Investigating Fear in Rainbow Trout (Oncorhynchus mykiss) Using the Conditioned-Suppression Paradigm

Trout learned the operant task of pendulum-pressing for a food-reward in a mean of 4.3 sessions lasting 1 hr. In a separate phase, fish also learned—through classical conditioning—to associate a neutral light cue with an aversive stimulus. When again allowed to pendulum-press for food, after aversive classical conditioning, there was a drop in the rate of responding. The mean rate dropped from 3.6–2.9 responses per min. Most important, when the light-stimulus was superimposed on a steady bout of pendulum-pressing, trout ceased to press the pendulum and did not resume activity until termination of the light-stimulus (mean number of responses during a 3-min interval immediately prior to light-stimulus = 14.3 vs. during 3-min light-stimulus = 0.1). Psychologists have used this decrease in operant responding, or “conditioned emotional response,” as a tool to examine the psychological nature of this type of aversive conditioning. In this study, the fish demonstrated various results under this paradigm similar to those shown by “higher” nonhuman animals, therefore challenging the view of fish as unconscious, nonsentient animals.     

Effects of Desacetyl-alpha-MSH on Lipid Mobilization in the Rainbow Trout, Oncorhynchus mykiss

Effects of melanocyte-stimulating hormone (MSH) and beta-endorphin on lipid mobilization were examined in the rainbow trout (Oncorhynchus mykiss). Plasma levels of fatty acid (FA) were measured after intra-arterial administration of alpha-MSH, desacetyl-alpha-MSH, beta-MSH, or beta-endorphin through a cannula in the dorsal aorta. Desacetyl-alpha-MSH at 1 ng/g body weight resulted in an increase in plasma FA levels 1-3 hr after the injection, whereas the other three peptides showed no significant effect at the same dose. There was no significant change in plasma levels of cortisol after administration of any of the peptides. Lipolytic enzyme activity in the liver was significantly increased in a dose-related manner 1 hr after single intra-peritoneal injection of desacetyl-alpha-MSH. The direct effect of desacetyl-alpha-MSH on lipolysis was examined in liver slices incubated in vitro. Lipase activity in the liver slice was stimulated in the medium containing desacetyl-alpha-MSH in a dose-related manner. The results indicate that desacetyl-alpha-MSH is a potent stimulator of lipid mobilization in the rainbow trout.     

Consistency in Context-specific Measures of Shyness and Boldness in Rainbow Trout, Oncorhynchus mykiss

Shyness and boldness has been considered a fundamental axis of human behavioural variation. At the extreme ends of this behavioural continuum subjects vary from being bold and assertive to shy and timid. Analogous patterns of individual variation have been noted in a number of species including fish. There has been debate on the nature of this continuum as to whether it depends on context. That is, whether it is domain‐general (as in humans), or context‐specific. The purpose of our study was to test if shyness and boldness depends on context in rainbow trout, Oncorhynchus mykiss and to this end we estimated boldness in five different situations. Our data provide evidence of a shy–bold behavioural syndrome in rainbow trout. Bold trout tended to be bold in four situations when the context was similar (when the context concerned foraging). However, in a different context, exploring a swim flume, the ranking was entirely different. We suggest that shyness and boldness depends on context in rainbow trout.     

Population Structure and Stock Identification of Steelhead Trout (Oncorhynchus mykiss) in British Columbia and the Columbia River Based on Microsatellite Variation

Variation at 13 microsatellite loci was surveyed from ～3 800 steelhead trout, Oncorhynchus mykiss, from 51 populations in British Columbia, Washington, and the Columbia River drainage. Mean F_ST over all 13 loci and 51 populations was 0.066. Regional structuring of populations was apparent, with Thompson River, upper Fraser River, and Columbia River populations forming distinct groups. In the Nass River, winter-run populations were distinct from the summer-run populations. Significant differences in allele frequencies were observed among regional stock groups at all loci. Analysis of variance components indicated that 5.7% of the total observed variation was distributed among 11 regions, and 2.3% of the variation was among populations within regions. Analysis of simulated mixed-stock samples suggested that variation at the microsatellite loci provided relatively accurate and precise estimates of stock composition for fishery management applications, and this was confirmed by application to actual fishery samples of known origin. Within the Fraser River drainage, individual steelhead trout can be identified to one of the three regions of origin with an accuracy of 94–97%. Microsatellites provided an effective way to determine population structure, and provided reliable estimates of stock composition in mixed-stock fisheries.     

