Salmon Fry Research Articles

Diet of the Torrent Sculpin, Cottus rhotheus, in the Cedar River, Washington: Effect of Season, Habitat Type, and Predator Size with Emphasis on Piscivory

Abstract Torrent Sculpin (Cottus rhotheus) can play an important role in riverine ecosystems in the Pacific Northwest, but factors that influence their feeding ecology are not well understood. To better understand how environmental conditions may influence the diet of Torrent Sculpin in the Cedar River, Washington, we collected diet information from fish across seasons and habitats. Numerically, aquatic insects were usually the dominant prey type for each size class in each sampling effort. Overall, Torrent Sculpin prey on a wide variety of aquatic invertebrates but can also take advantage of other prey types, such as fry of Sockeye Salmon (Oncorhynchus nerka), juvenile Chinook Salmon (O. tshawytscha), and eggs of Largescale Suckers (Catostomus macrocheilus), when these prey become abundant. In February and March, predation on Sockeye Salmon fry was substantially higher in large, deep pools (>2.5-m depth) than in either riffles or slow-water secondary habitats. Besides fry of Sockeye Salmon, the only salm...

Trophic Feasibility of Reintroducing Anadromous Salmonids in Three Reservoirs on the North Fork Lewis River, Washington: Prey Supply and Consumption Demand of Resident Fishes

AbstractThe reintroduction of anadromous salmonids in reservoirs is being proposed with increasing frequency, requiring baseline studies to evaluate feasibility and estimate the capacity of reservoir food webs to support reintroduced populations. Using three reservoirs on the north fork Lewis River as a case study, we demonstrate a method to determine juvenile salmonid smolt rearing capacities for lakes and reservoirs. To determine if the Lewis River reservoirs can support reintroduced populations of juvenile stream‐type Chinook Salmon Oncorhynchus tshawytscha, we evaluated the monthly production of daphnia Daphnia spp. (the primary zooplankton consumed by resident salmonids in the system) and used bioenergetics to model the consumption demand of resident fishes in each reservoir. To estimate the surplus of Daphnia prey available for reintroduced salmonids, we assumed a maximum sustainable exploitation rate and accounted for the consumption demand of resident fishes. The number of smolts that could have been supported was estimated by dividing any surplus Daphnia production by the simulated consumption demand of an individual Chinook Salmon fry rearing in the reservoir to successful smolt size. In all three reservoirs, densities of Daphnia were highest in the epilimnion, but warm epilimnetic temperatures and the vertical distribution of planktivores suggested that access to abundant epilimnetic prey was limited. By comparing accessible prey supply and demand on a monthly basis, we were able to identify potential prey supply bottlenecks that could limit smolt production and growth. These results demonstrate that a bioenergetics approach can be a valuable method of examining constraints on lake and reservoir rearing capacity, such as thermal structure and temporal food supply. This method enables numerical estimation of rearing capacity, which is a useful metric for managers evaluating the feasibility of reintroducing Pacific salmon Oncorhynchus spp. in lentic systems.Received April 24, 2016; accepted July 28, 2016 Published online October 11, 2016

Effects of experimentally elevated egg cortisol on offspring traits in two species of wild Pacific salmon

In fishes, elevated levels of cortisol in eggs can have carry-over effects on phenotypic and performance traits early in life. How responses to elevations in egg cortisol differ among species remains poorly understood. Using wild populations of chum salmon (Oncorhynchus keta) and sockeye salmon (O. nerka), we investigated whether experimentally-elevated concentrations of cortisol in newly fertilized eggs had effects on offspring morphology and/or burst swimming capacity. Immediately following fertilization, eggs were incubated for 2 h with water dosed with 0 ng/mL or 1000 ng/mL of cortisol. Embryos were reared to the fry life stage (complete yolk sac absorption). Morphology and burst swimming performance of fry were then assessed. Sockeye salmon fry reared from cortisol-treated eggs were smaller overall (i.e., smaller body, fins and eyes) compared to conspecifics reared from untreated eggs. In contrast, the morphology of chum salmon fry was not affected by the experimental elevation of egg cortisol. In both species, burst swimming duration was unaffected by egg cortisol treatment, while offspring reared from the cortisol-treated eggs initiated fewer bouts of burst swimming. Our results demonstrate that closely-related species can respond differently to elevations in egg cortisol, and not all offspring traits may be affected by these elevations in cortisol. Further efforts to establish links among offspring quality, maternal stress, and egg composition need to consider the potential for divergent responses among species and examine multiple measures of phenotype and performance throughout development.

