Juvenile Atlantic Salmon Research Articles

Spatial association of genetically similar Atlantic salmon juveniles and sex bias in spatial patterns in a river

Atlantic salmon (Salmo salar) juveniles were electrofished along a 300‐m stretch of a river to test for possible associations between genetic similarity and geographical distance between individuals. Multilocus DNA fingerprinting showed that genetically similar juveniles (1–4 years old) were found closer together in the river than less related individuals. However, the association between genetic similarity and geographical distance, although significant, was not strong. This may indicate that factors other than genetic relatedness influence the positioning in the river. A sex bias in the relationship between genetic similarity and geographical distance was caused by a difference between sexually mature and immature males. The study shows that sampling of salmon juveniles should be spread over a wide stretch of the river in order to avoid sampling relatives. Moreover, by including several year classes, the overall degree of genetic similarity is effectively reduced compared with sampling individuals of similar age.

Life‐history patterns in a southern population of Atlantic salmon

Juvenile Atlantic salmon Salmo salar in the river Esva, Asturias, north‐west Spain, developed a bimodal growth pattern during their first growing season. Segregation between the two modes was apparent by late autumn. All fish in the upper modal group (UMG) grew throughout the year and migrated downstream in the following spring (by April) at the age of 14 months. Some lower modal group (LMG) fish (56% of the main stem, 31% and 50% of the two tributaries) silvered like smolts and apparently migrated downstream the same spring, although c. 1·5 months after UMG fish. Larger LMG fish appeared more likely than smaller ones to migrate. LMG fish did not grow in winter, but they grew fast between March and May. Maturing male parr were detected first at 5 months old in July, and they occurred initially among the faster growers, >6·8 cm long. In spite of this, length of maturing males did not change from late summer and throughout the winter, whereas that of non‐maturing UMG and LMG fishes continued to diverge from September onwards. These findings suggest that favourable conditions for growth (very early start of a long growing season) at the southern limit of the species' range may influence the life‐history pattern of this population.

Life-history patterns in a southern population of Atlantic salmon

Juvenile Atlantic salmon Salmo salar in the river Esva, Asturias, north-west Spain, developed a bimodal growth pattern during their first growing season. Segregation between the two modes was apparent by late autumn. All fish in the upper modal group (UMG) grew throughout the year and migrated downstream in the following spring (by April) at the age of 14 months. Some lower modal group (LMG) fish (56% of the main stem, 31% and 50% of the two tributaries) silvered like smolts and apparently migrated downstream the same spring, although c. 1·5 months after UMG fish. Larger LMG fish appeared more likely than smaller ones to migrate. LMG fish did not grow in winter, but they grew fast between March and May. Maturing male parr were detected first at 5 months old in July, and they occurred initially among the faster growers, >6·8 cm long. In spite of this, length of maturing males did not change from late summer and throughout the winter, whereas that of non-maturing UMG and LMG fishes continued to diverge from September onwards. These findings suggest that favourable conditions for growth (very early start of a long growing season) at the southern limit of the species' range may influence the life-history pattern of this population.

Density-dependent habitat selection by juvenile Atlantic salmon (Salmo salar) in experimental riverine habitats

We investigated habitat use of Atlantic salmon (Salmo salar) parr in experimental riverine enclosures made up of pool, riffle, and run habitats over a range of densities (0.1-1.25 fish·m-2) to test the implicit assumption in habitat modelling that habitat selection does not change with population density. Results indicated that habitat use changed with population density, with relatively more parr in pools and fewer in runs at higher population densities. Temperature influenced parr distribution, with relatively more parr in runs and fewer in riffles and pools at higher temperatures. Parr distribution was primarily affected by hydromorphological differences among pool, riffle, and run habitats. Effects of population density and temperature on use of pool, riffle, and run habitats were often as large as effects of hydromorphological differences among pool, riffle, and run habitats on fish distributions over the range of temperatures and densities observed. Results varied considerably, despite controlled experimental conditions. We concluded that habitat selection by juvenile Atlantic salmon parr may be density dependent and potentially quite variable.

