Differential reproductive success and heritability of alternative reproductive tactics in wild Atlantic salmon (Salmo salar L.)

Abstract A critical step in understanding the evolution and maintenance of alternative reproductive tactics is to obtain accurate comparisons of their fitness and to determine factors influencing individual status. In this study, we first used individual multilocus genotypic information to compare reproductive success between two alternative reproductive tactics of anadromous Atlantic salmon (Salmo salar L.) in their natural environments. We also documented the effects of the quality of the rearing environment and of paternal reproductive tactics on heritability of juvenile growth, which is an important component of individual status. Results showed that large dominant salmon (multisea winter) had higher reproductive success than smaller satellite individuals (grilse). Also, there was a status difference associated with both habitat and male tactic. Overall, offspring produced in streams were bigger than those produced in the main river stretch. Grilse also produced bigger offspring than those fathered by multisea winter males. Heritability of juvenile growth was significant but varied according to quality of habitat: higher heritability estimates were observed in higher quality habitats (streams) than in lower quality habitats (main river stretch). Heritability estimates for juvenile growth varied as well, depending on male tactic, with progeny fathered by multisea winter males having higher values than those fathered by grilse. Together, these results indicate that a combination of additive genetic effects, parental life history and habitat quality will ultimately shape juvenile growth rate, which is the main determinant of status and of subsequent choice of life-history tactics.     

Genetic variation in haemolytic activity in Atlantic salmon (Salmo salar L.)

Spontaneous and antibody-dependent haemolytic activity against sheep red blood cells (SRBC) has been studied in serum from Atlantic salmon, Salmo salar L. Considerable increase in haemolytic activity was detected when SRBC were sensitized with haemolysin produced in Atlantic salmon. Haemolytic activity was sensitive both to divalent cations and to heat treatment. Significant reduction in haemolytic activity was detected after absorption with SRBC, indicating the presence of natural antibody against SRBC in Atlantic salmon serum. Persistent haemolytic activity of unsensitized SRBC in serum absorbed to remove natural antibodies was found, which suggests the activation of the alternative complement pathway, while the observed increased haemolytic activity in the presence of specific antibody against SRBC suggests activation of the classical complement pathway. Spontaneous and antibody-dependent haemolytic activity were both analysed in absorbed and non-absorbed sera in a family material of Atlantic salmon. The material consisted of 574 fish belonging to 57 fullsib groups within 20 paternal halfsib groups. Fish with signs of sexual maturity generally showed reduced haemolytic activity. Statistically significant effect of sire on the spontaneous haemolytic activity of both absorbed and nonabsorbed serum, and on antibody-dependent activity, provides evidence of significant additive genetic variation in both the alternative and the classical complement activation in Atlantic salmon. Neither on a phenotypical nor on a family basis were the two traits statistically correlated. The estimated heritabilities were 0.2–0.3 with a standard error of approximately 0.1.     

Cloning and characterization of alpha-amylase from Atlantic salmon (Salmo salar L.)

Amylase has a lower activity in carnivorous fish species, particularly in Atlantic salmon. We report the first cloning of a salmonid alpha-amylase cDNA from Atlantic salmon, a major species in aquaculture. By amino acid alignment of several species, we identified a seven amino acid deletion in one of the large loops of the enzyme in relatively close proximity to the active site, that could impair substrate binding. We also found the signal peptide to be less hydrophobic compared to other species. This may affect import into ER during protein synthesis. Active site residues were shown to be conserved. Amylase mRNA expression was shown in pancreatic tissue, liver, and in the heart. Using blocked p-nitrophenyl-maltoheptaoside as a substrate, we measured a low amylase activity in Atlantic salmon intestinal content, which was about half of the activity measured in Atlantic cod, whereas activity measured in rainbow trout was fourteen times higher. Amylase activities in all three species showed similar degree of reduction in hydrolytic activity in a dose-response trial with a wheat amylase inhibitor preparation. This indicates similar specific activity per amylase molecule.     

