Growth Rate In Atlantic Salmon Research Articles

Dietary inclusion of the red seaweed Asparagopsis taxiformis boosts production, stimulates immune response and modulates gut microbiota in Atlantic salmon, Salmo salar

Salmonids represent US$23 billion of global aquaculture value, yet Atlantic salmon farms lose approximately 10% of their production to diseases and parasites every year. New approaches to minimise such losses are urgently needed because current treatments (e.g. antibiotics) have environmental and human health impacts with increasing sea temperatures predicted to further exacerbate the impacts of disease. Immunostimulants that boost fish resistance to disease without negative environmental or human health impacts are currently being assessed. Seaweeds and their extracts are used as immunostimulants for land animals and are increasingly being investigated for use in finfish aquaculture, including for Atlantic salmon. Here we show that when the red seaweed Asparagopsis taxiformis and its extract were incorporated in Atlantic salmon feed, fish growth rates were enhanced up to 33%, feed intake was enhanced up to 13%, FCR were reduced, and innate immune responses were enhanced up to 58% compared to fish fed unsupplemented control diets over 4 weeks. Overall, fish fed the methanolic extract of A. taxiformis (at an inclusion of ~1% on a dry weight basis, D:D of feed) had the best combination of enhanced growth rate, feed intake and immune response. Fish fed the immunostimulant lipopolysaccharide (LPS) derived from Escherichia coli had the highest innate immune response in our trial, however LPS had no enhanced effect on growth or feed intake. Additionally, we provide evidence that the seaweed and LPS supplements modulated the expression of immune and stress-related genes in both the liver and head kidneys. More specifically, the fish fed the supplemented diets showed increased expression of the HSP70 gene in both their liver and head kidney after 2 weeks of treatment. At 4 weeks high HSP70 and lysozyme gene expression was observed in the fish fed the two seaweed methanolic extract diets. The seaweed diets also enhanced the diversity of bacterial communities within the hindgut of Atlantic salmon while the LPS treatment appeared to have the opposite effect. Whole A. taxiformis or its methanolic extracts could therefore be used as functional feed ingredients that boost the immune response and enhance the growth rate of Atlantic salmon without affecting feed efficiencies.

Influence of environmental and biological factors on the overwinter growth rate of Atlantic salmon Salmo salar parr in a UK chalk stream

AbstractSmolt lengths are increasingly recognised as an important determinant of salmonid marine survival rates. Overwintering growth rates could thus strongly influence adult return rates. In Atlantic salmon Salmo salar, most overwintering studies focus on rivers in harsh climates with minimal growth, yet in more southerly rivers, overwintering growth rates can be relatively high. Here, the factors influencing annual overwinter growth rates were tested for juvenile S. salar in a temperate chalk stream in southern England over 13 years, where over 10,000 salmon parr were tagged annually in autumn and a proportion recaptured the following spring during smolt emigration. Winters of higher and more variable water temperatures, with longer periods of high flows, showed increased overwintering growth rates. Faster growth rates were recorded from sites further upstream and that had lower parr densities; smaller individuals also grew more than expected for their initial size. These results suggest that a range of factors influences overwintering salmonid growth rates and can be used to inform management decisions to maximise the quality of emigrating smolts.

The Effect of Nonnative Salmonids on Social Dominance and Growth of Juvenile Atlantic Salmon

AbstractNonnative species have been shown to negatively impact the native community in which they are introduced. In the Great Lakes, competition with nonnative salmonids may be hindering the restoration efforts of Atlantic salmon Salmo salar, a once‐native top predator in Lake Ontario. We examined the effects of brown trout S. trutta and rainbow trout Oncorhynchus mykiss, two nonnative fishes in Lake Ontario, on the social dominance and growth rate of juvenile Atlantic salmon from three strains being used for reintroduction efforts in Lake Ontario. Using seminatural stream channels, we found that the presence of either rainbow trout or brown trout reduced aggression, dominance, and food consumption of the Atlantic salmon. Brown trout had the strongest effect, increasing aggression levels in the channels by a factor of two and sharply reducing the dominance of Atlantic salmon. When both nonnatives were present, initiated aggression by Atlantic salmon decreased by a factor of three and food consumption halved as compared with when the salmon were alone. Consequently, over a 7‐d time period, standard growth rate of the Atlantic salmon dropped from no change in mass when alone to a value of –0.3% per day when with the nonnative species. Of the three strains tested, one strain was least affected by the nonnative trouts, implicating genetic differences among the strains and suggesting that one strain may have greater poststocking success in Lake Ontario tributaries with naturalized populations of brown trout and rainbow trout.

