Introduced pathogens can affect fish populations, and three main factors affect disease occurrence: the environment, host, and pathogen. Manipulating at least one of these factors is necessary for controlling disease. Myxobolus cerebralis, the parasite responsible for salmonid whirling disease, became established in Colorado during the 1990s and caused significant declines in wild Rainbow Trout Oncorhynchus mykiss populations. Attempts to re-establish Rainbow Trout have focused on manipulating salmonid host resistance. A Rainbow Trout strain known as GR × CRR was developed for stocking in Colorado by crossing a whirling-disease-resistant strain known as the German Rainbow Trout (GR) with the Colorado River Rainbow Trout (CRR). The GR × CRR fish exhibit resistance similar to that shown by GR, and survival and reproduction were expected to be similar to those of CRR. One disadvantage of stocking GR × CRR is that outcrossing and backcrossing could decrease resistance, and laboratory studies have indicated that this can occur. A potential disadvantage of stocking pure GR is lower survival due to domestication. To compare fry survival between the strains, a field experiment was conducted in 1.6-km reaches of nine Colorado streams. Each stream was stocked in August 2014 with 5,000 GR × CRR and 5,000 GR individuals. In October 2014, April 2015, and August 2015, apparent survival was assessed. Two laboratory predation experiments were also conducted. The field experiment revealed that short-term apparent survival was influenced by stream, and growth rate was influenced by strain and stream. However, after 12 months, there was no difference in apparent survival or growth rate between the GR and GR × CRR strains. Laboratory experiments showed that survival did not differ between the strains when confronted with Brown Trout Salmo trutta predation. Our results indicate that the GR strain is a viable option for stocking in streams where M. cerebralis is enzootic. Further evaluation is needed to determine whether GR fish will survive to maturity and reproduce.

Portable radio frequency identification (RFID) PIT tag antenna systems are increasingly being used in studies examining aquatic animal movement, survival, and habitat use, and their design flexibility permits application in a wide variety of settings. We describe the construction, use, and performance of two portable floating RFID PIT tag antenna systems designed to detect fish that were unavailable for recapture using stationary antennas or electrofishing. A raft antenna system was designed to detect and locate PIT‐tagged fish in relatively long (i.e., ≥10 km) river reaches, and consisted of two antennas: (1) a horizontal antenna (4 × 1.2 m) installed on the bottom of the raft and used to detect fish in shallower river reaches (<1 m), and (2) a vertical antenna (2.7 × 1.2 m) for detecting fish in deeper pools (≥1 m). Detection distances of the horizontal antenna were between 0.7 and 1.0 m, and detection probability was 0.32 ± 0.02 (mean ± SE) in a field test using rocks marked with 32‐mm PIT tags. Detection probability of PIT‐tagged fish in the Cache la Poudre River, Colorado, using the raft antenna system, which covered 21% of the wetted area, was 0.14 ± 0.14. A shore‐deployed floating antenna (14.6 × 0.6 m), which covered 100% of the wetted area, was designed for use by two operators for detecting and locating PIT‐tagged fish in shorter (i.e., <2 km) river reaches. Detection distances of the shore‐deployed floating antenna were between 0.7 and 0.8 m, and detection probabilities during field deployment in the St. Vrain River exceeded 0.52. The shore‐deployed floating antenna was also used to estimate abundance of PIT‐tagged fish. Results suggest that the shore‐deployed floating antenna could be used as an alternative to estimating abundance using traditional sampling methods such as electrofishing. Received December 19, 2013; accepted July 1, 2014

Flavobacterium psychrophilum, the causative agent of bacterial coldwater disease (BCWD), is found in cultured and wild fishes worldwide and causes significant infection in captive salmonid populations (LaFrentz & Cain, 2004;Starliper, 2011). Mortality associated with infections can be as high as 90% (Barnes & Brown, 2011;Nilsen et al., 2011) depending on water temperature and developmental stage of the host (Decostere et al., 2001;Wood, 1974).Outbreaks causing high mortality can result in massive economic losses to producers of salmon and rainbow trout (Oncorhynchus mykiss, Walbaum) (Antaya, 2008). As a result, BCWD is considered one of the most important hatchery diseases in the world (Michel et al., 1999). Infections typically affect age-0 salmonids (Cipriano & Holt, 2005;Nicolas et al., 2008) but can also affect larger and older fish (LaFrentz & Cain, 2004). Infected fish show a broad range of clinical disease signs such as discoloration of the adipose fin, lesions, spiral swimming behaviour, "blacktail", spinal deformities, and pale

