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Kolarevic J.,NOFIMA | Takle H.,NOFIMA | Takle H.,AVS Chile S.A. | Felip O.,University of Barcelona | And 6 more authors.
Aquatic Toxicology | Year: 2012

The objective of this study was to determine the underlying physiological and molecular responses to long-term sublethal ammonia exposure in Atlantic salmon (Salmo salar) parr. Previous studies have predominately focused on mechanisms during acute, short-term exposure. For that purpose Atlantic salmon parr were exposed to four ammonia concentrations between 4 and 1800μmoll-1 total ammonia nitrogen (TAN), and subjected to two feeding regimes for 15 weeks. Elevated environmental ammonia and full feeding strength caused an initial increase in plasma ammonia levels ([Tamm]) after 22 days of exposure, which thereafter declined and remained similar to the control animals towards the end of the study. On the other hand, a progressive decrease in plasma urea levels was evident throughout the entire exposure period and depended on the concentration of environmental ammonia, with the largest decrease in urea levels observed at the highest ammonia concentrations (1700 and 1800μmoll-1 TAN). We hypothesized that the successful adaptation to long-term elevated ammonia levels would involve an increased capacity for carrier-facilitated branchial excretion. This hypothesis was strengthened by the first evidence of an up-regulation of branchial transcription of the genes encoding the Rhesus (Rh) glycoproteins, Rhcg1 and Rhcg2, urea transporter (UT) and aquaporin 3a (Aqp3a), during long-term exposure. Of the Rhesus glycoprotein (Rh) mRNAs, Rhcg1 was up-regulated at all tested ammonia levels, while Rhcg2 showed a concentration-sensitive increase. Increased transcription levels of V-type H+-ATPase (H+-ATPase) were observed at the highest ammonia concentrations (1700 and 1800μmoll-1 TAN) and coincided with an up-regulation of Rhcg2 at these concentrations. Transcription of UT and Aqp3a was increased after 15 weeks of exposure to low ammonia levels (470 and 480μmoll-1 TAN). A significant increase in brain glutamine (Gln) concentration was observed for full fed Atlantic salmon after 22 days and in fish with restricted feeding after 105 days of exposure to 1800 and 1700μmoll-1 TAN, respectively, without any concomitant decrease in brain glutamate (Glu) concentrations. These results suggest that Gln synthesis is an ammonia detoxifying strategy employed in the brain of Atlantic salmon parr during long-term sublethal ammonia exposure. Full feed strength had an additive effect on plasma [Tamm], while the restricted feeding regime postponed the majority of the observed physiological and molecular responses. In conclusion, Atlantic salmon parr adapts to the long-term sublethal ammonia concentrations with increased branchial transcription levels of ammonia and urea transporting proteins and ammonia detoxification in the brain. © 2012 Elsevier B.V.

Welch T.J.,U.S. Department of Agriculture | Good C.M.,The Conservation Funds Freshwater Institute
Aquaculture | Year: 2013

Recent reports indicate that novel Weissella sp. bacteria have been associated with disease outbreaks in cultured rainbow trout (Oncorhynchus mykiss) at commercial farms in China and Brazil. In the summer of 2011, a severe disease outbreak displaying similar clinical signs occurred at a commercial rainbow trout farm in western North Carolina. Observed signs included dark skin coloration, lethargic swimming, bilateral exophthalmia, corneal opacity, ocular hemorrhage, occasional corneal rupture, and in some cases cerebral hemorrhage. Mortality was most severe in larger fish approaching market size. Bacteria isolated from moribund fish were identified to the genus level as Weissella sp. by 16S rRNA gene sequence analysis and were 99% identical to the sequences of isolates collected from the Chinese and Brazilian outbreaks. Laboratory-based disease challenge experiments using the isolated pathogen replicated both the disease signs and induction of mortality in exposed healthy rainbow trout. Aqueous vaccine formulations containing formalin-inactivated whole-cell Weissella sp. antigens conferred significant protection against experimental infection when both the vaccine and the pathogen were delivered by injection (relative percent survival [RPS] of 87.5% and 85% at 38 and 72 days after vaccination, respectively). The Weissella sp. vaccine was equally effectivewhen combinedwith a commercially available Yersinia ruckeri vaccine, and this bivalent formulation did not alter the efficacy of the Y. ruckeri component of the vaccine. This is the first identification of this emerging rainbow trout disease, which we have termedWeissellosis, in the United States, and the spread of this pathogen might pose a significant threat to the domestic rainbowtrout aquaculture industry. Our results also suggest that a bivalent Weissella/Y. ruckeri vaccine could be used as an effective and economical means for controlling this pathogen. © 2013 Elsevier B.V.

