Interaction between hatchery and wild Pacific salmon in the Far East of Russia: A review

We review studies of interactions between hatchery and wild Pacific salmon in the Russian Far East. This includes the role of hatchery practices that result in premature migration to the sea and increased mortality, and data on feeding and territorial competition between juveniles of hatchery and wild origin. In the course of downstream migration many juvenile hatchery salmon are eliminated by wild salmon predation. During the marine period, Japanese hatchery chum salmon (Oncorhynchus keta) distribution overlaps the distribution of Russian wild salmon. Consequently, replacement of wild populations by hatchery fishes, as a result of abundant juvenile hatchery releases combined with extensive poaching in spawning grounds, is apparent in some Russian rivers. Interactions between the populations occur in all habitats. The importance of conservation of wild salmon populations requires a more detailed study of the consequences of interactions between natural and artificially reared fishes.     

Disruption of seasonality in growth hormone-transgenic coho salmon (Oncorhynchus kisutch) and the role of cholecystokinin in seasonal feeding behavior

Seasonal variation in daily food intake is a well-documented phenomenon in many organisms including wild-type coho salmon where the appetite is noticeably reduced during periods of decreased day length and low water temperature. This reduction may in part be explained by altered production of cholecystokinin (CCK) and growth hormone (GH). CCK is a hormone produced in the brain and gut that mediates a feeling of satiety and thus has an inhibitory effect on food intake and foraging behaviour. Growth hormone (GH) enhances feeding behaviour and consequently growth, but its production is reduced during winter. The objectives of this study were: first, to compare the seasonal feeding behaviour of wild and GH-transgenic coho salmon; second, to determine the behavioural effect of blocking the action of CCK (by using devazepide) on the seasonal food intake; and third, to measure CCK expression in brain and gut tissues between the two genotypes across seasons. We found that, in contrast to wild salmon, food intake in transgenic salmon was not reduced during winter indicating that seasonal control of appetite regulation has been disrupted by constitutive production of GH in transgenic animals. Blocking of CCK increased food intake in both genotypes in all seasons. The increase was stronger in wild genotypes than transgenic fish; however blocking CCK in wild-type fish in winter did not elevate appetites to levels observed in the summer. The response to devazepide was generally faster in transgenic than in wild salmon with more rapid effects observed during summer than during winter, possibly due to a higher temperature in summer. Overall, a seasonal effect on CCK mRNA levels was observed in telencephalon with levels during winter being higher compared to the summer in wild fish, but with no seasonal effect in transgenic fish. No differences in seasonal CCK expression were found in hypothalamus. Higher levels of CCK were detected in the gut of both genotypes in winter compared to summer. Thus, CCK appears to mediate food intake among seasons in both wild-type and GH-transgenic salmon, and an altered CCK regulation may be responsible at least in part for the seasonal regulation of food intake.     

Influences of illumination intensity on the nearest neighbour distance in coho salmon Oncorhynchus kisutch

Effects of illumination intensity on the nearest neighbour distance (NND) of coho salmon in an experimental aquarium were studied under illumination intensities ranging from 0 to 4000 Ix. The NNDs in sighted (intact) fish were divided into three groups according to the illumination intensities; the largest [1.15 times fork length (f.l.)] at 0 1x, the medium (0.78 to 0.84 f.l.) at 0.01 to 0.4 1x, and the least (0.60 to 0.66 f.l.) at 4–4000 1x. The fact that NNDs under 4 1x or higher illumination conditions were significantly smaller than those under 0.01 to 0.4 1x conditions suggests a change from photopic to scotopic vision. Blinded fish exhibited constant NNDs irrespective of illumination intensity and the value was similar to that of sighted fish under the 0 1x condition. The NNDs of blinded fish and sighted fish exposed to 0 1x were larger than the simulated NND calculated by hypothesizing that fish distribute randomly in the experimental aquarium. These results indicate that NND in a coho school is maintained primarily by vision, however, the NND is not determined by vision alone but by integrated senses.     

