Routes and survival of anadromous brown trout Salmo trutta L. post-smolts during early marine migration through a Danish fjord system
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Fjord
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ABSTRACT ABSTRACT Weight-length relationships provide a tool to assess the body condition of brown trout (Salmo trutta) populations inhabiting stream reaches where stressors, such as metals, have chronic, sub-lethal toxic impacts. A previously published brown trout standard-weight equation, Ws, overestimated Colorado brown trout weights. Weight-length data from 16 Colorado brown trout populations (n = 9, 8 16) were used to develop a regional standard weight (Wcl) equation based on fish from waters free of metal contamination. Relative-weights (Wr) were then compared between metal-contaminated and metal-free streams in Colorado using the Wcl equation. Brown trout Wr's were lower in metal contaminated streams than in stream reaches uncontaminated by metals. The development and use of regional standard weight equations is recommended to help assess the weight of brown trout inhabiting metal-contaminated stream reaches.
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1. The effects of high spring floods on survival and growth of juvenile Atlantic Salmon, Salmo salar, and Brown Trout, Salmo trutta , are explored, using data from a long‐term study in the River Saltdalselv, northern Norway. The flow regime in this river is typical for northern rivers. 2. There was considerable variation in year class strength of both species. 3. Mortality of Atlantic Salmon increased significantly in years with high discharge during the alevin stage as well as the first week after emergence. High discharge during the egg stage and more than 1 week after emergence seemed to be of minor importance. Water temperature at emergence was rather high (average 10·5 °C) and did not significantly affect year class strength. 4. Brown Trout emerged earlier than Atlantic Salmon at an average water temperature of 8·2 °C. Highest mortality was observed in years with low water temperatures at emergence as well as high discharge during the alevin stage. 5. For 1‐year‐old fish or older, the size of the spring peak flood did not influence mortality significantly. 6. Growth of Atlantic Salmon parr was diminished in years with a high peak spring flood. A similar effect on Brown Trout was not detected.
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At the southern European edge of Atlantic salmon ( Salmo salar ) distribution, all the hybrids found in nature are the product of crosses between female salmon and male brown trout ( Salmo trutta ). By artificially producing reciprocal crosses between salmon and trout, we demonstrate that unidirectional hybridization observed in nature is the result of postzygotic barriers that produce very high mortality rates (95%) in female trout × male salmon hybrids and not the consequence of prezygotic isolation or behavioural differences between the two species. Mortality of female trout × male salmon hybrids mainly occurs during the last phases of development, and a high percentage of these surviving hybrids showed external deformities that could compromise survival in the wild. Another important finding is the existence of paternal factor in embryo development. Using time to midhatch as an indicator of developmental rate, female salmon × male trout hybrids hatched faster than female trout × male salmon hybrids, with both developing at a rate intermediate to the pure crosses. The early emergence of female salmon × male trout hybrids, which have similar survival to pure salmons, could have fitness repercussions, since early emerging fry have a competitive advantage over later emerging fry.
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The activity level of calcium-dependent proteases of the calpain family in skeletal muscles of the atlantic salmon ( Salmo salar L.) and brown trout ( Salmo trutta L.) from some watercourses (the Zolotitsa River and Lopatka stream) draining to the White Sea (arkhangelsk region) was estimated. a correlation between length-weight parameters of the fish and the rate of calcium-dependent proteolysis in their skeletal muscles was demonstrated. atlantic salmon parr from the Zolotitsa River were larger and had a higher growth rate compared to salmon of the same age from rivers of the Murmansk Region. The comparison of length-weight parameters and data on the rate of calcium-dependent proteolysis in brown trout parr from three watercourses draining to the White Sea and Lake Onego rev ealed the lowest growth rate in fish aged 3+, 4+ from the Lopatka stream. The obtained results indicate that the growth rate of salmonids S. salar and S. trutta depends on the environmental condition and availability of food resources in the studied waters.
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Smoltification
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Administration of flumequine to brown trout S a h o trutta and Atlantic salmon Salmo salar, using bath treatments, resulted in significant serum levels of the antibiotic.Bath concentrations of 50. 100 and 500 ppm were tested for up to 5 h.Temperature, pH, and calcium hardness of the bath water were all found to influence serum levels achieved, as did the level of the drug in the bath.Following bath treatment, serum levels of flumequine greater than the minimum inhibitory concentrations for most susceptible fish pathogens were maintained for up to 14 d.Flumequine serum levels eliciting a toxic response in treated fish were determined.The efficacy of flumequine bath treatments in the control of furunculosis, caused by Aeromonas salmonicida, has been established and its application as both a prophylactic and a chemotherapeutic method for the control of bacterial infections is proposed.
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Otoliths of Atlantic salmon, Salmo salar L., are more slender than the otoliths of brown trout, Salmo trutta L. Discriminant analysis on otolith measurements of juvenile Atlantic salmon and brown trout from four river systems revealed a discriminant function which distinguished more than 94% of the cases. This function was tested by using data from a fifth river with cohabiting Atlantic salmon and brown trout: all Atlantic salmon and 91 % of the brown trout were correctly classified.
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Hybrids between Atlantic salmon and brown trout were detected in two of four watersheds studied in northern Spain. The proportions of hybrids in samples of 'salmon’ranged from 0 to 7–7% but they were not significantly heterogeneous among locations, resulting in a mean hybridization rate of 2–3%. This is the highest rate of natural hybridization so far reported and is significantly greater than rates observed elsewhere in Europe.
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Among 332 parr from the Swedish River Grönån examined by electrophoresis, 44 (13%) were hybrids between Atlantic salmon and brown trout. The hybrid frequencies in three sections of Grönån were significantly different (23. 8 and 2%). All hybrids are evidently of natural origin. and possible factors promoting hybridization are irregular overlapping spawning times. lack of separate spawning grounds, and involvement of sneakers.
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Summary The recapture of tagged brown trout (Salmo trutta L.) in two experimental streams gave over 60% recapture in the section of stream where they were released, and over 80% when adjacent areas were included. Operation of a downstream trap showed that there was little emigration from the area above the trap and it is concluded that most of the fish which disappear die.
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