Size-related habitat use in juvenile Atlantic salmon: the importance of intercohort competition

In stream-living salmonids, an underlying mechanism for the critical period after emergence has generally been assumed to be size-dependent swimming capacity constraining fry (age-0) to low-velocity habitats with reduced food availability and intense competition. A further plausible mechanism is that intercohort habitat exclusion confines fry to marginal habitats. This possibility was tested using a seminatural stream with 16 test arenas, each comprising one high-velocity, deep habitat and one low-velocity, shallow habitat. We observed groups of newly emerged Atlantic salmon (Salmo salar) fry, either alone or in sympatry with one or two age-1 salmon. Salmon fry used high-velocity areas (42.2 ± 0.4 cm·s−1) most extensively in the absence of intercohort competition, where they obtained more food than in low-velocity areas (3.3 ± 0.3 cm·s−1), even though foraging efficiency was lower (though not significantly so). In sympatry with older cohorts, fry increased their use of the low-velocity habitat, with a reduced foraging activity, suggesting that strong older cohorts in natural populations may have the potential to influence the strength of the recruiting cohort by negative density dependence due to interference competition for habitat.

Anadromous Salmonids in the Delta: New Science 2006-2016

As juvenile salmon enter the Sacramento–SanJoaquin River Delta (“the Delta”) they disperse among its complex channel network where they are subject to channel-specific processes that affect their rate of migration, vulnerability to predation, feeding success, growth rates, and ultimately, survival. In the decades before 2006, tools available to quantify growth, dispersal, and survival of juvenile salmon in this complex channel network were limited.Fortunately, thanks to technological advances such as acoustic telemetry and chemical and structural otolith analysis, much has been learned over the past decade about the role of the Delta in the life cycle of juvenile salmon. Here, we review new science between 2006and 2016 that sheds light on how different life stages and runs of juvenile salmon grow, move, and survive in the complex channel network of the Delta. One of the most important advances during the past decade has been the widespread adoption of acoustic telemetry techniques. Use of telemetry has shed light on how survival varies among alternative migration routes and the proportion of fish that use each migration route. Chemical and structural analysis of otoliths has provided insights about when juveniles left their natal river and provided evidence of extended rearing in the brackish or saltwater regions of the Delta. New advancements in genetics now allow individuals captured by trawls to be assigned to specific runs. Detailed information about movement and survival in the Delta has spurred development of agent-based models of juvenile salmon that are coupled to hydrodynamic models. Although much has been learned, knowledge gaps remain about how very small juvenile salmon (fry and parr) use theDelta. Understanding how all life stages of juvenile salmon grow, rear, and survive in the Delta is critical for devising management strategies that support a diversity of life history strategies.

Assessing the transferability of hydraulic habitat models for juvenile Atlantic salmon

Hydraulic habitat models are logistically and technically challenging and expensive to produce. They are therefore frequently transferred between rivers, often with different environmental conditions, without validation. Although studies have recognised problems with model transfer, few have assessed the consequences for model predictions. This study investigated the local (within sub-catchment) transfer of hydraulic habitat models developed for Atlantic salmon (Salmo salar) fry. Two adjacent reaches were chosen for the study, each containing pool, riffle, glide and run habitats. Detailed topographic surveys were used to develop hydraulic models for the study reaches. Substrate and cover were characterised using transects. Seasonal fish habitat use was characterised by electrofishing. Uniform saturation stocking was employed to ensure standard starting densities across all habitats. Generalised additive models were fitted to fry abundance data. Depth, velocity, dominant substrate and cover were used as predictor variables. The distribution of depth, velocity, dominant substrate and cover differed between the two reaches, but was consistent within reaches across seasons. Substrate exhibited the greatest inter-reach difference. Velocity and depth were the most important individual predictors of fry abundance, with the highest densities observed at moderate velocities (∼0.4ms−1) and low depths (∼0.1m) across all seasons. When models were transferred locally between reaches, those that were adjusted for inter-reach differences in mean fry abundance (i.e. those predicting changes in relative abundance) performed better than those transferred without adjustment. Complex models that included substrate and cover typically explained some of the variation in abundance in the transferred reach but performed less well than models containing hydraulic parameters alone. This potentially reflected inter-reach differences in the distribution of substrate and cover. This study suggests that (1) uniform stocking is useful for examining habitat-abundance relationships free from the influence of patchy egg deposition; (2) habitat models should be developed at sites offering maximum environmental complexity at a local level; (3) scientists and managers should avoid transferring models between locations with different environmental characteristics, especially in the absence of model validation; (4) complex models should be avoided, and those containing hydraulic variables alone should be considered, if predictions of habitat quality are to be made at new sites.