Spatial association of genetically similar Atlantic salmon juveniles and sex bias in spatial patterns in a river

Spatial association of genetically similar Atlantic salmon juveniles and sex bias in spatial patterns in a river

Revealing trends in densities of juvenile Atlantic salmon,Salmo salarL., in the subarctic River Teno using cluster analysis on long‐term sampling data

Abstract The density of juvenile Atlantic salmon,Salmo salarL., was monitored at 57 sites representing different habitats in the River Teno and two of its major tributaries from 1979 to 1995. Cluster analyses were used to combine sites with similar densities and to study trends in densities within clusters. It was found that management measures have played an important role in maintaining salmon stocks and there was some evidence of increasing juvenile salmon densities. Parr densities decreased significantly in one cluster containing 45% of the sites studied in the River Utsjoki, whereas densities increased significantly in one cluster in the River Teno and in one cluster in the River Inarijoki containing 38% of the sites in these rivers. Fry densities increased significantly in two clusters containing 16% of all the sites studied in the three rivers. In general, the mean densities in successive years in the clusters were independent. The results demonstrate the value of long‐term monitoring in ecological investigations.

Revealing trends in densities of juvenile Atlantic salmon,Salmo salarL., in the subarctic River Teno using cluster analysis on long‐term sampling data

The density of juvenile Atlantic salmon,Salmo salarL., was monitored at 57 sites representing different habitats in the River Teno and two of its major tributaries from 1979 to 1995. Cluster analyses were used to combine sites with similar densities and to study trends in densities within clusters. It was found that management measures have played an important role in maintaining salmon stocks and there was some evidence of increasing juvenile salmon densities. Parr densities decreased significantly in one cluster containing 45% of the sites studied in the River Utsjoki, whereas densities increased significantly in one cluster in the River Teno and in one cluster in the River Inarijoki containing 38% of the sites in these rivers. Fry densities increased significantly in two clusters containing 16% of all the sites studied in the three rivers. In general, the mean densities in successive years in the clusters were independent. The results demonstrate the value of long‐term monitoring in ecological investigations.

Sibling competition and the evolution of growth rates in birds

Variation among bird species in growth rates is traditionally attributed to differences in energy availability and developmental mode. However, the extent and form of competition among siblings for limited food resources may also be an important determinant. Kin-selection-based models of intrabrood competition suggest that nestling growth rates should be highest in those species in which siblings are likely to be less genetically related to one another (half-sibs rather than full-sibs). We test this novel prediction using the frequency of multiple paternity as an index of average sib relatedness within broods. As predicted, we find a significant positive association between the rate of multiple paternity within broods and nestling growth rates. Furthermore, this holds true when we control for the effects of variation in other factors that may be associated with variation in growth rate, such as body size, brood size, mating system and the form of parental care. We suggest, therefore, that variation in growth rate among bird species is not simply dependent on proximate ecological and developmental factors but is also strongly influenced by interactions, over an evolutionary time-scale, among kin.

Using 137Cs to measure and compare bioenergetic budgets of juvenile Atlantic salmon (Salmo salar) and brook trout (Salvelinus fontinalis) in the field

Through the 137Cs mass balance method, annual consumption rates were estimated for juvenile Atlantic salmon (Salmo salar) parr and precocious males as well as for brook trout (Salvelinus fontinalis) at four sites in the Ste-Marguerite River system, Québec. With explicit age analysis, consumption rates and growth rates were derived on an individual fish and age-class basis. These represent the first consumption estimates for Atlantic salmon in the wild. Precocious males had consumption rates 1.5 times greater than nonmaturing parr, while Atlantic salmon parr consumption rates were 2.7 times greater than brook trout. There was a strong positive relationship between individual annual consumption and growth rates for Atlantic salmon and brook trout at all sites. Subsequently the concept of field maintenance ration was introduced as the intercept of consumption over growth. Maintenance rations for Atlantic salmon parr ranged from 0.010 to 0.016 g·g-1·day-1 between sites. Brook trout had maintenance rations approximately half those of Atlantic salmon at 0.0059 g·g-1·day-1. Precocious male growth efficiencies were half those of nonmaturing parr despite higher feeding and growth rates. Brook trout growth efficiencies were significantly greater than those of Atlantic salmon parr. The lower growth efficiencies observed for Atlantic salmon are likely due to increased metabolic costs associated with higher activity. On average, Atlantic salmon parr spent 2.4-fold more energy in activity than brook trout. Atlantic salmon precocious males spent 1.7 times more energy in activity than parr.

