels. With this study, we first establish that fish liver remodelling might also occur in the stroma. When comparing Ohrid trout with other fish species, we noted interspecies similarities and differences with regard to the hepatocyte cytology during the breeding cycle. In our study, the semi-quantitative and stereological studies revealed that, from pre-vitellogenesis to post-spawning, although cytoplasmic vacuolation of the hepatocytes decreased, the basophilia increased. Overall, these cytological changes were only partially in agreement with the data from other trout studies. We believe that this is because of intrinsic interspecies differences in association with natural conditions. Thus, establishing normal patterns is crucial, at least for flagship species, namely to support interpretation of histopathological changes in biomonitoring.

Resistance Determinants of Pseudomonas Species from Aquaculture in Australia

There is limited information on antibiotic resistance determinants present in bacteria of aquaculture origin in Australia. The presence of integron and other resistance determinants was investigated in 129 Pseudomonasisolates derived from nine freshwater trout farms in Victoria (Australia). Polymerase chain reaction (PCR) was carried out for the detection of integrase genes Int1, Int2 and Int3, gene cassette array, integron-associated aadA, beta-lactamase resistance genes blaTEM and blaSHV. Genes coding for efflux pump mexA, mexB and oprM were also investigated as well as cadA and czr which are known to mediate resistance to cadmium. Class 1 integrons were detected in 30/129 (23 %) isolates while class 2 and class 3 was not detected in any of the isolates. aadA gene was detected in 28 of the 59 integrase positive isolates which are also resistant to streptomycin. The strA-strB, blaTEM or blaSHV genes were not detected in any of the strains. mexB was detected in 85/129 isolates and cadA gene in 59/92 isolates tested. The sequence analysis mexB from this study demonstrated similarity to the RND multidrug efflux transporter mexB and its homologue TtgB which in addition to multidrug efflux also transports toluene out of the cell. The sequence analysis of cadA confirms similarities to the cadmium translocating P-type ATPases, cadA of various Pseudomonas spp. Pseudomonas spp. carrying integrons, efflux gene and cadmium resistance genes are present in farm-raised fish and sediments even though no antibiotics were licensed for use in Australian aquaculture at the time of the study.

Incidence of class 1 integron and other antibiotic resistance determinants in Aeromonas spp. from rainbow trout farms in Australia

There is limited information on antibiotic resistance determinants present in bacteria of aquaculture origin in Australia. The presence of integron and other resistance determinants was investigated in 90 Aeromonas isolates derived from nine freshwater trout farms in Victoria (Australia). Polymerase chain reaction was carried out for the detection of integrase genes Int1, Int2 and Int3, gene cassette array, integron-associated aadA, sul1 and qac1 genes, streptomycin resistance genes strA-strB, β-lactamase resistance genes bla(TEM) and bla(SHV) , and tetracycline resistance genes tetA-E and tetM. Clonal analysis was performed by pulsed-field gel electrophoresis (PFGE). Class 1 integrons were detected in 28/90 (31%) and class 2 and class 3 in none of the strains, aadA gene in 19/27 (70%) streptomycin-resistant strains, sul1 in 13/15 (86.7%) sulphonamide-resistant strains and qac1 gene in 8/28 (28.6%) integron-bearing strains. Five strains from two different farms carried gene cassettes of 1000 bp each containing the aadA2 gene and PFGE analysis revealed genetic relatedness. tetC was detected in all and tetA in 9/18 (50%) tetracycline-resistant strains. The strA-strB, bla(TEM) or bla(SHV) genes were not detected in any of the strains. Aeromonas spp. carrying integrons and other resistance genes are present in farm-raised fish and sediments even though no antibiotics were licensed for use in Australian aquaculture at the time of the study.

THE NORTH CENTRAL AQUACULTURE REGION AS A POTENTIAL MARKET FOR FARM-RAISED HYBRID STRIPED BASS

Seafood restaurant chefs/managers, single-unit supermarket buyers, and supermarket chain buyers in the North Central Aquaculture Region were surveyed. Based upon familiarity with farm-raised hybrid striped bass and offer prices quoted, it appeared that seafood restaurants were the most promising retail outlet for the fish. However, only 41.7% of restaurant respondents knew that farmers raised hybrid striped bass as a food fish, and only 25.8% of the dollars spent on finfish and finfish products by restaurants went toward purchases of farm-raised fish. Results of the study suggested that successful large-scale marketing of farm-raised hybrid striped bass in the North Central Region would depend upon extensive product promotion and education of consumers and retailers, especially restaurateurs.

