Juvenile Brook Trout Salvelinus Fontinalis Research Articles

Recruitment dynamics of juvenile salmonids: Comparisons among populations and with classic case studies.

Understanding recruitment, the process by which individuals are added to a population or to a fishery, is critical for understanding population dynamics and facilitating sustainable fisheries management. Important variation in recruitment dynamics is observed among populations, wherein some populations exhibit asymptotic productivity and others exhibit overcompensation (i.e., compensatory density-dependence in recruitment). Our ability to understand this interpopulation variability in recruitment patterns is limited by a poor understanding of the underlying mechanisms, such as the complex interactions between density dependence, recruitment, and environment. Furthermore, most studies on recruitment are conducted using an observational design with long time series that are seldom replicated across populations in an experimentally controlled fashion. Without proper replication, extrapolations between populations are tenuous, and the underlying environmental trends are challenging to quantify. To address these issues, we conducted a field experiment manipulating stocking densities of juvenile brook trout Salvelinus fontinalis in three wild populations to show that these neighboring populations-which exhibit divergent patterns of density dependence due to environmental conditions-also have important differences in recruitment dynamics. Testing against four stock-recruitment models (density independent, linear, Beverton-Holt, and Ricker), populations exhibited ~twofold variation in asymptotic productivity, with no overcompensation following a Beverton-Holt model. Although environmental variables (e.g., temperature, pH, depth, substrate) correlated with population differences in recruitment, they did not improve the predictive power in individual populations. Comparing our patterns of recruitment with classic salmonid case studies revealed that despite differences in the shape and parameters of the curves (i.e., Ricker vs. Beverton-Holt), a maximum stocking density of about five YOY fish/m2 emerged. Higher densities resulted in very marginal increases in recruitment (Beverton-Holt) or reduced recruitment due to overcompensation (Ricker).

Gait transition speed as an alternate measure of maximum aerobic capacity in fishes

This study demonstrated that the transition from a steady to an unsteady locomotory gait (USTmax) in juvenile brook trout Salvelinus fontinalis can be measured easily using a new tilting raceway design and a simple experimental protocol. It was found that USTmax increased linearly with fork length (LF), and that this relationship was statistically identical in fish that swam volitionally in the raceway and those that were forced to perform, although slightly different data processing methods were needed in the latter to achieve this result. Furthermore, the relationship between LF and USTmax was statistically identical to that between LF and critical swimming speed (Ucrit), although LF in the former relationship explained 83% of the variance compared to 37% in the latter. This finding indicates that gait transition speed can be used to estimate maximum aerobic capacity, with less unexplainable variance than Ucrit. Gait transition speeds were also determined from Ucrit tests; however, this required measuring and incorporating ground speed into the analysis. USTmax as determined in the Ucrit tests was not significantly different from that measured in the raceway, suggesting that gait transition speed can be measured in raceways or swim tunnel respirometers.

Virulence ofAeromonas salmonicida: Lack of Relationship with Phenotypic Characteristics

Abstract The pathogenicity of 28 Aeromonas salmonicida isolates was investigated by intraperitoneal injection into juvenile brook trout Salvelinus fontinalis. Ten isolates were found to be virulent, killing 100% or 87–100% of experimental animals following injections of 1 × 106 or 1 × 103 colony-forming units (CFU)/fish, respectively. All virulent isolates possessed an A layer, autoaggregated in liquid culture, and were positive on Coomassie brilliant blue and Congo red (CR) media. Nine isolates, which were negative for all of the above characteristics, were avirulent in fish and caused no mortality following an injection of 1 × 106 CFU/fish. The last group of nine isolates was also avirulent (no mortality after an injection of 1 × 106 CFU/fish) and are referred to as A+ avirulent strains because they possess the same in vitro characteristics as the virulent strains described above. For all isolates, the following cell-surface-related properties were then investigated: Cell-surface hydrophobicity, presenc...