Gene expression comparison of resistant and susceptible Atlantic salmon fry challenged with Infectious Pancreatic Necrosis virus reveals a marked contrast in immune response.

BackgroundInfectious Pancreatic Necrosis (IPN) is a highly contagious birnavirus disease of farmed salmonid fish, which often causes high levels of morbidity and mortality. A large host genetic component to resistance has been previously described for Atlantic salmon (Salmo salar L.), which mediates high mortality rates in some families and zero mortality in others. However, the molecular and immunological basis for this resistance is not yet fully known. This manuscript describes a global comparison of the gene expression profiles of resistant and susceptible Atlantic salmon fry following challenge with the IPN virus.ResultsSalmon fry from two IPNV-resistant and two IPNV-susceptible full sibling families were challenged with the virus and sampled at 1 day, 7 days and 20 days post-challenge. Significant viral titre was observed in both resistant and susceptible fish at all timepoints, although generally at higher levels in susceptible fish. Gene expression profiles combined with gene ontology and pathway analyses demonstrated that while a clear immune response was observed in both resistant and susceptible fish, there were striking differences between the two phenotypes. The susceptible fish showed marked up-regulation of genes related to cytokine activity and inflammatory response that evidently failed to protect against the virus. In contrast, the resistant fish demonstrated a less pronounced immune response including up-regulation of genes relating to the M2 macrophage system.ConclusionsWhile only the susceptible phenotype shows appreciable mortality levels, both resistant and susceptible fish can become infected with IPNV. Susceptible fish are characterized by a much larger, yet ineffective, immune response, largely related to cytokine and inflammatory systems. Resistant fish demonstrate a more moderate, putative macrophage-mediated inflammatory response, which may contribute to their survival.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2600-y) contains supplementary material, which is available to authorized users.

Utilization of acid hydrolysed phosphorous from herring bone by-products in feed for Atlantic salmon (Salmo salar) start-feeding fry

The aim of this study was to test the efficacy of a new marine P ingredient from the bone fraction of herring by-products by evaluating the dietary impacts on growth, mineralization and skeletal development in Atlantic salmon fry. Five experimental diets were produced from a fish meal based diet, only differing in the dietary P source and level; low P control (5.5g/kg soluble P), intermediate P (6.5g/kg soluble P) and high P (8.0g/kg soluble P) from either fish bone hydrolysate (FBH1, FBH2) or from NaH2PO4 (NaP1, NaP2). The diets were given for 168days from start of feeding (0.17g fish) until 24weeks of feeding (33g). Weight and specific growth rate did not reveal diet dependent differences except in the initial 10week feeding period where fish fed FBH1 showed lower growth as compared to fish fed the Na–P diets. Mineralization of fish evaluated by whole body and bone ash and mineral contents showed diet dependent differences that were related to dietary P level, but not to P source. Fish fed the low P diet showed clear P deficiency signs with significantly reduced tissue ash and mineral content, reduced whole body Ca:P ratio and morphological deviation from the normal. Histological evaluation of the vertebrae after 19weeks of feeding (15g) revealed stagnation in cartilage development, with accumulation of mature chondrocytes in fish fed low P control and FBH1 diet. FTIR showed that fish fed FBH1 had lower mineralization and increased cross binding in the vertebral end plates. Fish fed FBH2 resembled the positive NaP1 control. Real time qPCR analyses confirmed the histological results, by showing up-regulating of col10a1 (a marker for mature cartilage) in fish fed low P diet and FBH1. Osteocalcin (a marker for mineralization) was also activated in fish fed the low P diet and FBH1, possibly indicating a compensatory regulation in response to inadequate P. The dietary impacts on histology, FTIR and qPCR analyses in the FBH1 fed fish disappeared at 24weeks of feeding (33g). In conclusion, the results showed that P solubilized from bone fraction of herring can be efficiently utilized for growth, mineralization and bone development in Atlantic salmon fry. However, in the initial weeks of feeding, the FBH was a less efficient P source compared to NaP. Overall, the data suggest that P from fish bone hydrolysate is more suited for fish of minimum 15g size. Statement of relevanceThe phosphate (P) rock reserve is a limited resource worldwide. Increased efficiency in the utilization of P and improved recycling of P from waste and manures are examples that could reduce the industry's vulnerability to the limited P supply while also reducing the negative environmental impacts. Recycling of P from fishery offal and development of new available P ingredients to farmed fish will significantly improve the sustainability of the aquaculture industry and reduce the environmental loss. In this paper we show that P hydrolysed from herring bone by-product is as efficient and good for salmon fry as commercially available NaP-salts.

