Freshwater Rainbow Trout Research Articles

Zonation of Ca2+ transport and enzyme activity in the caeca of rainbow trout - a simple structure with complex functions.

Trout caeca are vermiform structures projecting from the anterior intestine of the gastrointestinal tract. Despite their simple gross morphology, these appendages are physically distinct along the anterior-posterior axis, and ultrastructural evidence suggests zonation of function within the structures. Individual caeca from three sections (anterior, middle and posterior) were removed from the intestine of freshwater rainbow trout and investigated for ion transport and enzyme activity. Ca2+ absorption appeared as a combination of active and passive movement, with Michaelis-Menten kinetics observable under symmetrical conditions, and was inhibited by several pharmacological agents (ouabain, La3+ and a calmodulin antagonist). There was a decrease in ion transport function from adjacent to the intestine (proximal) to the distal tip of each caecum, along with decreasing transport from anterior to posterior for the proximal portion alone. Feeding increased the JMax and KM for Ca2+ absorption within all sections, whereas ion-poor water (IPW) exposure further increased the JMax and KM for Ca2+ transport in the anterior and middle sections. Increased Na+/K+-ATPase (NKA) and citrate synthase (CS) activity rates paralleled trends seen in Ca2+ transport. Feeding in freshwater and IPW exposure increased the glycolytic capacity of the caeca via increased pyruvate kinase (PK) and decreased lactate dehydrogenase (LDH) activity, while amino acid metabolism increased with IPW exposure through increased glutamate dehydrogenase (GDH) activity. Overall, feeding and IPW exposure each altered ionoregulation within the caeca of freshwater rainbow trout in a zone-specific pattern, with the anterior and proximal portions of the caeca being most affected. Increased carbohydrate and protein metabolism fueled the increased ATP demand of NKA through CS.

First confirmation of salmonid alphavirus infection in Arctic char Salvelinus alpinus and in Austria.

To date, sleeping disease (SD) caused by salmonid alphavirus 2 (SAV 2) has been reported in freshwater rainbow trout Oncorhynchus mykiss and Atlantic salmon Salmo salar. This study describes for the first time the occurrence of SD in farm-reared Arctic char Salvelinus alpinus and the occurrence of SAV in Austria. Clinical symptoms were indicative of the disease, and the diagnosis was confirmed by histopathology, infectivity in first passages of CHSE-214 cells and PCR. The phylogenetic analysis of the amplified SAV-nonstructural protein-3 (nsP3) fragment revealed the affiliation to the SAV 2 genotype.

Three generations of selective breeding improved rainbow trout (Oncorhynchus mykiss) disease resistance against natural challenge with Flavobacterium psychrophilum during early life-stage rearing

Bacterial cold water disease (BCWD) is a frequent cause of mortality in freshwater rainbow trout (Oncorhynchus mykiss) and the implementation of a family-based genetic selection program to improve disease resistance has been previously described. To quantify and understand the consequences of selection, three lines of outbred rainbow trout were created by divergent selection: ARS-Fp-R (resistant), ARS-Fp-C (control) and ARS-Fp-S (susceptible). Herein, results from both field and laboratory studies are described comparing survival of third-generation ARS-Fp-R line eggs/fish stocked at equal proportions to control and susceptible lines and reared together in a common environment. The survival of the pooled-line cohort was compared to the survival of an age-matched hatchery line, Fish Lake-DeSmet (FLDS) during early life-stage rearing. A typical BCWD outbreak occurred in the FLDS line while a more limited mortality event occurred in tanks containing the pooled lines. Mortalities from days 42–70 of the trial were saved for pedigree assignment and pathogen load measurement. After accounting for differences in early post-hatch survival, ARS-Fp-R line fish demonstrated two-fold lower BCWD-related mortality while ARS-Fp-S line fish demonstrated two-fold higher mortality; however, there was not a survival advantage of the ARS-Fp-R line fish over ARS-Fp-C line fish. At the end of the trial period, F. psychrophilum was not detected in spleen tissue of live-sampled ARS-Fp-R line fish while 10.3% of the ARS-Fp-C line and 36.4% of the ARS-Fp-S line fish exhibited detectable loads. Experimental challenge of the genetic lines with two different F. psychrophilum strains confirmed significantly higher survival of the ARS-Fp-R line fish as compared to either the ARS-Fp-S or FLDS genetic lines, albeit the susceptibility of the FLDS line was confounded by slower growth rate. These data demonstrate that three generations of artificial selection translated into improved survival following either natural or experimental exposure to F. psychrophilum. These data also suggest that hatchery lines, such as Fish Lake-DeSmet, may have higher relative susceptibility to BCWD thereby contributing to location outbreak severity.

