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Juvenile Brown Trout (juvenile + brown_trout)
Selected AbstractsEffects of size and morphology on swimming performance in juvenile brown trout (Salmo trutta L.)ECOLOGY OF FRESHWATER FISH, Issue 4 2003A. F. Ojanguren Abstract,,, Our study assesses swimming capacity (speed and stamina) and possible morphometric determinants of locomotor performance of juvenile brown trout (Salmo trutta L.). We addressed these issues at the individual level to have an approach of the functional significance of intraspecific variation in morphological design. Both swimming speed and endurance time showed significant positive relationships with fish length. Size-corrected values of speed and endurance time were negatively correlated suggesting a phenotypic trade-off between burst and prolonged swimming. Size was also highly correlated with all the morphological variables measured. Therefore, we used the residuals of the regressions of those variables on fish length to remove the effect of body size. A principal components analysis (PCA) summarised the 12 morphological variables into two factors, which accounted for 44.3% of the variance. PC1 combined several measures of body depth and width, whereas PC2 represented mainly postanal length relative to abdomen length. Relationships between the scores of the two factors and size-corrected values of maximum swimming speed and endurance time were weak. PC2 showed a significant positive relationship with endurance time; that is, individuals with longer caudal regions were able to swim against water flow for longer periods of time. Stoutness (PC1) showed a marginally significant negative correlation with endurance time. The lack of stronger relationships could be because of the low morphometric variability among the test individuals, all proceeding from the same population, reared in a common environment, and measured at the same ontogenetic stage. [source] The Bold and the Variable: Fish with High Heterozygosity Act Recklessly in the Vicinity of PredatorsETHOLOGY, Issue 1 2008Sampsa Vilhunen Variation in the innate behavioral response to predation threat is often assumed to reflect genetic differences among the prey individuals. To date, no published results, however, exist that would offer explanation for the origin of this behavioral variation within populations. Using microsatellites as markers, we estimated the genetic variability of juvenile brown trout (Salmo trutta) individuals whose behavior had been individually recorded in a trade-off situation where both predator chemical cues and food were present. Mean overall heterozygosity and the internal relatedness of fish associated significantly with their activity and foraging, so that the genetically more variable individuals showed more risk-prone behavior under predation risk. No association between genetic variability and behavior was found in trials where predator odors were not present. These results were consistent over the three study populations of brown trout with different backgrounds, suggesting that the phenomenon is of general nature in this species. Of the possible mechanisms suggested to enable the existence of the positive association between neutral microsatellite variation and fitness-related trait, the local effect hypothesis gained more support from our data than the general effect hypothesis. [source] Visual isolation furthers access to drift-feeding positions for subordinate juvenile brown trout (Salmo trutta) in dominance hierarchiesJOURNAL OF FISH BIOLOGY, Issue 2003J-M. Roussel Juvenile salmonids are visual predators that primarily feed on drifting invertebrates and compete for suitable feeding positions in swift water. We used an outdoor experimental stream to test the effect of visual isolation on agonistic interactions and habitat use by age-1 brown trout (Salmo trutta) in riffle-pool sections. We hypothesized that dominant fish defend suitable feeding positions in riffle and that visual obstruction between individuals enhance access to riffle for subordinates. Groups of juveniles, caught in the wild, were stocked in high and low visibility treatments. Visual isolation was manipulated by placing dark plastic ribbons or opaque Plexiglas boards onto the substrate of riffles. As expected, dominant fish held profitable positions in riffle and the proportion of fish in riffle significantly increased in presence of artificial structures. In high visibility treatment, the dominant fish despotically excluded subordinates from the riffle. In low visibility treatment, the proportion of fish that foraged on benthic prey in the pool and the number of major aggressive acts (chase, nip) decreased. Our results support the hypothesis that screening effect of physical structures in the water column loosen resource monopolization in dominance hierarchies of juvenile salmonids. [source] Genetic variation of body size, condition and pyloric caeca number in juvenile brown trout, Salmo trutta L.AQUACULTURE RESEARCH, Issue 6 2006Jean M Blanc Abstract Parental and individual variance components of body length, weight, condition (estimated as the second principal component of the length,weight relationship) and pyloric caeca number were investigated in 6-month-old brown trout (Salmo trutta L.) by the mean of two sib analyses, which provided consistent results. The average heritabilities (±SE) were 0.12 (±0.08) for length, 0.16 (±0.08) for weight, 0.47 (±0.14) for condition and 0.38 (±0.12) for pyloric caeca number. Maternal effects were also observed, although short of significance, in length, weight and caeca number. Correlations between caeca number and body size averaged +0.10 among individuals within lots, but genetic correlations were negative, i.e. about ,0.9 for length and ,0.7 for weight. There was no significant correlation between caeca number and condition. These results lead to question the role that pyloric caeca may play in growth, as well as their usefulness in fish breeding. [source] | |||||||||||||