Yersinia ruckeri isolates recovered from diseased Atlantic Salmon (Salmo salar) in Scotland are more diverse than those from Rainbow Trout (Oncorhynchus mykiss) and represent distinct subpopulations

Yersinia ruckeri is the etiological agent of enteric redmouth (ERM) disease of farmed salmonids. Enteric redmouth disease is traditionally associated with rainbow trout (Oncorhynchus mykiss, Walbaum), but its incidence in Atlantic salmon (Salmo salar) is increasing. Yersinia ruckeri isolates recovered from diseased Atlantic salmon have been poorly characterized, and very little is known about the relationship of the isolates associated with these two species. Phenotypic approaches were used to characterize 109 Y. ruckeri isolates recovered over a 14-year period from infected Atlantic salmon in Scotland; 26 isolates from infected rainbow trout were also characterized. Biotyping, serotyping, and comparison of outer membrane protein profiles identified 19 Y. ruckeri clones associated with Atlantic salmon but only five associated with rainbow trout; none of the Atlantic salmon clones occurred in rainbow trout and vice versa. These findings suggest that distinct subpopulations of Y. ruckeri are associated with each species. A new O serotype (designated O8) was identified in 56 biotype 1 Atlantic salmon isolates and was the most common serotype identified from 2006 to 2011 and in 2014, suggesting an increased prevalence during the time period sampled. Rainbow trout isolates were represented almost exclusively by the same biotype 2, serotype O1 clone that has been responsible for the majority of ERM outbreaks in this species within the United Kingdom since the 1980s. However, the identification of two biotype 2, serotype O8 isolates in rainbow trout suggests that vaccines containing serotypes O1 and O8 should be evaluated in both rainbow trout and Atlantic salmon for application in Scotland

Diet of rainbow trout in Lake Rotoiti: an energetic perspective

We characterised seasonal and ontogenetic changes in diet and prey energy density of rainbow trout (Oncorhynchus mykiss) in Lake Rotoiti, New Zealand, to better understand the prey requirements of trout in central North Island lakes. Common smelt (Retropinna retropinna) was the dominant prey item of rainbow trout larger than 200 mm (77.8% of diet by weight), followed by kōura (freshwater crayfish Paranephrops planifrons; 6.3%), common bully (Gobiomorphus cotidianus; 5.5%), and kōaro (Galaxias brevipinnis; 3.4%). Juvenile rainbow trout (<200 mm) consumed amphipods, aquatic and terrestrial insects, oligochaetes, tanaid shrimps, and smelt. Trout consumed kōaro only in autumn and winter; consumption of other species did not vary seasonally. The maximum size of smelt consumed increased with increasing trout size, but trout continued to consume small smelt even as large adults. Consumption of larger prey items (kōaro and kōura) also increased with increasing trout size. This study indicates the importance of smelt for sustaining rainbow trout populations, as predation on other species was relatively low. These findings provide a basis for bioenergetic modelling of rainbow trout populations in lakes of the central North Island of New Zealand

Accumulation of Geosmin and 2-methylisoborneol in European Whitefish Coregonus Lavaretus and Rainbow Trout Oncorhynchus Mykiss in RAS

Geosmin (GSM) and 2-methylisoborneol (MIB)-induced off-flavors can cause serious problems in a recirculating aquaculture system (RAS), such as delayed harvest and increased production costs, but also damage producers’ reputation. Traditionally, off-flavors have been removed by depuration before harvesting. Rainbow trout (Oncorhynchus mykiss) and European whitefish (Coregonus lavaretus) are commercially valuable species produced for consumers, both being suitable for rearing in RAS. In this study, European whitefish and rainbow trout were raised from juvenile up to 240 g (European whitefish) and 660 g (rainbow trout) to monitor the long-term accumulation of off-flavors. The concentrations in fillet of rainbow trout reached 3.6 ng·g-1 (MIB) and 5.6 ng∙g-1 (GSM) with lipid content of 22.5%, while for European whitefish up to 3.2 ng·g-1 (MIB) and 3.9 ng·g-1 (GSM) were found with 14.8% in lipid content. Concentrations up to 58 ng·L-1 (MIB) and 49 ng·L-1 (GSM) were found in the circulating water. Based on the results, the accumulation of MIB proceeds at similar pace for both species. In the case of GSM, the accumulation started similarly for both species but proceeded more quickly for rainbow trout after 140 days of the experiment, with a statistically significant difference (p < 0.05).202

Assessing movement of rainbow trout and common smelt between Lake Rotoiti and Lake Rotorua using otolith chemical signatures: A summary of work so far

This study used otolith microchemistry to investigate movement of common smelt and rainbow trout between Lake Rotorua and Lake Rotoiti. Rainbow trout were collected from Lake Rotoiti, Lake Rotorua and the Ohau Channel, and smelt were collected from several locations in Lake Rotoiti and Lake Rotorua

Digestibility in selected rainbow trout families and modelling of growth from the specific intake of digestible protein

