Adult Trout Research Articles

Uso de una PCR anidada para el diagnóstico del virus de la necrosis pancreática infecciosa (VNPI) en truchas de campo

El aislamiento en cultivo celular es el método principal para el diagnóstico del virus de la necrosis pancreática infecciosa (VNPI). Aunque es un método confiable, resulta costoso y conlleva tres semanas en proporcionar un resultado. Para disminuir el tiempo en el diagnóstico y aumentar la sensibilidad para la detección del VNPI, el objetivo del presente estudio fue establecer y evaluar el uso de una PCR anidada (PCRa) para un diagnóstico rápido del VNPI. Para ello, se diseñaron dos pares de iniciadores basados en secuencias mexicanas. El primer par (RT-PCR) amplificó un producto de 682 pb y el segundo par (PCRa) 229 pb del gen VP2. Posteriormente, se infectaron 70 crías de truchas arcoíris (Oncorhynchus mykiss) con la cepa virulenta MEX3-CSM-05 a una dosis de 1X105.8 DICC50%/0.02 ml. De cada organismo se colectó el riñón, el bazo, los sacos pilóricos, el hígado, el intestino y las branquias. Para evaluar las pruebas, se utilizaron 26 truchas adultas clínicamente sanas de granjas comerciales del Estado de México. La frecuencia de detección del VNPI mediante RT-PCR en las branquias fue de 87.1 %, en el hígado 61.4 %, en los sacos pilóricos 61.4 %, en el riñón 58.6%, en el intestino 35.7 % y en el bazo 32.9 % (P<0.05). Las muestras negativas a la RT-PCR resultaron positivas en la PCRa. Asimismo, se mostraron positivas las muestras de los órganos de las truchas de campo. En conclusión, la RT-PCR tuvo menor sensibilidad que la PCRa, la cual mostró una sensibilidad del 100%. Por lo tanto, la PCRa es mejor para un diagnóstico confiable del VNPI en peces infectados y enfermos.

Suture-less Implantation of Acoustic Transmitters in Two Salmonids

The surgical incision required to insert acoustic transmitters into fish peritoneal cavities is typically closed with sutures, staples, or cyanoacrylate adhesive. This study evaluated a novel tag insertion technique that did not use any method of wound closure. Twenty-six adult rainbow trout (Oncorhynchus mykiss) and 26 adult brown trout (Salmo trutta) received a small, 6 mm abdominal incision. A dummy acoustic transmitter tag was inserted into half (N = 13) of the fish in each species. Neither group received any wound closure; no sutures, staples, nor adhesives were used. Tag retention, wound healing, and fish survival were monitored weekly for 13 weeks post-surgery. No fish died over the course of the trial. Tag retention was 100% and 85% in the tagged rainbow trout and brown trout, respectively. The wounds in the untagged rainbow trout were all completely healed by six weeks post-surgery, while wounds of the tagged rainbow trout were completely healed at nine weeks post-surgery. Similarly, wounds in the untagged and tagged brown trout groups were completely healed by the fifth and eighth weeks respectively. This study documents the effectiveness of using a small incision with no wound closure methods during insertion of acoustic tags into rainbow trout and brown trout peritoneal cavities.

A serological survey on ınfectious pancreatic necrosis virus (IPNV), viral hemorrhagic septicemia virus (VHSV) and ınfectious hematopoietic necrosis virus (IHVN) from rainbow trout in Turkey

Infectious pancreatic necrosis (IPN), viral hemorrhagic septicemia (VHS) and infectious hematopoietic necrosis (IHN) are the most significant viral diseases of salmonid species. This study examined the seroprevalence of infectious pancreatic necrosis virus (IPNV), viral hemorrhagic septicemia virus (VHSV) and infectious hematopoietic necrosis virus (IHNV) in rainbow trout cultured in Turkey. A total of 597 serum samples of adult trout were obtained from 18 commercial trout farms in the Middle and Eastern Black Sea regions of Turkey and were then examined by the virus neutralization test. As a result of the test, VHSV and IHNV antibodies were not detected. However, IPNV antibodies were found in 11 of 18 trout farms (61.1%) and 45 of 597 serum samples (7.5%). Three viral agents characterized as causing persistent infections were serologically screened for the first time in Turkey. The high seropositivity rate against IPNV was namely caused by asympomatic carrier broodstock fish.