Alternate Directed Anthropogenic Shifts in Genotype Result in Different Ecological Outcomes in Coho Salmon Oncorhynchus kisutch Fry.

Domesticated and growth hormone (GH) transgenic salmon provide an interesting model to compare effects of selected versus engineered phenotypic change on relative fitness in an ecological context. Phenotype in domestication is altered via polygenic selection of traits over multiple generations, whereas in transgenesis is altered by a single locus in one generation. These established and emerging technologies both result in elevated growth rates in culture, and are associated with similar secondary effects such as increased foraging, decreased predator avoidance, and similar endocrine and gene expression profiles. As such, there is concern regarding ecological consequences should fish that have been genetically altered escape to natural ecosystems. To determine if the type of genetic change influences fitness components associated with ecological success outside of the culture environments they were produced for, we examined growth and survival of domesticated, transgenic, and wild-type coho salmon fry under different environmental conditions. In simple conditions (i.e. culture) with unlimited food, transgenic fish had the greatest growth, while in naturalized stream tanks (limited natural food, with or without predators) domesticated fish had greatest growth and survival of the three fish groups. As such, the largest growth in culture conditions may not translate to the greatest ecological effects in natural conditions, and shifts in phenotype over multiple rather than one loci may result in greater success in a wider range of conditions. These differences may arise from very different historical opportunities of transgenic and domesticated strains to select for multiple growth pathways or counter-select against negative secondary changes arising from elevated capacity for growth, with domesticated fish potentially obtaining or retaining adaptive responses to multiple environmental conditions not yet acquired in recently generated transgenic strains.

サケの雄親の回帰年齢が稚魚の初期成長に影響する可能性

サケの雌 5 尾（4 年魚）と雄 9 尾（3 年魚の雄 3 尾，4 年魚の雄 3 尾及び 5 年魚の雄 3 尾）を用いて総当たり交配を行い，稚魚の成長に影響する要因を雄親のサイズと年齢の違いから検討した。また，稚魚の体重に関する遺伝率の推定を行った。雄親の体重と稚魚の体重に明瞭な関係は見られなかったが，5 年魚の雄親から作出した稚魚の体重は 3 年魚や 4 年魚の雄親から作出した稚魚に比べて小さい傾向にあった。遺伝率は稚魚の成長に伴い高くなっていた。これよりサケの雄親の年齢は稚魚の成長に影響する要因の一つであると考えられた。

Susceptibility of ocean- and stream-type Chinook salmon to isolates of the L, U, and M genogroups of infectious hematopoietic necrosis virus (IHNV).

This study examined the susceptibility of Chinook salmon Oncorhynchus tshawytscha to viral strains from the L, U, and M genogroups of infectious hematopoietic necrosis virus (IHNV) present in western North America. The goal of this investigation was to establish a baseline understanding of the susceptibility of ocean- and stream-type Chinook salmon to infection and mortality caused by exposure to commonly detected strains of L, U, and M IHNV. The L IHNV strain tested here was highly infectious and virulent in both Chinook salmon populations, following patterns previously reported for Chinook salmon. Furthermore, ocean- and stream-type Chinook salmon fry at 1 g can also become subclinically infected with U and M strains of IHNV without experiencing significant mortality. The stream-type life history phenotype was generally more susceptible to infection and suffered greater mortality than the ocean-type phenotype. Between the U and M genogroup strains tested, the U group strains were generally more infectious than the M group strains in both Chinook salmon types. Substantial viral clearance occurred by 30 d post exposure, but persistent viral infection was observed with L, U, and M strains in both host populations. While mortality decreased with increased host size in stream-type Chinook salmon, infection prevalence was not lower for all strains at a greater size. These results suggest that Chinook salmon may serve as reservoirs and/or vectors of U and M genogroup IHNV.

