Freshwater Rainbow Trout Research Articles

Using physicochemical properties to predict the impact of natural dissolved organic carbon on transepithelial potential in the freshwater rainbow trout (Oncorhynchus mykiss) at neutral and acidic pH.

Dissolved organic carbon (DOC) is a complex mixture of molecules that varies in composition based on origin as well as spatial and temporal factors. DOC is an important water quality parameter as it regulates many biological processes in freshwater systems, including the physiological function of the gills in fish. These effects are often beneficial, especially at low pH where DOCs mitigate ion loss and protect active ion uptake. DOCs of different compositions and quality have varied ionoregulatory effects. The molecular variability of DOCs can be characterized using optical and chemical indices, but how these indices relate to the physiological effects exerted by DOCs is not well understood. We tested the effects of five naturally sourced DOCs, at both pH 7 and pH 4, on transepithelial potential (TEP) (a diffusion potential between the blood plasma and the external water) in rainbow trout. The five chosen DOCs have been well characterized and span large differences in physicochemical characteristics. Each of the DOCs significantly influenced TEP, although in a unique manner or magnitude which was likely due to their physicochemical characteristics. These TEP responses were also a function of pH. With the goal of determining which physicochemical indices are predictive of changes in TEP, we evaluated correlations between various indices and TEP at pH 7 and pH 4. The indices included: specific absorbance coefficient at 340nm, molecular weight index, fluorescence index, octanol-water partition coefficient, molecular charge, proton binding index, % humic acid-like, % fulvic acid-like, and % protein-like components by parallel factor analysis on fluorescence data (PARAFAC). Our results demonstrate the novel finding that there are three particularly important indices that are predictors of changes in TEP across pHs in rainbow trout: specific absorbance coefficient at 340nm, octanol-water partition coefficient; and proton binding index.

A meta‐analysis revealing the technical, environmental, and host‐associated factors that shape the gut microbiota of Atlantic salmon and rainbow trout

AbstractSalmonids, specifically Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss), are commonly farmed and their gut microbiota plays important roles for optimal growth, health, and physiology. However, differences in experimental design, technical factors and bioinformatics make it challenging to compare the results from different studies and draw general conclusions about their influence on the fish gut microbiota. For a more comprehensive understanding of the gut microbiota, we collected all the publicly accessible 16S rRNA gene sequencing data with clearly stated sample metadata from freshwater Atlantic salmon and rainbow trout intestinal contents and mucosa sequenced on the Illumina MiSeq platform. A total of 783 samples from 19 published studies were included in this meta‐analysis to test the impact of the technical, environmental, and host‐accociated factors. This meta‐analysis revealed that all the tested factors significantly influenced the alpha and beta diversities of the gut microbiota of salmon and trout. Technical factors, especially target region and DNA extraction kit, affected the beta diversity to a larger extent, while host‐associated and environmental factors, especially diet and initial fish weight, had a higher impact on the alpha diversity. Salmon had a higher alpha diversity and higher abundance of Enterococcus and Staphylococcus than trout, which had higher abundance of Weissella and Mycoplasma. The results of this meta‐analysis fill in a critical knowledge gap that demonstrate technical methodologies must be standardized and factors associated with host and environment need to be accounted for in the future design of salmonid gut microbiota experiments.

Effect of dietary macronutrient composition and buffering capacity on chyme characteristics and digestion kinetics in the gastrointestinal tract of freshwater rainbow trout (Oncorhynchus mykiss)