Full Water Quality Monitoring of a Traditional Flow-Through Rainbow Trout Farm

Traditional freshwater rainbow trout farms are still popular in some European countries such as Poland, France and Ireland. These systems generally operate in flow-through configuration. The impact such production systems might have on water quality remains mostly unknown. The present study was set up to fulfil this objective of monitoring water quality on different fish farm locations in order to identify the impacts of the whole farm (comparison of farm inlet and outlet) and at pond scale in order to understand the water quality dynamics and to better understand the impact of multiple water reuse (water passes) in a given pond on water quality. In the absence of any sort of water treatment, an increase in the number of water passes was shown to create an increase in ammonium concentration along the farm. Finally, this traditional flow-through rainbow trout production system was revealed to almost be at its full carrying capacity with respect to internal water quality parameters and fish welfare. To increase fish production, some water treatment techniques (solid/liquid separation, nitrification) would have to be introduced in order to optimize the rearing water quality for fish growth and to minimize the release of pollutants in the receiving water to limit the impact on the environment.

Comparative Immune- and Stress-Related Transcript Response Induced by Air Exposure and Vibrio anguillarum Bacterin in Rainbow Trout (Oncorhynchus mykiss) and Gilthead Seabream (Sparus aurata) Mucosal Surfaces.

Fish have to face various environmental challenges that may compromise the efficacy of the immune response in mucosal surfaces. Since the effect of acute stress on mucosal barriers in fish has still not been fully elucidated, we aimed to compare the short-term mucosal stress and immune transcriptomic responses in a freshwater (rainbow trout, Oncorhynchus mykiss) and a marine fish (gilthead seabream, Sparus aurata) to bacterial immersion (Vibrio anguillarum bacterin vaccine) and air exposure stress in skin, gills, and intestine. Air exposure and combined (vaccine + air) stressors exposure were found to be inducers of the cortisol secretion in plasma and skin mucus on both species in a time-dependent manner, while V. anguillarum bacterin exposure induced cortisol release in trout skin mucus only. This was coincident with a marked differential increase in transcriptomic patterns of stress- and immune-related gene expression profiles. Particularly in seabream skin, the expression of cytokines was markedly enhanced, whereas in gills the response was mainly suppressed. In rainbow trout gut, both air exposure and vaccine stimulated the transcriptomic response, whereas in seabream, stress and immune responses were mainly induced by air exposure. Therefore, our comparative survey on the transcriptomic mucosal responses demonstrates that skin and gut were generally more reactive in both species. However, the upregulation of immune transcripts was more pronounced in gills and gut of vaccinated trout, whereas seabream appeared to be more stress-prone and less responsive to V. anguillarum bacterin in gills and gut. When fish were subjected to both treatments no definite pattern was observed. Overall, the results indicate that (1) the immune response was not homogeneous among mucosae (2), it was greatly influenced by the specific traits of each stressor in each surface and (3) was highly species-specific, probably as a result of the adaptive life story of each species to the microbial load and environmental characteristics of their respective natural habitats.

