Recombinant genotypes in backcrosses of male Atlantic salmon × brown trout hybrids to female Atlantic salmon

When male hybrids of Atlantic salmon × brown trout were backcrossed to female Atlantic salmon, approximately 1% of diploid progeny hatched. These were shown to exhibit recombinant genotypes when examined electrophoreticalty at five enzyme loci. This is the first confirmation of genie recombination in backcrosses of these species. Triploidization greatly increases the proportion of backcross progeny which hatch.     

Occurrence of Atlantic salmon parr in redds at spawning time

Several Atlantic salmon parr of different sizes were found alive in salmon redds under a 10–30 cm layer of stones at spawning time. Parr, both mature and immature, remain inactive in redds during daylight but show nocturnal activity.     

Comparative proximate body composition of Atlantic salmon with emphasis on parr from fluvial and lacustrine habitats

The nutritional status of Atlantic salmon Salmo salar parr was assessed by examining how proximate body composition and energy content (kJ g⁻¹) were associated with the habitat rearing origin of parr utilizing fluvial or lacustrine areas. Comparisons were made among sampling sites within the two habitats, as well as between the two major habitat types applying both fixed effect and random effect models. Mean protein concentration varied from 13·87 to 15·67% among fluvial sites, and from 14·96 to 16·38% among lacustrine sampling locations. Mean fat concentration ranged from 1·71 to 3·32% and from 2·22 to 4·29% among fluvial and lacustrine locations, respectively, with energy concentration, on average, c . 11% higher in lacustrine parr. Interpretation of results of comparisons between habitats was dependent upon the statistical model used. Benefits associated with lacustrine rearing, such as greater body size and nutritional status, have implications for overwintering survival in fresh water as well as subsequent survival during initial sea entrance as smolts.     

Mating of anadromous Atlantic salmon, Salmo salar L., with mature male parr

Sexually mature male parr successfully mated with female anadromous Atlantic salmon, Salmo salar , in the absence of anadromous males. There was no significant difference between the proportion of eggs fertilized by mature male parr and anadromous males. One of the demographic consequences of our observations is that overfishing could eventually eliminate anadromy in male members of a population.     

Effect of increased flow on the behaviour of Atlantic salmon parr in winter

The effect of increased flow on movement and microhabitat use of Atlantic salmon Salmo salar parr in winter was investigated using radiotelemetry. To simulate hydropeaking operations, flow was increased four‐fold from 1·3 m³ s⁻¹ to 5·2 m³ s⁻¹ for 24 h periods. Flow did not affect fish habitat use or displacement and had little effect on fish activity within diel periods. During high flow periods in late winter, fish reduced night‐time activity. Stranding rates during flow reduction were also very low (only one fish).     

Stimulatory and inhibitory effects of testosterone on testes in Atlantic salmon male parr

Immature 1-year-old Atlantic salmon Salmo salar parr were implanted with Silastic capsules of different sizes filled with testosterone (T). Testosterone had both positive and negative effects on testicular weights, spermatogenesis and steroidogenesis. The positive effects: higher incidence of males with enlarged gonads, spermiation, and high plasma levels of 11-ketotestosterone (11-KT) and 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P), were most pronounced in males treated with small T capsules. The negative effects: suppression of gonadal development and depressed plasma levels of 11-KT and 17,20β-P compared with mature controls, were most evident in fish treated with large T capsules.     

Identification of QTLs affecting adaptive traits in Castanea sativa Mill

A QTL analysis for three different adaptive traits was performed in an F₁ progeny of Castanea sativa Mill. The female and male parents originated from two Turkish chestnut populations adapted to a drought and humid environment, respectively. QTLs for bud flush, growth and carbon isotope discrimination were detected over a 3‐year period. Bud set was also recorded in the last year of measurement. Thirty‐five individual QTLs were detected for phenology, 28 for growth and 17 for carbon isotope discrimination, most of them explaining a low to moderate proportion of the total phenotypic variance. QTLs were distributed throughout the whole genome. Temporally stable QTLs were identified for all the traits analysed, with phenology showing the higher proportion of stable QTLs. Interesting phenotypic correlations and co‐localizations among QTLs for different adaptive traits were observed, allowing the formulation of an hypothesis about the genetic adaptation of the female parent to drought.     