Phagocytosis by B-cells and neutrophils in Atlantic salmon (Salmo salar L.) and Atlantic cod (Gadus morhua L.)

Phagocytosis by fish cells has mostly been studied using adherent leucocytes, excluding suspended cells such as the majority of B-cells and neutrophils, but a recent study describes professional phagocytosis of latex beads and bacteria by B-cells from rainbow trout. In the present study, phagocytosis by B-cells and neutrophils from salmon and cod was studied. Leucocytes were isolated from peripheral blood (PBL) and head kidney (HKL). By flow cytometry analyses, proportions of MAb labelled cell populations with internalized fluorescent beads, as well as the number of beads within each cell, could be determined. Phagocytic capacity and ability were demonstrated in B-cells and neutrophils from salmon and cod. In salmon, B-cells had higher phagocytic ability than neutrophils in HKL, but not in PBL. For cod the phagocytic ability of B-cells were lower than for neutrophils in both HKL and PBL, but the phagocytic capacity of cod B-cells were higher than for neutrophils in both HKL and PBL. For salmon B-cells the phagocytic capacity was lower than or similar to neutrophils in HKL and PBL. The total phagocytic ability of leucocytes was different in the species studied. The highest phagocytic ability was observed in cod, showing similar values for PBL and HKL. Salmon PBL displayed about twice the phagocytic ability of cod PBL. There seemed to be some major differences between the two fish species concerning phagocytosis. In salmon, a rather large proportion of phagocytic leucocytes were phagocytic B-cells, indicating that B-cells may have an important function in particle clearance in this species. In cod, phagocytic leucocytes in HKL and PBL were mostly neutrophils, and only a small proportion of B-cells were phagocytic, supporting the more prominent role of innate immune functions in cod neutrophils.     

First feeding of Atlantic salmon (Salmo salar L.) under different photoperiods

Juvenile Atlantic salmon ( Salmo salar L. ) were first fed under four different static photoperiods (LD 24:0, LD 21:3, LD 18:6, LD 12:12) in two experiments. Under LD 24:0, continuous feeding or feeding 12 hours per day did not affect growth rate. In both experiments the roup on continuous light (LD 24:0) had highest growth rate. Growth was reduced on reduced dayfength. It is suggested that the difference in growth between long day (LD 21:3) and continuous light (LD 24:0) was caused by a growth inhibition during the dark period.

Zusammenfasung

Erste Nahrung des Atlantischen Lachses (Salmo salar L .)
Jungfische des atlantischen Lachses ( Salmo ralar L. ) wurden unter vier verschiedenen Photoperioden in zwei Experimenten erstmals gefüttert (LD 24:0; LD 21:3; LD 18:6; LD 12:12). Bei kontinuierlicher Fütterung (LD 24:0) oder Fütterung über 12 Stunden pro Tag, war die Wachsturnsrate nicht beeinflußt. In beiden Exerimenten hatte die Gruppe, die unter durchgehender Beleuchtung aufgezogen wurde, die höchste Wacgstumsrate. Das Wachsturn war bei kürzerer Tageslänge reduziert. Aus den Daten wird geschlossen, daß die Differenz im Wachstum zwischen dem Langtag (LD 21:3) und der durchgehenden Beleuchtung (LD 24:0) durch eine Wachtumshemmung während der Dunkelzeit verursacht wurde.     

Sperm traits in farmed and wild Atlantic salmon Salmo salar

Differences in sperm metabolism and morphology between wild and non‐local farmed Atlantic salmon Salmo salar were assessed by measuring metabolic enzyme activities and length of sperm flagella. No differences were observed between wild and farmed S. salar sperm with regards to cell counts or any of the biochemical variables assessed. Flagella of sperm cells were significantly longer in wild than farmed S. salar; however, this did not result in higher energy levels or different fertilization rates.     

The effects of handling on flounder (Platichthys flesus L.) and Atlantic salmon (Salmo salar L.)