Assessing the long-term causal effect of trout invasion on a native charr

Many studies have indicated that invasive species can drive declines in native species through interspecific competition. In freshwater ecosystems, brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss) have been implicated in reducing native species, especially congeneric salmonid fishes. However, demonstrating causality in the wild is problematic because non-natives might replace natives in areas where the former were extirpated by other environmental changes. Using the recently developed technique of multispatial convergent cross mapping (CCM) and a long-term monitoring data set (2002–2017) with spatial replication on both introduced and native salmonids in a Japanese stream, I tested whether an increase in non-native trout caused a decrease in native charr (Salvelinus leucomaenis). Native charr decreased their population density over time in contrast to the non-native brown trout and rainbow trout. The dominant species changed from native charr (64%) in 2002 to non-native trout (97%) by 2017. Multispatial CCM identified significant causal forcing of the native charr by both rainbow trout and brown trout, lending support for the hypothesis of displacement, rather than replacement, of a native species by non-native species. These results therefore suggest that eradicating the invasive trout species may aid the recovery of native charr in the region.

Carbonic anhydrase expression in the branchial ionocytes of rainbow trout.

Rainbow trout (Oncorhynchus mykiss) exposed to acid-base challenges activate branchial mechanisms for the excretion of acid-base equivalents. Current models of branchial acid-base excretion in freshwater rainbow trout propose two main ionocyte types: the peanut lectin agglutinin-positive (PNA+) mitochondrion-rich cell or ionocyte is believed to secrete HCO3- in exchange for Cl-, whereas H+ secretion is thought to occur across PNA- ionocytes in exchange for Na+ Both HCO3- and H+ are supplied by intracellular hydration of CO2 catalysed by cytosolic carbonic anhydrase (CAc). Immunohistochemical approaches revealed that under control conditions, CAc was detectable in 92.3±1.0% (N=11) of PNA- ionocytes, and the abundance of PNA- ionocytes increased in response to systemic acidosis elicited by 72 h exposure to water of low pH (nominally pH4.5), hypercapnia (1% CO2, nominally 7.6Torr) or hyperoxia (achieved by gassing water with pure O2), as did the abundance of PNA- ionocytes that exhibited immunofluorescence for CAc. However, just 4.3±0.6% (N=11) of PNA+ ionocytes expressed detectable CAc under control conditions. Marked increases in the abundance of CAc-positive PNA+ ionocytes were detected following exposure of trout to a base load via recovery from hypercapnia or base infusion (72 h infusion with 140 mmol l-1 NaHCO3). The percentage of CAc-positive PNA+ ionocytes also was increased in trout treated with cortisol (10 mg kg-1 hydrocortisone 21-hemisuccinate daily for 7 days). These results suggest that regulation of CA within PNA+ ionocytes and/or the abundance of CAc-positive PNA+ ionocytes plays a role in activating base secretion in response to systemic alkalosis.

Streptococcal infections of farmed fish

The genus Streptococcus is large and complex, accommodating a wide range of Gram positive bacteria. Only a few biotypes have been isolated from fish and the most pathogenic are those belonging to D serogroup, otherwise known as the Enterococci. Streptococcal septicaemia was first among cultured rainbow trout (Onchorynchus mykiss) in Japan in 1958. Since then, the disease has appeared sporadically or in epizootics among cultured or wild fish both in freshwater and marine environments all over the world. Among the freshwater species infected, rainbow trout (Onchorynchus mykiss) and tilapia (Oreochromis niloticus) are the most important species. Clinical signs vary among species of affected fish. The most common symptoms are loss of appetite, erratic swimming, darkening of body colour, eye lesions, external haemorrhagic lesions and ulcerations. The standard system for identification is based on the antigenicity of the carbohydrate moiety of the cell wall, according to a scheme devised by Lancefìeld in the 1930's. The American freshwater isolates obtained by Robinson & Meyer (1966), Plumb et al. (1974), Rasheed & Plumb (1984) were all typed Lancefield's group Β serotype in contrast to almost all of the much more frequent isolates from marine fish, which are usually untypable Enter ο co ecus-like strains. The Streptococcus strains isolated from yellowtail (Seriola sp), ayu (Plecoglosus altivelis) and flounder (Rhombosolea. sp) have similar biochemical reactions to Streptococcus iniae, a species isolated from dolphins by Pier & Madin (1976), which is defined in Bergey's Manual as a separate species. Kusuda et al.(1991) have analysed numerous strains from yellowtail infections in mariculture and in eels and have concluded, on the basis of DNA/DNA hybridization studies and biochemistry that a specific condition, caused by such streptococci, exists and that these bacteria were closest to Enterococci in characteristics and that infectious coccosis of marine fish, as seen in Japan, should be called "Enterococcal infection". Enterococci released from diseased fish seem to be the main source of infection. It has been shown that these bacteria remain in seawater and particularly in the mud around farms for a long time. Higher numbers of microorganisms exist in the seawater during summer months in contrast to the winter months when the bacterial load is higher in the mud (Kitao et al. 1979). Ghittino & Prearo (1992) have shown that in freshwater fish the outbreak of the disease was related to an organic pollution of the rivers supplying fish farms, associated with high water temperature (21-22°C). Wild fish can also be infected and spread the bacteria. It is generally believed that the infection is horizontal with infection occurring from direct contact with infected fish or contaminated fish food (Robinson & Meyer, 1996). The mechanisms of enterococcal infections pathogenicity are not yet fully understood.