Omega-3 Fatty Acids and Cancer Risk

To the Editor: The systematic review of the effects of omega-3 fatty acids on cancer risk by Dr MacLean and colleagues concluded that dietary supplementation with omega-3 fatty acids is unlikely to prevent cancer. We would like to raise some of our concerns about this review. Thirty-eightprospectivestudieswereselectedforreviewbased on prespecified criteria. However, none of these studies measured fatty acid composition in patients. The food frequency questionnaire and dietary records correlate poorly with direct measurements of fatty acids in patient samples and are prone to measurement error. Ultimately, the effect of omega-3 fatty acids depends on levels achieved in individuals. Fish cannot synthesizeomega-3fattyacidsdenovobutrather ingesteicosapentaenoic and docosahexaenoic acid present in phytoplanktonandzooplankton. Thus, some fish(especially farm-raised fish)arepoorsourcesofomega-3fattyacids.Wethereforethink that a more accurate conclusion of this study is that a preventive effect of omega-3 fatty acids on cancers is still uncertain. We also disagree with the authors on their assessment that animal studies “do not come close to replicating human exposures.” Animal models, especially those developed recently, can closely mimic the clinical course of cancer progression, and are invaluable tools for mechanistic studies that cannot be performed in humans. Animal diets are designed with varying ratios of omega-3 to omega-6 fatty acids, both of which are essential fatty acids required for mammals to survive. It is the ratio of omega-3 to omega-6 that is important for deducing their mechanistic functions, and animal diets have been formulated to reflect human consumption.

Polybrominated diphenyl ethers and polychlorinated biphenyls in commercially wild caught and farm-raised fish fillets in the United States

Wild caught and farm-raised fish fillets collected in fish markets and large-chain super markets located in the Maryland, Washington, DC, and North Carolina were measured for their polybrominated diphenyl ether (PBDE), polychlorinated biphenyl (PCB), and polychlorodibenzo- p-dioxins/dibenzofurans (PCDD/Fs) levels. PCB and PBDE concentrations were the highest in a wild bluefish fillet (800 and 38 ng/g wet weight, respectively) and the lowest in wild Coho salmon fillet (0.35 and 0.04 ng/g, respectively). Levels for both PCBs and PBDEs in ng/g wet weight decreased from bluefish with medians of 200 and 6.2, to rockfish 66 and 4.7, followed by farmed-raised salmon with 9.0 and 1.1, with the lowest in wild salmon, 4.0 and 0.3 ng/g for PCBs and PBDEs, respectively (PCBs are the sum of 25 congeners). The chlorinated biphenyl (CB)-153 and brominated diphenyl ether (BDE)-47 levels correlated in the 22 fish fillets with a Pearson correlation coefficient of 0.94. Bluefish, rockfish (striped bass), wild caught and farm-raised salmons all showed different linear regression slopes between CB-153 and BDE-47 of 7.5, 2.7, 0.97, and 1.5, respectively. A Wilcoxon rank sum test showed no significant difference in the CB-153/BDE-47 ratios between farmed raised and all species of wild salmon combined, but was significant between bluefish and rockfish, farmed raised salmon or wild salmon.

Dietary Omega-3 Fatty Acid Intake and Cardiovascular Risk

Dietary omega-3 fatty acids decrease the risk of cardiovascular disease (CVD). Both epidemiologic and interventional studies have demonstrated beneficial effects of omega-3 fatty acids on many CVD end points, including all CVD (defined as all coronary artery disease [CAD], fatal and nonfatal myocardial infarction [MI], and stroke combined), all CAD, fatal and nonfatal MI, stroke, sudden cardiac death, and all-cause mortality. Much of the evidence comes from studies with fish oil and fish; to a lesser extent, data relate to plant-derived omega-3 fatty acids. Cardioprotective benefits have been observed with daily consumption of as little as 25 to 57 g (approximately 1 to 2 oz) of fish high in omega-3 fatty acids, an intake equivalent to >or=1 fish meal weekly or even monthly, with greater intakes decreasing risk further in a dose-dependent manner, up to about 5 servings per week. Fish, including farm-raised fish and their wild counterparts, are the major dietary sources of the longer-chain omega-3 fatty acids. Sources of plant-derived omega-3 fatty acids include flaxseed, flaxseed oil, walnuts, canola oil, and soybean oil. Because of the remarkable cardioprotective effects of omega-3 fatty acids, consumption of food sources that provide omega-3 fatty acids--especially the longer-chain fatty acids (>or=20 carbons) from marine sources--should be increased in the diet to decrease CVD risk significantly.

Feeding trial on rainbow trout: comparison of dry fish feed and Baltic herring as a source of PCDD/Fs and PCBs.

