Individual Rainbow Trout Research Articles

Oral delivery of a dsRNA-Phytoglycogen nanoparticle complex enhances both local and systemic innate immune responses in rainbow trout

Salmonids are one of the most farmed fish species worldwide. These aquatic vertebrates rely heavily on their innate immune responses as the first line of defense to defend themselves against invading pathogens. Although commercial vaccines are available against some viral and bacterial pathogens affecting salmonids, their protective efficacy varies. Using a prophylactic inducer of local and systemic innate immune responses to limit infection could have significant implications in salmonid aquaculture. A potent inducer of innate immune responses in fish is double-stranded RNA (dsRNA), a molecule that all viruses make during their replicative cycle. Polyinosinic: polycytidylic acid (polyI:C) is a synthetic dsRNA commonly used to induce type I interferons (IFNs), interferon stimulated genes (ISGs) as well as an antiviral state in vertebrate species. Based on in vitro data it was hypothesized that both local and systemic innate immune responses, in salmonids, would be enhanced by orally delivering high molecular weight polyI:C (HMW polyI:C) using cationic phytoglycogen nanoparticles (NPs) as a delivery method. The present study investigates this hypothesis using two feed delivery methods. In the first in vivo study, to ensure an equal distribution of dose, individual rainbow trout (Oncorhynchus mykiss) were orally gavaged with feed moistened with a solution containing HMW-NP (polyI:C complexed with cationic phytoglycogen nanoparticles) or HMW polyI:C alone. In a second in vivo experiment, to better mimic a more realistic feeding scenario, rainbow trout were fed feed pellets to which HMW, or HMW-NP was added. The expression of IFN1 and ISGs (vig-3, Mx1) were quantified using real-time PCR in the intestine (local response) and head kidney (systemic response). The results of these studies indicate that HMW-NP induced a higher level of IFN1 and ISG expression in the intestine and head kidney compared to the HMW fed fish. The results of this study could lead to new advances in therapeutics for the aquaculture industry by utilizing the innate immune response against invading pathogens using an orally delivered stimulant.

Ecological Assessment and Evaluation of Potential Eradication Approaches for Introduced Redside Shiners in a Montane Lake

AbstractIntroduced species can alter the dynamics of food webs, species interactions, populations, and communities and can reduce a system’s recreational value. Several reports have documented the establishment of Redside Shiners Richardsonius balteatus in mountain lakes, resulting in declines in sizes and abundance of salmonid species. An illegal bait bucket release introduced Redside Shiners into Green Canyon Lake, Montana, USA, in the 1980s. Recently, local anglers began complaining of decreases in size and catch rates of Westslope Cutthroat Trout (WCT) Oncorhynchus clarkii lewisi. Our first objective was to understand the diet overlap between Redside Shiners and WCT in Green Canyon Lake. Based on δ15N and δ13C isotopic signatures and diet contents, we found little evidence that WCT were substantially preying upon Redside Shiners. We found moderate diet overlap between WCT and Redside Shiners, with both species predominately feeding on Diptera. For our second objective, we developed a population model to assess potential options for eradicating Redside Shiners. We observed Redside Shiners up to 7 years of age and with a maximum TL of 159 mm, high annual survival (50%), and mature females at age 2. We used an age‐structured model to evaluate two hypothetical suppression actions: piscicide application and stocking of Rainbow Trout O. mykiss. Four consecutive piscicide treatments had a 20% probability of eradicating Redside Shiners, increasing to a 100% eradication probability after seven treatments. Bioenergetic simulations indicated that an individual Rainbow Trout (500 g) would consume 1,759 g of Redside Shiners annually. Incorporating this predation mortality and a compensatory response (50% increase in age‐1 survival), we estimated that maintained abundances of up to 700 Rainbow Trout would not cause a decline in the Redside Shiner population. Our results suggest that eradication of an introduced prey fish like the Redside Shiner would be difficult and that effective removal will require dedicated effort and resources by managers.