Characterization of sex chromosomes in rainbow trout and coho salmon using fluorescence in situ hybridization (FISH)

With the aim of characterizing the sex chromosomes of rainbow trout (Oncorhynchus mykiss) and to identify the sex chromosomes of coho salmon (O. kisutch), we used molecular markers OmyP9, 5S rDNA, and a growth hormone gene fragment (GH2), as FISH probes. Metaphase chromosomes were obtained from lymphocyte cultures from farm specimens of rainbow trout and coho salmon. Rainbow trout sex marker OmyP9 hybridizes on the sex chromosomes of rainbow trout, while in coho salmon, fluorescent signals were localized in the medial region of the long arm of one subtelocentric chromosome pair. This hybridization pattern together with the hybridization of a GH2 intron probe on a chromosome pair having the same morphology, suggests that a subtelocentric pair could be the sex chromosomes in this species. We confirm that in rainbow trout, one of the two loci for 5S rDNA genes is on the X chromosome. In males of this species that lack a heteromorphic sex pair (XX males), the 5S rDNA probe hybridized to both subtelocentrics This finding is discussed in relation to the hypothesis of intraspecific polymorphism of sex chromosomes in rainbow trout.     

Comparison of genetically based antipredator behaviour in hatchery and wild coho fry from a coastal Oregon river: interpreting a negative result

Coho salmon Oncorhynchus kisutch fry derived from wild and hatchery stocks demonstrated no difference in responsiveness to an overhead fright stimulus in laboratory experiments.     

Spatial and temporal distribution of coho salmon carcasses in a stream in the Pacific Northwest,USA

During two consecutive spawning seasons, the movement and distribution of naturally occurring coho salmon (Oncorhynchus kisutch) carcasses were monitored, and the effectiveness of large woody debris (LWD) in retaining carcasses in a stream was evaluated. In both seasons studied, the proportion of carcasses trapped by LWD increased as the season progressed. Densities of salmon carcasses were higher in slow waters such as stream edges and backwaters throughout the study periods. The average distance drifted by carcasses was 19.5m in the first season and 32.1 m in the second season. These results support the notion that LWD contributes to retention of salmon carcasses and enhances availability of salmon-derived nutrients for organisms near salmon spawning grounds.     

Prior residence, body size and the dynamics of territorial disputes between male freshwater angelfish

Territorial interactions between pairs of size mismatched, sexually mature male angelfish Pterophyllum scalare were investigated in three different conditions: with the larger fish resident (the large resident condition), with the smaller fish resident (the small resident condition) and in a neutral territory (the neutral condition). In the two resident conditions, approximately half of the intruders had previously held territories and half had not. In all categories of fight, one fish showed submissive postures and lost the fight; eventual losers performed both attack and threat at a lower rate than eventual winners. Attack rate declined as the encounter progressed, while rate of performance of threat postures increased. In fights on neutral territories, the larger fish won all fights. In all fights with a resident-intruder asymmetry, the resident fish won the encounter, regardless of relative size. In eventual winners but not in eventual losers, levels of attack were lowest in the neutral encounters. In the small resident condition, levels of attack (corrected for activity of the resident) were lower in intruders that had previously held a breeding territory. Relative size influenced behaviour shown during fights, in that overall intensity was correlated negatively with size differential in all conditions. Thus although prior residence is the primary determinant of the outcome of territorial encounters in this species, both relative body size and prior possession of territory also influence the nature of the interaction.     