Evaluating management options for two fisheries that conflict through predator–prey interactions of target species

When one wild species is food for another and both have their hunting enthusiasts, then conflict can arise. This is particularly true and complicated in fishing, where trophic links are strongly influenced by body-size ratios, alternative prey are available, populations are strongly density dependent and all their parameters are hard to quantify. We examine this problem with a specific example of trout-pike interaction in Irish lakes using a multi-species size-structured population model, set within a quantitative management action assessment framework. We use an informal Bayesian uncertainty analysis to account for empirical imprecision and test a range of stakeholder suggested scenarios for management of the pike and trout fisheries, under three different hypotheses about the abundance of non-trout prey availability. Trout fishing always diminished adult trout biomass. Fishing for pike always increased trout biomass but less effectively as biomasses of alternative (to trout) prey increased. Adult pike cannibalism was found to significantly alleviate predation pressure on trout when alternative prey was not plentiful, less so when it was.

Daily estimates reveal fine-scale temporal and spatial variation in fish survival across a stream network

Environmental drivers of population vital rates, such as temperature and precipitation, often vary at short time scales, and these fluctuations can have important impacts on population dynamics. However, relationships between survival and environmental conditions are typically modeled at coarse temporal scales, ignoring the role of daily environmental variation in survival. Our goal was to determine the importance of fine-scale temporal variation in survival to population dynamics of stream salmonids. We extended the Cormack–Jolly–Seber model to estimate daily survival rates from seasonal samples of individually marked brook trout (Salvelinus fontinalis) in a stream network. Daily variation in temperature and flow were strongly associated with survival, but relationships varied between juvenile and adult trout and among streams. In all streams, juveniles had higher mortality in warm, low-flow conditions, but in the two larger streams, cold, high-flow conditions also reduced juvenile survival. Adult survival decreased during low flows, particularly in the fall spawning period. Differing survival responses among stream network components to short-term environmental events created shifts in optimal location for maximum survival across life stages, seasons, and years.

Quantifying thermal refugia connectivity by combining temperature modeling, distributed temperature sensing, and thermal infrared imaging

Abstract. Watershed-scale stream temperature models are often one-dimensional because they require fewer data and are more computationally efficient than two- or three-dimensional models. However, one-dimensional models assume completely mixed reaches and ignore small-scale spatial temperature variability, which may create temperature barriers or refugia for cold-water aquatic species. Fine spatial- and temporal-resolution stream temperature monitoring provides information to identify river features with increased thermal variability. We used distributed temperature sensing (DTS) to observe small-scale stream temperature variability, measured as a temperature range through space and time, within two 400 m reaches in summer 2015 in Nevada's East Walker and main stem Walker rivers. Thermal infrared (TIR) aerial imagery collected in summer 2012 quantified the spatial temperature variability throughout the Walker Basin. We coupled both types of high-resolution measured data with simulated stream temperatures to corroborate model results and estimate the spatial distribution of thermal refugia for Lahontan cutthroat trout and other cold-water species. Temperature model estimates were within the DTS-measured temperature ranges 21 % and 70 % of the time for the East Walker River and main stem Walker River, respectively, and within TIR-measured temperatures 17 %, 5 %, and 5 % of the time for the East Walker, West Walker, and main stem Walker rivers, respectively. DTS, TIR, and modeled stream temperatures in the main stem Walker River nearly always exceeded the 21 ∘C optimal temperature threshold for adult trout, usually exceeded the 24 ∘C stress threshold, and could exceed the 28 ∘C lethal threshold for Lahontan cutthroat trout. Measured stream temperature ranges bracketed ambient river temperatures by −10.1 to +2.3 ∘C in agricultural return flows, −1.2 to +4 ∘C at diversions, −5.1 to +2 ∘C in beaver dams, and −4.2 to 0 ∘C at seeps. To better understand the role of these river features on thermal refugia during warm time periods, the respective temperature ranges were added to simulated stream temperatures at each of the identified river features. Based on this analysis, the average distance between thermal refugia in this system was 2.8 km. While simulated stream temperatures are often too warm to support Lahontan cutthroat trout and other cold-water species, thermal refugia may exist to improve habitat connectivity and facilitate trout movement between spawning and summer habitats. Overall, high-resolution DTS and TIR measurements quantify temperature ranges of refugia and augment process-based modeling.