Oral administration of Sargassum polycystum extracts stimulates immune response and increases survival against Aeromonas hydrophila infection in Oncorhynchus mykiss

This study investigated the immunomodulatory effects of Sargassum polycystum extract administration in rainbow trout (Oncorhynchus mykiss). S. polycystum methanolic extract was administered orally using feeding needles to individual rainbow trout at the dose of 0 (control), 1 (S1), 3 (S3) and 5 (S5) mg/100 μl/per fish twice a day for 7 days. On 1st, 5th, 3rd and 7th day, blood and tissues were collected from the fish and changes in humoral immune responses and immune‐related gene expressions were determined. The result of oxidative radical production showed no difference during early stage of the experiment and was lately decreased (P < 0.05). Lysozyme activity increased on 3rd and 7th day of the study in S5 fish group and on 5th day in S3 group compared to control (P < 0.05). Myeloperoxidase activity had an increased level on the 1st and 3rd day in S1, S5 and S5 fish groups, respectively. IL-1β gene was significantly up-regulated in kidney and intestine in all experimental groups (except on the 1st day, in the intestine of S5 fish group) compared to control (P < 0.05). IL-8 gene expression was elevated on 1st and 3rd day in kidney of all experimental fish groups. IL-6 transcript enhanced in a dose-dependent manner on 3rd and 7th day. IL-10 and IL-12 genes were also up-regulated. Survival in all treated fish groups challenged with Aeromonas hydrophila was significantly increased compared to that of control. The highest survival rate was recorded in S5 fish group (83.65%) followed by S3 fish group (82.62%). Our results suggest that S. polycystum aqueous methanolic extract is an effective immunostimulant and provide protection against A. hydrophila infection in rainbow trout at a dose of 3–10 mg/20 g body weight/day.

Detection and Identification of Bacterial Pathogens in Rainbow Trout (Oncorhynchus mykiss) Samples from Fish Farms in Iran

Rainbow trout (Oncorhynchus mykiss) infections are the most important risk factor causing losses in fish farming industry. The aim of the present study was to identify and determine the frequency of bacterial pathogens Streptococcus iniae, S. parauberis, Lactococcus garvieae, L. lactis, Flavobacterium branchiophilum, F. psychrophilum and Yersinia ruckeri in diseased rainbow trout samples collected from different fish farms in Zanjan, Iran. A total of 103 individual diseased rainbow trout including 412 organ samples of liver, kidney, gills and eye organs were collected from 17 fish farms. Overall, 92 (89.3%) out of 103 rainbow trout were positive for the presence of at least one tested pathogen. According to culture and biochemical tests, 199 (48.3%) bacterial isolates were detected. However, molecular analysis confirmed 92.4% (184/199) of isolates. The most common isolated pathogen was L. garvieae (56.3%, 112/199), followed by S. iniae (11.5%, 23/199), F. branchiophilum (9.5%, 19/199) and Y. ruckeri (9.1%, 18/199). Lactococcus lactis and F. psychrophilum were detected with lowest frequency (2.5%, 5/199). Considering the high frequency of bacterial infections in our study, it seems that appropriate surveillance and control measures are essential to prevent the emergence and transmission of bacterial pathogens in rainbow trout farms.

A new potential therapeutic remedy against Aeromonas hydrophila infection in rainbow trout (Oncorhynchus mykiss) using tetra, Cotinus coggygria.