Growth hormone transgenesis does not influence territorial dominance or growth and survival of first-feeding Atlantic salmon Salmo salar in food-limited stream microcosms

This study explored the relative competitive ability and performance of first-feeding growth hormone (GH) transgenic and non-transgenic Atlantic salmon Salmo salar fry under low food conditions. Pair-wise dominance trials indicated a strong competitive advantage for residents of a contested foraging territory. Transgenic and non-transgenic individuals, however, were equally likely to be dominant. Similarly, in stream environments with limited food, the transgene did not influence the growth in mass or survival at high or low fry densities. Fry in low-density treatments, however, performed better than fry in high-density treatments. These results indicate that, under the environment examined, the growth performance of GH-transgenic and non-transgenic S. salar may be similar during first feeding, an intense period of selection in their life history. Similarities in competitive ability and growth performance with wild-type fish suggest that the capacity of transgenic S. salar to establish in natural streams may not be inhibited during early life history.     

Patterns of intra- and inter-population genetic diversity in Alaskan coho salmon: Implications for conservation

Little is known about the genetic diversityof coho salmon in Alaska, although this arearepresents half of the species' North Americanrange. In this study, nine microsatellite lociwere used to genotype 32 putative coho salmonpopulations from seven regions of Alaska. Theprimary objectives were to estimate andevaluate the degree and spatial distribution ofneutral genetic diversity within and amongpopulations of Alaskan coho salmon. Geneticanalysis yielded four results that provideinsight into forces influencing geneticdiversity in Alaskan coho salmon and haveimportant conservation implications: 1)significant population differentiation wasfound within each region; 2) the degree ofdifferentiation (F _ST = 0.099) amongpopulations was as large or larger than thatreported for other Pacific salmon species inAlaska; 3) phenetic clustering of populationsshowed weak geographic concordance; 4) stronggenetic isolation by distance was only apparentat the finest geographic scale (within adrainage). These results suggest that cohosalmon populations are small relative topopulations of other Pacific salmon, and thegenetic diversity within and among coho salmonpopulations is influenced primarily by geneticdrift, and not gene flow. Resource managementand conservation actions affecting coho salmonin Alaska must recognize that the populationsare generally small, isolated, and probablyexhibit local adaptation to different spawningand freshwater rearing habitats. These factorsjustify managing and conserving Alaskan cohosalmon at a fine geographic scale.     

Genetic assessment of the effects of streamscape succession on coho salmon Oncorhynchus kisutch colonization in recently deglaciated streams

Measures of genetic diversity within and among populations and historical geomorphological data on stream landscapes were used in model simulations based on approximate Bayesian computation (ABC) to examine hypotheses of the relative importance of stream features (geomorphology and age) associated with colonization events and gene flow for coho salmon Oncorhynchus kisutch breeding in recently deglaciated streams (50–240 years b.p .) in Glacier Bay National Park (GBNP), Alaska. Population estimates of genetic diversity including heterozygosity and allelic richness declined significantly and monotonically from the oldest and largest to youngest and smallest GBNP streams. Interpopulation variance in allele frequency increased with increasing distance between streams (r = 0·435, P < 0·01) and was inversely related to stream age (r = –0·281, P < 0·01). The most supported model of colonization involved ongoing or recent (<10 generations before sampling) colonization originating from large populations outside Glacier Bay proper into all other GBNP streams sampled. Results here show that sustained gene flow from large source populations is important to recently established O. kisutch metapopulations. Studies that document how genetic and demographic characteristics of newly founded populations vary associated with successional changes in stream habitat are of particular importance to and have significant implications for, restoration of declining or repatriation of extirpated populations in other regions of the species' native range.     

