Introduction and management of Myxobolus cerebralis-resistant rainbow trout in Colorado

2013 Summer.Includes bibliographical references.To view the abstract, please see the full text of the document

Survival and reproduction of Myxobolus cerebralis-resistant rainbow trout introduced to the Colorado river and increased resistance of age-0 progeny.

Myxobolus cerebralis caused severe declines in rainbow trout populations across Colorado following its introduction in the 1980s. One promising approach for the recovery of Colorado's rainbow trout populations has been the production of rainbow trout that are genetically resistant to the parasite. We introduced one of these resistant crosses, known as the GR×CRR (cross between the German Rainbow [GR] and Colorado River Rainbow [CRR] trout strains), to the upper Colorado River. The abundance, survival, and growth of the stocked GR×CRR population was examined to determine if GR×CRRs had contributed offspring to the age-0 population, and determine whether these offspring displayed increased resistance and survival characteristics compared to their wild CRR counterparts. Apparent survival of the introduced GR×CRR over the entire study period was estimated to be 0.007 (±0.001). Despite low survival of the GR×CRRs, age-0 progeny of the GR×CRR were encountered in years 2008 through 2011. Genetic assignments revealed a shift in the genetic composition of the rainbow trout fry population over time, with CRR fish comprising the entirety of the fry population in 2007, and GR-cross fish comprising nearly 80% of the fry population in 2011. A decrease in average infection severity (myxospores fish-1) was observed concurrent with the shift in the genetic composition of the rainbow trout fry population, decreasing from an average of 47,708 (±8,950) myxospores fish-1 in 2009 to 2,672 (±4,379) myxospores fish-1 in 2011. Results from this experiment suggest that the GR×CRR can survive and reproduce in rivers with a high prevalence of M. cerebralis. In addition, reduced myxospore burdens in age-0 fish indicated that stocking this cross may ultimately lead to an overall reduction in infection prevalence and severity in the salmonid populations of the upper Colorado River

Factors Affecting Post-Challenge Survival of Flavobacterium psychrophilum in Susceptible Rainbow Trout from the Literature

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

The upper Colorado River study site.

<p>The 4.2-57 at the upstream end and Sheriff Creek at the downstream end. Locations in which fish were sampled in 2006 and 2007 (box), fry were sampled in all years of the study (triangles), and fish were stocked in 2006 (circles) and 2010 (squares) are shown.</p

The effects of abiotic enrichment and predator training on the behavior, morphology, and survival of a species of conservation concern

Abstract Conservation practitioners often rely on captive breeding programs to supplement wild populations at risk of extinction. While supplementation has been successful for some taxa, the success of using hatchery fish to supplement wild populations is severely impacted by predation. Elevated predation on hatchery fish may arise because hatchery environments often differ from wild environments and constrain the ability of hatchery fish to be adapted to the environments in which they are released. We assessed the effects of abiotic enrichment on the expression of behavioral and morphological phenotypes across three populations of a species of conservation concern, the Arkansas darter (Etheostoma cragini). We also used a factorial approach to assess whether abiotic enrichment and predator training increases survival during encounters with a novel predator. We found that abiotic enrichment affected ecomorphological attributes associated with fins; generally, measures of the caudal and pectoral fin decreased in the treatment group compared to the control treatment. Behaviorally, darters reared with abiotic enrichment increased feeding and decreased movement compared to the control group. Importantly, we found that in combination with predator training, abiotic enrichment increased the probability of surviving first encounters with a predator. We therefore recommend conservation practitioners incorporate abiotic enrichment and predator training in hatchery programs. Captive breeding programs are used to supplement wild populations at risk of extinction, but hatchery‐reared fish often do not survive after release. Using the threatened Arkansas darter, we show that abiotic enrichment and predator training of hatchery populations impact behavior and morphology and increase the probability of surviving first encounters with a non‐native predator

Proportion (SE bars) of the brown trout and rainbow trout fry populations exhibiting signs of <i>M. cerebralis</i> infection.

<p>Fry were collected from the upper Colorado River in 2009 (brown trout: N = 277; rainbow trout: N = 29), 2010 (brown trout: N = 64; rainbow trout: N = 41), and 2011 (brown trout: N = 138; rainbow trout: N = 19).</p

The upper Colorado River study site.

<p>The 4.2-57 at the upstream end and Sheriff Creek at the downstream end. Locations in which fish were sampled in 2006 and 2007 (box), fry were sampled in all years of the study (triangles), and fish were stocked in 2006 (circles) and 2010 (squares) are shown.</p

Model-averaged monthly apparent survival rate (φ; SE bars) for the GR×CRR.

<p>Survival rates apply only to the GR×CRR fish that were stocked in the upper Colorado River in June 2006. Date ranges (x-axis) represent the periods between primary sampling occasions for the adult rainbow trout population.</p

Adult GR×CRR and CRR abundance (N km⁻¹; SE bars).

<p>Abundances were estimated within the upper Colorado River study section for the years 2008 to 2011.</p

The effect of a single pre-release exposure to conspecific alarm cue on post-stocking survival in three strains of rainbow trout (Oncorhynchus mykiss)

Significant resources go toward rearing and stocking fish globally, yet post-stocking survival is often low, largely due to high predation rates on hatchery-reared fish. Antipredator behavior has been enhanced in many species through exposure to chemical cues that simulate predation events, but the implementation of such protocols may be logistically challenging. It has been suggested that a single exposure of hatchery fish to chemical cues while en route to stocking locations may be sufficient to enhance antipredator behavior and improve survival. We tested whether a one-time exposure to conspecific alarm cues while en route to a stocking site increased post-stocking survival of three strains of rainbow trout (Oncorhynchus mykiss (Walbaum, 1792)). We found no difference in mortality rates between strains or between treatment fish (exposed to alarm cues) and control fish (not exposed to alarm cues), suggesting that this quick and easy protocol was insufficient, and that more complex techniques should be explored to increase post-stocking survival.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author