The New Zealand mudsnail Potamopyrgus antipodarum is an invasive species that can be transported to and established in new bodies of water on gear used by aquatic professionals, anglers, and aquatic recreationists. Sparquat 256, a standard disinfectant for controlling the spread of mudsnails, was recently discontinued by the manufacturer. Our objective was to find an industrial‐strength, commercially available quaternary ammonium compound (QAC) that could replace Sparquat 256 for disinfection purposes. The efficacy of three products—Quat 4, Green Solutions High Dilutions Disinfectant 256 (GS 256), and Super HDQ Neutral (Super HDQ)—were tested using bath disinfection at multiple concentrations and exposure durations. For bath disinfection purposes, GS 256 and Super HDQ were the most effective. Super HDQ caused higher mortality rates at 48 h postexposure and was therefore tested and found to be highly effective for spray disinfection to prevent transporting mudsnails on field equipment. Regardless of the QAC chosen, we recommend a bath disinfection rate of 0.4% and a spray disinfection rate of 0.8% QACs in solution with an exposure duration of 10 min. These concentrations meet or exceed minimum effective disinfection requirements for quagga mussels Dreissena rostriformis bugensis, zebra mussels Dreissena polymorpha, whirling disease Myxobolus cerebralis, and chytrid fungus Batrachochytrium dendrobatidis.Received January 8, 2015; accepted November 8, 2015 Published online March 22, 2016

Habitat restoration activities continue to increase in large rivers, but many of these projects focus on improving juvenile or adult habitats. Incorporating the habitat associations of fry into restoration designs will allow for broader successes from restoration for all life stages and may be useful for either multispecies or specific-species management. This study investigated the habitat associations of rainbow trout Oncorhynchus mykiss and brown trout Salmo trutta fry in the upper Colorado River, focusing on the mean substrate size (D 50 ), velocity (m s À1 ), depth (m) and presence of wood in near-shore habitats. S. trutta and O. mykiss were found in higher numbers in fry sites with a D 50 of 151 mm (ranging from 96 to 206 mm), velocities ranging from 0.20 to 0.23 m s À1 and depths ranging from 0.17 to 0.18 m. Although there was considerable overlap in habitat associations between the two species, there may be opportunities for single-species management, if this is a goal of such restoration activities, by adjusting design criteria based on differing habitat associations. In addition, the results suggest that including larger particle sizes in near-shore habitats and upstream of fry sites could decrease Tubifex tubifex habitat and thereby fry infection severity by reducing exposure to Myxobolus cerebralis. Stocking, interspecific competition and/or the presence of pathogens can affect fry habitat associations and cause deviations from demonstrated suitability indices. As such, evaluating system-specific differences in habitat associations may allow future habitat restoration activities to be more effective.

Infectious bacterial pathogens are a concern for aquaculture as estimates suggest that billions of US dollars are lost annually in aquaculture due to disease. One of the most prevalent salmonid pathogens is the bacterium Flavobacterium psychrophilum that causes bacterial coldwater disease. We reviewed the published F. psychrophilum literature and conducted a Bayesian analysis to examine large-scale patterns in rainbow trout (Oncorhynchus mykiss) mortality associated with laboratory challenge. We incorporated factors that were common across a majority of the laboratory exposure studies and these included bacterial dose, culture time, exposure method, bacterial isolate, experimental duration, and fish weight. The comparison showed that injection as the exposure method produced higher mortality than bath immersion, bacterial isolates differed in their effect on mortality, and bacterial dose has an interactive effect with fish weight and exposure method. Our comparison allows for inference on factors affecting rainbow trout mortality due to exposure to F. psychrophilum and suggests avenues to further optimize research protocols to better reach study goals.

Both biotic and abiotic factors can influence the survival and growth of age-0 salmonids. Diseases, such as whirling disease, can also affect salmonid demographics and population dynamics. Here, we conducted a supplementary analysis and evaluated specific stream characteristics that may have been responsible for the differences in growth and survival of two whirling disease resistant Rainbow Trout Oncorhynchus mykiss strains observed by Avila et al. (2018). We used regression modeling to analyze the influence of the biotic and abiotic characteristics of nine streams on the short-term apparent survival and growth of two Rainbow Trout strains, 5,000 German Rainbow Trout and 5,000 German Rainbow Trout × Colorado River Rainbow Trout in each stream. Akaike's information criterion (AIC c ) model selection was used to identify the factors that most affected short-term survival and growth. Average stream temperature had the largest (positive) effect, β temp = 0.060, on short-term survival. Rainbow Trout strain, average stream temperature (β temp = 1.55), competitor biomass (β competitor biomass = −0.002), and predator number (β predator number = 0.01) additively affected short-term growth. Our results indicate that both biotic and abiotic factors are important short-term determinants of Rainbow Trout poststocking performance and may account for the differences in survival and growth that we observed among stocking locations.