The aim of this study was to investigate the impact of dietary macronutrient composition and buffering capacity (BC) on chyme characteristics and digestion kinetics in freshwater rainbow trout (Oncorhynchus mykiss). Dietary macronutrient composition was altered by changing the protein-to-energy ratio (P:E) while keeping the fat-to-starch ratio constant. Dietary BC was increased by supplementation of CaCO3. The experiment lasted for 6 weeks. Fish were fed four diets having high and low P:E ratio and high and low CaCO3 level. This experiment was planned according to a 2x2x2 factorial design. The three factors were dietary P:E ratio, BC and time sampling after feeding (3 and 7 h). Chyme was collected from four gastrointestinal tract (GIT) segments (stomach, proximal, middle and distal intestine) and analysed for dry matter (DM), pH, osmolality, crude protein (CP) and mineral content. Relative water fluxes (RWF), electrolyte fluxes, kinetic of digestion and faecal digestibility (ADCs) were measured using yttrium oxide (Y2O3) as an inert marker. All chyme characteristics (including water fluxes) were not influenced by the interaction effect between dietary factors and sampling time (p > 0.05). Both dietary treatments did not affect chyme DM in the stomach. Low P:E diet increased (p < 0.001) chyme DM in all the intestinal segments. Dietary CaCO3 only affected (p < 0.05) chyme DM in the distal intestine. Low P:E diet decreased (p < 0.001) chyme pH in all GIT segments compared to the high P:E diet. Low CaCO3 diet decreased chyme pH in the proximal and middle intestine (p < 0.05) compared to the high CaCO3 diet. RWF were affected only by the dietary P:E ratio in the stomach and in the proximal intestine. Fish fed the high P:E diet had a lower water influx in the stomach and a higher water influx in the proximal intestine than fish fed the low P:E diet. Dietary P:E ratio affected electrolyte fluxes in the GIT, while no effect of CaCO3 was detected. Both dietary factors had a minimal or no effect on the kinetic of digestion in the different GIT segments, while a significant effect was present in all ADCs. Our findings suggest that dietary macronutrient composition, rather than buffering capacity, is the primary factor responsible for changes in chyme characteristics, water and ion fluxes in the GIT of freshwater rainbow trout. Furthermore, changes in dietary macronutrient composition and buffering capacity significantly affect faecal digestibility but are not reflected in digestion kinetics.

Do extreme postprandial levels of oxygen, carbon dioxide, and ammonia in the digestive tract equilibrate with the bloodstream in the freshwater rainbow trout (Oncorhynchus mykiss)?

The gastrointestinal tract (GIT) lumen of teleosts harbors extreme conditions, especially after feeding: high PCO2 (20-115Torr), total ammonia (415-3710μM), PNH3 (79-1760μTorr in the intestine), and virtual anoxia (PO2 < 1Torr). These levels could be dangerous if they were to equilibrate with the bloodstream. Thus, we investigated the potential equilibration of O2, CO2, and ammonia across the GIT epithelia in freshwater rainbow trout by monitoring postprandial arterial and venous blood gases in vivo and in situ. In vivo blood was sampled from the indwelling catheters in the dorsal aorta (DA) and subintestinal vein (SIV) draining the posterior intestine in the fasting state and at 4 to 48h following catheter-feeding. To investigate possible ammonia absorption in the anterior part of the GIT, blood was sampled from the DA, SIV and hepatic portal vein (HPV) from anaesthetized fish in situ following voluntary feeding. We found minimal equilibration of all three gases between the GIT lumen and the SIV blood, with the latter maintaining pre-feeding levels (PO2 = 25-49Torr, PCO2 = 6-8Torr, and total ammonia = 117-134μM and PNH3 = 13-30μTorr at 48h post-feeding). In contrast to the SIV, we found that the HPV total ammonia more than doubled 24h after feeding (128 to 297μM), indicative of absorption in the anterior GIT. Overall, the GIT epithelia of trout, although specialized for absorption, prevent dangerous levels of PO2, PCO2 and ammonia from equilibrating with the blood circulation.

In vitro toxicity assessment of polyethylene terephthalate and polyvinyl chloride microplastics using three cell lines from rainbow trout (Oncorhynchus mykiss)

The RTgill-W1 (gill), RTG-2 (gonad), and RTL-W1 (liver) cell lines derived from a freshwater fish rainbow trout (Oncorhynchus mykiss), were used to assess the toxicity of polyethylene terephthalate (PET) and two forms of polyvinyl chloride (PVC). Two size fractions (25-μm and 90-μm particles) were tested for all materials. The highest tested concentration was 1 mg/ml, corresponding to from 70 000 ± 9000 to 620 000 ± 57 000 particles/ml for 25-μm particles and from 2300 ± 100 to 11 000 ± 1000 particles/ml for 90-μm particles (depending on the material). Toxicity differences between commercial PVC dry blend powder and secondary microplastics created from a processed PVC were newly described. After a 24-h exposure, the cells were analyzed for changes in viability, 7-ethoxyresorufin-O-deethylase (EROD) activity, and reactive oxygen species (ROS) generation. In addition to the microplastic suspensions, leachates and particles remaining after leaching resuspended in fresh exposure medium were tested. The particles were subjected to leaching for 1, 8, and 15 days. The PVC dry blend (25 μm and 90 μm) and processed PVC (25 μm) increased ROS generation, to which leached chemicals appeared to be the major contributor. PVC dry blend caused substantially higher ROS induction than processed PVC, showing that the former is not suitable for toxicity testing, as it can produce different results from those of secondary PVC. The 90-μm PVC dry blend increased ROS generation only after prolonged leaching. PET did not induce any changes in ROS generation, and none of the tested polymers had any effect on viability or EROD activity. The importance of choosing realistic extraction procedures for microplastic toxicity experiments was emphasized. Conducting long-term experiments is crucial to detect possible environmentally relevant effects. In conclusion, the tested materials showed no acute toxicity to the cell lines.