The effects of abiotic factors and intraspecific versus interspecific competition on the diel activity patterns of Atlantic salmon (Salmo salar) fry

We conducted semi-natural experiments to measure the relative contribution of various environmental factors and intraspecific and interspecific competition with an exotic invader on the daytime and crepuscular activity levels of Atlantic salmon ( Salmo salar ) fry. We demonstrated that interspecific competition with the exotic rainbow trout ( Oncorhynchus mykiss ) significantly increases the daytime activity of Atlantic salmon. The effect of intraspecific competition on the daytime activity of salmon was half that of interspecific competition. This indicates that the effect of rainbow trout was a combination of increasing density and the identity of the competitor. We also demonstrated that the effect of rainbow trout was probably the result of territorial interference between species. Moreover, we showed that water temperature simultaneously played an important role in explaining daytime activity of Atlantic salmon. During twilight, we observed no effect of competition on salmon activity, but environmental cues other than temperature (e.g., invertebrate drift, cloud cover) became significant predictors of activity. Feeding and growth rates of Atlantic salmon were not affected by the different levels of competition. Nevertheless, the exotic species may have a major impact by exposing the native species to increased risks of daytime predation.

Competition, predation and flow rate as mediators of direct and indirect effects in a stream food chain

Using semi-natural stream channels, we estimated the effects of competition and predation exerted by juvenile and adult exotic rainbow trout (Oncorhynchus mykiss) on the diel activity pattern of juvenile native Atlantic salmon (Salmo salar), a secondary consumer. We also evaluated the direct and indirect effects of competition, predation and abiotic factors (water depth and velocity) on the growth rate of salmon, the biomass of invertebrate grazers (primary consumers) and the biomass of periphytic algae (primary producers; chlorophyll a). The presence of chemical cues emanating from adult predatory trout reduced the daily activity of juvenile Atlantic salmon. In contrast, competition imposed by juvenile rainbow trout forced Atlantic salmon to be more active during the day, even if adult rainbow trout were also present. We found no effect of either competition or of predatory cues on the growth rate of Atlantic salmon, and no evidence of indirect effects on either the biomass of invertebrates or the biomass of chlorophyll a. In contrast, we demonstrated that this food chain (fish--invertebrate grazers--periphytic algae) was under the control of a critical abiotic factor, the water velocity, and of bottom-up processes. We concluded that the exotic species directly increases the risk of predation of the native Atlantic salmon, but behavioral compensation probably limits the effects on growth rate. The competition and predation imposed by the invaders had no indirect effects on lower trophic levels. Top-down effects may have been mitigated by the dominant influence of water velocity controlling all components of the food chain and by elevated levels of primary production.

The aetiology of spinal deformity in Atlantic salmon, Salmo salar L.: influence of genetic factors on the frequency and severity in freshwater stages

A radiographic study was carried out on 2-year groups of pre-smolt parr to detect the comparative frequency of vertebral change in a range of defined pedigreed families of high growth rate of Atlantic salmon, Salmo salar L., reared under identical conditions. The observed frequency of deformity was related to the observed deformity level in the seawater parental generation, and to a potentially uncontrolled environmental determinant, i.e. stripping date. High and low parental deformity groups of families were found to produce offspring that had very similar levels of radiographically detectable spinal deformities in the pre-smolt parr, suggesting no genetic link. With regard to stripping date, the overall incidence was nearly half that seen in the preceding year (8.7% cf 16.6%). However, a non-significant trend to fewer radiographic spinal deformities was seen in the later stripping period.