Cystathionine β-Synthase in the Brain of the Trout Oncorhynchus mykiss after Unilateral Eye Damage and in Conditions of in vitro Cultivation

Expression of cystathionine β-synthase (CBS) in the brain of adult trout under normal conditions and 1 week after an eye injury was assessed using Western blot analysis. The study of CBS distribution in the brain of intact trout and after a mechanical eye injury in the telencephalon, tectum, cerebellum, and brainstem was carried out by the method of immunoperoxidase labeling on free-floating sections. The results of the study showed an increase in CBS expression in different brain divisions after an eye injury. In the visual projection center of the brain (tectum), radial glia cells expressing CBS were revealed after the injury. The emergence of CBS+ heterogeneous radial glia in the trout tectum after eye injury indicates the ability of the reactive neural stem cells (NSC) to synthesize hydrogen sulfide. CBS+ fibers and cells were found in the proliferative zones of cerebellum (valvula) and telencephalon (ventral region). In the intact trout tegmentum, CBS expression was observed in large neurons of the dorsal region and in the proliferative zones. After the eye injury, reactive neurogenic niches appeared in the brainstem, and no CBS-immunopositivity was detected in the periventricular zone. The increased expression of H2S-producing CBS enzyme after a traumatic impact can probably be explained by the neuroprotective functions of hydrogen sulfide, which are implemented in the matrix zones of the brain associated with reparative neurogenesis. A cultivation of trout brain cells showed the formation of neurosphere-like complexes, a part of which exhibited CBS-immunopositivity in the monolayer.

Drought impacts to trout and salamanders in cool, forested headwater ecosystems in the western Cascade Mountains, OR

Climate change projections for the western United States suggest that many regions will experience increasing frequency and severity of droughts. In summer 2015, the Pacific Northwest experienced a drought with early onset of stream low flows, reduced summer discharge, and elevated temperatures. We evaluated population responses of two dominant stream predators—coastal cutthroat trout (Oncorhynchus clarkii clarkii) and coastal giant salamander (Dicamptodon tenebrosus)—across nine Cascade Mountain streams. Drought conditions impacted both trout and salamanders, but their responses differed. Adult trout abundance and biomass were significantly lower in 2015 relative to 2014, a year with discharge and temperature closer to historical norms. Juvenile trout abundance did not differ between years but juveniles were significantly larger in 2015. Salamander abundance and biomass were not significantly different between years but body condition was lower in all nine streams in 2015. Differences in temperature among streams did not explain trout or salamander responses. Habitat was important for trout responses with trout abundance and biomass experiencing smaller declines in systems with more deep pool area. Despite notable short-term drought impacts to trout and salamanders in 2015, populations recovered to pre-drought conditions within two years in all but the smallest stream.

Histological, transcriptomic and in vitro analysis reveal an intrinsic activated state of myogenic precursors in hyperplasic muscle of trout

BackgroundThe dramatic increase in myotomal muscle mass in post-hatching fish is related to their ability to lastingly produce new muscle fibres, a process termed hyperplasia. The molecular and cellular mechanisms underlying fish muscle hyperplasia largely remain unknown. In this study, we aimed to characterize intrinsic properties of myogenic cells originating from hyperplasic fish muscle. For this purpose, we compared in situ proliferation, in vitro cell behavior and transcriptomic profile of myogenic precursors originating from hyperplasic muscle of juvenile trout (JT) and from non-hyperplasic muscle of fasted juvenile trout (FJT) and adult trout (AT).ResultsFor the first time, we showed that myogenic precursors proliferate in hyperplasic muscle from JT as shown by in vivo BrdU labeling. This proliferative rate was very low in AT and FJT muscle. Transcriptiomic analysis revealed that myogenic cells from FJT and AT displayed close expression profiles with only 64 differentially expressed genes (BH corrected p-val < 0.001). In contrast, 2623 differentially expressed genes were found between myogenic cells from JT and from both FJT and AT. Functional categories related to translation, mitochondrial activity, cell cycle, and myogenic differentiation were inferred from genes up regulated in JT compared to AT and FJT myogenic cells. Conversely, Notch signaling pathway, that signs cell quiescence, was inferred from genes down regulated in JT compared to FJT and AT. In line with our transcriptomic data, in vitro JT myogenic precursors displayed higher proliferation and differentiation capacities than FJT and AT myogenic precursors.ConclusionsThe transcriptomic analysis and examination of cell behavior converge to support the view that myogenic cells extracted from hyperplastic muscle of juvenile trout are intrinsically more potent to form myofibres than myogenic cells extracted from non-hyperplasic muscle. The generation of gene expression profiles in myogenic cell extracted from muscle of juvenile trout may yield insights into the molecular and cellular mechanisms controlling hyperplasia and provides a useful list of potential molecular markers of hyperplasia.