温度・餌環境が異なる河川に放流されたサケ稚魚の成長比較

サケ稚魚の河川内での成長と温度・餌環境との関係を調べるために，これらの環境条件が異なる千歳川本流とその支流ママチ川に放流を行った。その結果，ママチ川に放流した稚魚の方が胃充満度は高く，高成長だった。水温はママチ川の方が高かったため，ママチ川の方が高成長だった理由として，第一に高水温による採餌活性上昇が考えられた。餌料生物密度は千歳川の方が高密度だと推測された。ただし，餌料生物をめぐる競合個体の密度を定量化できなかったため，餌料生物密度の成長への影響については言及できなかった。

Oral vaccination of first-feeding Atlantic salmon, Salmo salar L., confers greater protection against yersiniosis than immersion vaccination

Yersinia ruckeri is a ubiquitous pathogen of finfish capable of causing major mortalities in farmed fish stocks. It can be transmitted vertically from parent to progeny as well as horizontally in the water column from both clinically infected fish and asymptomatic carriers, and is consequently capable of infecting fish at early stages of development. Immunisation strategies that can protect small fry are therefore critical for the effective management of fish health, as is the ability to detect covertly infected fish. In this study, first-feeding Atlantic salmon fry (<0.5g) were immunised either by oral administration of a microencapsulated Y. ruckeri vaccine formulation (0.38g initial weight), or via immersion in bacterin suspension (0.26g), with and without a booster immersion vaccination at 1g size. Protection in groups receiving only immersion immunisation did not differ significantly from untreated controls when challenged with Y. ruckeri at approximately 5g size, while orally immunised fish were significantly better protected than untreated controls (F=4.38, df=4,10, P=0.026), with RPS varying between 29.4% (ORAL) and 51% (ORAL+DIP). A quantitative real-time PCR assay was used to successfully detect covertly infected fish among challenge survivors, indicating more than 50% of surviving fish in each group were infected with no significant differences between immunised fish and untreated controls.

Downstream migration of fry of pink salmon Oncorhynchus gorbuscha (Walbaum) in the Malaya Huzi River (Northeastern Sakhalin)

Patterns of downstream migration in pink salmon fry are investigated; data on migration time, its seasonal and daily dynamics, morphobiological characteristics of fry, and total number of migrants are obtained. Behavioral features of fry during the migration both in the main stream and in the estuary of the river are studied. Mechanisms of fry distribution in the flow and its connection with hydraulic structure of the flow and active behavioral elements are revealed. A comparison of two alternative methods for quantitative assessment of downstream migrants has proved the efficiency of both of them.

Juveniles of pink and chum salmon in the Iska River (Sakhalin Bay, Okhotsk Sea) in the fresh-water period

Juveniles of pink and chum salmon are investigated in the Iska River flowing into the Okhotsk Sea. The pink juveniles begin their seaward migration in May, with the ice melting, the migration lasts about 40 days, approximately from May 20 to July 5. The seaward migration of chum juveniles begins in the same time but ends in 5-10 days later. The portion of pink salmon fry with the remains of yolk sac is 82-94 %; even in the end of their migration it is rather high, up to 76 %. This species juveniles begin to feed in the river, in particular in «dry» years, the portion of feeding fry increases with disappearance of the yolk sac up to 78 % (by the stomach fullness). Both pink and chum juveniles migrate at night only. Hydrological conditions influence on the timing of migration: it is close to normal dates in conditions of high water level and strong water flow but delayed in conditions of low water discharge (that’s why the portion of juveniles feeding in the river is higher in those years). Year-to-year dynamics of the juveniles and spawners abundance is traced for the 1951-2012. The pink salmon escapement to the Iska changed from 11.0 · 10 3 (in 2004) to 1344.4 · 10 3 (in 1958) ind., on average 280.0 · 10 3 ind. for even years and from 22.7 · 10 3 (in 1959) to 2005.8 · 10 3 (in 2007) ind., on average 372.9 · 10 3 ind. for odd years. The number of pink salmon downstream migrants changed from 0.8 · 10 6 (in 1954) to 40.9 · 10 6 (in 1964), on average 10.9 · 10 6 ind. for even years and from 1.0 · 10 6 (in 2005) to 41.8 · 10 6 (in 1957), on average 8.9 · 10 6 ind. for odd years.