Linking models of animal behaviour and habitat management: Atlantic salmon parr and river discharge

Understanding preferences of animals is of fundamental importance for modelling habitat quality and quantity. Important theoretical developments, for example using ideal free and ideal despotic distributions (IDD), have enabled biologists to build conceptual frameworks for relating habitat preferences of individual animals to distributions and dynamics of populations. At the same time, managers of natural resources have established predictive empirical models as a basis for understanding habitat quality. For example, the Physical Habitat Simulation model (PHABSIM) has been widely applied for managing river flows. The aim of this study was to conduct experiments, using Atlantic salmon parr, to test whether observed population distributions could be predicted using simple behaviour theory and PHABSIM. We show that predictions from PHABSIM depend crucially on population density, discharge and the interaction between density and discharge at the time when the model is parameterized. These findings can, in part, be explained by consideration and application of the IDD. However, the results of the experiments also suggest that models derived from first behavioural principles may need to be unexpectedly complex and species‐specific if they are to capture the population response to variations in water discharge effectively.     

Interhabitat and instream movements of large Atlantic salmon parr in a Newfoundland watershed in winter

Radio‐telemetry was used to investigate movement of large, mainly mature male (80%) Atlantic salmon Salmo salar parr in Stoney River, Newfoundland during early winter (November; water temperature 6·0 ± 0·1° C) and mid‐winter (January to February; 0·8 ± 0·0° C). Site fidelity of parr in early winter was low. Parr moved between fluvial and lacustrine habitats and were active throughout the diel cycle. Parr caught in fluvial habitats in mid‐winter were smaller and younger than parr caught in early winter. Site fidelity of parr in mid‐winter was greater than in early winter. Parr in mid‐winter moved between fluvial and adjacent small lacustrine habitats, but avoided a larger pond inhabited by large piscivorous fishes. Instream movement rates in mid‐winter were lower than in early winter and occurred primarily during hours of darkness (dawn, dusk and night). Fluvial habitats were relatively stable and ice‐free throughout the study periods. These results suggested that large Atlantic salmon parr utilize a variety of habitats and remain active throughout the winter, even under stable environmental conditions.     

Functional models for growth and food consumption of Atlantic salmon parr, Salmo salar, from a Norwegian river

1. The chief objectives were to analyse and model experimental data for maximum growth and food consumption of Atlantic salmon parr (Salmo salar) collected from a cold glacier fed river in western Norway. The growth and feeding models were also applied to groups of Atlantic salmon growing and feeding at rates below the maximum. The growth models were validated by comparing their predictions with observed growth in the river supplying the experimental fish.
2. Two different models were fitted, one originally developed for British salmon and the other based on a model for bacterial growth. Both gave estimates for optimum temperature for growth at 18–19 °C, somewhat higher than for Atlantic salmon from Britain. Higher optimal temperature for growth in salmon from a cold Norwegian river than from British rivers does not concur with predictions from the thermal adaptation hypothesis.
3. Model parameter estimates differed among growth groups in that the lower critical temperature for growth increased from fast to slow growing individuals. In contrast to findings for brown trout (Salmo trutta), the optimum temperature for growth did not decrease with decreasing levels of food consumption.
4. A new and simple model showed that food consumption (expressed in energy terms) peaked at 19.5–19.8 °C, which is similar to the optimal temperature for growth. Feeding began at a temperature 1.5 °C below the lower temperature for growth and ended about 1 °C above the maximum temperature for growth. Model parameter estimates for consumption differed among growth groups in a manner similar to the growth models. Maximum consumption was lower for Atlantic salmon than for brown trout, except at temperatures above 18 °C.
5. By combining the growth and food consumption models, growth efficiency was estimated and reached a maximum at about 14 °C for fast growing individuals, increasing to nearly 17 °C for slow growing ones, although it was lower overall for the latter group. Efficiency also declined with increasing fish size. Growth efficiency was generally higher for Atlantic salmon than for brown trout, particularly at high temperature.     