Different antibiotic-based drugs are being used for the treatment of Aeromonas hydrophila infection in rainbow trout, and several studies emphasize the use of medicinal plants as immunostimulants for prophylactic measure against Aeromoniasis disease. However, therapeutic effects of aqueous methanolic extracts of tetra (Cotinus coggygria) against A.hydrophila in rainbow trout were not investigated. Four different concentrations of tetra extract (0 [control], 4, 8 and 12mg/100µl) and also two different positive control groups (florfenicol and doxycycline antibiotics) were administered orally using feeding needles to individual rainbow trout, Oncorhynchus mykiss of all experimental groups twice a day after intramuscular inoculation of A.hydrophila. The study period was for 10days. On 0th, 3rd, 7th and 10th day, blood and tissues were collected from the fish and changes in humoral immune responses, haematology and immune-related gene expressions were determined. In the study, superoxide radical production was decreased generally in all experimental groups except in 12mg tetra and florfenicol treatments compared to control (p<.05). Lysozyme activity was generally decreased (p<.05), or no differences were observed in all experimental groups compared to the control. Myeloperoxidase activity was significantly increased in florfenicol-treated fish group on 7th day (p<.05). Generally, myeloperoxidase activity showed an increase in almost all tetra-treated groups. Haematological parameters increased but were not significantly high enough in treatments. Almost all immune-related gene expressions were significantly enhanced on 3rd and 10th day of the study. Survival rate of 53.33% was found in control group. There were no significant differences in survival between control and 4mg tetra-treated group (p>.05). All the other groups' survival rate was significantly increased compared to control. The highest survival rate was found in florfenicol group (80%). In 12mg tetra-, doxycycline- and 8mg tetra-treated groups, survival rate was recorded as 74.44%, 70% and 70%, respectively. Our results suggest that tetra methanolic extract is an effective therapeutic remedy against A.hydrophila infection in rainbow trout at the dose of 24mg/32.34gbodyweight/day.

Use of Cover for Concealment Behavior by Rainbow Trout: Influences of Cover Structure and Area

AbstractConcealment behavior by stream salmonids can benefit individuals and populations, but the availability of concealment habitat may be limited in many streams. Quantification of concealment habitat is likely to be a valuable process in the management of stream salmonids; it is a necessary step in the application of spatially explicit, individual‐based models that incorporate concealment behavior. We conducted a series of laboratory experiments with Rainbow Trout Oncorhynchus mykiss to aid in the identification and quantification of concealment habitat. Overall, individual Rainbow Trout about 12 cm FL readily used low‐ceiling spaces with one, two, or four openings for concealment. Structures analogous to weakly undercut banks were used less. Mean use of different cover types was less variable in an experiment in which groups of three fish were tested. Individuals in groups rarely shared cover spaces, even though in another experiment individual fish readily occupied spaces less than 25% of the area of the spaces they rarely shared. One cover structure that was not preferred in a simple choice experiment was used as much as the preferred structure when the former was the only cover available, indicating that habitat preference experiments provide limited information when the issue is whether fish are willing to use specific habitats.Received February 16, 2016; accepted June 18, 2016 Published online October 14, 2016

Behavioral responses of a highly domesticated, predator naïve rainbow trout to chemical cues of predation

Fisheries management agencies allocate significant proportions of available resources to rear fish for stocking in lakes, rivers, and reservoirs. However, domesticated fish reared in a hatchery environment may fail to exhibit normal antipredator behavior and can have relatively low survival when released into natural habitats. Exposing hatchery fish to natural predator cues can provide information about their capacity to exhibit appropriate behavioral responses and has the potential to enhance antipredator behavior and subsequent survival in the wild. We investigated immediate behavioral responses to an acute exposure to chemical cues of predation in highly domesticated, hatchery-reared rainbow trout Oncorhynchus mykiss. We used a frequently stocked and economically important strain of rainbow trout, the German Rainbow (GR), which is resistant to whirling disease but particularly susceptible to predation. We exposed individual rainbow trout to alarm cues from conspecifics, kairomones from brown trout Salmo trutta predators, and a combination of the two cues. Fish exposed to these cues exhibited changes in behavior expected to reduce predation risk, including a reduction in time spent actively swimming and exploring, and an increase in time spent frozen. Thus, these highly domesticated, hatchery-reared fish retain the innate ability to express appropriate responses to the threat of predation. Future research should investigate whether repeated exposure to predation cues in a hatchery setting could translate to long-term enhancement of antipredator behavior and increased survival rates, as this would provide a rapid, simple and low cost way to increase the efficiency of stocking programs for recreational purposes and, more importantly, native fish restoration and conservation.