Alginate Microencapsulation for Oral Immunisation of Finfish: Release Characteristics, Ex Vivo Intestinal Uptake and In Vivo Administration in Atlantic Salmon, Salmo salar L.

This study examined the feasibility of alginate microcapsules manufactured using a low-impact technology and reagents to protect orally delivered immunogens for use as immunoprophylactics for fish. Physical characteristics and protein release kinetics of the microcapsules were examined at different pH and temperature levels using a microencapsulated model protein, bovine serum albumin (BSA). Impact of the microencapsulation process on contents was determined by analysing change in bioactivity of microencapsulated lysozyme. Feasibility of the method for oral immunoprophylaxis of finfish was assessed using FITC-labelled microcapsules. These were applied to distal intestinal explants of Atlantic salmon (Salmo salar) to investigate uptake ex vivo. Systemic distribution of microcapsules was investigated by oral administration of FITC-labelled microcapsules to Atlantic salmon fry by incorporating into feed. The microcapsules produced were structurally robust and retained surface integrity, with a modal size distribution of 250-750 nm and a tendency to aggregate. Entrapment efficiency of microencapsulation was 51.2 % for BSA and 43.2 % in the case of lysozyme. Microcapsules demonstrated controlled release of protein, which increased with increasing pH or temperature, and the process had no significant negative effect on bioactivity of lysozyme. Uptake of fluorescent-labelled microcapsules was clearly demonstrated by intestinal explants over a 24-h period. Evidence of microcapsules was found in the intestine, spleen, kidney and liver of fry following oral administration. Amenability of the microcapsules to intestinal uptake and distribution reinforced the strong potential for use of this microencapsulation method in oral immunoprophylaxis of finfish using sensitive immunogenic substances.

Parasites of the fry of the coho salmon, Oncorhynchus kisutch (Walbaum, 1792), from the Kronotskaya River (Eastern Kamchatka)

Fry of the coho salmon, Oncorhynchus kisutch (Walbaum, 1792), which were caught in the Kronotskaya River, were found to include six species of parasites belonging to four classes: Monogenea (Salmonchus alaskensis), Cestoda (Proteocephalus longicollis), Nematoda (Sterliadochona ephemeridarum, Cucullanus truttae, Philonema oncorhynchi), and Acantocephala (Neoechinorhynchus salmonis). The intensity of the parasitic invasion was not above three specimens per fish.

Experimental infection of six North American fish species with the North Carolina strain of spring Viremia of Carp Virus

Spring viremia of carp virus (SVCV) is a rhabdoviral pathogen associated with disease outbreaks in cultured and wild fish worldwide. Common carp (Cyprinus carpio carp), and koi (C. carpio koi) suffer the highest mortalities from SVCV infections, while other cyprinid fish species have varying susceptibility. Although salmonid fish typically are considered refractory to infection by SVCV, there have been a few reports suggesting infection has occurred in rainbow trout (Oncorhynchus mykiss). There have been no reports of Percid fish being infected with SVCV. Since the first North American outbreak of SVCV at a North Carolina koi farm in 2002 there have been eight subsequent detections or outbreaks of SVCV among fish species from the families of Cyprinidae and Centrarchidae within the US and Canada. Thus, this exotic virus is considered a potential threat to native and cultured fish populations in North America. We performed multiple experimental challenges with fish species from three families (Salmonidae, Cyprinidae, and Percidae) to identify the potential risk associated with SVCV exposure of resident fish populations in North America.Three salmonid species, rainbow and steelhead trout (Oncorhynchus mykiss), Chinook salmon (O. tshawytscha), and sockeye salmon (O. nerka), were challenged by immersion or injection with the North Carolina SVCV isolate. Two cyprinid species, koi and fathead minnow (Pimephales promelas) and one percid species, yellow perch (Perca flavescens) were also challenged. Koi were highly susceptible to SVCV up to 11months of age and fathead minnows had chronic disease expression with moderate mortality (29%). SVCV also induced moderate mortalities (33%) in yellow perch fry. Virus challenged salmonid fish had cumulative percent mortalities ranging from 0 to 100%, with sockeye salmon fry being the most vulnerable. A sub-sample of mortalities and survivors were screened for virus by plaque assay and reverse transcription polymerase chain reaction. In general, all mortalities tested positive for SVCV with high viral titers while survivors had variable persistence of SVCV with overall lower virus titers. Our SVCV challenges of multiple North American fish species suggested that host age is a key factor in determining disease outcome. Other factors, such as fish broodstock, virus strain, water temperature, and rearing conditions in association with the intrinsic level of species susceptibility may also impact infection dynamics. This is the first report of SVCV infecting a species (yellow perch) in the family Percidae and that sockeye salmon fry can suffer similarly high mortalities as the primary SVCV host species.