Cytokine modulation by stress hormones and antagonist specific hormonal inhibition in rainbow trout (Oncorhynchus mykiss) and gilthead sea bream (Sparus aurata) head kidney primary cell culture

A tight interaction between endocrine and immune systems takes place mainly due to the key role of head kidney in both hormone and cytokine secretion, particularly under stress situations in which the physiological response promotes the synthesis and release of stress hormones which may lead into immunomodulation as side effect. Although such interaction has been previously investigated, this study evaluated for the first time the effect of stress-associated hormones together with their receptor antagonists on the expression of cytokine genes in head kidney primary cell culture (HKPCC) of the freshwater rainbow trout (Oncorhynchus mykiss) and the seawater gilthead sea bream (Sparus aurata). The results showed a striking difference when comparing the response obtained in trout and seabream. Cortisol and adrenocorticotropic hormone (ACTH) decreased the expression of immune-related genes in sea bream but not in rainbow trout and this cortisol effect was reverted by the antagonist mifepristone but not spironolactone. On the other hand, while adrenaline reduced the expression of pro-inflammatory cytokines (IL-1β, IL-6) in rainbow trout, the opposite effect was observed in sea bream showing an increased expression (IL-1β, IL-6). Interestingly, this effect was reverted by antagonist propranolol but not phentolamine. Overall, our results confirm the regional interaction between endocrine and cytokine messengers and a clear difference in the sensitivity to the hormonal stimuli between the two species.

Particle surface area and bacterial activity in recirculating aquaculture systems

Suspended particles in recirculating aquaculture systems (RAS) provide surface area that can be colonized by bacteria. More particles accumulate as the intensity of recirculation increases thus potentially increasing the bacterial carrying capacity of the systems. Applying a recent, rapid, culture-independent fluorometric detection method (Bactiquant®) for measuring bacterial activity, the current study explored the relationship between total particle surface area (TSA, derived from the size distribution of particles >5μm) and bacterial activity in freshwater RAS operated at increasing intensity of recirculation (feed loading from 0.043 to 3.13kgfeedm−3 make-up water). Four independent sets of water samples from different systems were analyzed and compared including samples from: (i) two individual constructed wetlands treating the effluent system water from two commercial, freshwater rainbow trout (Oncorhynchus mykiss) farms of different recirculation intensity; (ii) an 8.5m3 pilot scale RAS; and (iii) twelve identical, 1.7m3 pilot scale RAS assigned one of four micro-screen treatments (no micro-screen, 100, 60, or 20μm mesh size micro-screens) in triplicate. There was a strong, positive, linear correlation (p<0.05) between TSA and bacterial activity in all systems with low to moderate recirculation intensity (i.e. feed loading ≤1kgfeedm−3 make-up water). However, the relationship apparently ceased to exist in the systems with highest recirculation intensity (feed loading 3.13kg feedm−3 make-up water; corresponding to 0.32m3 make-upwaterkg−1 feed). This was likely due to the accumulation of dissolved nutrients sustaining free-living bacterial populations, and/or accumulation of suspended colloids and fine particles less than 5μm in diameter, which were not characterized in the study but may provide significant surface area. Hence, the study substantiates that particles in RAS provide surface area supporting bacterial activity, and that particles play a key role in controlling the bacterial carrying capacity at least in less intensive RAS. Applying fast, culture-independent techniques for determining bacterial activity might provide a means for future monitoring and assessment of microbial water quality in aquaculture farming systems.