The effect of 9 min of net confinement on two marine teleost species, the flounder and the Atlantic salmon, was investigated in order to gauge how different species respond to the same stress stimulus. Net confinement in both species induced significant elevations in plasma cortisol, glucose, lactate, osmolality, and monovalent ion levels; the responses to net confinement in salmon were generally of a greater magnitude. In both species, handling induced significant alterations in PFFA levels though there were marked species differences in the qualitative and quantitative aspects of this response. Plasma protein levels were significantly elevated only in the flounders. In general, the two species responded similarly to the net confinement with differences only in the absolute levels and durations of the responses.     

Energetics in Atlantic salmon (Salmo salar L.) parr fed elevated dietary cadmium

Atlantic salmon (Salmo salar L.) parr were reared for 4 months on experimental diets supplemented with Cd (0.5, 5, 25, 125, or 250 mg Cd x kg(-1)) to assess the long-term energetic changes based on the digestibility and biochemical deposition of the major dietary nutrients and to evaluate a maximum tolerable dietary toxicant concentration. Growth did not differ significantly (P>0.05) from the control groups. The biochemical composition of the carcass, but not the viscera, was negatively affected by dietary Cd exposure. The significant decreases in protein, lipid, and glycogen concentrations in the carcass (P<0.05, 25 mg x kg(-1) compared to control groups) caused a reduction in calculated whole-body energy content in fish fed 125 mg x kg(-1)compared to control groups. This reduction in calculated whole-body energy content was explained by a concurrent significant disturbance to the gastrointestinal function (measured as reduced digestibility). Only at the highest dietary Cd exposure (250 mg x kg(-1)), increased metabolic costs to cope with Cd toxicity was thought to contribute significantly to the reduction in carcass energy content. The most important factor effecting calculated total energetics was nutrient digestibility. Based on the logarithmic effective median concentration for reduced calculated energy digestibility (dietary Cd concentration corresponding to 50% reduction, EC50), the maximum tolerable dietary Cd concentration is 11 mg x kg(-1) diet.     

Arsenobetaine in Atlantic salmon (Salmo salar L.): influence of seawater adaptation

Glycine betaine has been suggested to improve the maintenance of ionic and osmotic homeostasis during seawater adaptation in teleost fish. Arsenobetaine may also behave as an osmolyte, due to its structural similarity to glycine betaine. The influence of seawater adaptation on intestinal uptake and muscle accumulation of arsenobetaine in the teleost Atlantic salmon (Salmo salar L.) was investigated. Atlantic salmon (freshwater and seawater adapted) were given a single oral dose of arsenobetaine, which was absorbed over the intestine within 6 h after exposure. Seawater adapted Atlantic salmon had significantly higher levels of accumulated arsenobetaine in blood compared to the freshwater adapted salmon. However, seawater adaptation had no effect on the levels of accumulated arsenobetaine in muscle tissue. Similar retention of the administered dose was found in muscle tissue in both freshwater and seawater adapted salmon, with 49+/-6% and 50+/-10% retention after 144 h, respectively. Results indicate that muscle retention was not influenced by salinity in seawater adapting teleosts.     

Migration of smolts of Atlantic salmon (Salmo salar L.) and sea trout (Salmo trutta L.) in a chalkstream

Synopsis Migration of smolts in the River Piddle, Dorset, was studied over three years in relation to factors that could influence downstream movement. The river originates mostly from groundwater springs, resulting in stable flows and low turbidity except in very rainy weither. Fish were intercepted at the tidal limit in a fixed trap-net, and measurements of water temperature, discharge, turbidity, barometric pressure, rainfall and solar radiation taken nearby. Slightly increased turbidity and discharge following heavy rain initiated major movements during two nights of the total of 55 days studied. At other times large-scale movements rock place during sunny warm afternoons. Both solar radiation and water temperature were correlated with intensity and timing of movement. The pattern of migration is different from that reported on other rivers, reflecting the relatively stable flow regime of the chalkstream.     

Energetic cost of spawning in male and female Atlantic salmon (Salmo salar L.)

