Growth Of Juvenile Salmon Research Articles

Effects of dietary reduced glutathione on the growth and antioxidant capacity of juvenile Atlantic salmon (Salmo salar)

Effects of dietary reduced glutathione on the growth and antioxidant capacity of juvenile Atlantic salmon (<i>Salmo salar</i>)

Fasting in freshwater severely affects growth of juvenile chum salmon when entering cold seawater

We conducted rearing experiments to examine the cumulative effects of fasting in freshwater and transfer to cold seawater on the growth of juvenile chum salmon. In the first experiment in May 2016, juvenile fish were either fed or fasted in freshwater for 5 days and acclimatized to seawater of either optimal (10 °C) or cold (5 °C) temperature for 10 days with feeding. Despite resumed feeding, fish that were fasted in freshwater and transferred to cold seawater showed the poorest growth. Serum levels of insulin-like growth factor (IGF)-I, a positive indicator of growth, were also the lowest in this group, suggesting a synergistic negative effect of fasting in freshwater and transfer to cold seawater on growth in chum salmon. A similar experiment in May 2017 suggested that the depressed growth and serum IGF-I in cold seawater might be due to the predominant allocation of energy to liver glycogen. On the one hand, serum levels of IGF-binding protein-1b, a negative indicator of growth, were not affected by seawater temperature but by fasting in seawater. The present study shows that relatively short-termed fasting in freshwater critically affects growth of juvenile chum salmon transferred to cold seawater.

Spatial variability in ocean‐mediated growth potential is linked to Chinook salmon survival

AbstractEarly ocean survival of Chinook salmon, Oncorhynchus tshawytscha, varies greatly inter‐annually and may be the period during which later spawning abundance and fishery recruitment are set. Therefore, identifying environmental drivers related to early survival may inform better models for management and sustainability of salmon in a variable environment. With this in mind, our main objectives were to (a) identify regions of high temporal variability in growth potential over a 23‐year time series, (b) determine whether the spatial distribution of growth potential was correlated with observed oceanographic conditions, and (c) determine whether these spatial patterns in growth potential could be used to estimate juvenile salmon survival. We applied this method to the fall run of the Central Valley Chinook salmon population, focusing on the spring and summer period after emigration into central California coastal waters. For the period from 1988 to 2010, juvenile salmon growth potential on the central California continental shelf was described by three spatial patterns. These three patterns were most correlated with upwelling, detrended sea level anomalies, and the strength of onshore/offshore currents, respectively. Using the annual strength of these three patterns, as well as the overall growth potential throughout central California coastal waters, in a generalized linear model we explained 82% of the variation in juvenile salmon survival estimates. We attributed the relationship between growth potential and survival to variability in environmental conditions experienced by juvenile salmon during their first year at sea, as well as potential shifts in predation pressure following out‐migration into coastal waters.

Survival, Tag Retention, Growth, and Wound Healing of Juvenile Chinook Salmon (Oncorhynchus tshawytscha) Surgically Implanted with a Dummy Acoustic Tag

Tag effect studies are paramount in interpreting the results of survival studies. The objective of this study was to analyze the influence of tag implantation and tag burden on the survival, tag retention, growth, and wound healing of juvenile Chinook Salmon 7.8 ± 0.9 g initial weight. Fish were obtained from the Merced River Hatchery, held for 7 d, and then surgically implanted with Juvenile Salmon Acoustic Telemetry System (JSATS) SS300 dummy tags (0.3 g in air). Tag burden ranged from 2.9–4.8% (3.86 ± 0.43%, mean ± standard deviation). Weight and fork length were taken immediately before tag implantation. All fish (i.e., control and dummy-tagged) were also implanted with a visible implant alpha tag next to the dorsal insertion. Control and dummy-tagged fish were held in a single tank for 30 d. Any fish that died during the 30-d period were noted. At the end of the holding period, all fish were euthanized, weighed, measured, and necropsied. All dummy-tagged fish retained their dummy tag, and survival rates between the two groups were similar. Wound healing was also similar across the range of tag burdens analyzed. Specific growth rates, however, differed significantly between the two groups, with control fish growing at a rate of 1.08 ± 0.38% d− 1 compared to 0.55 ± 0.48 % d− 1 in dummy-tagged fish (P &lt; 0.001). Tag burdens and specific growth rates for dummy-tagged fish (P = 0.961) did not correlate, nor did initial weight and specific growth rate for control (P = 0.363) or dummy-tagged (P = 0.983) fish. The cause of the decreased growth rate in dummy-tagged fish remains unknown. Determining the cause of decreased growth in tagged juvenile Chinook Salmon, and how that decreased growth may influence survival in the wild, should be investigated further.