Feeding modes in stream salmonid population models: is drift feeding the whole story?

Drift-feeding models are essential components of broader models that link stream habitat to salmonid populations and community dynamics. But is an additional feeding mode needed for understanding and predicting salmonid population responses to streamflow and other environmental factors? We addressed this question by applying two versions of the individual-based model inSTREAM to a field experiment in which streamflow was varied in experimental units that each contained a stream pool and the adjacent upstream riffle. The two model versions differed only in the feeding options available to fish. Both versions of inSTREAM included drift feeding; one also included a search feeding mode to represent feeding in which food availability is largely independent of streamflow, such as feeding from the benthos, or feeding from the water column or the water’s surface in low water velocities. We compared the abilities of the two model versions to fit the observed distributions of growth by individual rainbow trout (Oncorhynchus mykiss) in the field experiment. The version giving fish the daily choice between drift or search feeding better fit observations than the version in which fish fed only on drift. Values for drift and search food availability from calibration to the individual mass changes of fish in experimental units with unaltered streamflow yielded realistic distributions of individual growth when applied to experimental units in which streamflow was reduced by 80 %. These results correspond with empirical studies that show search feeding can be an important alternative to drift feeding for salmonids in some settings, and indicate that relatively simple formulations of both processes in individual-based population models can be useful in predicting the effects of environmental alterations on fish populations.

The physiology of rainbow trout in social hierarchies: two ways of looking at the same data

Salmonids form dominance hierarchies in environments, where space or food are limiting. Our first objective was to investigate the physiology of individual rainbow trout in 4-fish hierarchies. Our second was to compare conclusions drawn from grouping physiological data on the basis of social rank with those based on relating individual physiology to individual aggressive behavior. To create a social hierarchy, groups of 4 juvenile trout were fed (1% ration) using a darkened feeding container, twice daily (morning and evening). Each morning feeding was videotaped to record aggressive behavior, thereby facilitating the assignment of a social status rank to each fish. On days 5 and 10-11, physiological parameters were measured in fish fasted for 24h. Social hierarchies formed in all tested groups. One fish would become dominant, whereas the three subordinate individuals would each assume a stable social rank. When classified according to this social rank, the three subordinate individuals all displayed similar physiology, different from the physiology of the dominant fish. The latter included higher ammonia excretion rate, greater protein utilization in aerobic metabolism, greater feeding, higher specific growth rate, greater increase in condition factor, and lower routine oxygen consumption rate. However, when individual aggression was taken into account, a continuous gradient was observed between aggression and physiology for most parameters, regardless of social status. These relationships could be improved by normalizing the aggression score to the overall level of aggression in each hierarchy. We argue that individual behavior should be considered instead of just social rank when studying the physiology of trout in social hierarchies.

Costs of being extreme — Do body size deviations from population or sire means decrease vitality in rainbow trout?

In animals, large or small body size may carry health costs. Large deviations from physiologically benign growth range can divert resources from vital body functions and cause developmental defects, thereby constraining the welfare and productivity of animals. When analyzing the phenotypic costs associated with growth variation, it is unclear whether slow or fast growth should be determined relative to an individual's own family background or relative to population's overall genetic level. That is, should the body size of an individual be related to its parental (genotypic) average, instead of a general population mean? Using the data from 60,518 individual rainbow trout, Oncorhynchus mykiss, we tested whether the negative and positive deviations of tagging body weight (one-summer-old fish, average weight 51g) relative to either a common population mean or sire-family means differently predict the probability of mortality and vertebrae defects during the subsequent grow-out period. Based on the logistic regression analysis, neither types of body weight deviation predicted the probability of vertebrae defect. In contrast, the probability of mortality showed a significant negative relationship with deviations of weight. The smallest individuals with large negative deviation from their sire-family means possessed the highest risk of death. However, there was a high positive correlation between the deviation types calculated from sire-family and population means (r=0.93), and thus their ability to predict mortality was very similar. This finding does not support our physiological capacity hypothesis stating that the phenotypic vitality costs would be more strongly associated with an individual's body size relative to its family's genetic mean level, rather than relative to the overall population mean. Rapid fingerling growth was not phenotypically related to either of the vitality costs studied. The largest fish, both with respect to population and sire-family means, had the lowest risk of death and were no more or less liable to developmental vertebral defects, compared to their smaller counterparts. These results emphasize the importance of narrowing growth variation, especially from the lower end of the growth profile, using mating and selection designs to reduce fish mortality during the communal grow-out period.