The Pax2 and Pax6 Transcription Factors in the Optic Nerve and Brain of Trout Oncorhynchus mykiss after a Mechanical Eye Injury

The distribution of the Pax2+ transcription factor in the optic nerve after a mechanical eye injury on the side of damage and in the contralateral nerve has been studied in the trout Oncorhynchus mykiss. It has been found that injury of the optic nerve in this fish species causes Pax2+ reactive astrocytes involved in the initial stages of optic nerve axon regeneration to increase in number, especially in the area of the head and the proximal part of the optic nerve. As the optic nerve in trout is damaged, a significant growth of the heterogeneous population of Pax6+ cells occurs in the brain divisions that have direct retinal inputs, diencephalon, and optic tectum. A part of the Pax6+ cells have an undifferentiated phenotype and are a component of reactive neurogenic niches located in the periventricular zone and parenchymal regions of the brain. Another population of Pax6+ cells has the radial glial phenotype and appears as a result of activation of the constitutive neurogenic domains also within the newly formed reactive neurogenic niches. Thus, due to the optic nerve injury, a pronounced neurogenic response associated with the appearance of reactive neurogenic niches and radial glia arises both in the brain divisions with direct retinal projections and in those lacking the retinal projections as well as in remote regions. The results obtained indicate that the damage to the optic nerve causes an increased reactive neurogenesis in the brain of adult trout.

Multiple challenges confront a high-effort inland recreational fishery in decline

Catch-and-release regulations designed to protect fisheries may fail to halt population declines, particularly in situations where fishing effort is high and when multiple stressors threaten a population. We demonstrate this claim using Alberta’s Bow River, which supports a high-effort rainbow trout (Oncorhynchus mykiss) fishery where anglers voluntarily release &gt;99% of their catch. We examined the population trend of adult trout, which were tagged and recaptured using electrofishing surveys conducted intermittently during 2003–2013. We constructed Bayesian multisession capture–recapture models in Stan to obtain abundance estimates for trout and regressed trend during two periods to account for variation in sampling locations. General patterns from all models indicated the population declined throughout the study. Potential stressors to this system that may have contributed to the decline include whirling disease (Myxobolus cerebralis), which was detected for the first time in 2016, notable floods, and release mortality. Because disease and floods are largely uncontrollable from a management perspective, we suggest that stringent tactics such as angler effort restrictions may be necessary to maintain similar fisheries.

Warm water temperatures and shifts in seasonality increase trout recruitment but only moderately decrease adult size in western North American tailwaters

Dams throughout western North America have altered thermal regimes in rivers, creating cold, clear “tailwaters” in which trout populations thrive. Ongoing drought in the region has led to highly publicized reductions in reservoir storage and raised concerns about potential reductions in downstream flows. Large changes in riverine thermal regimes may also occur as reservoir water levels drop, yet this potential impact has received far less attention. We analyzed historic water temperature and fish population data to anticipate how trout may respond to future changes in the magnitude and seasonality of river temperatures. We found that summer temperatures were inversely related to reservoir water level, with warm temperatures associated with reduced storage and with dams operated as run-of-river units. Variation in rainbow trout (Oncorhynchus mykiss) recruitment was linked to water temperature variation, with a 5-fold increase in recruitment occurring at peak summer temperatures (18 °C vs. 7 °C) and a 2.5-fold increase in recruitment when peak temperatures occurred in summer rather than fall. Conversely, adult trout size was only moderately related to temperature. Rainbow and brown trout (Salmo trutta) size decreased by ~24 mm and 20 mm, respectively, as mean annual and peak summer temperatures increased. Further, rainbow trout size decreased by ~29 mm with an earlier onset of cold winter temperatures. While increased recruitment may be the more likely outcome of a warmer and drier climate, density-dependent growth constraints could exacerbate temperature-dependent growth reductions. As such, managers may consider implementing flows to reduce recruitment or altering infrastructure to maintain coldwater reservoir releases.