Effect of dietary electrolyte balance on the interplay between water fluxes and digestive functioning along the gastrointestinal tract of freshwater rainbow trout (Oncorhynchus mykiss)

Aquaculture feed formulation is shifting from fish meal and fish oil toward other ingredients, such as plant-based ingredients, which lead to different levels and forms of minerals in diets. Dietary minerals are essential not only for growth, but also for acid-base balance and the homeostasis of fish body fluids. The gastrointestinal tract (GIT) is involved in the process of osmoregulation of salt and water during digestion, but this process can be hampered when the dietary electrolyte balance (dEB = Na - K + Cl, mEq/kg) is altered. To better understand the interaction between feeding and osmoregulation along the GIT, two diets with low (−100 mEq/kg) and high (+600 mEq/kg) dEB were designed. Freshwater rainbow trout (average initial weight, 306 g) were fed for 6 weeks. Faeces were collected during the last week for digestibility analyses. The final sampling took place over three days, with fish being sampled at 2 time points after feeding (3 and 7 h) and dissected to collect chyme from 4 GIT segments: stomach, proximal, middle and distal intestine. Chyme was analysed for dry matter, pH, osmolality, crude protein (CP) and mineral content. Yttrium oxide (Y2O3) was used as an inert marker to measure water fluxes, mineral fluxes, and nutrient digestibility from different gut segments. Both dEB and time after feeding altered (p < 0.05) chyme characteristics and water fluxes in the stomach and proximal intestine, but there was no interaction effect (p > 0.05). dEB also affected (p < 0.01) chyme pH and sodium (Na) fluxes in the stomach. Faecal digestibility of dry matter (DM) and CP was higher (p < 0.001) when fish were fed a high dEB diet compared to a low dEB diet. The opposite was observed for Ca availability, which was lower at the high dEB diet than at the low dEB diet (p < 0.001). In contrast to faecal digestibility, CP and mineral digestibility measured in the different gut segments were different predominantly in the middle and distal intestine. Our findings suggest that the GIT plays a role in regulating the alterations caused by the contrasting dEB, and that this regulation is stronger in the middle and distal intestine. Furthermore, this regulation affects nutrient and mineral digestibility in the middle and distal segments of the GIT.

Usage pattern of chemicals, biologicals and veterinary medicinal products in Indian aquaculture

AbstractThe use of chemicals, biologicals and veterinary medicinal products (VMPs) helps in healthy and sustainable fish production. Information on the use of these products is essential for assessing farming practices, potential human health and environmental risks. A questionnaire‐based nationwide survey covering aquaculture farms (n = 2936) producing carps, tilapia, pangasius and rainbow trout in freshwater and shrimp in brackishwater estimated the use of 52 different types of inputs which included disinfectants (597 g t−1), probiotics (2.28 kg t−1), environmental modifiers (22.82 kg t−1), nutritional supplements (1.96 kg t−1), natural anti‐infective agents (293 g t−1), herbicide and piscicides (844 g t−1), antibiotics (2 mg PCU−1), antifungal (4 mg PCU−1), and antiparasitic (14 mg PCU−1) agents. The bulk of these inputs was used for soil and water quality improvement and had low environmental and human safety concerns. The multivariate analysis revealed significant variation in the frequency and quantity of compounds use among farm groups. Redundancy analysis revealed a significant association between the number of products used and stocking density. The survey also showed a considerable influence of education and farming experience on the usage pattern of aquaculture inputs. Results of the study indicated greater reliance of farmers on the use of disinfectants for biosecurity, nutritional supplements for enhanced growth and environmental modifiers for maintaining soil and water quality in culture systems. Though there was no use of restricted antibiotics and antiparasitic agents, the development and implementation of standard regulatory guidelines are essential for safe and effective use of inputs for sustainable aquaculture.