Characterization of the effects of binary metal mixtures on short-term uptake of Ag, Cu, and Ni by rainbow trout (Oncorhynchus mykiss)

Single metal Biotic Ligand Models (BLMs) have been developed for a number of metals and model organisms. While these BLMs improve our ability to regulate metals in the aquatic environment, in reality, organisms are often simultaneously exposed to metal mixtures. Recently, several attempts have been made to develop mixture BLMs (mBLMs). Some of these models assume competitive interactions between all metals, while others assume only metals with a similar mode of action (e.g., Na+ or Ca2+ antagonists) will competitively interact. To begin testing these assumptions in the mBLM framework, standard 3-h gill metal binding assays with Ag, Cu, and Ni (primary metals), were performed in vivo on freshwater rainbow trout. Fish were exposed across a range of concentrations encompassing the 96-h LC50 for that metal to characterize uptake kinetics for each of these three primary metals (radiolabelled) in the presence and absence of a secondary metal (Ag, Cd, Cu, Ni, Pb, or Zn; not radiolabelled). We observed a complex series of interactions in binary mixtures that frequently contradicted theoretical expectations. Metals with similar modes of action did competitively interact in some instances, but not others, and when they did compete the competition was not necessarily reciprocal (e.g., Cu inhibited Ag uptake but Ag did not inhibit Cu uptake). We also observed examples of interactions between metals with dissimilar modes of action and several examples of metals stimulating the uptake of other metals. The underlying mechanisms for these unexpected interactions are unclear, but suggest that many of the current assumptions in mBLMs regarding the number and types of metal uptake sites and corresponding metal interactions are not correct. Careful characterization of metal mixture interactions is clearly needed before a reliable mBLM can be developed.

Tight Junction Proteins In Adult Rainbow Trout Skin: Regional Distribution, Response To Environmental Salinity, And Potential Regulatory Mechanisms

Freshwater (FW) fishes reside exist in aquatic habitats that are more dilute than their inner fluids. This leads to passive ion loss across tissues that directly interface with the surrounding medium, such as the gill and skin. The barrier properties of adult teleost fish skin in FW are well documented and in most cases, the trunk skin of adult fishes is void of any significant capacity for active ion movement. Therefore, despite its complex structure and extensive contact with the external environment, the skin of adult fishes is classically regarded as a relatively static, passive barrier to diffusional ion loss in FW. Nevertheless, recent observations have revealed the presence of a considerable number of genes encoding tight junction (TJ) proteins in the adult skin of several fish species. In addition, some studies have also shown that select TJ proteins in the skin of fish significantly alter in abundance upon exposure to environments that vary in ionic composition. This suggests that the molecular architecture of the skin TJ complex may play an important role in regulating skin permeability during environmental change. Despite this, almost nothing is known about how the molecular physiology of the TJ complex in this boundary tissue is regulated. Additionally, structural and functional differences are known to exist along the dorsoventral axis of the adult fish skin. However, none of the studies conducted to date, have taken this documented regional heterogeneity into account. This study examined TJ protein response to environmental change (acclimation to ion‐poor water, IPW) in freshwater (FW) rainbow trout (Oncorhynchus mykiss) skin. Changes in TJ protein abundance along the dorsoventral axis of the trout skin taken into consideration, as were possible roles for prolactin and cortisol, hormones involved in salinity‐dependent regulation of TJ/passive permeability. Differences in abundance of cldn‐3a, −5b, −6, −10c, −30, −32a and zo‐1 were detected along the dorsoventral axis of rainbow trout skin and many of these were found to be enriched in the lateral and dorsolateral regions. In addition, cldn mRNA abundance altered in response to IPW acclimation in a region‐specific manner. Osmoregulatory hormones, cortisol and prolactin, and their receptors were implicated in the regulation of Cldn transcript abundance in rainbow trout skin. These data provide a unique look at the region‐specific endocrine regulation of TJ complex components in adult fish skin.Support or Funding InformationThis work was funded by National Science and Engineering Research Council of Canada