Morphology and Growth of Lateral Line Organs of the Rainbow Trout (Oncorhynchus mykiss)

Abstract The morphology and growth of selected lateral line organs of the rainbow trout (Oncorhynchus mykiss) are described. Canal neuromasts of the infraorbital and operculo–mandibular canal of three different–sized trout have been examined by light microscopy. The number of neuromasts and pores, as well as their distribution, is constant in all sizes of fish. However, the area and estimated number of hair cells (HC) of the examined neuromasts increase with size and with a correlation coefficient (r²) of 0.90 and 0.87, respectively. It was found that area and estimated hair cell number of neuromasts increase 6-fold in fish from 10 to 30 cm total length (TL). Based on calculation of the hair cell number in small and large fish, a net addition of 1 and 6 HC per day is suggested for IO and OM neuromasts, respectively.     

Skeletal Anomaly Monitoring in Rainbow Trout (Oncorhynchus mykiss,Walbaum 1792) Reared under Different Conditions

The incidence of skeletal anomalies could be used as an indicator of the “quality” of rearing conditions as these anomalies are thought to result from the inability of homeostatic mechanisms to compensate for environmentally-induced stress and/or altered genetic factors. Identification of rearing conditions that lower the rate of anomalies can be an important step toward profitable aquaculture as malformed market-size fish have to be discarded, thus reducing fish farmers’ profits. In this study, the occurrence of skeletal anomalies in adult rainbow trout grown under intensive and organic conditions was monitored. As organic aquaculture animal production is in its early stages, organic broodstock is not available in sufficient quantities. Non-organic juveniles could, therefore, be used for on-growing purposes in organic aquaculture production cycle. Thus, the adult fish analysed in this study experienced intensive conditions during juvenile rearing. Significant differences in the pattern of anomalies were detected between organically and intensively-ongrown specimens, although the occurrence of severe, commercially important anomalies, affecting 2–12.5% of individuals, was comparable in the two systems. Thus, organic aquaculture needs to be improved in order to significantly reduce the incidence of severe anomalies in rainbow trout.     

The earliest stages in the development of the circulatory system of the Rainbow Trout Oncorhynchus mykiss

The older literature suggests that the development of the blood vascular system in teleosts differs from that of other vertebrates. The evidence, however, came mostly from studies of salmonid embryos beyond the stages when blood cells had begun to circulate, which overlooked earlier developmental stages. The development of the blood vessels of the rainbow trout are illustrated from the time of the first heartbeat to the stage of eye pigment formation. Unless they can be injected with a dye solution, the earliest vessels to develop remain invisible until blood flow makes them visible. By the time of the first heartbeat stage, the embryo has a dorsal aorta, caudal artery and vein, a few transverse vessels, and even the beginning of a vitelline network. One feature peculiar to teleosts is the development of the intermediate cell mass, from which the erythrocytes and a temporary capillary network are formed rather than from the yolk sac. Development of the early posterior cardinal and the subintestinal vein occurs much as in other vertebrates. Previous investigators missed these earliest phases of development because of the difficulty of making them visible. Early formation and transformation of the vascular system of the rainbow trout generally conforms to that seen in vertebrates, except as modified by the temporary presence of the intermediate cell mass and the specialized teleostean yolk mass. With the reduction of the intermediate cell mass, the primary circulatory system for yolk utilization is transformed into a secondary one for respiratory and metabolic functions, as happens usually among vertebrates. J. Morphol. 233:215–236, 1997. © 1997 Wiley-Liss, Inc.     

Effect of Encapsulated Lactobacillus bulgaricus on Innate Immune System and Hematological Parameters in Rainbow Trout (Oncorhynchus mykiss), Post-Administration of Pb

Probiotics and Antimicrobial Proteins - The present study was conducted to investigate the effects of probiotic and encapsulated Lactobacillus bulgaricus on hematological and immunological factors...     