Growth, immune response, antioxidant capability, and disease resistance of juvenile Atlantic salmon (Salmo salar L.) fed Bacillus velezensis V4 and Rhodotorula mucilaginosa compound

A feeding trial of 62 days was conducted to investigate the effects of dietary administration of a probiotics compound consisting of Bacillus velezensis V4 CGMCC 10149 and Rhodotorula mucilaginosa CGMCC 1013 on growth, immune response, antioxidant capability, and disease resistance of juvenile Atlantic salmon (Salmo salar L.) reared in a recirculating aquaculture system (RAS). Atlantic salmon were distributed in four equal groups, each with three replicates, which received one of the following experimental diets: Control (non-supplemented diet); T1 (B. velezensis V4 5 × 106 CFU g−1, R. mucilaginosa 5 × 107 CFU g−1), T2 (B. velezensis V4 1.5 × 107 CFU g−1, R. mucilaginosa 1.5 × 108 CFU g−1), and T3 (B. velezensis V4 2.5 × 107 CFU g−1, R. mucilaginosa 2.5 × 108 CFU g−1). Administration of the probiotics compound had significant effects on growth performance, feed utilization, immune response, and antioxidant capability of Atlantic salmon, and mortality was significantly reduced (P < 0.05). After the feeding trial, fish were challenged with Aeromonas salmonicida (A. salmonicida) and cumulative mortality was recorded for the next 7 days. The cumulative mortality was lower in Atlantic salmon fed with the probiotics compound, especially in the T1 group, compared to the control. These results demonstrated that multi-probiotics had beneficial effects as an antibiotic replacer in terms of growth performance, non-specific immune responses and disease resistance in salmon. The present study demonstrated B. velezensis V4 and R. mucilaginosa compound as a beneficial dietary probiotics for juvenile Atlantic salmon reared in a RAS with the capability of improving growth performance and enhancing disease resistance by immunomodulation.

4. Evaluating coastal survivability and growth of juvenile chum salmon, and their adult return

4. Evaluating coastal survivability and growth of juvenile chum salmon, and their adult return

Chronic exposure to increased water temperature reveals few impacts on stress physiology and growth responses in juvenile Atlantic salmon

Fish are subjected to a variety of stressors under common cage aquaculture conditions. While short-term exposure to a stressor often results in an adaptive response to cope with stress, repeated and/or chronic exposure to stress can result in negative impacts on fish welfare and production. In fish, little is known about the impact of long-term exposure to stressors, including elevated water temperature. In this study we examined and developed temporal response profiles of physiological indicators of stress and growth in juvenile Atlantic salmon (Salmo salar) exposed to 12 °C, 16 °C, and 20 °C for 99 days. Five times throughout the study we quantified plasma cortisol, glucose and cholesterol levels, and growth. Fish body mass and fork length were not significantly different amongst temperatures after 99 days. Plasma cortisol was significantly elevated at 16 °C when comparing day 8 with 99, while at 12 °C plasma cortisol increased from day 1 to day 8, then returned to initial levels (day 1 and 8) after 99 days. Plasma glucose and cholesterol were not significantly different amongst the temperatures throughout the experiment. In addition, at the end of the experiment we quantified eye darkening, and identified the development of a bimodal growth distribution in all temperatures. Fish with a fork length ≤ 240 mm were categorised as lower mode (LM) and those with a fork length > 240 mm as in the upper mode (UM) of growth. Plasma cholesterol was significantly lower in the LM group in all three temperatures, but plasma cortisol and glucose levels did not differ between modes. Eye darkening also did not differ between modes, but increased significantly in the groups exposed to 16 °C and 20 °C when compared with 12 °C. This study showed a clear physiological stress response (elevated levels of cortisol) and eye darkening in fish maintained at 16 °C but not at 12 °C or 20 °C, suggesting that some aspects of the physiological responses available to deal with chronic stress are affected by temperature.