Effects of early experience on the reproductive performance of Atlantic salmon

To examine the link between early experience and subsequentreproductive performance, we experimentally manipulated theearly experience of Atlantic salmon (Salmo salar). Salmon ofa common genetic background were reared as juveniles eithernaturally in the river or artificially in a hatchery (sea ranched),depriving them of river experience, and then allowed to growto maturity naturally in the ocean. At maturity, the competitiveand reproductive abilities of these fish were compared in fourexperiments quantifying reproductive success. Although levelsof aggressive behavior were similar, the experience-deprived,sea-ranched males were involved in more prolonged aggressiveencounters and incurred greater wounding and mortality thanwild males. Furthermore, sea-ranched males were less able tomonopolize spawnings and as a result obtained 51% the reproductivesuccess of wild males across the experiments. This reproductiveinferiority varied directly with the male density and bias inthe sex ratio, reflecting the intensity of male breeding competition.A lower intensity of female than male competition was likelyresponsible for the lack of differences in breeding performancebetween sea-ranched and wild females. Sea-ranched females, however,produced smaller eggs than wild females, apparently in responseto their higher juvenile growth rate. Differences in migratorybehavior were also apparent, as sea-ranched males and femalesascended the River Imsa later than wild fish. Our results indicatethat early experience has implications for subsequent adultreproductive performance, affecting the development of specializedskills and traits important not only for early life, but alsolater life.     

Discovery and characterization of single nucleotide polymorphisms in coho salmon,Oncorhynchus kisutch

Molecular population genetic analyses have become an integral part of ecological investigation and population monitoring for conservation and management. Microsatellites have been the molecular marker of choice for such applications over the last several decades, but single nucleotide polymorphism (SNP) markers are rapidly expanding beyond model organisms. Coho salmon (Oncorhynchus kisutch) is native to the north Pacific Ocean and its tributaries, where it is the focus of intensive fishery and conservation activities. As it is an anadromous species, coho salmon typically migrate across multiple jurisdictional boundaries, complicating management and requiring shared data collection methods. Here, we describe the discovery and validation of a suite of novel SNPs and associated genotyping assays which can be used in the genetic analyses of this species. These assays include 91 that are polymorphic in the species and one that discriminates it from a sister species, Chinook salmon. We demonstrate the utility of these SNPs for population assignment and phylogeographic analyses, and map them against the draft trout genome. The markers constitute a large majority of all SNP markers described for coho salmon and will enable both population‐ and pedigree‐based analyses across the southern part of the species native range.     

Variation in migration pattern,broodstock origin,and family productivity of coho salmon hatchery populations in British Columbia,Canada, derived from parentage‐based tagging

In salmonid parentage‐based tagging (PBT) applications, entire hatchery broodstocks are genotyped, and subsequently, progeny can be nonlethally sampled and assigned back to their parents using parentage analysis, thus identifying their hatchery of origin and brood year (i.e., age). Inter‐ and intrapopulation variability in migration patterns, life history traits, and fishery contributions can be determined from PBT analysis of samples derived from both fisheries and escapements (portion of a salmon population that does not get caught in fisheries and returns to its natal river to spawn). In the current study of southern British Columbia coho salmon (Oncorhynchus kisutch) populations, PBT analysis provided novel information on intrapopulation heterogeneity among males in the total number of progeny identified in fisheries and escapements, the proportion of progeny sampled from fisheries versus escapement, the proportion of two‐year‐old progeny (jacks) produced, and the within‐season return time of progeny. Fishery recoveries of coho salmon revealed heterogeneity in migration patterns among and within populations, with recoveries from north and central coast fisheries distinguishing “northern migrating” from “resident” populations. In northern migrating populations, the mean distance between fishery captures of sibs (brothers and sisters) was significantly less than the mean distance between nonsibs, indicating the possible presence of intrapopulation genetic heterogeneity for migration pattern. Variation among populations in productivity and within populations in fish catchability indicated that population selection and broodstock management can be implemented to optimize harvest benefits from hatcheries. Application of PBT provided valuable information for assessment and management of hatchery‐origin coho salmon in British Columbia.     