Irradiation of rainbow trout at early life stages results in a proteomic legacy in adult gills. Part A; proteomic responses in the irradiated fish and in non-irradiated bystander fish

Exposure to a single 0.5 Gy X-ray dose of eggs at 48 h after fertilisation (48 h egg), eyed eggs, yolk sac larvae (YSL) and first feeders induces a legacy effect in adult rainbow trout. This includes the transmission of a bystander effect to non-irradiated adult trout which had swam with the irradiated fish. The aim of this study was to investigate this legacy by analysing the gill proteome of these irradiated and bystander fish. Irradiation at all of the early life stages resulted in changes to proteins which play a key role in development but are also known to be anti-tumorigenic and anti-oxidant: upregulation of haemoglobin subunit beta (48 h egg), haemoglobin, serum albumin 1 precursor (eyed eggs), clathrin heavy chain 1 isoform X10 (eyed eggs and first feeders), and actin-related protein 2/3 complex subunit 4 (first feeders), downregulation of pyruvate dehydrogenase, histone 1 (48 h egg), triosephosphate isomerase (TPI), collagen alpha-1(1) chain like proteins (YSL), pyruvate kinase PKM-like protein (YSL and first feeders), ubiquitin-40S ribosomal proteins S27 and eukaryotic translation initiation factor 4 A isoform 1B (first feeders). However irradiation of YSL and first feeders (post hatching early life stages) also induced proteomic changes which have a complex relationship with tumorigenesis or cancer progression; downregulation of alpha-1-antiprotease-like protein precursor, vigilin isoform X2 and nucleoside diphosphate kinase (YSL) and upregulation of hyperosmotic glycine rich protein (first feeders). In bystander fish some proteomic changes were similar to those induced by irradiation: upregulation of haemoglobin subunit beta (48 h egg), haemoglobin (eyed eggs), actin-related protein 2/3 complex subunit 4, hyperosmotic glycine rich protein (first feeders), and downregulation of alpha-1-antiprotease-like protein, vigilin isoform X2, nucleoside diphosphate kinase (YSL), pyruvate kinase PKM-like protein and ubiquitin-40S ribosomal protein S27a-like (first feeders). Other proteomic changes were unique to bystander fish; downregulation of TPI, ubiquitin-40S ribosomal protein S2 (eyed egg), cofilin-2, cold-inducible RNA-binding protein B-like isoform X3 (YSL) and superoxide dismutase (first feeder), and upregulation of haemoglobin subunit alpha, collagen 1a1 precursor, apolipoprotein A-1-1 and A-1–2 precursor (first feeders). These bystander effect proteomic changes have been shown to be overwhelmingly anti-tumorigenic or protective of the fish gill.

Changes in the Status of Native Brook Trout on Laurel Hill, Southwestern Pennsylvania

To evaluate the status of native Salvelinus fontinalis (Brook Trout) on Pennsylvania's Laurel Hill, we sampled fish, assessed habitat, and documented water quality from 20 non-randomly selected headwater streams of northwest- and southeast-facing slopes. In late spring and early summer of 2011 and 2014–2016, we sampled fish communities and measured specific conductance (μS/cm), total alkalinity (mg/l as CaCO3), pH, and total dissolved aluminum (2011 and 2016). In addition, in 2015 we determined land-use patterns, riparian canopy, and substrate composition. Mean pH values among the streams recently assessed were significantly higher than historic values; however, all other water-quality parameters were similar. Native Brook Trout were present in all streams, and annual natural reproduction was evident in 90% of streams. Even though fish were present, we observed marked declines in total catch in both 0-age and adult trout; the overall reduction approached 60% when compared with those documented in 1983. We discuss possible causes for the observed declines, including acid deposition, introduction of nonnative/invasive species, water withdrawal, habitat fragmentation/alteration, predation, and climate change.