Erratum: Simulated juvenile salmon growth and phenology respond to altered thermal regimes and stream network shape

Erratum: Simulated juvenile salmon growth and phenology respond to altered thermal regimes and stream network shape

Assessing Indices of Growth for Field Studies of Juvenile Salmon: An Experiment and Synthesis

AbstractThe hypothesis that size‐selective mortality in the first marine year is a major regulator of recruitment in Pacific salmon Oncorhynchus spp. has led to interest in assessing the recent growth of field‐caught fish. Understanding differences in relative growth across years, regions, habitats, and prey fields may provide insights into factors influencing survival. Plasma insulin‐like growth factor 1 (IGF1), muscle RNA : DNA ratio (RD), and scale circulus spacing have all been used as indices of recent growth in juvenile salmonids. We concurrently assessed these growth rate indices in a laboratory study of postsmolt, young‐of‐the‐year, ocean‐type Chinook Salmon O. tshawytscha. We synthesized results with previous work to inform selection of appropriate growth rate indices for field studies on juvenile salmonids. Muscle samples suitable for RD analysis were obtained nonlethally and without subsequent growth impacts, even for very small juvenile salmon (75–99 mm FL). Plasma IGF1 concentration was strongly correlated with growth rate (R2 = 0.79), while loge(RD) and mean spacing of the outer two circuli were moderately correlated with growth rate (R2 = 0.47 and 0.44, respectively). Relationships between the two biochemical indices and growth rate were independent of body size at the start of the experiment. Conversely, initially larger fish formed wider circuli for a given growth rate. Insulin‐like growth factor 1 and RD responded to a change in growth conditions within 4 and 6 d, respectively. Rate of circulus formation varied positively with growth rate, meaning that outer circulus spacing indexed shorter periods of growth in faster‐growing fish. Our results confirm the value of plasma IGF1 as an index of recent growth in juvenile salmon. Although scales (marginal circulus spacing) and white muscle (RD) can both be sampled nonlethally, scale sampling presents a number of practical advantages.

Eelgrass as Valuable Nearshore Foraging Habitat for Juvenile Pacific Salmon in the Early Marine Period

AbstractThe early marine period is a critical life history stage for growth and survival of anadromous juvenile Pacific salmon. The integrity of nearshore ecosystems where juvenile salmon reside and the capacity of these habitats to provide prey can thus influence overall salmon returns. Eelgrass Zostera marina beds in particular are considered critical nearshore habitat. By examining how juvenile salmon use this habitat during their early marine life, we gain insight into the trophic dynamics in these ecosystems and help gauge the effects of accelerating eelgrass loss and nearshore habitat development on juvenile salmon. This project investigated the role of eelgrass as juvenile salmon foraging habitat. We compared juvenile Chum Salmon Oncorhynchus keta and juvenile Chinook Salmon O. tshawytscha diets to prey availability in zooplankton tows and in epifaunal eelgrass samples across a gradient of eelgrass density in the Comox Estuary, British Columbia. Harpacticoid copepods dominated the diets of both juvenile Chum Salmon and Chinook Salmon and were found in abundance in eelgrass blades. We complemented diet analysis with carbon (δ13C) and nitrogen (δ15N) stable isotope analysis to examine the relative contribution of zooplankton, eelgrass epifaunal invertebrates, and terrestrial invertebrates to the diet of juvenile Chum Salmon. Juvenile Chum Salmon isotope ratios closely reflected those of eelgrass invertebrates, suggesting that eelgrass invertebrates made up approximately 80% of the diets of juvenile Chum Salmon. Our results highlight the value of eelgrass in providing nearshore foraging opportunities for juvenile salmon and suggest that eelgrass habitat protection and restoration may provide critical support for growth, thereby easing the transition of juvenile salmon from freshwater to the marine environment.

Evidence for depressed growth of juvenile Pacific salmon (Oncorhynchus) in Johnstone and Queen Charlotte Straits, British Columbia

AbstractJuvenile salmon traveling northwestward to the Pacific Ocean from the Strait of Georgia migrate through and take residence in both Johnstone and Queen Charlotte Straits. Johnstone Strait is a narrow and deep passage that is tidally mixed daily, resulting in a nearly isothermal water column, surface to the bottom (approximately 250 m). The trophic gauntlet hypothesis (McKinnell, Curchitser, Groot, Kaeriyama, &amp; Trudel, ) suggests that Johnstone Strait provides a poor growth environment for fish required to transit this area during their migration, due to the oceanographic conditions found there. Using insulin‐like growth factor‐1 (IGF1), a hormone used to assess short‐term growth (within 5–7 days) in fishes, growth was measured in individual juvenile salmon from five species in the Northern Strait of Georgia, Johnstone Strait, Queen Charlotte Strait, and Queen Charlotte Sound in the summer of 2012, 2013, and 2014. All five juvenile salmon species had significantly lower IGF1 concentration in both Johnstone and Queen Charlotte Straits as compared to the Northern Strait of Georgia. These results are consistent with some aspects of the tropic gauntlet hypothesis as growth of juvenile salmon in both Johnstone and Queen Charlotte Straits were significantly lower than found in the Northern Strait of Georgia across all salmon species and all years. In addition, these results demonstrate the utility of growth indices for assessing the effects of environmental variation on juvenile salmon in the presence of a strong ecological driver.