Aquacultured Rainbow Trout (Oncorhynchus mykiss) Possess a Large Core Intestinal Microbiota That Is Resistant to Variation in Diet and Rearing Density

As global aquaculture fish production continues to expand, an improved understanding of how environmental factors interact in fish health and production is needed. Significant advances have been made toward economical alternatives to costly fishmeal-based diets, such as grain-based formulations, and toward defining the effect of rearing density on fish health and production. Little research, however, has examined the effects of fishmeal- and grain-based diets in combination with alterations in rearing density. Moreover, it is unknown whether interactions between rearing density and diet impact the composition of the fish intestinal microbiota, which might in turn impact fish health and production. We fed aquacultured adult rainbow trout (Oncorhynchus mykiss) fishmeal- or grain-based diets, reared them under high- or low-density conditions for 10 months in a single aquaculture facility, and evaluated individual fish growth, production, fin indices, and intestinal microbiota composition using 16S rRNA gene sequencing. We found that the intestinal microbiotas were dominated by a shared core microbiota consisting of 52 bacterial lineages observed across all individuals, diets, and rearing densities. Variations in diet and rearing density resulted in only minor changes in intestinal microbiota composition despite significant effects of these variables on fish growth, performance, fillet quality, and welfare. Significant interactions between diet and rearing density were observed only in evaluations of fin indices and the relative abundance of the bacterial genus Staphylococcus. These results demonstrate that aquacultured rainbow trout can achieve remarkable consistency in intestinal microbiota composition and suggest the possibility of developing novel aquaculture strategies without overtly altering intestinal microbiota composition.     

Stable Expression of a Foreign Gene, Delivered by Gene Gun, in the Muscle of Rainbow Trout Oncorhynchus mykiss

We report the efficient delivery of a foreign gene into muscle of rainbow trout Oncorhynchus mykiss with a gene gun. The foreign gene was a reporter gene, chloramphenicol acetyltransferase (CAT). Two CAT-containing plasmids were used: pCMV-CAT, which contains cytomegalovirus immediate early promoter, and pSV2-CAT, which contains the simian virus 40 early promoter. All plasmids were introduced by particle bombardment using a gene gun. During the 90-day sampling period following bombardment, CAT was strongly and stably expressed in the muscle of all the fish bombarded with pCMV-CAT and pSV2-CAT. No CAT expression was detected in the blood samples until 90 days after introduction, when it was found in only one fish from the pCMV-CAT group and one from the pSV2-CAT group. The stable and long-term expression of plasmid DNA in muscle makes muscle an attractive target tissue for the introduction of viral DNA for the purpose of DNA vaccination. Received June 5, 1999; accepted November 2, 1999.     

Topographical Mapping of the Rainbow Trout (Oncorhynchus mykiss) Microbiome Reveals a Diverse Bacterial Community with Antifungal Properties in the Skin

The mucosal surfaces of wild and farmed aquatic vertebrates face the threat of many aquatic pathogens, including fungi. These surfaces are colonized by diverse symbiotic bacterial communities that may contribute to fight infection. Whereas the gut microbiome of teleosts has been extensively studied using pyrosequencing, this tool has rarely been employed to study the compositions of the bacterial communities present on other teleost mucosal surfaces. Here we provide a topographical map of the mucosal microbiome of an aquatic vertebrate, the rainbow trout (Oncorhynchus mykiss). Using 16S rRNA pyrosequencing, we revealed novel bacterial diversity at each of the five body sites sampled and showed that body site is a strong predictor of community composition. The skin exhibited the highest diversity, followed by the olfactory organ, gills, and gut. Flectobacillus was highly represented within skin and gill communities. Principal coordinate analysis and plots revealed clustering of external sites apart from internal sites. A highly diverse community was present within the epithelium, as demonstrated by confocal microscopy and pyrosequencing. Using in vitro assays, we demonstrated that two Arthrobacter sp. skin isolates, a Psychrobacter sp. strain, and a combined skin aerobic bacterial sample inhibit the growth of Saprolegnia australis and Mucor hiemalis, two important aquatic fungal pathogens. These results underscore the importance of symbiotic bacterial communities of fish and their potential role for the control of aquatic fungal diseases.     

Effects of Simultaneous vs. Sequential Settlement on the Territorial Behaviour of Juvenile Rainbow Trout (Oncorhynchus mykiss)

The aggression hypothesis predicts that territories will be smaller and more numerous when individuals arrive simultaneously rather than sequentially, because of the prior residency effect, whereas the attraction hypothesis predicts the opposite. In this study, we test the predictions of these contrasting hypotheses by releasing 12 juvenile rainbow trout (Oncorhynchus mykiss) either simultaneously, all on 1 d, or sequentially, two per day for 6 d, in artificial streams. After the fish spent an average of 1 wk in the streams, we quantified the number of territories established, territory size, aggression rate and growth rate. There was evidence of a prior residency effect – early arrivers were more aggressive and grew faster than late arrivers – but this effect did not alter the number or size of territories established. We concluded that the temporal patterns of arrival have no strong effects on the territorial dynamics of juvenile rainbow trout.     