Environmental adaptation in fish induced changes in the regulatory region of fatty acid elongase gene, elovl5, involved in long-chain polyunsaturated fatty acid biosynthesis

Fish are the main source of long-chain polyunsaturated fatty acids (LC-PUFA) for human consumption. In the process of evolution via natural selection, adaptation to distinct environments has likely driven changes in the endogenous capacity for LC-PUFA biosynthesis between marine and freshwater fishes. However, the molecular mechanisms underlying adaptive changes in this metabolic pathway are poorly understood. Here, we compared the transcriptional regulation of elongation of very long chain fatty acids protein 5 (Elovl5), which is one of the critical enzymes in LC-PUFA biosynthesis pathway, in marine large yellow croaker (Larimichthys crocea) and freshwater rainbow trout (Oncorhynchus mykiss). Comparative transcriptomic and absolute mRNA quantification analyses revealed that the expression of elovl5 in rainbow trout was markedly higher than that in large yellow croaker. Correspondingly, the number of chromatin accessible areas in the regulatory region of elovl5 in rainbow trout was higher than in large yellow croaker, which revealed that chromatin accessibility in the regulatory region of elovl5 in rainbow trout was higher. Furthermore, the differences in sequence and activity of the elovl5 promoter were observed between rainbow trout and large yellow croaker, and transcription factors including CCAAT/enhancer-binding protein β (CEBPβ), GATA binding protein 3 (GATA3) and upstream stimulatory factor 2 (USF2) displayed different regulatory roles on elovl5 expression between the two species. We propose that changes in the gene regulatory region driven by natural selection likely play a key role in differences in elovl5 expression and the activity of Elovl5, which may influence the LC-PUFA biosynthesis capacities of rainbow trout and large yellow croaker. These findings may also provide opportunities to improve the quality of aquatic products and, consequently, human health.

Absence of zoonotic parasites in salmonid aquaculture in Denmark: Causes and consequences

A parasitological investigation of Danish farmed freshwater (180 fish) and marine rainbow trout (170 fish), Oncorhynchus mykiss , was performed with an emphasis on the occurrence of zoonotic parasites. Reliability of the parasitological methods applied was assessed by examining fish from a stock of wild Atlantic cod Gadus morhua caught in the Sound (Øresund). While wild fish carried a number of zoonotic parasites, we found that farmed fish, both in the fresh and marine environment, were free of these parasites. Non-zoonotic trout parasites found were eye-flukes Diplostomum paracaudum, D. pseudospathaceum and Eubothrium crassum in maricultured rainbow trout. The acanthocephalan Echinorhynchus truttae and Diplostomum sp. were found in freshwater trout. In contrast, wild cod were infected with five different nematode species ( Anisakis simplex , Contracaecum osculatum , Pseudoterranova decipiens , Hysterothylacium aduncum , Cucullanus cirratus ), three trematode species ( Lepidapedon elongatum , Cryptocotyle lingua , Hemiurus communis ), one copepod species ( Lernaeocera branchialis ) and one myxozoan ( Myxobolus aeglefini ). The risk factors associated with aquaculture production in an infectious aquatic environment are analyzed and reasons for absence of zoonotic parasites in aquacultured trout are pinpointed. Based on the analysis recommendations for management practices securing parasite freedom in aquacultured fish are given. • Salmonid aquaculture in Denmark is free from zoonotic parasites. • Fish parasitological methods are validated by examination of wild fish. • Risk factors associated with aquaculture production are evaluated. • Recommendations for prevention of zoonotic parasite introduction are presented.

Determination of VP2 sequence-based virulence motifs and phylogenetic analysis of domestic Turkish IPNV ısolates.