Behavioural and Growth Responses of a Territorial Fish (Atlantic Salmon, Salmo salar, L.) to Multiple Predatory Cues

AbstractAntipredatory behaviours are important fitness components. The probability of survival decreases if animals fail to respond to signs of danger, but in contrast, energetic costs increase if the response to the threat is exaggerated. We conducted a laboratory experiment designed to examine the behavioural and growth responses of a territorial fish (Atlantic salmon fry, Salmo salar, L.) to different predatory cues (no predatory cues, chemical cues alone, physical cues alone and combined chemical and physical cues). We evaluated the response of Atlantic salmon, focussing on behaviours linked to predator avoidance and to other fitness‐enhancing activities (territory defence and energy acquisition) both during the day and the night. The cost of such responses in terms of growth was assessed and we compared the relative contributions of behaviours in explaining individual growth rate, according to each predation treatment. We demonstrated that the magnitude and nature of behavioural modification varied according to the response variables we considered. An index of predator avoidance and the distance from the food source were affected in an additive fashion by predatory cues (interaction term, p = 0.469 and p = 0.888 for the index of predator avoidance and the distance from the food source respectively); the effect of physical cues was stronger than the effect of chemical cues and the effect of the combined cues was highest. An index of territoriality was affected in a threshold‐like fashion (interaction term, p = 0.040); chemical or physical cues alone had no effect but when both cues were combined, Atlantic salmon significantly reduced their territorial defence. An index of foraging activity was not significantly affected by predatory cues (alone or combined). We detected no effect on the growth rate of Atlantic salmon (p = 0.328). Finally, we found that the relative contribution of behaviours in explaining individual growth rate changed according to the treatments we considered. Overall, these results demonstrated that fish were able to accurately integrate multiple predatory cues and that this information was used to modulate their antipredatory response. Behaviours involved in the response were relatively independent of each other, allowing fish to adopt behavioural tactics that maximized the ratio of net energy gain to predator avoidance.

Sea growth, smolt age and age at sexual maturation in Atlantic salmon

Relationships between growth at sea, smolt size and age at sexual maturation of Atlantic salmon Salmo salar were tested. The fish were offspring of brood stocks sampled in eight Norwegian rivers at latitudes between 59° and 70° N, hatchery reared and released at smolting at the mouth of the River Imsa (59° N). Smolt size influenced the subsequent growth rate of Atlantic salmon. The larger the fish were at release, the slower the yearly length increment at sea. Mean sea age at sexual maturity, measured as proportion of the returning adults attaining sexual maturity at sea age 2 years, was significantly correlated with mean growth rate during the first year at sea and mean smolt size (r2= 0·74, P < 0·001). Fish attaining maturity at a relatively high sea age were more fast growing during their first year at sea than those maturing at a younger age. The results indicate that high sea age at sexual maturation is a population‐specific characteristic and associated with high early growth rate at sea.

The disruption of dominance hierarchies by a non-native species: an individual-based analysis

We studied the effects of the exotic rainbow trout (Oncorhynchus mykiss) on the performance and the dominance hierarchy of native Atlantic salmon (Salmo salar) at the group and individual level using laboratory and semi-natural experiments. At the group level, we compared the effects of interspecific and intraspecific competition (substitutive and additive design) on behavioural responses and growth of young-of-the-year Atlantic salmon. At the individual level, the same design was used to evaluate: (1) the temporal consistency of behavioural responses, dominance hierarchy and growth rate of Atlantic salmon; (2) the pattern of correlations between behaviours; and (3) the relationship between individual growth rate and behaviour. In the laboratory, group-level analyses revealed a weak but similar effect of rainbow trout and intraspecific competition on the behaviour and growth of Atlantic salmon. In contrast, individual-based analyses demonstrated that rainbow trout (but not intraspecific competition) strongly affected behavioural strategy, dominance hierarchy and growth trajectory of individual Atlantic salmon. Specifically, behaviours, dominance status and growth rate of salmon were temporally consistent in the intraspecific environment, while these patterns were disrupted when rainbow trout were present. Similarly, we found that rainbow trout strongly affected behavioural correlations and the relationships between individual growth rate and behaviour. The semi-natural experiments confirmed these results as interspecific competition affected relationships between individual growth rate of salmon, initial weight and activity index. Overall, individual-based analyses highlighted important mechanisms that were concealed at the group level, and that may be crucial to understand ecological and evolutionary consequences of exotic species. Moreover, these results demonstrated that competition with an exotic species disrupts the hierarchical relationship among native individuals and may therefore represent a potential for a shift in selective pressure.

Do delivery rate and pellet size affect growth rate in Atlantic salmon (Salmo salar L.) raised under semi-commercial farming conditions?

