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Notes: Surveyed populations of salmonid species from 13 different localities in southern Norway, revealed large differences in gill-raker number, both within and between species. The findings indicate that phenotypic plasticity (expressed as variation in gill-raker number) is more common among the plankti-vores than the benthi-and piscivorous species, due to the former's dependence on gill-rakers when feeding. The number and morphology of gill-rakers did not always reflect the presence of other fish species (competitors), indicating that other factors, such as different immigration history of the various species, influence gill-raker number.Brown trout were the more stable of the species, with mean gill-raker number of either 15 or 16, and the total range of means being only 6% of the grand mean. Whitefish and Arctic char were the other extremes, with population means between 21–35 (representing 47% of grand mean) and 21–27 (25 %), respectively.〈section xml:id="abs1-2"〉〈title type="main"〉ZusammenfassungFutterwabl und Konkurrenz bei Lachsfischen anband Zahl und Form der KiemenstäbchenEine Untersuchung von verschiedenen Lachsfischarten aus 13 verschiedenen Populationen in Süd-Norwegen zeigt, daß Anzahl und Form der Kiemenstäbchen innerhalb einer Art und zwischen den Arten stark variieren.Die Ergebnisse deuten an, daß die phänotypische Varianz (ausgedrückt als Variation in der Anzahl der Kiemenstäbchen) bei den planktonfressenden Arten größer ist als bei den benthosoder fischfressenden. Die Kiemenstäbchendichte und-morphologie spiegelt nicht immer das Vorhandensein anderer Fischarten (Konkurrenten) wider, was darauf hindeutet, daß andere Faktoren, wie z. B. unterschiedliche Einwanderungen, die Anzahl der Stäbchen beeinflussen könnten.Die Forelle war die stabilste Art, mit 15–16 Kiemenstäbchen und einer Gesamtvarianz von 6%. Saibling und Renke variierten am meisten und zwar mit einem Durchschnitt von 21–27 (25 % Varianz) und 21–35 (47% Varianz).〈section xml:id="abs1-3"〉〈title type="main"〉RésuméSelection de la nourriture et concurrence chez les salmonidés, reflétés par le nombre et la forme des lames branchialesDes études de differentes espèces de poissons saumonés provenant de treize populations differentes du sud de la Norvége, ont montré de grandes differences dans le nombre et la forme des lames branchiales tant à l'interieur qu'entre les espèces.Les résuhats indiquaient que des variances phenotypiques (exprimées comme variation du nombre de lames branchiales), sont plus courants chez des espèces planctivores que chez des benthivores ou piscivores. La densité et la morphologie des lames branchiales ne reflétaient pas toujours la présence d'autres espèces (des competiteurs). Cela indique que des facteurs different comme par example l'histoire d'immigration ont une influence sur le nombre de lames branchiales.La truite etait l'espèce la plus stable, avec 15–16 lames branchiales en moyenne, et une variance totale de 6%. L'ombre chevalier et le lavaret étaient les plus variables avec une moyenne de population de 21–27 (25 % variance) et 21–35 (47 % variance) respectivement.

Notes: . Atlantic salmon, Salmo salar L., parr and smolts from three Norwegian rivers were examined with respect to whether or not they had been released from a hatchery. The hatchery background was known for some released fish and could be ascertained for others from their aberrant body morphology and eroded fins. Fish released after one winter in a hatchery had opaque otoliths like the fish examined from two hatcheries. Naturally produced fish showed a distinct, seasonal growth pattern in the otoliths, alternating between opaque summer zones and hyaline winter zones. Fish released as fry showed an otolith pattern similar to that of naturally produced fish. A test revealed little discrepancy between two independent otolith readings even though the test reading was conducted without any information about the fish accompanying the otoliths. The results suggest that examination of otoliths may help distinguish between juveniles that are hatchery-reared and juveniles that are naturally produced in the river, provided that the hatchery-reared fish have a 1-year history in the hatchery prior to release.