Infectious pancreatic necrosis (IPN) is a highly contagious disease of young salmonid fish and is one of the most severe economic diseases in aquaculture. In Turkey, an increase in infectious pancreatic necrosis virus (IPNV) outbreaks in freshwater rainbow trout have been reported in recent years. This study aimed to analyze the VP2 gene from recent IPNV isolates from Turkey to determine whether there are epidemiological links between IPNV isolates from rainbow trout (Oncorhynchusmykiss; 62) and sea bass (Dicentrarchuslabrax; 1), wild turbot (Scophthalmusmaximus; 1) and the environment in order to investigate potential wild and farmed fish interactions. In this study, 62 Turkish IPNV isolates collected over 10years (2005-2014) from rainbow trout, sea bass and turbot were genotypically characterized. The phylogenetic analysis indicated that Turkish IPNV isolates are closely related to strains from Denmark, Iran and Spain and that all Turkish IPNV isolates belong to genogroup V, serotype A2 (Sp strain). Furthermore, low genetic diversity was found among the Turkish isolates (identity, 95.5%-100% nucleotides and 97.8%-100% amino acids). The result of the analysis of the amino acid residues found at positions 217, 221 and 247 (proline, threonine and alanine, respectively) could be associated with virulence.

Continuous gastric saline perfusion elicits cardiovascular responses in freshwater rainbow trout (Oncorhynchus mykiss)

When in seawater, rainbow trout (Oncorhynchus mykiss) drink to avoid dehydration and display stroke volume (SV) mediated elevations in cardiac output (CO) and an increased proportion of CO is diverted to the gastrointestinal tract as compared to when in freshwater. These cardiovascular alterations are associated with distinct reductions in systemic and gastrointestinal vascular resistance (RSys and RGI, respectively). Although increased gastrointestinal blood flow (GBF) is likely essential for osmoregulation in seawater, the sensory functions and mechanisms driving the vascular resistance changes and other associated cardiovascular changes in euryhaline fishes remain poorly understood. Here, we examined whether internal gastrointestinal mechanisms responsive to osmotic changes mediate the cardiovascular changes typically observed in seawater, by comparing the cardiovascular responses of freshwater-acclimated rainbow trout receiving continuous (for 4 days) gastric perfusion with half-strength seawater (½ SW, ~ 17 ppt) to control fish (i.e., no perfusion). We show that perfusion with ½ SW causes significantly larger increases in CO, SV and GBF, as well as reductions in RSys and RGI, compared with the control, whilst there were no significant differences in blood composition between treatments. Taken together, our data suggest that increased gastrointestinal luminal osmolality is sensed directly in the gut, and at least partly, mediates cardiovascular responses previously observed in SW acclimated rainbow trout. Even though a potential role of mechano-receptor stimulation from gastrointestinal volume loading in eliciting these cardiovascular responses cannot be excluded, our study indicates the presence of internal gastrointestinal milieu-sensing mechanisms that affect cardiovascular responses when environmental salinity changes.

Population pharmacokinetics/pharmacodynamics modelling of enrofloxacin for the three major trout pathogens Aeromonas salmonicida, Flavobacterium psychrophilum and Yersinia ruckeri

Enrofloxacin is a fluoroquinolone antimicrobial agent used in freshwater rainbow trout against the main pathogenic bacteria Aeromonas salmonicida, Yersinia ruckeri and Flavobacterium psychrophilum. However, the current “standard” dose (10 mg/kg/day for 10 days) was based only on some old, rather limited experimental data, and needed to be re-assessed. Thus, a pharmacokinetic-pharmacodynamic (PKPD) approach was used by combining a population PK model with new epidemiological data (Minimum Inhibitory Concentrations (MIC)) of the three bacterial species to determine optimal enrofloxacin doses in rainbow trout.Ninety-six rainbow trout (half diploid, half triploid) were randomly assigned to four different groups and received oral (gavage) and then intravenous administration of enrofloxacin at four different doses (range 5–60 mg/kg). Individual blood samples were taken to develop a population PK model.Enrofloxacin should be considered as a long-acting drug in trout due to the observed long plasma half-life (>100 h), which is therefore inadequate with the “standard” dosage based on daily oral administrations. Moreover, the fish ploidy had an impact on the PK of enrofloxacin with a longer persistence of enrofloxacin in triploid individuals, which raises the question of the withdrawal period to apply. The absolute bioavailability of oral enrofloxacin was estimated at ~88%.For F. psychrophilum, the provisional epidemiological cut-off value (CONRI), calculated according to the NRI method, was equal to 0.03 μg/mL. For A. salmonicida and Y. ruckeri, however, no clear bimodal distribution of MIC could be observed, and therefore no relevant CONRI could be obtained.According to our model, a single oral dose of ~5 mg/kg should provide sufficient exposure to treat the wild-type population of F. psychrophilum for 4 days, while complying with the PKPD breakpoints. Then, a maintenance dose of ~2.5 mg/kg could possibly be re-administered every 4 days. The absence of a CONRI did not allow to predict an optimal dose for the two other bacteria. As more than 70% of A. salmonicida isolates in our data set have an enrofloxacin MIC ≥0.25 μg/mL, it seems that enrofloxacin should not be recommended against this bacterium.The PKPD approach allowed us to refine the dosing regimens in rainbow trout, for a more sustainable approach. These new dosing regimens have yet to be clinically confirmed.