Pfeiffer T.J.,U.S. Department of Agriculture | Summerfelt S.T.,The Conservation Funds Freshwater Institute | Watten B.J.,U.S. Geological Survey
Aquacultural Engineering | Year: 2011

Many methods are available for the measurement of dissolved carbon dioxide in an aqueous environment. Standard titration is the typical field method for measuring dissolved CO 2 in aquaculture systems. However, titrimetric determination of dissolved CO 2 in marine water aquaculture systems is unsuitable because of the high dissolved solids, silicates, and other dissolved minerals that interfere with the determination. Other methods used to measure dissolved carbon dioxide in an aquaculture water included use of a wetted CO 2 probe analyzer, standard nomographic methods, and calculation by direct measurements of the water's pH, temperature, and alkalinity. The determination of dissolved CO 2 in saltwater based on partial pressure measurements and non-dispersive infra-red (NDIR) techniques with a CO 2 gas analyzer are widely employed for oceanic surveys of surface ocean CO 2 flux and are similar to the techniques employed with the head space unit (HSU) in this study. Dissolved carbon dioxide (DC) determination with the HSU using a infra-red gas analyzer (IRGA) was compared with titrimetric, nomographic, calculated, and probe measurements of CO 2 in freshwater and in saltwater with a salinity ranging from 5.0 to 30ppt, and a CO 2 range from 8 to 50mg/L. Differences in CO 2 measurements between duplicate HSUs (0.1-0.2mg/L) were not statistically significant different. The coefficient of variation for the HSU readings averaged 1.85% which was better than the CO 2 probe (4.09%) and that for the titrimetric method (5.84%). In all low, medium and high salinity level trials HSU precision was good, averaging 3.39%. Differences existed between comparison testing of the CO 2 probe and HSU measurements with the CO 2 probe readings, on average, providing DC estimates that were higher than HSU estimates. Differences between HSU and titration based estimates of DC increased with salinity and reached a maximum at 32.2ppt. These differences were statistically significant (P<0.05) at all salinity levels greater than 0.3ppt. Results indicated reliable replicated results from the head space unit with varying salinity and dissolved carbon dioxide concentrations. © 2010.

Good C.,The Conservation Funds Freshwater Institute | Davidson J.,The Conservation Funds Freshwater Institute | Welsh C.,The Conservation Funds Freshwater Institute | Snekvik K.,Washington State University | Summerfelt S.,The Conservation Funds Freshwater Institute
Aquacultural Engineering | Year: 2011

A controlled four-month trial was conducted to compare the effects of ozonation (oxidation-reduction potential setpoint=250mV) versus no ozonation on rainbow trout Oncorhynchus mykiss performance, health, and welfare in replicated WRAS operated at low exchange rates (0.26% of the total recirculating flow) and high feed loadings (3.9kg/day per m3/day makeup flow). Rainbow trout at 74±2g (mean±standard error) in size were randomly stocked into six replicated 9.5m3 WRAS (1000 fish per system). Ozonation of the three treatment WRAS began two months post-stocking following biofilter acclimation when fish were 295±1g. Fish were maintained at densities between 40kg/m3 and 80kg/m3 throughout the study at water temperatures of approximately 13-17°C. By study's end, percentage survival for both groups was high (>98%). Fish in ozonated systems weighed significantly (p<0.05) more at study's end than fish from the non-ozonated systems (1161±6g vs. 993±12g, respectively). Histopathological evaluation revealed increased levels of gill epithelial hyperplasia and hypertrophy, as well as hepatic lipidosis, in fish from ozonated systems; however, all lesions were subclinical. Fin condition was good overall in both groups, although fish from non-ozonated WRAS had better (p<0.05) dorsal fin indices than fish in the ozonated cohort. The major blood chemistry finding was higher (p<0.05) urea nitrogen in fish from non-ozonated systems (15.33±0.90mg/dL, vs. 6.800±0.470mg/dL in fish from ozonated WRAS). Overall, the results of this study indicate that raising rainbow trout to market size in ozonated WRAS improves fish performance without significantly impacting their health and welfare. © 2011 Elsevier B.V.

Good C.,The Conservation Funds Freshwater Institute | Davidson J.,The Conservation Funds Freshwater Institute | Welsh C.,The Conservation Funds Freshwater Institute | Summerfelt S.,The Conservation Funds Freshwater Institute
Aquacultural Engineering | Year: 2010

Chronic exposure to elevated levels of dissolved carbon dioxide (CO2) has been linked to reduced growth, physiological disturbances and negative health outcomes in intensively reared fish. Although pumping to a degassing tower can lower concentrations of dissolved CO2 in water recirculation aquaculture systems (WRAS), pumping can be a significant cost for operators. A 6-month trial was conducted to compare the effects of high (24 ± 1 mg/L; partial pressure = 8.79 mm Hg) and low (8 ± 1 mg/L; partial pressure = 2.91 mm Hg) dissolved CO2 concentrations on rainbow trout Oncorhynchus mykiss performance and health in replicated WRAS operated at low-exchange rates (0.26% of the total recirculating flow). Rainbow trout (62 ± 1 g) were randomly stocked into six replicated WRAS and into three small tanks within a flow-through system to provide a physiological comparison. All study fish were maintained at densities between 25 and 80 kg/m3, at water temperatures of approximately 13-14 °C, and at dissolved oxygen concentrations of approximately saturation. A 24-h photoperiod was provided and all fish groups were fed equal portions every 2 h during the study period. Fish health and performance were assessed with daily mortality and monthly length and weight data collection, as well as multiple tissue samplings for histopathological assessment. At the study's end, percentage survival for both groups was high (>97%). No significant (p < 0.05) differences in growth or survival were observed between CO2 treatments. No nephrocalcinosis or related pathologies were noted. Skin and gill pathologies were common in both treatment groups; however, there were few statistically significant differences between groups for any of the tissue types evaluated: high CO2 fish were more likely to exhibit lymphocytic portal hepatitis, while the low CO2 treatment group exhibited greater gill epithelial hyperplasia. None of the pathologies observed were substantive or likely to cause mortality. The results of this study indicate that raising rainbow trout to market size in WRAS with CO2 concentrations of 24 mg/L does not significantly affect their overall health and performance. © 2009 Elsevier B.V. All rights reserved.

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