Mature male parr buried among eggs in an Atlantic salmon redd

A mature mate parr of Atlantic salmon was found buried among eggs 28 cm beneath the gravel surface in a salmon redd. Egg mortality in this egg-pocket was considerably higher than in neighbouring egg-pockets (52 v. 3%), presumably due to decay.     

The effect of intragastric transmitters on feeding behaviour of Atlantic salmon, Salmo salar; parr during autumn

The proportion of Atlantic salmon parr (146 265 mm total length) that fed in laboratory tanks during autumn was 0% in fish filled with intragastric transmitters compared with 78 100% in controls.     

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.     

Enhanced growth and feeding rate in Atlantic salmon parr occupying a lacustrine habitat in the River Utsjoki, northern Scandinavia

The length, weight and stomach fullness index of salmon parr from a lake were higher than in a fluvial habitat on the same river in northern Finland, but no differences in diet composition were detected between the habitats in August. The most important food items of the parr in both habitats were insect pupae and adults. Some lake parr also fed on fish.     

Responses of immature male masu salmon parr to the urine of mature males

Responses of male masu salmon Oncorhynchus masou parr to mature male urine were investigated in a Y-maze trough. Immature masu salmon made fewer entries into the channel conditioned by mature male urine than that with control water. This phenomenon may suggest that immature males avoid sexually active males in the spawning season.     

Effect of stripping on the length, condition and gonadal state of mature male Atlantic salmon, Salmo salar L., parr during autumn and winter

Hatchery-reared mature male Atlantic salmon parr were shorter than immature parr of the same age through the winter period and this difference increased prior to smolting in spring. Stripping had no effect on growth. In autumn mature male parr had a higher condition factor (CF) than immature parr, but from early January no difference was observed between unstripped mature males and immature parr. Stripping reduced the CF of male parr but the difference had disappeared by the time of smolting when the CFs of both mature groups were lower than that of immature fish. The quantity of expressible milt in stripped males decreased from c . 3% body weight in November and December to <0.05% by 2 March, after which no further milt expression was recorded. Milt expression in previously unstripped males was about 1% of body weight on 2 March, similar to that of stripped males 1 month earlier.     

Mid-winter activity and movement of Atlantic salmon parr during ice formation events in a Norwegian regulated river

A telemetry study in a Norwegian regulated river was conducted through a 12-day period in mid-winter 2003. The objective was to study activity (defined as number of movement per hour) and movement (defined as distance moved per hour) during different ice formation events. Twenty-four Atlantic salmon (Salmo salar L.) parr were radio tagged and continuously monitored by both manually tracking (N = 24) and by fixed recording stations (N = 15). Detailed data on climate, flow and ice formation and its spatial distribution were collected and used in the analyses. Fish activity was not found to be affected by their size (L _F). There was a significant difference in activity between diel periods with highest activity during dusk (5–6 p.m.). Between high and low flow (mean ± SD, 21.1 m³ s⁻¹ ± 1.7 SD and 11.1 m³ s⁻¹ ± 1.7 SD, respectively) no significant difference in activity was found. During the experiment extensive anchor ice growth occurred mainly in the riffle part with thickness up to 50 cm. Juveniles tend to avoid riffle section during anchor ice formation and exploited ice covered areas, indicating critical and preferable habitats respectively. Further, a significant difference in movement was found between five selected ice events with highest mean movement during an anchor ice event and lowest mean movement during an ice break up with no anchor ice formation. No significant difference in activity or movement between parr exposed to frazil ice and parr not exposed were found.     

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).     

The use of genetic marking to assess the reproductive success of mature male Atlantic salmon parr (Salmo salar, L.) under natural spawning conditions

The reproductive success of mature male Atlantic salmon parr ( Salmo salar ) under natural spawning conditions was estimated using the polymorphism at the MEP - 2 * locus as a genetic marker. The percentage of eggs per redd fertilized by parr varied considerably over the five redds examined (0·9–27.7%, mean 10·8%), but a gametic contribution from mature parr was detected in each case. Parr reproductive success has important implications for the population structure and evolution of the Atlantic salmon through its effect on gene flow.     

Use of radio telemetry and electrofishing to assess spawning by transplanted Atlantic salmon

The river Ingdalselva, which drains to the Trondheims fjord, has no local salmon population due to an impassable waterfall 500 m upstream from the outlet. In the period 1994–97, a total of 31 mature Atlantic salmon (19 females and 12 males) from the rivers Orkla (1994–96) and Vigda (1997) were radio-tagged and released in the river Ingdalselva before spawning. The main goal of the project was to find out whether the fish would stay and spawn in the river, and if the observations during the spawning period could be used to indicate where spawning had taken place. Some fish left the river shortly after release, but 77% of the fish stayed in the river during the spawning period in October. Most of the females (74%) spawned in the river, including multi-sea winter salmon of approximately 10 kg. Some fish remained at the site of the release, while others migrated downstream to hiding places where they stayed until spawning. Long distance upstream migrations were not observed. The observations of the fish during the spawning period were used to identify spawning areas. Electrofishing for salmon fry in the spawning areas the following year in all cases produced fry, and in two of the years salmon fry were also found in areas where no spawning activity had been registered. Radio-tracking was an efficient method for determining whether transplanted salmon would remain in a `new'n river during the spawning season and for locating spawning areas, particularly when the fish were tracked daily.     