Effects of constant and diel cyclic temperatures on the liver and intestinal phospholipid fatty acid composition in rainbow trout Oncorhynchus mykiss during seawater acclimation

BackgroundRainbow trout is an economically important fish in aquaculture and is a model species in environmental physiology. Despite earlier research on the seawater adaptability of rainbow trout at different temperature regimes, the influence on the liver and intestine in this species is still unknown. Two trials were conducted to investigate the effects of constant and diel cyclic temperatures on phospholipid fatty acid (PLFA) composition in the liver and intestine of rainbow trout during seawater acclimation.ResultsAt the end of growth trial 1, fish at 9 and 12.5 °C showed significantly higher ratios of unsaturated to saturated (U/S) and unsaturation index (UI) than those at 16 °C in liver and intestine phospholipids. After day 1 of seawater acclimation, the U/S, UI, and average chain length (ACL) of liver and intestinal phospholipids in fish at 16 °C significantly increased. Two weeks after seawater acclimation, the liver and intestinal PLFA composition adapted to salinity changes. In trial 2, significantly higher U/S, UI, and ACL were found in intestinal phospholipids at 13 ± 2 °C. On the first day after seawater acclimation, UI and ACL in liver phospholipids significantly increased at 13 °C, while fish at 13 ± 2 °C showed significantly decreased U/S, UI, and ACL in the intestine. At the end of growth trial 2, liver PLFA compositions were stable, whereas intestinal PLFA at 13 and 13 ± 1 °C showed significantly decreased U/S, UI, and ACL. A two-way analysis of variance and principal component analysis revealed significant effects of different constant temperatures, seawater acclimation, and their interaction on the liver and intestinal phospholipids, a significant effect of diel cyclic temperature on intestinal phospholipids, and the effects of seawater acclimation and its interaction with diel cyclic temperature on liver phospholipids.ConclusionTemperatures of 9 and 12.5 °C could elevate membrane fluidity and thickness in the liver and intestine of rainbow trout in freshwater, whereas no significant effects were found with diel temperature variations. After seawater acclimation, constant and diel cyclic temperatures significantly influenced the membrane fluidity and thickness of the liver and intestine. Compared with constant temperature, diel temperature variation (13 ± 2 °C) can enhance the adaptability of rainbow trout during seawater acclimation.

Fatty acids profile, atherogenic and thrombogenic indices in freshwater fish common carp (Cyprinus carpio) and rainbow trout (Oncorhynchus mykiss) from market chain

The study examined the fatty acids composition and main nutrients composition in two freshwater fish species in the Czech Republic during one year. Samples of common carp and rainbow trout were taken from a market chain during a year. All samples were homogenized and analyzed for lipid, protein, water, and ash contents. Energy value (E), sum of polyunsaturated fatty acids (PUFA), monounsaturated fatty acids (MUFA) and saturated fatty acids (SFA), atherogenic index (AI) and thrombogenic index (TI) were then calculated. The freshwater fish on the Czech market chain have beneficial average value content of unsaturated fatty acids, Σ MUFA+PUFA in carp is 69.46% of all fatty acids, similar average value of Σ MUFA+PUFA - 70.83% is in rainbow trout. The calculated average value of AI in carp is 0.52 (SD = 0.06), AI in rainbow trout is 0.63 (SD = 0.07), the average TI in carp is 0.63 (SD = 0.09), TI in rainbow trout is 0.49 (SD = 0.05). Freshwater fish in the Czech market chain have beneficial value of PUFA, so AI and TI indices are low in both species of analysed fish. Regular consumption of fish meat is important in the prevention of cardiovascular diseases.