Biological Characteristics of Fish Germ Cells and their Application to Developmental Biotechnology

We have revealed several unique characteristics of germ cell development using rainbow trout, including the fact that spermatogonia transplanted into the peritoneal cavity of newly hatched embryos migrate toward recipient gonads, that spermatogonia transplanted into female recipients start oogenesis and produce functional eggs and that diploid germ cells transplanted into triploid trout can complete gametogenesis. By combining these unique features of fish germ cells, we established allogeneic and xenogeneic transplantation systems for spermatogonia in several fish species. Spermatogonia isolated from the mature testes of vasa-green fluorescent protein (Gfp) transgenic rainbow trout were transplanted into the peritoneal cavity of triploid masu salmon newly hatched embryos. These spermatogonia migrated toward recipient salmon genital ridges with extending pseudopodia and were subsequently incorporated into them. We further confirmed that the donor-derived spermatogonia resumed gametogenesis and produced sperm and eggs in male and female salmon recipients, respectively. By inseminating the resulting eggs and sperm, we obtained only rainbow trout offspring in the F1 generation, suggesting that the triploid salmon recipients produced functional gametes derived only from donor trout. We further confirmed that this intra-peritoneal transplantation of germ cells is applicable to several marine fishes, which could be of benefit in the production of bluefin tuna that has a large broodstock (>100 kg) and is difficult to maintain in captivity. Gamete production of bluefin tuna could be more easily achieved by generating a surrogate species, such as mackerel, that can produce tuna gametes.

Variation in Sensory Profile of Individual Rainbow Trout (Oncorhynchus mykiss) from the Same Production Batch

The variation in sensory profile of rainbow trout (Oncorhynchus mykiss), belonging to the same aquaculture production batch and handled the same way, was explored by using objective sensory profiling on heat-treated minced fillets. In addition, quality index, mechanical texture, pH, fat, and water content were measured. Different groups of fish were sampled 3 different times during a production day. The results showed significant differences in the sensory profiles of individual fish within all 3 groups as well as significant differences between the groups. Differences in mechanical texture were found between individuals in 2 of the 3 groups and between the groups. No differences were found in quality index neither between individuals nor groups. A significant negative correlation between lipid content and firm texture was observed, but in general, the chemical and physical measurements could not explain the differences in the sensory profiling or in the mechanical texture measurements. The results showed that significant differences in the sensory profiles of individual fish from the same aquaculture production batch may occur. Furthermore, the results also showed sensory differences between groups of samples taken at different times during a production day.

Development of a sensitive and controlled real-time RT-PCR assay for viral haemorrhagic septicaemia virus (VHSV) in marine salmonid aquaculture

A survey was undertaken to determine the potential distribution of viral haemorrhagic septicaemia virus (VHSV) in marine cage-based salmonid farms in Scotland. A rapid, accurate and sensitive quantitative real-time RT-PCR (qRT-PCR) assay was developed, targeting a conserved region of the nucleoprotein (N) gene of the virus. The qRT-PCR assay was shown to be more sensitive than the conventional VHSV RT-PCR. A validation protocol included several different virus isolates as the target and confirmed that the assay could detect all European VHSV genotypes (I, II and III). Both endogenous and exogenous controls were designed to control for integrity of template and distinguish between true VHSV positives and contamination with the positive control material. In total, the universal European VHSV qRT-PCR assay with exogenous positive control was applied to screen 2040 individual Atlantic salmon Salmo salar and 150 individual rainbow trout Oncorhynchus mykiss. No evidence of the presence of VHSV in association with either salmonid species in Scottish marine farms was detected. However, both marine Atlantic salmon and rainbow trout are still considered possible carriers of VHSV, which remains a potential threat to freshwater farming. Therefore, a continued surveillance of these species in marine environment is recommended.