Environmental enrichment and prior experience of live prey improve foraging behaviour in hatchery‐reared Atlantic salmon

Atlantic salmon salmo salar L. parr were reared for 3 months under standard hatchery conditions or in a structurally enriched tank (containing plants, rocks and novel objects). Half of each of these fish had prior exposure to live prey in the form of live bloodworm while the other half were fed hatchery‐pellets. After 12 days all fish were tested on a novel live prey item (brine shrimp). A significant interaction between the two factors (prior exposure to live prey and rearing condition) revealed that foraging performance was only enhanced in fish that had been reared in a complex environment and exposed to live prey. It appears that the ability to generalize from one live prey type to another is only enhanced in fish that had been reared in an enriched environment. The findings support the assertion that the provision of enriched environments in combination with exposure to live prey prior to release may significantly improve the post‐release survival rates of hatchery‐reared fishes. As both the environmental enrichment and the prior foraging experience procedures were comparatively simple, the provision of such pre‐release experiences are likely to prove cost effective to hatcheries.     

The blood vasculature of the gastrointestinal tract in chinook, Oncorhynchus tshawytscha (Walbaum), and coho, O. kisutch (Walbaum), salmon

The venous and arterial vasculature of the chinook and coho salmon gastrointestinal tract were examined using corrosion casts and India ink injection techniques. Observations derived from 28 individuals of various sizes and of both sexes were used to construct simplified venous and arterial plans. Examination of the blood vasculature revealed the presence of a variety of anastomoses hitherto undescribed in teleosts.     

Interaction of growth hormone overexpression and nutritional status on pituitary gland clock gene expression in coho salmon,Oncorhynchus kisutch

Clock genes are involved in generating a circadian rhythm that is integrated with the metabolic state of an organism and information from the environment. Growth hormone (GH) transgenic coho salmon, Oncorhynchus kisutch, show a large increase in growth rate, but also attenuated seasonal growth modulations, modified timing of physiological transformations (e.g. smoltification) and disruptions in pituitary gene expression compared with wild-type salmon. In several fishes, circadian rhythm gene expression has been found to oscillate in the suprachiasmatic nucleus of the hypothalamus, as well as in multiple peripheral tissues, but this control system has not been examined in the pituitary gland nor has the effect of transgenic growth modification been examined. Thus, the daily expression of 10 core clock genes has been examined in pituitary glands of GH transgenic (T) and wild-type coho salmon (NT) entrained on a regular photocycle (12L: 12D) and provided either with scheduled feeding or had food withheld for 60?h. Most clock genes in both genotypes showed oscillating patterns of mRNA levels with light and dark cycles. However, T showed different amplitudes and patterns of expression compared with wild salmon, both in fed and starved conditions. The results from this study indicate that constitutive expression of GH is associated with changes in clock gene regulation, which may play a role in the disrupted behavioural and physiological phenotypes observed in growth-modified transgenic strains.     

Growth depensation and aggression in laboratory reared coho salmon: the effect of food distribution and ration size

Groups of recently emerged coho salmon fry Oncorhynchus kisutch were reared for 3 months on food that appeared either asynchronously at a single location (localized) or synchronously and spatially dispersed (dispersed). Groups were further subdivided into those receiving low (1%) or high (3% body weight per day) rations, with five replicate groups for each treatment combination. At low ration there was greater growth depensation, i.e. growth variation, in groups receiving localized as compared to dispersed food. At high ration there was no difference. There was no effect of food distribution upon mean fish weight, but groups receiving high rations had greater mean fish weights than groups receiving low rations. There was no overall difference in the frequency of chasing between any of the treatment combinations. However, in localized food groups, dominants defended positions close to where food entered the tank, giving them greater access than subordinates. In dispersed food groups, while dominants also defended particular areas, this did not result in greater access to food. These results demonstrate that although feeding methodology may not directly influence the frequency of aggressive interactions, feeding methods which facilitate food monopolization by dominants can accelerate the growth of these individuals at the expense of subordinates. In aquacultural applications where greater size is desirable, or otherwise selected for, this may result in the unintentional selection for increased aggressiveness.     

Patterns on a parr: Drivers of long‐term salmon parr length in U.K. and French rivers depend on geographical scale

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