Distribution of Infectious Pancreatic Necrosis Virus (IPNV) Based on Surveillance Programs in Freshwater Trout Farms of Mexico.

Diagnostic testing was performed between 2000 and 2012 to determine the distribution of infectious pancreatic necrosis virus (IPNV) in the main states of the Mexican Republic with freshwater Rainbow Trout Oncorhynchus mykiss (Walbaum) farms. This virus was positively identified from Rainbow Trout farms in seven of the eight states assessed. Due to nonnormal data distribution, a logistic regression model was applied for statistical analysis, the results of which indicated that virus prevalence was variable between states, with moderate but significant differences. Regarding the time periods evaluated, IPNV prevalence was higher during the first years of the study. The susceptible, infected, removed model was used to examine this phenomenon, which indicated that the decreased prevalence during the latter years of the study could be associated with a real elimination of the infection. The information of the cases analyzed also suggests a relationship with the irregularity in the submission of samples to the laboratory and emphasizes other factors that have contributed to the transmission of IPNV throughout the country. Received November 10, 2014; accepted December 5, 2015.

Procedures for the reconstruction, primary culture and experimental use of rainbow trout gill epithelia.

This protocol describes how to reconstruct and culture the freshwater rainbow trout gill epithelium on flat permeable membrane supports within cell culture inserts. The protocol describes gill cell isolation, cultured gill epithelium formation, maintenance, monitoring and preparation for use in experimental procedures. To produce a heterogeneous gill epithelium, as seen in vivo, seeding of isolated gill cells twice over a 2-d period is required. As a consequence, this is termed the double-seeded insert technique. Approximately 5-12 d after cell isolation and seeding, preparations develop electrically tight gill epithelia that can withstand freshwater on the apical cell surface. The system can be used to study freshwater gill physiology, and it is a humane alternative for toxicity testing, bioaccumulation studies and environmental water quality monitoring.

Comparison of collagen characteristics of sea- and freshwater-rainbow trout skin.

Proximate composition, volatile basic nitrogen content, and concentrations of collagen in skin samples from either sea- (S-RT) or freshwater-rainbow trout (F-RT) were characterized and compared, to assess the effect of the sea or freshwater habitat on these parameters. Results of amino acid composition, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, thermal denaturation assay and Fourier transform infrared (FT-IR) spectroscopy of acid-soluble collagens were comparable between the two sample sets. Both acid-soluble collagens from sea- and freshwater-rainbow trout skins contained glycine as the major amino acid and high alanine, proline, and hydroxyproline contents, and was found to be predominantly composed of α1-, α2-, and β-chains. FT-IR spectra of ASCs from S-RT and F-RT skins were quite similar. These findings suggest that different rainbow trout habitats (seawater and freshwater) do not affect amino acid composition and molecular weight properties of ASCs from S-RT and F-RT skins.

Restricted process water limits starch gelatinization, and reduces digestibility of starch, lipid, and energy in extruded rainbow trout (Oncorhynchus mykiss) diets