Notes: Six naturally reproduced 0+ rainbow trout were caught in a Norwegian river in 1994. This is the second report and first recorded sample of descendants from anadromous parents found in a Norwegian river. If this is not a unique event, the finding bodes ill for future conservation of native anadromous Salmonids.

Notes: We studied reproductive traits in nine anadromous brown trout, Salmo trutta L., populations in seven Norwegian rivers. Within populations we found a positive significant correlation between fish length and fecundity in all populations, and between fish length and egg diameter in five populations. There were significant differences in these relationships between populations from different rivers, and between populations from different locations within rivers. When adjusted for variation in fish length, mean fecundity and mean egg diameter showed a negative significant correlation among populations. The ratio of gonadal weight to somatic weight (gonadosomatic index) varied significantly among populations but was not associated with variation in fish length. Comparatively few large eggs were found in brown trout populations co-existing with several other fish species.

Notes: Electrophoretic studies of proteins remain a primary source of insight into genetic diversity in many species including the Atlantic salmon Salmo salar, one of the most culturally and economically important fish species of the North Atlantic region. Since 1966, 〉350 scientific papers on protein variation have been published encompassing 25 000+ salmon from over 400 locations in 〉200 river systems across the species’ distribution. Variation has been detected at 30% of the 110 protein loci screened, though most studies examine 〈40. The method has been applied largely to the investigation of population structure and differentiation, but work has also led to the systematic revision of the genus Salmo and remains the primary source of insight into hybridization in the wild with brown trout Salmo trutta. Spatial patterns of differentiation show temporal stability, both within and among river systems, and strongly support structuring of the species into river and tributary specific populations and the designation of European and North American populations as distinct sub-species. They also show widespread regional differentiation within both continents, beyond the marked subcontinental differences between Baltic Sea and Atlantic Ocean populations in Europe. Most of the differentiation probably reflects gene flow and founder events associated with colonization following the retreat of the glaciers from much of the species’ modern range. However, variation at MEP-2* shows strong correlations with environmental temperature, both within and among rivers, and associations with phenotypic performance. This suggests selection is acting on the locus and provides compelling evidence for the local adaptation of populations. Protein studies have led to more population centred management of the species and have been exploited in the discrimination of regional stocks in mixed stock analysis in high seas fisheries, particularly in the Baltic Sea, and as markers for the assessment of stocking success. They have also advanced insight into how the genetic character of populations can be changed in cultivation and the potential impact of salmon aquaculture and stocking on wild populations. The method has been largely superseded by DNA based analyses, but the results remain highly relevant to Atlantic salmon management and conservation and are an irreplaceable data set for studying genetic stability of populations over time.

Notes: 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.

Notes: Summary Reproductive potentials of transplanted curthroat trout (Salmo clarki) and Dolly Varden charr (Salvelinus malma) and of their donor stocks were estimated from life history data. We found good agreement between observed and predicted age at maturity in all populations, and cannot reject the hypothesis that the fish matured at the age maximizing the overall lifetime reproductive potential ( $$\Delta \mu _{\iota } = 0 = In \left( {{{a_i^p } \mathord{\left/ {\vphantom {{a_i^p } {a_i^L }}} \right. \kern-\nulldelimiterspace} {a_i^L }}} \right) + A_i + {{B_i } \mathord{\left/ {\vphantom {{B_i } T}} \right. \kern-\nulldelimiterspace} T}$$ ). Our estimates were insensitive to probable variations in female fecundity, adult mortalityrate and maximum body length. Small changes in either juvenile mortality-rate or individual growth-rate had marked effects on the estimations, as did changes in the Malthusian parameter (r). Three alternative mechanistic explanations of how age at maturity is determined could be rejected. We suggest that fish are able to adjust the maturity age non-genetically to changes in growth-rate, and that temporal variations in juvenile survival-rate allow coexistence of genotypes coding for different ages at maturity at the same growth-rate.