Food availability and the nocturnal vs. diurnal foraging trade‐off in juvenile salmon

1.Much attention has been devoted to explaining the spatial distribution of foraging animals, but rather little to their temporal distribution (i.e. whether they are diurnal, nocturnal or crepuscular). Many animals face predictable diel cycles of food availability or predation risk, and so the approach of measuring the relative ratio of mortality risk to food gained (the ‘minimize μ/f’ rule) can be applied equally as well to different time periods of the day as to alternative food patches or habitats.2.This method is used here to investigate the diel activity patterns of juvenile Atlantic salmon, which have previously been shown to become increasingly biased towards nocturnal activity in winter, hiding for much of the day in streambed refuges. Calculations based on published data show that nocturnal foraging in winter is far safer per unit of food obtained than is diurnal, despite greatly reduced food capture efficiency at night‐time light levels.3.Using an automated activity monitoring system based on passive integrated transponder (PIT) tags, this study shows that winter diel activity patterns in salmon are dependent on food availability. A change in food density led to a parallel change in time spent in the refuge, but (as predicted by the μ/frule) the effect was greatest at the time of day with the least favourable ratio of predation cost to feeding benefit. Thus an experimental increase in food availability led to a 16% reduction in time spent in nocturnal foraging but a 98% reduction in time spent foraging by day, with fish spending only 0·6% of the daylight hours out of the refuge at the highest food density.4.However, brief daytime foraging bouts had a major impact on growth rates (presumably because feeding efficiency was much greater in daylight), especially when food was scarce. Daytime feeding was thus profitable in terms of rapid food acquisition but normally suboptimal in terms of risk of predation.5.Daily activity patterns are therefore suggested to be the result of a complex trade‐off between growth and survival, which takes account of diel fluctuations in food availability, food capture efficiency and predation risk; individual variation in the extent of diurnal feeding in salmon may result from state‐dependent differences in the benefits of rapid feeding and growth.

Does Carnobacterium divergens isolated from Atlantic salmon, Salmo salar L., colonize the gut of early developing turbot, Scophthalmus maximus L., larvae?

It is well established from endothermic animals that the adhesion of lactic acid bacteria involves host speci®city (Fuller 1986). In juvenile ®sh, JoEborn, Olsson, Westerdahl, Conway & Kjellberg (1997) reported by in vitro tests that a Carnobacterium sp. isolated from Atlantic salmon, Salmo salar L., colonized the gastrointestinal tract of rainbow trout, Onchorynchus mykiss (Walbaum). However, no information from ®sh larvae is available on whether the adhesion of lactic acid bacteria involves host speci®city. This is relevant in the context of whether or not it is possible to colonize the gastrointestinal tract of larvae at early stages with probiotics, notably Gram-positive bacteria, such as lactic acid bacteria, or by a resident micro ora, which may contribute to nutrition. The following bacteria were used in the present study: Vibrio pelagius isolated from copepod-fed turbot, Scophthalmus maximus L., larvae (Munro, Barbour & Birkbeck 1994), which is unusual in that it contains the polyunsaturated fatty acid eicosapentaenoic acid (20:5 n-3) (Ringu, Sinclair, Birkbeck & Barbour 1992), and a lactic acid bacterium, Carnobacterium divergens, isolated from Atlantic salmon. The main reason for using this species was that it produced a substance that inhibited the growth of both Vibrio anguillarum and Proteus vulgaris (Strum 1988), and Aeromonas salmonicida (Ringu 1999). Recently, colonization of different bacterial strains in larval turbot was determined using an enzyme-linked immunosorbent assay (ELISA) (Ringu, Birkbeck, Munro, Vadstein & Hjelmeland 1996; Ringu & Vadstein 1998). The purpose of the current study, was to evaluate whether a C. divergens, orginally isolated from Atlantic salmon, was able to colonize the gut of turbot larvae by adding this bacterial species to the rearing water and to compare these results with those for larvae exposed to V. pelagius, by using the ELISA method. Furthermore, a previous study (Ringu et al. 1996) demonstrated that antisera used in ELISA showed high sensitivity against homologous bacterial antigens and very little crossreaction with heterologous bacteria. Turbot eggs were obtained from Tinfos Aqua, Norway, and 1000 eggs were incubated in 80-L circular tanks with at bottoms in static water. A detailed description of larval rearing conditions and cultivation of live feed (Brachionus plicatilis SINTEFstrain) is given by Ringu et al. (1996). The following bacterial strains were used: C. divergens, originally isolated from young Atlantic salmon juveniles (Strum 1988); and Vibrio pelagius, isolated from copepod-fed turbot larvae (Munro et al. 1994). Vibrio pelagius was identi®ed as described by Munro et al. (1994) using the `Bacterial Identi®er' program (Bryant, Lee, West & Colwell 1986). Carnobacterium divergens was identi®ed using carboR

An analysis of the distribution of juvenile Atlantic salmon (Salmo salar) in nature as a function of relatedness using microsatellites

The major objective of this study was to test the hypothesis that juvenile Atlantic salmon kin occupy adjacent territories in their natural habitat in order to profit from the benefits associated with kin‐biased behaviours, as has been observed under controlled laboratory conditions. Microsatellites were used to establish the relatedness of salmon fry (in their first summer of life) and parr (in their second and third summer of life) captured in adjacent territories. We did not observe a relationship between the proximity and the relatedness of either parr of the same cohort or fry in their natural habitat. Although many pairs of fry were identified as being related when sampled immediately after emergence, most family groups did not occupy adjacent territories. The high dispersal potential in rivers, the low occupation rate of the habitat and the incidence of half‐sibs in nature most probably reduce the opportunity and advantage of kin‐biased behaviour, in contrast to laboratory studies conducted in artificial, high‐density conditions.