Fish is an important source of dietary intake of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and polychlorinated biphenyls (PCBs). To assess bioaccumulation of PCDD/Fs and PCBs in farm-raised fish, rainbow trout were fed with either Baltic herring or dry fish feed. Baltic herring feed had a PCDD/F sum concentration of 125 ng kg(-1) dry weight (d.w.), and dry fish feed contained 18.2 ng kg(-1) d.w. of PCDD/Fs. The PCB concentrations of Baltic herring and dry fish feed were 188 and 48.7 microg kg(-1) d.w., respectively. After feeding with Baltic herring for 4 months, the PCDD/F concentration of the rainbow trout fillet was 27.3 ng kg(-1) fresh weight (f.w.), which was 7.0-fold higher than the initial concentration. The PCDD/F concentration and congener profile in rainbow trout had become almost the same as in Baltic herring. PCDD/Fs were accumulated in the fillet with an efficiency of 21%. Feeding of rainbow trout with dry fish feed resulted in a PCDD/F concentration of 8.08 ng kg(-1) f.w., denoting a 2.1-fold increase from the initial level. The accumulation efficiency was 29%. Time trends in PCB concentrations followed those of PCDD/Fs. After 4 months, the PCB sum concentration in herring-fed rainbow trout was 94.4 pg kg(-1) f.w., whereas in dry fish feed-fed rainbow trout it was 38.6 microg kg(-1) f.w. Accumulation efficiencies of PCBs were higher than those of PCDD/Fs. Based on the accumulated PCDD/F and PCB concentrations, it was estimated that frequent consumption of rainbow trout fed with Baltic herring could lead to a human daily intake that exceeds the recommendation of WHO.

Cytochrome P450 1A induction in gudgeon Gobio gobio : Laboratory and Field Studies

The induction of cytochrome P450 1A was studied in gudgeon (Gobio gobio), a common European cyprinid, using both farm-raised and field-caught fish. The effects of sex, reproductive status and past exposure to xenobiotics were assessed. When exposed to beta-naphthoflavone (bNF), reared gudgeon showed a dose-dependent increase of EROD activity with a plateau observed at doses from 20 mg kg-1 (females) and 5 mg kg-1 (males). The sexual difference in EROD activity was related to the gonadosomatic index (GSI) of the female whatever the level of induction. Dose and sex effects were confirmed by the immunodetection of CYP1A protein. More than 1 month was necessary for EROD activity to decrease to baseline levels. A second bNF injection after 32 days gave similar levels of induction, suggesting that EROD induction by bNF was not impaired by a pretreatment. Wild fish were brought from two sites in the Rhone river basin: a low contaminated site (Ain) and a highly contaminated site (Rhone). Wild gudgeon were highly induced by bNF in laboratory conditions, except males from the Rhone site which exhibited EROD levels as high as the EROD plateau found in laboratory conditions. A 2- month depuration period in clean water was necessary for EROD activity in wild gudgeon to decrease to baseline levels. These results provide better knowledge of the main factors of modulation of the induction in gudgeon as well as on the influence of the history of exposure to inducers.

External Costs of Aquaculture Production in West Virginia

Temperate hill-lands of the U.S.A. such as those in West Virginia are areas from which increasing output of farm-raised fish may be possible. However, the downstream economic impacts of current and projected future effluent as a result of aquaculture production have not been extensively studied. Using an externality framework and a combination of primary and secondary data, this study determines pollution prevention costs (PPC), and downstream pollution damage costs resulting from fish farm wastewater effluent measured as willingness to pay (WTP) for restoring water quality. PPC is estimated at $0.11 per kg of trout produced (which would add 6% to private production cost), and WTP is estimated at $0.49 per kg of trout produced (representing 25% of private production cost) at current production and price levels. This study shows that installation of filtration units is a low-cost (less than 6% of total cost) and an effective technology for controlling pollution at the source. Internalizing external costs (adding this 6% to private production costs) is one strategy that could contribute to sustainable growth of the aquaculture industry.

Reduction in Hepatic Microsomal P-450 and Related Catalytic Activity in Farm-Raised Red Drum

Hepatic microsomal factors were investigated in red drum Sciaenops ocellatus, an important aquaculture and sportfish species. Constitutive and induced levels of microsomal cytochrome P-450 and P-420, catalytic activities of 7-ethoxyresorufin O-deethylase (EROD) and NADPH–cytochrome-c reductase, and the extent of membrane lipid peroxidation were compared in juvenile farm-raised and wild fish. We detected smaller amounts of active cytochrome P.450 and more cytochrome P-420, the denatured form of cytochrome P-450, in farm-raised than in wild red drum. Lipid peroxide formation was significantly higher and EROD catalytic activity was decreased in farm-raised red drum, whereas wild fish exhibited significantly higher levels of cytochrome P-450 and EROD activity. No significant alterations in NADPH–cytochrome-c reductase activity were observed in farm-raised fish. The livers from farm-raised red drum had higher levels of cellular lipid, which correlated with higher levels of lipid peroxides and were apparently associated with the loss of active cytochrome P-450. These data indicate that farm-raised fish fed a commercial, potentially lipogenic, diet may be less capable of metabolizing endobiotics, drugs, and hydrocarbon pollutants, and suggest that substantially increased hepatic lipid deposition may have potentially dangerous toxicological implications for these animals.