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Two brown trout Salmo trutta stocks of different origin (wild Polish, domestic commercial) came into secondary contact after deliberate releases conducted in virgin rivers systems of the Subantarctic Kerguelen Islands (70° E 49° S). Samples obtained in 2001–2003 and a historical sample from 1993 were analysed for genetic variation at seven microsatellite loci and one allozyme locus ( LDH-C1*). Bayesian clustering analysis demonstrated that rapid genetic differentiation formed separate genetic units in neighbouring rivers in less than 20 years. These genetic units were characterized by a large proportion of Polish genotypes mixed with some genomes of domestic origin (up to 30%). A different colonization strategy of the naturalized stocks, likely related with differential performance, was identified as a cause of rapid population differentiation in this area. [ABSTRACT FROM AUTHOR]

Presents information on a study which investigated the alternative mating strategies in Atlantic salmon and brown trout. Description of fish samples; DNA analyses; Reproduction by alternative male phenotypes in Atlantic salmon; Rates of hybridization observed between Atlantic salmon and brown trout in southern European rivers.

The spatial and temporal patterns of dispersal and the survival of Atlantic salmon (Salmo salar L.) fry and parr were analysed over 1 year in a small stream of the Basque Country (south-west France). Dispersal just after emergence was studied with eight drift nets placed 10 to 800 m downstream from an artificial redd stocked with 15 000 eyed eggs. Subsequent distribution of parr was determined by electrofishing in June, October, and February in representative sections of the stream including habitats 750 m upstream and 2400 m downstream from the redd. Early dispersal following emergence lasted 12 days for the majority (95%) of the fry population. Most fry (71%) settled within the first 200 m downstream from the redd, and 91% within the first 400 m. In June, parr were found 2400 m downstream and 750 m upstream, with 68% of the population established within 900 m downstream, and only 4% upstream. In October, there was a slight downstream shift of densities. In February, 56% of the parr were found within 900 m downstream and 11% upstream. Survival from egg planting to first dispersal in March was 51.9% and 11.3% over 1 year. [ABSTRACT FROM PUBLISHER]

Brown trout were introduced into the Kerguelen Islands (subantarctica) in 1958. Since then, acclimatized populations have colonized adjoining rivers and have undergone a differentiation into migratory and sedentary forms in either lakes or the sea. In the Kerguelen rivers, free of indigenous fish and characterized by an elementary structure, relationships between environmental factors and trout population parameters are more direct and thus easier to demontrate.The sea trout population of the Baie Norvegienne (SW Kerguelen) has been sampled for 18 years. Annual growth increments in the river and in the sea were backcalculated and validated. Population densities were determined by electrofishing inventories in test areas representative of the different biotas. Mean annual air temperatures were obtained from the recordings of the meteorological station at Port-aux-Francais, close to the study area. Examination of correlations with growth showed a highly significant effect of temperature for the age groups: first year in the river and first and second year at sea, which were not subjected to strong spatial competition. No effect of temperature was observed among second and third year age groups in the river for which favourable areas and feeding resources were less abundant due to a highly significant increase in population density. [ABSTRACT FROM PUBLISHER]