Content of minerals in muscle tissue of diploid rainbow trout (Oncorhynchus mykiss) in freshwater (Derbent Dam) and seawater (The Black Sea)

Content of minerals in muscle tissue of diploid rainbow trout (Oncorhynchus mykiss) in freshwater (Derbent Dam) and seawater (The Black Sea)

The ontogeny of Na+ balance during rapid smoltification in pink salmon (Oncorhynchus gorbuscha).

Pink salmon hatch in fresh water, but their highly anadromous life history requires them to migrate into the ocean immediately after gravel-emergence, at a very small size. During their down-river migration these larvae undergo rapid smoltification that completely remodels their osmoregulatory physiology. At this time, the larvae reportedly have high whole-body Na+ contents and we hypothesised that the active accumulation of internal Na+ occurs in preparation for ocean entry. Using a comparative approach, the present study characterised the ontogeny of Na+ regulation in larvae of the anadromous pink salmon and the fresh-water rainbow trout. Our results indicate that larvae from both species actively accumulated Na+; however, whole-body Na+ content was higher in rainbow trout larvae compared to pink salmon. The time-course of this response was similar in the two species, with highest Na+-uptake rates ([Formula: see text]) shortly after yolk sac absorption, but the mechanism of Na+ accumulation differed between the species. Rainbow trout larvae greatly increased [Formula: see text] to overcompensate for a large simultaneous increase in Na+-efflux rate ([Formula: see text]), whereas pink salmon mounted a smaller increase in [Formula: see text] while maintaining tight control over [Formula: see text], which is supported by a significantly lower paracellular permeability. Our results indicate that the transient accumulation of internal Na+ is not a unique feature of the highly anadromous life history in pink salmon and may be a common ontogenetic pattern during larval development in salmonids; and perhaps it is associated with the development of the cardiovascular system during the larvae's transition to a more active lifestyle.

Gill amoebae from freshwater rainbow trout (Oncorhynchus mykiss): In vitro evaluation of antiparasitic compounds against Vannella sp.

Gill parasitic infections challenge farming of rainbow trout (Oncorhynchus mykiss, Walbaum) in freshwater facilities. Apart from flagellates (Ichthyobodo, (Pinto) and ciliates (Ichthyophthirius (Fouquet), Ambiphrya (Raabe), Apiosoma (Blanchard), Trichodinella (Sramek-Husek) and Trichodina (Ehrenberg)), we have shown that amoebae are prevalent in Danish trout farms. Gills were isolated from farmed rainbow trout in six fish farms (conventional and organic earth pond and recirculated systems) and placed on non-nutrient agar (NNA) moistened with modified Neff's amoeba saline (AS) (15°C). Gill amoebae from all examined fish colonized the agar and were identified based on morphological criteria showing species within the genera Trinema (Dujardin) (family Trinematidae), Vannella (Bovee) (family Vannellidae). In addition, hartmannellid amoebae were recorded. We established a monoculture of Vannella sp., confirmed the genus identity by PCR and sequencing and performed an in vitro determination of antiparasitic effects (dose-response studies) of various compounds including sodium chloride (NaCl), hydrogen peroxide, peracetic acid, formalin, aqueous garlic and oregano extracts and a Pseudomonas H6 surfactant. All amoebae were killed in concentrations of 16.90mg/ml (garlic), 17.90mg/ml (oregano), NaCl (7.5mg/ml), hydrogen peroxide (100µg/ml), peracetic acid (0.03µg/ml), formaldehyde (25µg/ml) and the Pseudomonas H6 surfactant (250µg/ml).