Energetic expenditure during spawning of male and female 1 -sea-winter Atlantic salmon, Salmo salar L., was measured. Before spawning, the somatic energy content per unit weight did not differ between the sexes. The testes content offat was 0.24, of carbohydrate 8.89, of water 1.21 and of ash 1.61 times as high as that of the ovaries. Just prior to spawning, mean gonadosomatic index (GSI; wet weight, %) in males was 4.36 and in females 20.26, and expressed as energy ratios (kJ, %) 4.47 and 27.75, respectively. During spawning the energy loss of male soma was higher (35.57%) than that of females (25.00%). This was a result of higher loss of fat in males than in females. Total energy cost of spawning in males and females was on average 51.8 and 51.4%, respectively.     

Multiple central-place territories in wild young-of-the-year Atlantic salmon Salmo salar

1. The space use of central-place foragers, animals that forage from and return to a single central place such as a nest, burrow or sleeping site, is well documented. Limited data, however, exist for multiple central-place foragers that alternate among several central places. 2. The conventional view of stream-dwelling salmonids suggests that they conform to the central-place territorial model (CPTM) by (i) attacking prey and intruders from one primary foraging station, and defending (ii) small (iii) exclusive areas that (iv) increase with body size. 3. Recent studies suggest greater variability in salmonid space-use than would be expected by the CPTM, but tend to focus on the time allocated towards different activities rather than their distribution in space, especially for young-of-the-year (YOY) fish that are hard to tag and monitor in the wild. 4. In this study, the validity of CPTM was tested by mapping the daily space use of 50 YOY Atlantic salmon in a natural stream via repeated observations of tagged fish in diverse habitats, and by comparing these to earlier estimates of territory use in YOY salmonids. 5. The 50 YOY Atlantic salmon were multiple central-place foragers. All fish visited more than one foraging station (median = 12.5 stations), visited most stations (68.5%) repeatedly, showed limited fidelity to a particular station and typically attacked prey only while holding a position at a station. 6. The multiple central-place territories of the 50 fish were large (mean = 0.932 m(2)) compared to earlier territory size estimates (mean = 0.107 m(2)) for salmonids of similar size and, surprisingly, did not increase with body size. Focal fish attacked intruders from similar distances as reported earlier for much smaller territories, suggesting that large territories are less exclusively defended at any given time. 7. Overall, this study provides a new view on foraging and territoriality in stream salmonids, and on the small but diverse literature on multiple central-place foragers. Further studies, however, are needed to clarify the evolutionary benefits and population consequences of multiple central-place space-use in mobile animals.     

Paternal reproductive strategy influences metabolic capacities and muscle development of Atlantic salmon (Salmo salar L.) embryos

Male Atlantic salmon follow a conditional strategy, becoming either "combatants" that undertake a seaward migration and spend at least a year at sea or "sneakers" that remain in freshwater and mature as parr. A variety of physiological indices showed significant but small differences between the offspring of males that use these two reproductive tactics. Offspring fathered by anadromous male Atlantic salmon (Salmo salar L.) showed greater muscular development and muscle metabolic capacities but lower spontaneous movements than those fathered by mature male parr. At hatch and at maximum attainable wet weight (MAWW), offspring fathered by anadromous males had higher activities of mitochondrial (cytochrome C oxidase and citrate synthase) and glycolytic (lactate dehydrogenase [LDH]) enzymes than progeny of mature male parr. Enzymatic profiles of progeny of anadromous fathers also suggested greater nitrogen excretion capacity (glutamate dehydrogenase) and increased muscular development (creatine kinase and LDH) than in the progeny of mature parr. At MAWW, juveniles fathered by mature parr made considerably more spontaneous movements, presumably increasing their energy expenditures. For juveniles fathered by anadromous males, total cross-sectional areas of white and red muscle at hatch were higher due to the greater number of large-diameter fibers. We suggest that the slightly lower metabolic capacities and muscular development of alevins fathered by mature parr could reflect differences in energy partitioning during their dependence on vitellus. Greater spontaneous movements of offspring of mature male parr could favor feeding and growth after the resorption of the vitellus.