Restoration of native Mediterranean brown trout Salmo cettii Rafinesque, 1810 (Actinopterygii: Salmonidae) populations using an electric barrier as a mitigation tool

This study assessed the effectiveness of a novel conservation strategy for the native brown trout populations in Sardinia (Italy). The conservation measures included: (i) installation of an electric fish barrier; (ii) removal of all the resident introgressed brown trout upstream from the barrier; (iii) restocking of the upstream region with native Sardinian trout genetically characterised; and (iv) estimation of native trout population size with prediction of future growth. Introgressed brown trout were removed using multiple-pass electrofishing methods in a 2-km region upstream from the barrier. In two eradication campaigns, conducted in 2010 and 2012, a total of 1801 trout were captured, comprising a total biomass of 55,501 g. The capture efficiency analysis showed total capture rates of over 99% were achieved for parr (0+ age cohort), and 100% for adult trout. After the eradication campaigns we restocked this area with native brown trout (Adriatic lineage, AD, according to the mitochondrial DNA control region nomenclature). The monitoring campaigns showed good survival (S = 60%) and reproduction of 3.1 recruits/adult trout. Successful breeding was recorded starting from the summer of 2015 and a self-sustaining population resulted after only two restocking events. The results of this restoration project allow recommendations to be made for future conservation eradication and repopulation projects for restoration of typical Mediterranean streams.

Influence of essential oils in diet and life-stage on gut microbiota and fillet quality of rainbow trout (Oncorhynchus mykiss)

Developing fish farming to meet the demands of food security and sustainability in the 21st century will require new farming systems and improved feeds. Diet and microbe interactions in the gut is an important variable with the potential to make a significant impact on future fish farming diets and production systems. It was monitored the gut microbiota of farmed rainbow trout using 16S rRNA profiling over 51 weeks during standard rearing conditions and feeding diet with supplementation of an essential oils (MixOil) mixture from plants (at a concentration in diet of 200 mg/kg). Gut microbiota 16S rRNA profiling indicated that the fish gut was dominated by Actinobacteria, Proteobacteria, Bacteroidetes and Firmicutes. Although the dietary supplementation with MixOil had no impact on either the composition or architecture of gut microbiota, significant changes in alpha and beta diversity and relative abundance of groups of gut bacteria were evident during growth stages on test feeds, especially upon prolonged growth on finishing feed. Fish fillet quality to guarantee palatability and safety for human consumption was also evaluated. Significant differences within the gut microbiota of juvenile and adult trout under the same rearing conditions were observed, The addition of essential oil blend affected some physicochemical characteristics of trout fillets, including their resistance to oxidative damage and their weight loss (as liquid loss and water holding capacity) during the first period of storage, that are two important parameters related to product shelf life and susceptibility to spoilage. The results highlighted the need for further studies concern dietary microbiome modulation at different life stages and its influence on animal health, growth performance and final product quality.

Single-Cell Reconstruction of Oxytocinergic Neurons Reveals Separate Hypophysiotropic and Encephalotropic Subtypes in Larval Zebrafish.

Oxytocin regulates a diverse set of processes including stress, analgesia, metabolism, and social behavior. How such diverse functions are mediated by a single hormonal system is not well understood. Different functions of oxytocin could be mediated by distinct cell groups, yet it is currently unknown whether different oxytocinergic cell types exist that specifically mediate peripheral neuroendocrine or various central neuromodulatory processes via dedicated pathways. Using the Brainbow technique to map the morphology and projections of individual oxytocinergic cells in the larval zebrafish brain, we report here the existence of two main types of oxytocinergic cells: those that innervate the pituitary and those that innervate diverse brain regions. Similar to the situation in the adult rat and the adult midshipman, but in contrast to the situation in the adult trout, these two cell types are mutually exclusive and can be distinguished based on morphological and anatomical criteria. Further, our results reveal that complex oxytocinergic innervation patterns are already established in the larval zebrafish brain.