Dendroentomological and forest management implications in the Interior Douglas-fir zone of British Columbia, Canada

Douglas-fir (Pseudotsuga menziesii var. glauca Mirb. Franco) forests in the Interior of British Columbia, Canada, show periodic defoliation due to western spruce budworm (WSB) (Choristoneura occidentalis Freeman) outbreaks. Tree defoliation causes a reduction in radial growth and is therefore visible in tree rings. In this paper, we identify WSB defoliation history, and critically examine the potential for using dendrochronological analysis by comparing tree-ring estimates with insect surveys. WSB defoliation history was investigated using cores from Douglas-fir growing in the Lac du Bois region of the Kamloops Forest District. Years with an abrupt decrease in radial growth were considered as negative pointer years that potentially reflected WSB outbreaks. The comparison with ponderosa pine (Pinus ponderosa Dougl., ex P. & C. Laws.) (a non-host species) permitted differentiation between growth reductions in Douglas-fir due to climatic effects and those due to defoliation by WSB. The dendrochronological data were matched with information reporting visible damage in Forest Insect Disease Survey (FIDS) and British Columbia Ministry of Forest records. Our objective-based method using ring-width measurements from host and non-host chronologies was compared with qualitative techniques based on the software program OUTBREAK. We were able to distinguish seven distinct outbreak events in 300 years of record.     

Evidence for the Presence of Glucosensor Mechanisms Not Dependent on Glucokinase in Hypothalamus and Hindbrain of Rainbow Trout (Oncorhynchus mykiss)

We hypothesize that glucosensor mechanisms other than that mediated by glucokinase (GK) operate in hypothalamus and hindbrain of the carnivorous fish species rainbow trout and stress affected them. Therefore, we evaluated in these areas changes in parameters which could be related to putative glucosensor mechanisms based on liver X receptor (LXR), mitochondrial activity, sweet taste receptor, and sodium/glucose co-transporter 1 (SGLT-1) 6h after intraperitoneal injection of 5 mL.Kg^-1 of saline solution alone (normoglycaemic treatment) or containing insulin (hypoglycaemic treatment, 4 mg bovine insulin.Kg^-1 body mass), or D-glucose (hyperglycaemic treatment, 500 mg.Kg^-1 body mass). Half of tanks were kept at a 10 Kg fish mass.m^-3 and denoted as fish under normal stocking density (NSD) whereas the remaining tanks were kept at a stressful high stocking density (70 kg fish mass.m^-3) denoted as HSD. The results obtained in non-stressed rainbow trout provide evidence, for the first time in fish, that manipulation of glucose levels induce changes in parameters which could be related to putative glucosensor systems based on LXR, mitochondrial activity and sweet taste receptor in hypothalamus, and a system based on SGLT-1 in hindbrain. Stress altered the response of parameters related to these systems to changes in glycaemia.     

Dendroentomological and forest management implications in the Interior Douglas-fir zone of British Columbia,Canada

Douglas-fir (Pseudotsuga menziesii var. glauca Mirb. Franco) forests in the Interior of British Columbia, Canada, show periodic defoliation due to western spruce budworm (WSB) (Choristoneura occidentalis Freeman) outbreaks. Tree defoliation causes a reduction in radial growth and is therefore visible in tree rings. In this paper, we identify WSB defoliation history, and critically examine the potential for using dendrochronological analysis by comparing tree-ring estimates with insect surveys. WSB defoliation history was investigated using cores from Douglas-fir growing in the Lac du Bois region of the Kamloops Forest District. Years with an abrupt decrease in radial growth were considered as negative pointer years that potentially reflected WSB outbreaks. The comparison with ponderosa pine (Pinus ponderosa Dougl., ex P. & C. Laws.) (a non-host species) permitted differentiation between growth reductions in Douglas-fir due to climatic effects and those due to defoliation by WSB. The dendrochronological data were matched with information reporting visible damage in Forest Insect Disease Survey (FIDS) and British Columbia Ministry of Forest records. Our objective-based method using ring-width measurements from host and non-host chronologies was compared with qualitative techniques based on the software program OUTBREAK. We were able to distinguish seven distinct outbreak events in 300 years of record.     

Ethological Features of the Ontogenesis of the Locomotor System in Bony Fish (by the Example of the Rainbow Trout Oncorhynchus mykiss Walbaum)

Biology Bulletin - The features of the structural adaptive changes in the somatic muscles of rainbow trout are presented at various stages of early post-hatching ontogenesis. The development of the...