Scenario analysis of the effects of the Great East Japan Earthquake on the chum salmon population-enhancement system

The Great East Japan Earthquake may have resulted in increased mortality of artificially propagated chum salmon fry (2010 year class) from Iwate Prefecture (CSI), both in the hatchery and after release. Individuals from the 2010 year class will return in 2014–2015. To evaluate the potential for future issues associated with the effects of the earthquake, we simulated CSI population dynamics using a model that incorporated stratified earthquake-influenced survival rates λ l (l = 0.00−1.00 at intervals of 0.25) under various scenarios. Under laissez-faire scenarios (median exploitation rate E Med) under low post-release survival rate S Low and all λ l , the median number of hatchery-released fry $$H^{\prime }_{t}$$ did not reach the target H * in 2014 and 2015. The probability P j,t of not meeting the targets was 0.56−1.00 (2014) and 0.79−1.00 (2015). Meanwhile, with simulation of a low exploitation rate, S Low, and a higher λ l (0.50), the P j,t in 2014 and 2015 was 0.00−0.17 and 0.21−0.72, respectively. Under S Med and S High, $$H^{\prime }_{t}$$ reached H * at λ l (>0.50) regardless of E l , and the cumulative catch varied primarily with S l . Our results suggest that simulations can provide a method of predicting potential issues and can offer insight into strategies to minimize future problems.

Ontogeny of the Digestive System of Atlantic Salmon (Salmo salar L.) and Effects of Soybean Meal from Start-Feeding

Despite a long history of rearing Atlantic salmon in hatcheries in Norway, knowledge of molecular and physiological aspects of juvenile development is still limited. To facilitate introduction of alternative feed ingredients and feed additives during early phases, increased knowledge regarding the ontogeny of the digestive apparatus in salmon is needed. In this study, we characterized the development of the gastrointestinal tract and accessory digestive organs for five months following hatch by using histological, biochemical and molecular methods. Furthermore, the effects of a diet containing 16.7% soybean meal (SBM) introduced at start-feeding were investigated, as compared to a fishmeal based control diet. Salmon yolk sac alevins and fry were sampled at 18 time points from hatch until 144 days post hatch (dph). Histomorphological development was investigated at 7, 27, 46, 54 and 144 dph. Ontogenetic expression patterns of genes encoding key digestive enzymes, nutrient transporters, gastrointestinal peptide hormones and T-cell markers were analyzed from 13 time points by qPCR. At 7 dph, the digestive system of Atlantic salmon alevins was morphologically distinct with an early stomach, liver, pancreas, anterior and posterior intestine. About one week before the yolk sac was internalized and exogenous feeding was started, gastric glands and developing pyloric caeca were observed, which coincided with an increase in gene expression of gastric and pancreatic enzymes and nutrient transporters. Thus, the observed organs seemed ready to digest external feed well before the yolk sac was absorbed into the abdominal cavity. In contrast to post-smolt Atlantic salmon, inclusion of SBM did not induce intestinal inflammation in the juveniles. This indicates that SBM can be used in compound feeds for salmon fry from start-feeding to at least 144 dph and/or 4-5 g body weight.