Abstract How the daily feed ration is presented is an important aspect of feed management. In order to evaluate the effects of delivery rate and pellet size, Atlantic salmon ( Salmo salar L.) were raised in small (5×5×10 m), semi-commercial cages and were fed using 14 combinations of pellet sizes (0.03–2.68 g) and delivery rates (82.5–1320 g·min −1 (0.1–31.1 pellets·fish −1 ·min −1 )). Treatment groups were compared using the growth rate (Thermal Unit Growth Coefficient, TGC). No significant linear effect on growth due to pellet size or delivery rate could be detected. For pellet size, however, indications point to a non-linear relationship with growth rate. Salmon grew well (mean TGC (±S.D.)=2.68±0.49) irrespective of treatment indicating a high level of plasticity in the salmon's ability to adjust to changes in pellet size and delivery rates within the ranges used and under the conditions tested here.

Digestive protease activities and free amino acids in white muscle as indicators for feed conversion efficiency and growth rate in Atlantic salmon ( Salmo salar L.)

The aim of the present experiment was to screen several biochemical indices in fish and their interrelations in order to select variables for future studies of growth rate and feed conversion. Several parameters [trypsin activity, chymotrypsin activity, free amino acids (FAA) in plasma and white muscle, and RNA and RNA/protein ratio in the white muscle] were measured together with specific growth rate (SGR), feed intake and feed conversion efficiency (FCE) in four groups of diploid or triploid Atlantic salmon (Salmo salar L.) reared under different light regimes. SGR was measured on individually tagged fish, whereas feed intake and feed conversion was estimated on tank basis. A principal component analysis (PCA) explained 80.6% of the variance in the data, using all measured parameters, regardless of ploidy and light regime. Muscle free hydroxyproline showed the highest correlation, alone explaining 55% of SGR variability. The SGR also significantly correlated with trypsin activity (r=0.34), the activity ratio of trypsin to chymotrypsin (T/C) (r=0.39), plasma essential FAA (EAA) (r=0.39), plasma total FAA (TFAA) (r=0.37), the ratio of essential to non-essential FAA (EAA/NEAA) in the white muscle (r=−0.45), muscle RNA (r=−0.45) and RNA/protein ratio (r=−0.41). Tank FCE correlated positively (r=0.97) with SGR, T/C ratio and muscle free hydroxyproline, and negatively (r=−0.90) with muscle EAA/NEAA. The groups reared under continuous light (LL) regime showed significantly higher SGR than simulated natural photoperiod (SNP) groups, and with an apparently higher FCE. A higher growth rate was associated with either a higher consumption rate and/or a higher feed utilization. A negative correlation between muscle RNA concentration and SGR may indicate that increased growth rate under LL regime was not caused by an increased protein deposition rate.

The foraging and antipredator behaviour of growth-enhanced transgenic Atlantic salmon

Growth rate has been established as a key parameter influencing foraging decisions involving the risk of predation. Through genetic manipulation, transgenic salmon bred to contain and transmit a growth hormone transgene are able to achieve growth rates significantly greater than those of unmanipulated salmon. Using such growth-enhanced transgenic Atlantic salmon, we directly tested the hypothesis that relative growth rates should be correlated with willingness to risk exposure to a predator. We used size-matched transgenic and control salmon in two experiments where these fish could either feed in safety, or in the presence of the predator. The first experiment constrained the predator behind a Plexiglas partition (no risk of mortality), the second required the fish to feed in the same compartment as the predator (a finite risk of mortality). During these experiments, transgenic salmon had rates of consumption that were approximately five times that of the control fish and rates of movement approximately double that of controls. Transgenic salmon also spent significantly more time feeding in the presence of the predator, and consumed absolutely more food at that location. When there was a real risk of mortality, control fish almost completely avoided the dangerous location. Transgenic fish continued to feed at this location, but at a reduced level. These data demonstrate that the growth enhancement associated with the transgenic manipulation increases the level of risk these fish are willing to incur while foraging. If the genetic manipulation necessary to increase growth rates is achievable through evolutionary change, these experiments suggest that growth rates of Atlantic salmon may be optimized by the risk of predation.