Simulated juvenile salmon growth and phenology respond to altered thermal regimes and stream network shape.

It is generally accepted that climate change will stress coldwater species like Pacific salmon. However, it is unclear what aspect of altered thermal regimes (e.g., warmer winters, springs, summers, or increased variability) will have the greatest effect, and what role the spatial properties of river networks play. Thermally diverse habitats may afford protection from climate change by providing opportunities for aquatic organisms to find and use habitats with optimal conditions for growth. We hypothesized that climate-altered thermal regimes will change growth and timing of life history events such as emergence or migration but that changes will be moderated in topologically complex stream networks where opportunities to thermoregulate are more readily available to mobile animals. Because climate change effects on populations are spatially variable and contingent upon physiological optima, assessments of risk must take a spatially explicit approach. We developed a spatially-structured individual based model for Chinook Salmon (Oncorhynchus tshawytscha) in which movement decisions and growth were governed by water temperature and conspecific density. We evaluated growth and phenology (timing of egg emergence and smolting) under a variety of thermal regimes (each having a different minimum, rate of warming, maximum, and variability) and in three network shapes of increasing spatial complexity. Across networks, fish generally grew faster and were capable of smolting earlier in warmer scenarios where water temperatures experienced by fish were closer to optimal; however, growth decreased for some fish. We found that salmon size and smolt date responded more strongly to warmer springs and summers than to warmer winters or increased variability. Fish in the least complex network grew faster and were ready to smolt earlier than fish in the more spatially complex network shapes in the contemporary thermal regime; patterns were similar but less clear in warmer thermal regimes. Our results demonstrate that network topology may influence how fish respond to thermal landscapes, and this information will be useful for incorporating a spatiotemporal context into conservation decisions that promote long-term viability of salmon in a changing climate.

Strain-specific survival and growth of juvenile Atlantic salmon in Central New York tributaries

Abstract Reintroduction of Atlantic salmon Salmo salar in the Lake Ontario watershed represents a historical challenge for fisheries managers dating to the late 1800s. To assess the feasibility for reintroduction, strain-specific differences in survival and growth was evaluated in central New York tributaries in 2014 and 2015. Fry of Lake Memphremagog and Sebago Lake strains were stocked at target densities of 100 fry/100 m 2 in tributaries within the Ontario Drumlins and Fish Creek regions. Salmon abundance, density, and survival was estimated at each stocking location. Standardized mass-specific growth rate ( G s ) and absolute growth in length ( G L ) of age-0 parr and age-1 pre-smolts was evaluated with two-way analysis of variance. For both strains, survival was largely site-dependent in the Drumlins region and stream-dependent in the Fish Creek region. The Lake Memphremagog strain exhibited faster growth, suggesting that physiological adaptations of this strain make it a more suitable candidate for reintroduction in the region when the source is available. However, limited availability of the Lake Memphremagog strain may direct future efforts to employ the more widely-evaluated and available Sebago Lake strain.

Linking functional response and bioenergetics to estimate juvenile salmon growth in a reservoir food web.

Juvenile salmon (Oncorhynchus spp.) use of reservoir food webs is understudied. We examined the feeding behavior of subyearling Chinook salmon (O. tshawytscha) and its relation to growth by estimating the functional response of juvenile salmon to changes in the density of Daphnia, an important component of reservoir food webs. We then estimated salmon growth across a broad range of water temperatures and daily rations of two primary prey, Daphnia and juvenile American shad (Alosa sapidissima) using a bioenergetics model. Laboratory feeding experiments yielded a Type-II functional response curve: C = 29.858 P *(4.271 + P)-1 indicating that salmon consumption (C) of Daphnia was not affected until Daphnia densities (P) were < 30 · L-1. Past field studies documented Daphnia densities in lower Columbia River reservoirs of < 3 · L-1 in July but as high as 40 · L-1 in August. Bioenergetics modeling indicated that subyearlings could not achieve positive growth above 22°C regardless of prey type or consumption rate. When feeding on Daphnia, subyearlings could not achieve positive growth above 20°C (water temperatures they commonly encounter in the lower Columbia River during summer). At 16–18°C, subyearlings had to consume about 27,000 Daphnia · day-1 to achieve positive growth. However, when feeding on juvenile American shad, subyearlings had to consume 20 shad · day-1 at 16–18°C, or at least 25 shad · day-1 at 20°C to achieve positive growth. Using empirical consumption rates and water temperatures from summer 2013, subyearlings exhibited negative growth during July (-0.23 to -0.29 g · d-1) and August (-0.05 to -0.07 g · d-1). By switching prey from Daphnia to juvenile shad which have a higher energy density, subyearlings can partially compensate for the effects of higher water temperatures they experience in the lower Columbia River during summer. However, achieving positive growth as piscivores requires subyearlings to feed at higher consumption rates than they exhibited empirically. While our results indicate compromised growth in reservoir habitats, the long-term repercussions to salmon populations in the Columbia River Basin are unknown.