Demonstrating freedom from Gyrodactylus salaris (Monogenea: Gyrodactylidae) in farmed rainbow trout Oncorhynchus mykiss

This paper describes an approach to demonstrate freedom of individual rainbow trout farms from Gyrodactylus salaris Malmberg, 1957. The infection status of individual farms is relevant should G. salaris be introduced into a country or zone previously known to be free of the parasite. Trade from farms where G. salaris may have been introduced would be restricted until freedom had been demonstrated. Cage, fish and parasite sample sizes were calculated based on the minimum detectable prevalence (P*), test characteristics, population size, and Type I and II errors. Between 5 and 23 cages per farm would need to be sampled to demonstrate freedom at a cage level P* of 10%. The number of fish sampled per cage depended mainly on the test sensitivity (probability of correctly identifying an infected fish). Assuming a test sensitivity of 99% at the fish level, 59 fish per cage are needed (P* = 5%). Since G. salaris may exist in mixed infection with G. derjavini, testing a sample of gyrodactylid parasites may not result in the parasite being detected when present. Test sensitivity at the fish level depends on the number of gyrodactylids on the fish, the proportion of which are G. salaris and the number examined. Assuming a P* of 5% (i.e. G. salaris are at least 5% of the gyrodactylid population), between 20 and 73 parasites per fish would need to be sampled (depending on abundance) to maintain the Type I error at 0.01 (thus a fish level test sensitivity of 99%). This work identifies the critical information, and further research, needed to assess freedom from G. salaris with a known level of confidence; this is essential to provide a sound scientific basis for decision-making about disease control measures.

Gene transcript changes in individual rainbow trout livers following an inflammatory stimulus

Inflammatory stimuli elicit liver synthesis and subsequent release into the plasma of several proteins (positive acute phase proteins, APP) with functions in innate immunity, tissue repair and restoration of homeostasis. To expand the basis for evaluating the degree of conservation of the APR in vertebrates and to assess the extent to which genes encoding both cellular and plasma proteins are affected, we profiled transcriptional changes in livers of individual rainbow trout ( Oncorhynchus mykiss) after intraperitoneal injection of Listonella ( Vibrio) anguillarum bacterin in Freund's Incomplete Adjuvant. Twenty genes were down-regulated, some unexpectedly such as complement component 3 and α2-macroglobulin. Sixteen up-regulated genes included three encoding proteins involved in iron metabolism (hepcidin, haptoglobin, and intelectin), from which we infer that sequestration of iron is likely to be a major component of the trout APR. Activated genes encoding proteins of unknown functions included precerebellin-like plasma protein, and differentially regulated trout protein which is predicted to be cell surface associated. The only complement component that increased was C7. Genes encoding proteins that are probably not released into plasma included two fatty acid binding proteins, two transport proteins (SEC61 and a Na–Ca exchanger), GAPDH, an amino transferase, and a hydrolase. When microarray data and quantitative RT-PCR analyses were used to evaluate specific transcripts, variations were notable between individual fish, possibly a basis for natural variation in susceptibility to infectious diseases. This study suggests novel hypotheses relating to NFκB, albumin-related protein, pentraxin, hypoferremia and the complement cascade. While the capacity to mount an APR is conserved throughout vertebrate evolution, the responding genes vary from species to species, and considerable variation is observed from individual to individual within a species.