Feed intake, growth and feed utilization of offspring from wild and selected Atlantic salmon ( Salmo salar)

The aim was to assess whether selection for increased growth rate in Atlantic salmon ( Salmo salar) is associated with increased feed intake and/or better feed utilization. Growth responses of offspring from selected and wild lines of Atlantic salmon (initial weight 814±14 g and 533±12 g, respectively) were tested in a 14-week experiment. Selected and wild salmon increased body weight by 79 and 39%, respectively, during the experiment. Relative feed intake (DFI), thermal growth coefficient (TGC) and feed efficiency ratio (FER) were significantly higher in the selected (DFI: 0.67% BW d −1, TGC: 2.96×10 −3 and FER: 1.16), than in the wild, line (DFI: 0.48% BW d −1, TGC: 1.39×10 −3 and FER: 0.93). FER was positively correlated with mean growth rate ( r=0.90, n=6, P<0.05), and differences between the lines indicated a 4.6% increase in FER per generation of selection. Fish of the selected line had a significantly lower intake of protein and energy per kilogram gain, so the higher growth rate of the selected line was the result of both greater feed consumption and more efficient feed utilization for growth. This implies that selection for increased growth rate in Atlantic salmon may improve both of these traits.

Changes in physiological parameters and feeding behaviour of Atlantic salmon Salmo salar infected with sea lice Lepeophtheirus salmonis.

Atlantic salmon Salmo salar L. artificially infected with salmon lice Lepeophtheirus salmonis (Krøyer 1837) recovered from detrimental physiological changes and skin damage induced by preadult lice as the parasites matured. Growth rates of Atlantic salmon remained unaffected by lice infection, but food consumption decreased with increasing feeding and movement of the lice prior to and post-mating, correlating with the appearance of head erosions and detrimental changes in physiological integrity. Food consumption of the fish increased as the lice moulted to the adult stage and gravid female lice settled in a posterior location on the fish, subsequently reducing the impact of infection and allowing recovery of the skin damage. However, the impact of preadults was limited, as the decrease in food consumption of fish at 21 d post-infection had no effect on either the specific growth rate or condition factor of the fish. Furthermore, the intensity of lice infections at each of the sample days was not correlated with food consumption, specific growth rate or any of the haematological or physiological parameters measured, either before or after infection, indicating that lice intensity was independent of social dominance/subordinance. This work has provided the first evidence that infected fish can recover from the detrimental changes caused by lice infection, even when they are still infected with lice. If fish can survive the preadult stage of lice, then the mortal impact of lice infections is greatly reduced.

Continuous light increases growth rate of Atlantic salmon ( Salmo salar L.) postsmolts in sea cages

Groups of Atlantic salmon ( Salmo salar L.) postsmolts were reared in sea cages under natural light or continuous additional light from 20 February to 24 June. The two light regimes were combined with two feeding regimes in a 2 by 2 factorial design. No significant differences in growth rate were found between the feeding regimes. Growth rate and incidence of grilsing were highest in the groups subjected to continuous additional light.

Genetic variation in growth rate of Atlantic salmon with different trypsin-like isozyme patterns

The growth rates of three different year-classes (1984, 1985 and 1987) of Atlantic salmon ( Salmo salar) were studied using trypsin-like isozyme pattern in the pyloric caeca as a biological genetic marker. The fish with the homozygote variant TRP-2(92/92) and with the heterozygote variant TRP-2(92/100) had higher average weight than those with the genotypes which did not possess the variant TRP-2(92). The difference in weight between the two groups (with and without TRP-2(92) variant) was significant from smolt until the end of the experiment in autumn of the first sea-year (1984 year-class) and until spring in the second sea-year (1985 year-class). The difference was about 30%, and decreased to 10% at maturation. The specific growth rate was critical during the first sea-year. The fish with the allele TRP-2(92) showed the advantage of faster growth in the first sea-year, especially during winter time. With the covariation of significant difference in weight (until the autumn in the second sea-year) among different families, higher production of food fish of at least 20% could be possible at the time of slaughter during the second sea-year with the use of a selective breeding programme based either on trypsin-like isozyme pattern and family or on the isozyme pattern of individuals. The effects of selection by using the variant TRP-2(92) could be observed within the period of the generation selected.