Abstract Five diets were produced with crude protein (CP) from hydrolysed wheat gluten (HWG) replacing graded (0, 12.5, 25, 50, 75%) amounts of CP from LT fish meal. Diets with 0–25% of CP from HWG were extruded with 19–20% water added in the extruder. Water addition was limited to 11% of the extrudate for the 50% HWG diet, and no water was added to the diet with 75% CP from HWG in order to obtain even flow of material in the extruder. Based on the degree of starch gelatinization (DG), estimated by differential scanning calorimetry (DSC), the diets with 19–20% process water were characterized by high gelatinization (HG), medium DG was obtained by limiting water addition to 11% (MG), and low gelatinization (LG) was the result of extruding without water added. Each diet was fed to two groups of rainbow trout in freshwater, and feces were obtained by abdominal stripping. Yttrium oxide (Y 2 O 3 ) was used as inert marker. The average apparent digestibility of starch ranged from 97 to 99% in the HG group, to 76% in the MG group, and 52% in the LG group. The AD of starch increased linearly (R 2 = 0.99) with increasing water addition in the extruder. The AD of lipid was reduced in MG and LG groups, and there was a linear (R 2 = 0.87) relationship between AD of starch and AD of lipid. As a consequence of AD of starch being quantitatively more influenced by water supplementation in the extruder than the AD of lipid, the regression of water supplementation on AD of energy was best explained (R 2 = 0.99) by a 2nd degree polynomial function, in which both the 1st and 2nd degree components were > 0. The findings emphasize the necessity of using sufficient process water during extrusion of salmonid diets both to ensure efficient digestion of starch and lipid. Statement of relevance This paper will increase the awareness in the feed industries of the necessity to secure complete gelatinization in extruded diets, since it is of high importance for digestible energy in the feed.

Interactive effects of waterborne metals in binary mixtures on short-term gill–metal binding and ion uptake in rainbow trout (Oncorhynchus mykiss)

Metal binding to fish gills forms the basis of the biotic ligand model (BLM) approach, which has emerged as a useful tool for conducting site-specific water quality assessments for metals. The current BLMs are designed to assess the toxicity of individual metals, and cannot account for the interactive effects of metal mixtures to aquatic organisms including fish. The present study was designed mainly to examine the interactive effects of waterborne metals (Cd, Zn, Cu, Ag, and Ni) in specific binary combinations on short-term (3h) gill–metal binding and essential ion (Ca2+ and Na+) uptake (a physiological index of toxicity) in fish, using juvenile freshwater rainbow trout (Oncorhynchus mykiss) as the model species. We hypothesized that binary mixtures of metals that share a common mode of uptake and toxicity (e.g., Cd and Zn – Ca2+ antagonists, Cu and Ag – Na+ antagonists) would reduce the gill binding of each other via competitive interactions and induce less than additive effects on ion transport. In addition, the mixture of metals that have different modes of uptake and toxicity (e.g., Cd and Cu, or Cd and Ni) would not exhibit any interactive effects either on gill–metal binding or ion transport. We found that both Zn and Cu reduced gill–Cd binding and vice versa, however, Ni did not influence gill–Cd binding in fish. Surprisingly, Ag was found to stimulate gill–Cu binding especially at high exposure concentrations, whereas, Cu had no effect on gill–Ag binding. The inhibitory effect of Cd and Zn in mixture on branchial Ca2+ uptake was significantly greater than that of Cd or Zn alone. Similarly, the inhibitory effect of Cu and Ag in mixture on branchial Na+ uptake was significantly greater than that of Cu or Ag alone. The inhibitory effects of Cd and Zn mixture on Ca2+ uptake as well as Cu and Ag mixture on Na+ uptake were found to follow the principles of simple additivity. In contrast, no significant additive effect on either Ca2+ or Na+ uptake was recorded in fish exposed to the mixture of Cd and Cu. Overall, we found that although the effects of metal mixture interactions on gill–metal binding did not always match with our original assumptions, the effects of metal mixtures on toxicity in fish were generally consistent with our predictions. The findings of the present study have important implications for improving the BLM approach to assess metal mixture toxicity in fish.

Ionoregulatory Aspects of the Osmorespiratory Compromise during Acute Environmental Hypoxia in 12 Tropical and Temperate Teleosts.