Evaluation of quantitative real-time PCR for rapid assessments of the exposure of sentinel fish to Myxobolus cerebralis

Pathogen-free rainbow trout (Oncorhynchus mykiss) aged 735 degree days were experimentally exposed to a low dose of infectious Myxobolus cerebralis (20 triactinomyxons fish(-1)). Three time periods were chosen for sampling that included 10 days (d), 67 d, and 5 months (mo) post exposure. Five diagnostic assays were used: (1) conventional single-round polymerase chain reaction (PCR), (2) nested PCR, (3) real-time TaqMan PCR, (4) pepsin-trypsin digest, and (5) histopathology. M. cerebralis was detected among individual rainbow trout by all of the PCR diagnostic tests employed at each of the three sampling time points. This result demonstrates that any of these three diagnostic approaches are capable of detecting the parasite from infected fish tissues under the conditions tested. Real-time PCR provided good biological evidence that parasite replication increases temporally as shown by quantification values that were significantly different (P<0.0001) at 10 d as compared to 67 d and 5 mo postexposure. Although sampling at 10 d by real-time PCR may be too early to accurately predict quantities of the parasite that will be present at 5 mo, it does forecast the proportions of fish that are likely to be infected at 67 d and 5 mo postparasite exposure. Real-time PCR could potentially be used as a quantitative diagnostic PCR tool to predict parasite load and outcome of M. cerebralis infection.

Does Individual Variation in Stress Responses and Agonistic Behavior Reflect Divergent Stress Coping Strategies in Juvenile Rainbow Trout?

Individual rainbow trout were transferred to visual isolation in experimental aquaria. As a measure of the speed of acclimation, individual food intake was quantified during the first 6 d following transfer. Following acclimation, aggression was quantified by subjecting the fish to three resident-intruder tests, with 30 d of recovery between the tests. Moreover, between the resident-intruder tests (i.e., two times) the fish were exposed to an unfamiliar environment and their cortisol response was measured. The results of this study show that individuals of juvenile rainbow trout differ distinctly in their response to changes in their environment, and that this diversity in behavior is reflected by consistent behavioral traits displayed by individual fish. These traits have proven to be consistent not only over time but also across situations, revealing two distinct behavioral profiles, in the same manner as shown in studies on proactive and reactive mammals. Our results also show that the reactivity of the hypothalamic-pituitary-interrenal (HPI) axis, when exposed to a stressor, is a consistent physiological trait in juvenile rainbow trout. We found that difference in HPI axis reactivity is linked to the different behavioral profiles. However, HPI axis reactivity could not be linked directly to the singular behavioral traits measured. In other words, we did not find that the consistent behavioral traits shown by the fish were associated with a difference in HPI axis reactivity in the same manner as the reactivity of the hypothalamic-pituitary-adrenocortical axis does in mammals. Taken together, our results show that stress coping strategies akin to what has been described as reactive and proactive stress coping in mammals appear to exist in juvenile rainbow trout.

Branchial release of free cortisol and melatonin by rainbow trout

Individual rainbow trout Oncorhynchus mykiss were held in a specially constructed tank that enabled water to be collected separately from the anterior and posterior ends of the fish. Measurement by radioimmunoassay showed that &gt;95% of the cortisol and melatonin released into the water originated from the anterior end (dominated by the gills). High performance liquid chromatography confirmed the identity of both hormones.

Diel changes in endolymph aragonite saturation rate and mRNA expression of otolith matrix proteins in the trout otolith organ