Effect of time of day, time of year, and life history strategy on time budgeting in juvenile Atlantic salmon, <i>Salmo salar</i>

Effect of time of day, time of year, and life history strategy on time budgeting in juvenile Atlantic salmon, <i>Salmo salar</i>

Effects of potential xenoestrogens (DEHP, nonylphenol and PCB) on sexual differentiation in juvenile Atlantic salmon (Salmo salar)

Abstract The effects of 17β-estradiol and potential xenoestrogens were investigated on Atlantic salmon (Salmo salar). Juvenile salmon fed diets containing 15 and 30 mg 17β-estradiol kg-1 food for 4 weeks after yolk-sac resorption differentiated into 88 and 100% phenotypic females, respectively. The reference group, fed uncontaminated food, consisted of 49% females. A significant overrepresentation of phenotypic females (64%) was recorded in the group fed 1500 mg di-2-ethylhexyl phthalate kg-1 food. Atlantic salmon fed diets contaminated with nonylphenol showed no differences in sex ratios compared with the control group. A significantly increased liver somatic index was detected for groups exposed to diets contaminated with 15 and 30 mg 17β-estradiol, 300 mg nonylphenol or 1500 mg di-2-ethylhexyl phthalate kg-1 food. Intraperitoneal injections of nonylphenol, di-2-ethylhexyl phthalate, or polychlorinated biphenyls 58, 104, 112 and 188 did not induce synthesis of vitellogenin which is considered to be a hallmark for estrogenic activity in in vivo testing. Therefore, in vivo assays, that is, intraperitoneal injection, can not always predict how endocrine processes in organisms are affected by pollutants.

Characterization of the heat shock protein response of Atlantic salmon (Salmo salar)

The heat shock protein (hsp) response of juvenile Atlantic salmon, Salmo salar was investigated in isolated tissues subjected to various degrees of thermal shock. Distinct but overlapping arrays of proteins from the major hsp families (hsps 100, 90, 70, 60 and small hsps) were induced in branchial lamellae, hepatic tissue and erythrocytes. The two most prominent proteins induced by heat shock (MW ≅ 65 and 66 kDa) were found to be antigenic homologues of mammalian hsps72/73. A 2.6 kb transcript upregulated by the same conditions hybridized with cDNA probes to both human and salmon hsp70. Branchial lamellae exhibited the greatest degree of thermotolerance and mounted the most significant heat shock response. Moderate thermal shock induced more species of proteins in branchial lamellae than in hepatic tissue or erythrocytes, with the rate of hsp65/66 synthesis increased by as much as five fold. Thermal shock induced hsp65/66 eight fold in erythrocytes. In contrast, hepatic tissue which was least tolerant of thermal shock, lacked the inducible hsp65 and exhibited minimal induction of hsp66. Persistence of hsps was tested in erythrocytes, where elevated levels remained in the cells for at least 48 h after heat shock. The temporal pattern and magnitude of the hsp response in the stenothermal Atlantic salmon differed from that previously reported for eurythermal species. Also notable was the limited hsp response mounted by salmon tissues exposed to sodium arsenite, a known inducer of hsps. The characteristics of the hsp response to thermal shock support the significance of these proteins in adaptation of Atlantic salmon to environmental insult.

Diel feeding rhythms and daily food consumption of juvenile Atlantic salmon in the River Alta, northern Norway

Diel feeding rhythms and daily food consumption of juvenile Atlantic salmon in the River Alta, northern Norway

Immunohistochemical analysis of the vitellogenin response in the liver of Atlantic salmon exposed to environmental oestrogens