The effect of ultrasonic tags on the growth rates of Atlantic salmon, Salmo salar L., parr of varying size just prior to smolting

The attachment of dummy, ultrasonic, acoustic tags, of the Stirling Mk. VI design, to pre‐smolt Atlantic salmon parr significantly affected fish growth rates. Fish less than 160 mm in length lost weight and showed no change in length. Fish over 160 mm in length put on weight, though at a rate significantly lower than that of untagged controls. For fish between 160 and 180mm in length, the increase in length was significantly smaller in tagged fish than in untagged controls. Over 180 mm in length, no difference could be detected in the length gains of tagged and untagged fish.Smaller tagged fish gave up maintaining station and showed signs of distress at an earlier stage in the experiment than larger tagged fish. Tag‐related mortality was inversely related to fish size. All but two of the control fish survived the experiment and continued to maintain station throughout.The results suggest that the minimum length of Atlantic salmon parr on which this design of acoustic tag could be employed is 160 mm, and that caution is needed in the interpretation of track lengths longer than l0 daysof parr in the size range 160–180 mm.

Colonization of Inland Lakes in the Great Lakes Region by Rainbow Smelt, Osmerus mordax: Their Freshwater Niche and Effects on Indigenous Fishes

Rainbow smelt, Osmerus mordax, have colonized numerous inland lakes in eastern North America, primarily as a result of introductions by humans. Smelt often establish large populations in these lakes and influence indigenous fishes both directly (predation) and indirectly (competition). Smelt have a eurythermal life history, which results in spatial segregation of their larvae, juvenile, and adults, and are omnivorous feeders, eating a range of food types from zooplankton to fish. As a result, smelt interact strongly with a wide spectrum of prey and predator species. Effects on other species are mediated via food web interactions resulting in recruitment and growth changes in some species and redirection of energy flow and storage. Species most often affected are cold-water and cool-water species whose niches are most similar to juvenile and adult smelt. Increased growth rates of Atlantic salmon (Salmo salar) and lake trout (Salvelinus namaycush) and recruitment failure of lake whitefish (Coregonus clupeaformis) are the best documented responses to invasion by smelt. Many other species are probably also affected, although the effects vary greatly between lakes. Variation in the smelt metabolic niche (as expressed by relative growth efficiency) is due to variations in prey size and availability and is reflected in differences in smelt body size between lakes. Smelt body size, in turn, is related to the variable effects that they have on other species.

Different Adaptation Strategies of Atlantic Salmon (Salmo salar) Populations to Extreme Climates with Special Reference to some Cold Norwegian Rivers

Some of the salmon rivers on the western and northern coasts of Norway are very cold, and the sea temperature outside these rivers is almost always higher than that in the river. Growth rates of Atlantic salmon (Salmo salar) parr and smolt ages and sizes have been examined in three such cold rivers. We found indications that the lower temperature limit for growth of Atlantic salmon is not a fixed temperature, but varies from population to population according to the temperature regime of their environment. Smolts are small, with average sizes of 12–13 cm total length. Females dominated in number among the smolts, but the dominance was less pronounced than in most other rivers. Strategies used by Norwegian salmon in cold rivers are therefore different from those employed by salmon in the northern extremes of the salmon's range in Canada.

The effect of feeding thyroid hormones on saltwater tolerance and growth rate of Atlantic salmon

Two experiments, involving the addition of thyroid hormones to the diet of salmon parr (Salmo salar) were carried out. The prime purpose of these experiments was to study the effect of feeding thyroid hormones on saltwater tolerance. Saltwater tolerance is interrelated with size and therefore growth rate was investigated. In experiment I three different thyroid preparations were used: thyroid extract, 3,5,3′-triiodo-L-thyronine (T3), and thyroxine (T4). Each thyroid preparation was fed to two different sizes of fish with two different concentrations in the diet. T3 gave the best overall results, both for saltwater tolerance and growth rate. No interaction was found between fish size and concentration of thyroid hormone in the diet. In experiment II three different concentrations of T3 in the diet were fed to salmon parr of two different ages. Feeding T3 improved saltwater tolerance and growth rate of 7-month-old fish but had a negative effect upon growth for 19-month-old fish. For the 7-month-old fish 10 mg T3/kg dry food gave the best effect on saltwater tolerance, while 1 mg T3/kg dry food was enough to improve growth. It is concluded that it is possible to induce smoltification in underyearling Atlantic salmon out of season by feeding thyroid hormones.