Social dominance and body size in Atlantic salmon parr, Salmo solar L.

Dominance relationships between pairs of Atlantic salmon parr of known size were assessed at various times during their first year of life. In tests conducted between first feeding and early July, the larger of two fish was dominant in only 54% of pairs, regardless of the magnitude of the size difference between the fish. In September, there was a stronger association between size and status, especially in pairs with a large size differential, where the dominant was larger in 72% of cases. In groups of parr tested in April of the following year, there was no relationship between size and status, the larger of two fish being dominant in 48% of cases, regardless of the magnitude of the size differential. This result suggests that status in early social interactions may depend on behavioural properties rather than size and that the larger size of dominant fish reported in a number of salmonids might be a consequence and not a cause of high status.     

The effect of the rate of temperature increase on the critical thermal maximum for parr of Atlantic salmon and brown trout

The critical thermal maximum for salmon and trout parr was not affected significantly by age or acclimation temperature, and increased asymptotically with the rate of temperature increase. Mean thermal maxima were estimated with poor precision at high and low rates of temperature increase, and high precision at rates of 1 and 2°Ch⁻¹.     

Genetic protein variation and natural selection in Atlantic salmon (Salmo salav, L.) parr

The principal focus of this study was an examination of the relationship between diallelic variation at the MEP-2 * locus and growth and survival in Atlantic salmon parr. In addition, patterns of growth and survival among genotypes at the AAT-I *, IDDH-I * and ZDHP-2 * loci were also examined. Significant differences in growth were found among MEP-2 * genotypes, with * 100/ 100 homozygotes largest in one of two independent comparisons and the * 125/I25 homozygotes largest in the other. No growth differences were observed among genotypes at any other locus. Although no significant differences were found in survival among genotypes at any locus, results of joint analysis of the patterns of growth and survival among MEP-2 * genotypes were consistent with a model of positive size-selective mortality. The demonstration of growth differences among MEP-2 * genotypes in parr and smolts may indicate an association between selection on this locus in fresh water and previously reported differences in sea-age at maturity among MEP-2 * genotypes in Atlantic salmon.     

Genetic variation at enzyme loci in the southernmost European populations of Atlantic salmon

Genetic variation was studied at 8 allozyme loci in six severely endangered wild Spanish populations of Salmo salar located at the southernmost geographical limit of European Atlantic salmon. Low levels of variation were detected and no significant deviations from Hardy–Weinberg equilibrium were found.     

Migratory and reproductive behaviour of female adult Atlantic salmon, Salmo salar L., in a spawning stream

Migration and spawning behaviour of eight Atlantic salmon adult females were analysed by radio-tracking in relation to the degree of sexual maturity in a spawning tributary of the R. Sélune. Six of them were grilse and four of them were ripe. All the fish migrated upstream until reaching their spawning site at a distance of 4–12 km from the trap. The daily migration rate up to this site was inversely correlated with the length of the female. Spawning occurred in all fish at the same time when the water temperature increased dramatically. Spawning lasted 1–10 days according to the fish. After spawning, females quickly moved downstream only small distances and then stayed in approximately the same location until death. This study concluded that ripeness did not influence behaviour on the spawning migration and describes certain characteristics of the reproductive phase in a spawning tributary.     

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.     

An evaluation of the quality of fall-fingerling Atlantic salmon (Salmo salar L.) released to natural lacustrine nursery areas in Newfoundland,Canada

Results of experiments on controlled releases of fall-fingerling Atlantic salmon to lacustrine habitats in Newfoundland are reviewed in terms of survival during freshwater residence and smolt yield per unit of standing water habitat. Average survival from parr to smolt in three consecutive annual releases was 12.9% and we conclude that the quality of fall-fingerling salmon, produced from our semi-natural rearing techniques, was satisfactory. Year-class survival decreased progressively with consecutive releases. Rate of increase in juvenile salmon biomass remained stable over the duration of the study, suggesting that the average annual biomass of 1.6 kg ha^–1 of juvenile salmon released did not exceed habitat carrying capacity. Precocity did not appear to represent a significant deterrent to fall-fingerling survival. Annual smolt yield (by year-class) from stocking ranged from 53 to 130 ha^–1 (mean = 77 smolts ha^–1).     

Effects of surgically implanted transmitters on swimming performance, food consumption and growth of wild Atlantic salmon parr

Experiments were conducted on wild Atlantic salmon Salmo salar parr to determine the effect of surgically implanted dummy transmitters on swimming performance, food consumption and growth. Swimming performance of tagged fish (tag 1·7–3·7% of fish mass) was similar to that of control fish 1, 5 and 10 days after surgery. Negative effects on growth, however, were found up to day 36 of a 45 day experiment (tag 0·9–2·6% of fish mass). Consumption rates were similar between tagged and control fish and did not explain differences in growth.     

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.