Variation in size, condition, and abundance of juvenile chum salmon (Oncorhynchus keta) in relation to marine factors in Southeast Alaska

Understanding how environmental conditions influence productivity of Pacific salmon (Oncorhynchus spp.) requires identifying relationships between ocean-driven processes and early marine growth and survival. We studied size, condition, and abundance of juvenile chum salmon (O. keta) captured in July in Icy Strait, Alaska over 17 years (1997−2013). We investigated relationships between these juvenile chum salmon characteristics and a suite of marine variables expressed at basin-wide, regional, and local scales using correlation and multivariate analyses. Juvenile chum salmon tended to be longer in years with warmer sea-surface temperatures in spring and summer. Average energy density was higher in years when variables such as local winds and mixed-layer depth indicated enhanced water-column mixing in June and July. Marine factors at the regional scale, specifically freshwater discharge and upwelling, were associated with the abundance of juvenile chum salmon. Catch per unit effort of juvenile chum salmon was higher in years with greater freshwater discharge and more intense downwelling in the prior winter, suggestive of mechanisms increasing recruitment of juvenile chum salmon through enhanced primary productivity and possibly reduced predation risk. Overall, our study supported previous work suggesting that a strong Aleutian Low indicates good conditions for salmon recruitment in the Gulf of Alaska, although we found that local conditions explained more variation in juvenile chum salmon responses than did basin-scale climate indicators. Furthermore, our work revealed a compelling role for freshwater discharge in driving ecological mechanisms that influence the growth and survival of juvenile salmon in the nearshore marine waters of Southeast Alaska.

Effects of density during freshwater and early marine rearing on juvenile sockeye salmon size, growth, and migration

Effects of density during freshwater and early marine rearing on juvenile sockeye salmon size, growth, and migration

Reduced growth in wild juvenile sockeye salmon Oncorhynchus nerka infected with sea lice.

Daily growth rings were examined in the otoliths of wild juvenile sockeye salmon Oncorhynchus nerka to determine whether infection by ectoparasitic sea lice Caligus clemensi and Lepeophtheirus salmonis was associated with reduced host body growth, an important determinant of survival. Over 98% of the sea lice proved to be C. clemensi and the fish that were highly infected grew more slowly than uninfected individuals. Larger fish also grew faster than smaller fish. Finally, there was evidence of an interaction between body size and infection status, indicating the potential for parasite-mediated growth divergence.

Effects of dietary fatty acids on juvenile salmon growth, biochemistry, and aerobic performance: A laboratory rearing experiment

A three-phase experiment measured the effects of prey quality and fasting on juvenile Chinook salmon (Oncorhynchus tshawytscha) performance. The first phase was designed to evaluate the effect of dietary levels of two essential fatty acids, docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), on salmon growth. Salmon were reared for 12weeks on three diets varying in proportions of krill (Thysanoessa spinifera and Euphausia pacifica) and northern anchovy (Engraulis mordax). Supplements of DHA and EPA were added to the formulated diets to achieve DHA:EPA ratios (0.6, 0.9, and 1.5) representative of naturally occurring prey. Growth rates over 12weeks were not significantly different among diet treatments, which may be because DHA and EPA were provisioned at or above minimum requirements. Salmon maintained DHA at high levels (>20% of total fatty acids) across all treatments and sampling periods, whereas EPA reflected dietary concentrations after 12weeks. Fatty acids were incorporated into salmon muscle at varying rates but on average reflected diet after 1 to 2months, similar to bulk stable isotopes of carbon and nitrogen. The second phase of the experiment was designed to evaluate fasting effects on salmon size, growth, and lipid storage over 4weeks. Fed fish were heavier, grew faster, and had significantly more storage lipids than fasted fish. The third phase was designed to evaluate aerobic performance in fasted fish. Critical swim speeds were found to be positively related to salmon body size and storage lipids, but not prior diet quality, evidence that larger salmon with higher energy reserves may be better suited for overwinter survival due to their ability to swim faster than smaller leaner individuals. These results provide mechanistic support for the idea that body condition prior to the first ocean winter is important for juvenile salmon survival.