Comparison of West Balkan adult trout habitat predictions using a Pseudo-2D and a 2D hydrodynamic model

Abstract Hydraulic-habitat models combine the dynamic behavior of river discharge with geomorphological and ecological responses. In this study, they are used for estimating environmental flow requirements. We applied a Pseudo-two-dimensional (2D) model based on the one-dimensional (1D) HEC-RAS model and an in-house 2D (FLOW-R2D) hydrodynamic model to a section of river for several flows in respect of summer conditions of the study reach, and compared the results derived from the models in terms of water depths and velocities as well as habitat predictions in terms of weighted usable area (WUA). In general, 2D models are more promising in habitat studies since they quantify spatial variations and combinations of flow patterns important to stream flora and fauna in a higher detail than the 1D models. Relationships between WUA and discharge for the two models were examined, to compare the similarity as well as the magnitude of predictions over the modelled discharge range. The models predicted differences in the location of maxima and changes in variation of velocity and water depth. Finally, differences in spatial distribution (in terms of suitability indices and WUA) between the Pseudo-2D and the fully 2D modelling results can be considerable on a cell-by-cell basis.

Behavioral response of brook trout and brown trout to acidification and species interactions

Many factors have been associated with the decline of brook trout (Salvelinus fontinalis) throughout their native range including acidification and competition with brown trout (Salmo trutta), an introduced species. We observed the behavior of wild, adult brook trout and brown trout (alone and in combination) within study reaches that were manipulated to vary the level of acidity and CO2. The aims of the study were to address 1) if acidification affects the segregation patterns of wild, adult brook trout and brown trout and 2) whether interactions among brook trout and brown trout influence the distribution of brook trout in acidified waters. After manipulating acidity levels, the majority of indwelling fish responded to acidification by moving to more neutral conditions (62 % of brook trout and 68 % of brown trout). Indwelling brook trout spent less time in acidic conditions during the acid treatment (41 ± 5 %) than during the control period (94 ± 2 %). Indwelling brown trout spent less time in the acid conditions during the acid treatment (44 ± 4 %) than during a control period (98 ± 1 %). The proportion of time spent in the acid water by indwelling trout decreased as negative interactions with other fish (such as chasing) increased. Presence of the opposite species did not influence the proportion of time spent in the acidic conditions. The results of this study do not support the hypothesis that acidification mediates the segregation of brook trout and brown trout in streams.

ST2 from rainbow trout quenches TLR signalling, localises at the nuclear membrane and allows the nuclear translocation of MYD88

The mammalian interleukin 1 receptor-like 1 receptor (IL1RL1), commonly known as ST2, is thought to downregulate TLR signalling by sequestering the signalling adapter MYD88 (myeloid differentiation primary response protein 88). ST2 sequences are known in several fish species, but none of them have functionally been examined. We characterised ST2 from rainbow trout (Oncorhynchus mykiss) and the structure of its encoding gene. The primary sequence of ST2 is only weakly conserved from fish to human. However, the amino acid sequences forming the interfaces for ST2 and MYD88 interaction are well conserved throughout evolution. High similarity of the gene segmentation unambiguously proves the common ancestry of fish and mammalian ST2. Trout ST2 and trout MYD88 genes were constitutively expressed in embryonic, larval and adult trout. In vivo infection with Aeromonas salmonicida did not modulate the mRNA levels of both factors. Overexpressing trout ST2 in the mammalian HEK-293 reconstitution system of TLR2 signalling quenched the Escherichia coli–induced activation of NF-κB and SAA promoters in a dose-dependent fashion. The expression of GFP-tagged trout ST2 in human HEK-293 or trout CHSE-214 cells surprisingly revealed that (i) ST2 localised abundantly at the nuclear membrane rather than at the cell membrane and (ii) the coexpression of both ST2 and MYD88 allowed the translocation of trout MYD88 from cytoplasm to nucleus, as assessed using confocal microscopy and Western blotting. Hence, we validated that trout ST2 is a dampener of TLR signalling and interacts with MYD88. The spatial distribution of these factors raises questions about how this repressive mechanism functions.