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 294:249-256 (2005) - doi:10.3354/meps294249 Diel changes in endolymph aragonite saturation rate and mRNA expression of otolith matrix proteins in the trout otolith organ Yasuaki Takagi1,*, Hidekazu Tohse1,2, Emi Murayama2,3, Tsuyoshi Ohira2,4, Hiromichi Nagasawa2 1Graduate School of Fisheries Sciences, Hokkaido University, Minato, Hakodate, Hokkaido 041-8611, Japan2Graduate School of Agricultural and Life Sciences, The University of Tokyo, Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan3Present address: Unité Macrophages et Développement de l’Immunité, Département de Biologie du Développement, Institut Pasteur, 25 rue du Dr Roux, 75724 Paris cedex 15, France4Present address: Japan International Research Center for Agricultural Sciences, Owashi, Tsukuba, Ibaraki 305-8686, Japan *Email: takagi@fish.hokudai.ac.jp ABSTRACT: In the teleost fish otolith, the alternate deposition of CaCO3-rich and protein-rich layers results in the formation of daily increments. In order to clarify the mechanism of daily increment formation, a precise understanding of the relationship between ionic and organic controls of otolith growth is essential. In the present study, we studied diel variations in the aragonite saturation rate (Sa) of the endolymph and the mRNA expression of 2 major otolith matrix proteins, OMP-1 and otolin-1, in the saccular tissue. A new technique for simultaneously quantifying endolymph Sa and mRNA expression in the saccular tissue from an individual rainbow trout was developed. Endolymph Ca2+ levels, CO2 partial pressure (PCO2) and pH were simultaneously measured using an automatic pH/gas/electrolyte analyzer, and the Sa was calculated. Total RNA was isolated from sacculi of individual fish after the endolymph was obtained. cDNAs were synthesized and used to quantify OMP-1 and otolin-1 mRNA expression levels by real-time PCR. Significant diel variations were observed in endolymph pH and PCO2 levels in an antiphasic manner. Endolymph Sa did not exhibit significant diel variations and was maintained at a value of more than 2.0, indicating that the endolymph was kept supersaturated with respect to aragonite during the day-night cycle. Expression of otolin-1 mRNA had apparent diel variations with high levels at night, whereas that of OMP-1 mRNA was almost constant. These data strongly suggest an organic control of daily increment formation in the otolith. The most probable candidate protein for daily increment formation is otolin-1. KEY WORDS: Calcification · mRNA expression · Endolymph · Daily increment · Aragonite · Otolith · Rainbow trout Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 294. Online publication date: June 09, 2005 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2005 Inter-Research.

Physiological response of wild rainbow trout to angling: impact of angling duration, fish size, body condition, and temperature

This study evaluated the immediate physiological response of wild rainbow trout to catch-and-release angling in the Alagnak River, southwest Alaska. Information was recorded on individual rainbow trout (n = 415) captured by angling including landing time and the time required to remove hooks (angling duration), the time to anesthetize fish in clove oil and withdraw blood, fish length and weight, and water temperature at capture locations. Plasma cortisol, glucose, ions (sodium, potassium, chloride), and lactate were analyzed to determine the effects of angling duration, fish size, body condition, and temperature. Levels of plasma ions did not change significantly during the observed physiological response and levels of plasma glucose were sometimes influenced by length (2000, 2001), body condition (2001), or temperature (2001). Levels of plasma cortisol and lactate in extended capture fish (angling duration greater than 2 min) were significantly higher than levels in rapid capture fish (angling duration less than 2 min). Rapid capture fish were significantly smaller than extended capture fish, reflecting that fish size influenced landing and handling times. Fish size was related to cortisol and lactate in 2002, which corresponded to the year when larger fish were captured and there were longer landing times. Body condition (i.e., weight/length regression residuals index), was significantly related to lactate in 2000 and 2001. Water temperatures were higher in 2001 (mean temperature ± S.E., 13 ± 2 °C) than in 2002 (10 ± 2 °C), and fish captured in 2001 had significantly higher cortisol and lactate concentrations than fish captured in 2002. The pattern of increase in plasma cortisol and lactate was due to the amount of time fish were angled, and the upper limit of the response was due to water temperature. The results of this study indicate the importance of minimizing the duration of angling in order to reduce the sublethal physiological disturbances in wild fish subjected to catch-and-release angling, particularly during warmer water temperatures. It is also important to note that factors such as fish size may influence both the duration of angling and subsequent physiological response.