Electrofishing studies in the 1990s established that higher frequencies of pulsed DC (e.g., 60 Hz) generally result in more spinal injury to fish in comparison with lower pulse frequencies (e.g., 30 Hz). In response to those findings, some agencies adopted low pulse frequency standards to minimize fish injury. However, those earlier studies did not assess whether capture efficiency (CE) was also influenced by pulse frequency. We sampled small trout streams (1–6‐m average width; SE = 0.14 m) by backpack electrofishing with settings of 30 and 60 Hz to evaluate the effect of pulse frequency on both CE and spinal injury rates for Cutthroat Trout Oncorhynchus clarkii , Rainbow Trout O. mykiss , and Brook Trout Salvelinus fontinalis…Read More

Photo Credit: Jim Reynolds

The Rainbow Trout Oncorhynchus mykiss is a salmonid fish that is maintained in aquaculture facilities and used as a source of protein around the world. Veterinarians need accurate, efficient tools and straightforward assessments to evaluate the health status of fish, like Rainbow Trout, that are cultivated on farms. In this study, two genetically distinct broodstock lines of Rainbow Trout originally obtained from two different U.S. states but propagated at Rushing Waters Trout Farm (Palmyra, Wisconsin) were evaluated. Groups originating from both states (State A: n = 20; State B: n = 20) were surveyed with a modified health assessment in a prospective, randomized, single‐blind study…Read More

Photo Credit: Dr. Michael Collins

In temperate waters, growth and mortality of bony fishes are frequently estimated from age information derived from the examination of annular rings on hard structures (e.g., otoliths). However, determining ages from hard structures can be time consuming, often requires sacrificing fish, and has associated costs for supplies and personnel time in processing or reading structures. Subsampling based on a target number of fish per length bin is commonly used to reduce time and costs but may introduce biases into the estimation of population characteristics. We wanted to understand how interactive effects of bin width, gear selectivity, and length‐at‐age variability influence the estimation of growth parameters, total instantaneous mortality (Z), and age frequency…Read More

Photo Credit: Corbin D. Hilling

The South Fork Snake River supports one of the few remaining robust populations of fluvial Yellowstone Cutthroat Trout Oncorhynchus clarkii bouvieri in Idaho. Since the early to mid‐2000s, salmonid populations on the South Fork Snake River have been intensively monitored and managed to limit the abundance of introduced Rainbow Trout O. mykiss, which have been increasing in abundance relative to Yellowstone Cutthroat Trout. Integrated population models (IPMs) were built using multiple data sets (abundance, survival, and fecundity data) to evaluate the effectiveness of management actions…Read More

Photo Credit:  Conor McClure