Induction of vitellogenin (Vtg) in oviparous vertebrates has been used as a biomarker of response for environmental oestrogens. This study reports the cellular localization of oestrogen- and xenoestrogen-induced Vtg synthesis in the liver of juvenile Atlantic salmon (Salmo salar). Paraffin-embedded liver sections were incubated with homologous monoclonal antibody against Atlantic salmon Vtg. Following intraperitoneal (ip) exposure of fish to estradiol-17beta E2; 5 mg kg-1 or 4-nonylphenol NP; 125 mg kg-1, Vtg induction was primarily demonstrated immunohistochemically in the cytoplasm of hepatocytes, endothelial cells and within hepatic sinusoids. Vtg staining of hepatocytes was not evenly distributed, as there was a high degree of polarization toward the sinusoid. The intensity of positive Vtg staining was stronger in the liver sections of E2-treated fish, compared with NP-treated fish. Hepatocytes of E2-, NP- and vehicle (control)-treated fish showed normal cellular structures, thus showing no evidence of histopathological changes. In parallel, indirect enzyme-linked immunosorbent assay (ELISA) and immunoblot analysis of plasma Vtg levels show significant induction of Vtg in E2- and NP-treated fish, as compared with untreated (control) fish. The present study demonstrates the applicability of immunohistochemistry in studies of cellular structures, processes and responses of fish exposure to oestrogen and oestrogen-mimicking compounds.

Diel feeding rhythms and daily food consumption of juvenile Atlantic salmon in the River Alta, northern Norway

Atlantic salmon fry (0+) sampled from the River Alta exhibited only minor differences in stomach content weights and feeding rates throughout diel periods, but feeding rates were generally lowest at night. In contrast, salmon parr (1+ to 3+) had large diel fluctuations in stomach content weight, with the largest weights usually being recorded during the night and early morning. Accordingly, their feeding rates were highest at night. This nocturnal feeding pattern was consistent throughout all sampling occasions, and appeared to reflect a persistent feeding periodicity in the salmon parr. The daily food consumption rates of both fry and parr were highest during midsummer and decreased towards autumn.

Status of sanitary control measures in French aquaculture

Summary The French legislation on sanitary control measures in aquaculture follows closely the European ad hoc Directives (EEC 91–67, 93–54, 95–22) and Decisions (e.g. EC 92–532 and 96–240). The decree of December 1995 relates to notifiable diseases: salmon infection anaemia (SIA), viral haemorrhagic septicaemia (VHS) and infectious haematopoietic necrosis (IHN). The Departmental Order of April 1997 relates to the placing of aquaculture animals and products on the market. The import of living fish from third countries is ruled by Departmental Orders of June 1994. Because of the long standing historical efforts on sanitary conditions in aquaculture, a major part of the fish farming production is today realized in approved facilities (Decisions CE 95–125, 95–481, 97–227). On the request of the fish farmers' union, an epidemiological survey should be carried out in the nonapproved areas to derive future control measures. National or regional projects on medical or sanitary control have also been established for other significant fish diseases, particularly for infectious pancreatic necrosis, sleeping disease, viral encephalopathy and retinopathy, bacterial kidney disease. Vaccination is used against enteric redmouth disease and attempts are currently underway against furunculosis. An epidemiological survey on gyrodactylosis is under consideration, although no incidence in Atlantic salmon juveniles of Gyrodactylus salaris has ever been reported in France.

Regulation of Gill Cytosolic Corticosteroid Receptors in Juvenile Atlantic Salmon: Interaction Effects of Growth Hormone with Prolactin and Triiodothyronine

The potential effects of growth hormone (GH), prolactin (Prl), and triiodothyronine (T3) on gill Na+,K+-ATPase activity and corticosteroid receptor (CR) concentration (Bmax) and dissociation constant (Kd) were examined in juvenile Atlantic salmon (Salmo salar). Compared to controls, fish injected with GH (ovine, 5.0 μg g−1) had significantly greater gill Na+,K+-ATPase activity after 7 and 14 days. Gill CRBmaxandKdwere significantly elevated on day 7, but not day 14. T3also significantly increased CRBmax. The effect of GH on CRBmaxwas also additive with T3(5.0 μg g−1) treatment. There was a synergistic effect on CRBmaxwhen purified coho salmon GH (csGH, 0.1 μg g−1) was injected in combination with T3(1.6 μg g−1). Prl (ovine, 5.0 μg g−1; purified coho salmon, 0.1 μg g−1) did not significantly alter gill CRBmax. Although Prl limited the increase in CRBmaxby GH, the effect was not signicant. T3and Prl did not have an effect onKd. GH significantly increased gill Na+,K+-ATPase activity, T3administration did not have a significant effect, and Prl-treated fish had significantly lower gill Na+,K+-ATPase activity. The results indicate that T3acts additively with GH, while Prl has no effect in regulating CRBmax. An increase in cytosolic CR by GH and T3, but not Prl, may regulate gill responsiveness to cortisol and be an important mechanism in the endocrine control of physiological changes during the parr–smolt transformation.