In the traditional osmorespiratory compromise, as seen in the hypoxia-intolerant freshwater rainbow trout (Oncorhynchus mykiss), the branchial modifications that occur to improve O2 uptake during hypoxia result in unfavorable increases in the fluxes of ions and water. However, at least one hypoxia-tolerant freshwater species, the Amazonian oscar (Astronotus ocellatus), shows exactly the opposite: decreased branchial flux rates of ions, water, and nitrogenous wastes during acute hypoxia. In order to find out whether the two strategies were widespread, we used a standard 2-h normoxia, 2-h hypoxia (20%-30% saturation), 2-h normoxic recovery protocol to survey 10 other phylogenetically diverse tropical and temperate species. Unidirectional influx and efflux rates of Na(+) and net flux rates of K(+), ammonia, and urea-N were measured. The flux reduction strategy was seen only in one additional species, the Amazonian tambaqui (Colossoma macropomum), which is similarly hypoxia tolerant and lives in the same ion-poor waters as the oscar. However, five other species exhibited evidence of the increased flux rates typical of the traditional osmorespiratory compromise in the trout: the rosaceu tetra (Hyphessobrycon bentosi rosaceus), the moenkhausia tetra (Moenkhausia diktyota), the bluegill sunfish (Lepomis macrochirus), the zebra fish (Danio rerio), and the goldfish (Carassius auratus). Four other species exhibited no marked flux changes during hypoxia: the cardinal tetra (Paracheirodon axelrodi), the hemigrammus tetra (Hemigrammus rhodostomus), the pumpkinseed sunfish (Lepomis gibbosus), and the Atlantic killifish (Fundulus heteroclitus). Overall, a diversity of strategies exist; we speculate that these may be linked to differences in habitat and/or lifestyle.

해수산 무지개송어(Oncorhynchus mykiss) 가공부산물(프레임육)의 식품학적 품질 특성 조사

This study compared the meat quality of sea rainbow trout Oncorhynchus mykiss frame muscle (S-FR-TY) and fillet (S-FI-TY) with the frame muscle of freshwater rainbow trout (F-FR). There was a difference of < 1% in the proximate composition of S-FR-TY vs. S-FI-TY, and of S-FR-TY vs. F-FR. The Hunter a value of F-FR-TY was lower compared with that of F-FR cultured in Jecheon (F-FR-JC), but higher than that of F-FR cultured in Pyeongtaek (FFR-PT). However, no difference in the Hunter a value of S-FR-TY compared with any other F-FR was observed. The odor intensity of S-FR-TY was lower compared with that of F-FR, while the taste of S-FR-TY was milder than that of S-FI-TY, but stronger than that of F-FR. Although its total amino acid content was lower, the essential amino acid content of S-FR-TY was higher compared with S-FI-TY; the potassium content of S-FR-TY was also significantly greater. S-FR-TY contained high levels of nutritional and functional components, such as anserine, lysine, threonine, and eicosapentaenoic and docosahexaenoic acid. These results suggest that S-FR-TY could be used as a resource of canned food or fish jerky for children.

The role of acid-sensing ion channels in epithelial Na+ uptake in adult zebrafish (Danio rerio).

Acid-sensing ion channels (ASICs) are epithelial Na(+) channels gated by external H(+). Recently, it has been demonstrated that ASICs play a role in Na(+) uptake in freshwater rainbow trout. Here, we investigate the potential involvement of ASICs in Na(+) transport in another freshwater fish species, the zebrafish (Danio rerio). Using molecular and histological techniques we found that asic genes and the ASIC4.2 protein are expressed in the gill of adult zebrafish. Immunohistochemistry revealed that mitochondrion-rich cells positive for ASIC4.2 do not co-localize with Na(+)/K(+)-ATPase-rich cells, but co-localize with cells expressing vacuolar-type H(+)-ATPase. Furthermore, pharmacological inhibitors of ASIC and Na(+)/H(+)-exchanger significantly reduced uptake of Na(+) in adult zebrafish exposed to low-Na(+) media, but did not cause the same response in individuals exposed to ultra-low-Na(+) water. Our results suggest that in adult zebrafish ASICs play a role in branchial Na(+) uptake in media with low Na(+) concentrations and that mechanisms used for Na(+) uptake by zebrafish may depend on the Na(+) concentration in the acclimation medium.