Ontogenetic shifts in the diets of juvenile Chinook Salmon: new insight from stable isotopes and fatty acids

Variations in marine prey availability and nutritional quality can affect juvenile salmon growth and survival during early ocean residence. Salmon growth, and hence survival, may be related to the onset of piscivory, but there is limited knowledge on the interplay between the prey field, environment, and salmon ontogeny. Subyearling Chinook Salmon (Oncorhynchus tshawytscha) and their potential prey were sampled in coastal waters off Willapa Bay, USA to explore this issue. Three seasonal prey assemblages were identified, occurring in spring (May), early summer (June – July), and late summer (August – September). The onset of piscivory, based on salmon stomach contents, fatty acids, and stable isotopes occurred later in 2011 compared to 2012, and coincided with the appearance of Northern Anchovy (Engraulis mordax). Salmon fork length (FL) and carbon isotope values (δ13C) increased with a fatty acid biomarker for marine phytoplankton and decreased with a freshwater marker, indicating dietary carbon sources changed as salmon emigrated from the Columbia River. Salmon FL also increased with nitrogen isotope ratios (δ15N), trophic position, and a fatty acid marker for piscivory – a consequence of the ontogenetic shift in diet to fish. Salmon grew faster and obtained larger size and condition by September 2011 compared to 2012, which was related to inter-annual differences in ocean conditions and the duration over which Northern Anchovy were available. Our results support the idea that juvenile salmon growth depends on the onset and duration of piscivory, suggesting both of these factors may be important components of lifetime growth and fitness.

The effects of increasing dietary levels of soy protein concentrate (SPC) on the immune responses and disease resistance (furunculosis) of vaccinated and non-vaccinated Atlantic salmon (Salmo salar L.) parr

Juvenile salmon, with an initial weight of 9 g, were fed three experimental diets, formulated to replace 35 (SPC35), 58 (SPC58) and 80 (SPC80) of high quality fishmeal (FM) with soy protein concentrate (SPC) in quadruplicate tanks. Higher dietary SPC inclusion was combined with increased supplementation of methionine, lysine, threonine and phosphorus. The experiment was carried out for 177 days. On day 92 salmon in each tank were bulk weighed. Post weighing eighty salmon from each tank were redistributed in two sets of 12 tanks. Salmon from the first set of tanks were vaccinated, while the second group was injected with phosphate buffer saline (PBS). Salmon were sampled on day 92 (pre-vaccination), day 94 (2 days post vaccination [dpv]/PBS injection [dpPBSinj]) and day 154 (62 dpv/dpPBSinj) of the trial for the assessment of their immune responses, prior to the performance of salmon bulk weights for each tank. On day 154, fish from each tank were again bulk weighed and then seventeen salmon per tank were redistributed in two sets of twelve tanks and intra-peritoneally infected with Aeromonas salmonicida. At Day 154, SPC80 demonstrated lower performance (weight gain, specific growth rate and thermal growth coefficient and feed conversion ratio) compared to SPC35 salmon. Reduced classical and total complement activities for salmon fed diets with over 58% of protein from SPC, were demonstrated prior to vaccination. Reduced alternative complement activity was detected for both SPC58 and SPC80 salmon at 2 dpv and for the SPC80 group at 62 dpv. Total and classical complement activities demonstrated no differences among the dietary groups after vaccination. Numerical increases in classical complement activity were apparent upon increased dietary SPC levels. Increased phagocytic activity (% phagocytosis and phagocytic index) was exhibited for the SPC58 group compared to SPC35 salmon at 62 dpPBSinj. No differences in serum lysozyme activity, total IgM, specific antibodies, protein, glucose and HKM respiratory burst were detected among the dietary groups at any timepoint or state. Mortalities as a result of the experimental infection only occurred in PBS-injected fish. No differences in mortality levels were demonstrated among the dietary groups. SPC58 diet supported both good growth and health in juvenile Atlantic salmon while SPC80 diet did not compromise salmon’ immunity or resistance to intraperitoneally inflicted furunculosis.