Effects of copper on a reconstructed freshwater rainbow trout gill epithelium: Paracellular and intracellular aspects

The barrier properties and intracellular responses of a primary cultured trout gill epithelium (containing both mitochondria-rich and pavement cells) were examined over 24 h of copper (Cu) exposure (0, 200 and 1000 μg/L) in apical fresh water. Transepithelial resistance (TER) and mRNA abundance of tight junction proteins zonula occludens-1, occludin, cingulin, claudin-8d and -28b were examined as endpoints of barrier function and the paracellular pathway. Intracellular endpoints analyzed were Cu accumulation, Na+ content, carbonic anhydrase activity and mRNA abundance of carbonic anhydrase (ca-II) and Na+/K+ ATPase (nka α1a and nka α1b isoforms). After a brief initial drop in TER in the 1000 μg Cu/L treatment, Cu at both levels increased TER over the first 6 h of exposure but there were no differences among groups from 12 h onwards. After 24 h of Cu exposure, there were no differences in mRNA abundance of any of the tight junction proteins examined. Cu accumulation occurred at 1000 μg Cu/L (5.5-fold increase), but no depletion of Na+ content. Carbonic anhydrase activity decreased significantly (by 76%), however Cu exposure did not alter the transcript abundance of ca-II, nka α1a, or nka α1b. This study provides a first report of carbonic anhydrase sensitivity to Cu exposure in a cultured model gill epithelium. We conclude that Cu impacts the permeability of this model during the early stages of exposure and that the use of carbonic anhydrase inhibition as an endpoint of metal toxicity in this model preparation may be useful for future mechanistic investigations and environmental monitoring.

Sensory Freshness Assessment of Ice Stored Rainbow Trout (Oncorhynchus mykiss)

Sensory quality characteristics of fish are very important factors on acceptance and market value of the product. Quality assessment of fish should be precise, fast, systematic and comprehensive regarding freshness attributes. The objectives of this study were to describe weather the QIM (Quality Index Method) scheme for salmonides can be used to determine the freshness and describe the sensory changes during storage. Quality assessment of the fresh water rainbow trout (n=36) was performed on day 1, 7, 14 and 21 of ice storage on temperatures from 0.6-0.8°C. Through the QIM scheme the specific freshness attribute deterioration can be very well described and the QIM score produced a clear result, which showed that the deterioration of fish is linear and has a strong correlation with the time of storage. The QIM scheme for farmed salmon can be used to evaluate the freshness of the rainbow trout. It can also be used to ascertain and predict the remaining shelf life of rainbow trout stored in ice. Under similar conditions, the maximal shelf life of ungutted rainbow trout is 14±2 days or 15 demerit points of framed salmon QIM scheme.

An in vitro analysis of intestinal ammonia transport in fasted and fed freshwater rainbow trout: roles of NKCC, K+ channels, and Na+, K+ ATPase.

We examined mechanisms of ammonia handling in the anterior, mid, and posterior intestine of unfed and fed freshwater rainbow trout (Oncorhynchus mykiss), with a focus on the Na+:K+:2Cl- co-transporter (NKCC), Na+:K +-ATPase (NKA), and K+ channels. NKCC was localized by immunohistochemistry to the mucosal (apical) surface of enterocytes, and NKCC mRNA was upregulated after feeding in the anterior and posterior segments. NH4+ was equally potent to K+ in supporting NKA activity in all intestinal sections. In vitro gut sac preparations were employed to examine mucosal ammonia flux rates (Jmamm, disappearance from the mucosal saline), serosal ammonia flux rates (Jsamm, appearance in the serosal saline), and total tissue ammonia production rates (Jtamm = Jsamm - Jmamm). Bumetanide (10-4 mol L-1), a blocker of NKCC, inhibited Jsamm in most preparations, but this was largely due to reduction of Jtamm; Jmamm was significantly inhibited only in the anterior intestine of fed animals. Ouabain (10-4 mol L-1), a blocker of NKA, generally reduced both Jmamm and Jsamm without effects on Jtamm in most preparations, though the anterior intestine was resistant after feeding. Barium (10-2 mol L-1), a blocker of K+ channels, inhibited Jmamm in most preparations, and Jsamm in some, without effects on Jtamm. These pharmacological results, together with responses to manipulations of serosal and mucosal Na+ and K+ concentrations, suggest that NKCC is not as important in ammonia absorption as previously believed. NH4+ appears to be taken up through barium-sensitive K+ channels on the mucosal surface. Mucosal NH4+ uptake via both NKCC and K+ channels is energized by basolateral NKA, which plays an additional role in scavenging NH4+ on the serosal surface to possibly minimize blood toxicity or enhance ion uptake and amino acid synthesis following feeding. Together with recent findings from other studies, we have provided an updated model to describe the current understanding of intestinal ammonia transport in teleost fish.