Sublethal effects of the pesticide Diazinon on olfactory function in mature male Atlantic salmon parr

Diazinon, an organophosphate pesticide, had a sublethal effect on the olfactory system of mature male Atlantic salmon parr. The olfactory responses of the parr to prostaglandin F_2a (PGF_2a) were studied after exposure of the epithelium to different concentrations of Diazinon in water. Electrophysiological recordings from the epithelium indicated that the responses to this prostaglandin were significantly reduced at nominal concentrations as low as 1.0μg l⁻¹ and the threshold of detection was reduced 10-fold at 2.0 μg 1⁻¹ . Mature male salmon parr exposed for a period of 120 h to Diazinon (nominal concentrations 0.3, 0.8, 1.7, 2.7, 5.6, 13, 28 and 45 μg 1 ⁻¹) also had significantly reduced levels of the reproductive steroids, 17,20β-dihydroxy-4-pregnen-3-one, testosterone and gonadotrophin II in the blood plasma after priming with ovulated female salmon urine. Both prostaglandin F_2a and ovulated female urine are known to have important roles in synchronizing reproductive physiology and behaviour in salmonids as well as other fish species. The results are therefore discussed in relation to the possible sublethal effects of Diazinon on reproduction in the Atlantic salmon and possible effects on populations of salmonids.     

Otolith and somatic growth rates in Atlantic salmon parr, Salmo salar L: evidence against coupling

It is often assumed that otolith growth is in some way dependent on somatic growth (i.e. that the two processes are coupled). We examined the relationships between sagitta radius and fork length in 0+ Atlantic salmon parr that would subsequently smolt aged 1 + (UMG fish) or 2+ (LMG fish). Repeated measurements of fork lengths of individually marked parr, taken over a 211-day period from first feeding, were compared to sagitta radii on the same measuring dates (obtained by analysis of daily increments). The results showed that there was a linear relationship between fork length and otolith radius in UMG parr. However, this was not true for LMG parr. These fish enter a state of natural anorexia in their first autumn (despite excess food), but their otoliths continued to grow at the same rate despite the virtual cessation of somatic growth; they had therefore developed disproportionately large otoliths by the end of the study period. The relative growth rates of soma and otoliths first changed in LMG fish in late July/early August; this is the most precise estimate yet obtained of the timing of divergence in the developmental pathways of UMG and LMG parr. The rate of sagitta accretion was consistently lower in LMG parr, possibly indicating a lower metabolic rate in these fish. The results are discussed in relation to previous theories of the relationship between otolith and somatic growth.     

Movements and habitat use by PIT-tagged Atlantic salmon parr in early winter: the influence of anchor ice

1. Movements and habitat use by Atlantic salmon parr in Catamaran Brook, New Brunswick, were studied using Passive Integrated Transponder technology. The fish were tagged in the summer of 1999, and a portable reading system was used to collect data on individual positions within a riffle‐pool sequence in the early winter of 1999. Two major freezing events occurred on November 11–12 (Ice 1) and November 18–19 (Ice 2) that generated significant accumulations of anchor ice in the riffle. 2. Individually tagged parr (fork length 8.4–12.6 cm, n = 15) were tracked from 8 to 24 November 1999. Over this period, emigration (40%) was higher from the pool than from the riffle. Of the nine parr that were consistently located, seven parr moved <5 m up‐ or downstream, and two parr moved more than 10 m (maximum 23 m). Parr moved significantly more by night than by day, and diel habitat shifts were more pronounced in the pool with some of the fish moving closer to the bank at night. 3. During Ice 2, there was relatively little movement by most of the parr in the riffle beneath anchor ice up to 10 cm in thickness. Water temperature was 0.16 °C above the freezing point beneath anchor ice, suggesting the existence of suitable habitats where salmon parr can avoid supercooling conditions and where they can have access to low velocity shelters. To our knowledge, these are the first data on habitat use by Atlantic salmon parr under anchor ice.