The experiments aimed to clarify variations in digestibility of dietary nutrients in rainbow trout. Furthermore, the objective was to study how differences in digestibility might be related to growth and feed utilisation at various growth rates. When comparing the results from the experiments it appeared that particularly protein digestibility was closely related to specific growth rate and feed conversion ratio at high growth rates. As a tool to visualise the relationship between protein digestibility and growth of rainbow trout a growth model was developed based on the specific intake of digestible protein, and general assumptions on protein content and protein retention efficiency in rainbow trout. The model indicated that increased protein digestibility only partly explained growth increase and that additional factors were important for growth increment

Growth, Food Habits, and the Relative Effectiveness of Stocking Rainbow Trout (Salmo gairdneri) in South-Central South Dakota

The effectiveness of stocking rainbow trout (Salmo gairdneri) in 47 selected stock ponds in south-central South Dakota was analyzed in 1977 and 1978. Rainbow trout were captured in 31 (66.0%) ponds during the study. Twenty-five of the 31 ponds (80.6%) appeared to have excellent rainbow trout populations. Rainbow trout stocked in ponds with a resident largemouth bass (Micropterus salmoides) population had poor survival. The growth rates and condition factors for 93 and 463 rainbow trout in 1977 and 1978, respectively, were excellent. The average total length for age-groups I and II rainbow trout in 1977 was 195 and 224 mm, respectively. The values for age-groups I, II, III, and V rainbow trout in 1978 were 184, 290, 366, and 499 mm, respectively. The average coefficient of condition value for all rainbow trout in 1977 was 1.04 and 1.07 for all trout in 1978. Stomachs were removed from 463 rainbow trout in 1978. Hemipterans and gastropods were the dominant food organisms eaten. Other organisms frequently consumed were coleopterans, dipterans, odonates, and cyprinids. Odonates and cyprinids were more frequently consumed by larger trout. The maximum surface temperatures recorded were 26.0 C in 1977 and 28.5 C in 1978. All ponds contained water with temperatures and dissolved oxygen levels within the reported tolerance ranges of rainbow trout. Several ponds, however, contained marginal levels and may have been responsible for our failure to capture rainbow trout in 16 ponds

Survival, Abundance, and Relative Predation of Wild Rainbow Trout in the Deerfield Reservoir System, South Dakota

Rainbow Trout Oncorhynchus mykiss are routinely stocked in Black Hills streams and reservoirs to enhance angling opportunities for the public, however in most cases, hatchery-reared Rainbow Trout do not successfully recruit to establish natural populations. One exception is the Deerfield Reservoir system, where it is estimated that up to 25% of the Rainbow Trout population consists of naturally produced, wild Rainbow Trout. While recruitment of wild Rainbow Trout to the Deerfield Reservoir fishery does occur, annual stockings of 12,000 hatchery Rainbow Trout have continued. In recent years, adipose fin clips were used to identify hatchery Rainbow Trout stocked into Deerfield Reservoir, however the personnel and time requirements of fin clipping resulted in the termination of fin clips in May 2014. An elimination or reduction of hatchery stockings may be considered in the future management of the Deerfield Reservoir Rainbow Trout population, however a lack of knowledge regarding factors such as predation, movement and emigration patterns, relative abundance, and apparent survival of wild Rainbow Trout has generated a need for additional research in order to help guide future management decisions. In addition, the termination of fin clipping requires the identification and evaluation of new techniques for the classification of wild and hatchery Rainbow Trout in Deerfield Reservoir. Thus the objectives of our research were to 1) investigate the predation on young Rainbow Trout and the diet composition of fishes in Deerfield Reservoir, 2) quantify the relative abundance, growth, and apparent survival of wild Rainbow Trout in the Deerfield Reservoir system, 3) describe the movement patterns and emigration rates of wild Rainbow Trout from tributary streams into Deerfield Reservoir, and 4) evaluate the use of stable isotope analysis and otolith microchemistry for the classification of wild and hatchery Rainbow Trout origins. Juvenile Rainbow Trout were not found in the diets of Rock Bass Ambloplites rupestris, Yellow Perch Perca flavescens, and adult (\u3e200 mm) Rainbow Trout in Deerfield Reservoir and indicated that the risk of predation upon Rainbow Trout is negligible. The diet composition of all species consisted primarily of aquatic invertebrates and dietary overlap did exist among Rainbow Trout, Yellow Perch, and Rock Bass. While diets were similar among species with regard to aquatic invertebrate prey, the degree of diet overlap with Rainbow Trout was generally low (range 0.2- 0.57). We found that the relative abundance of wild Rainbow Trout in tributary streams was greater in South Fork Castle Creek than in Castle Creek. Rainbow Trout movement and emigration from tributaries into Deerfield Reservoir was monitored in both tributaries using 12 mm passive integrated transponder (PIT) tags which showed that within and among stream movement was minimal throughout our study. We tagged 380 Rainbow Trout and in subsequent sampling events recaptured 81 unique fish using backpack electrofishing. Of these 81 fish only 3 were recaptured outside of the 100 m site in which they were tagged, resulting in 96% fidelity to original tagging site. Out of the total 380 tagged Rainbow Trout, another 73 (19%) unique fish were detected by an instream passive PIT tag reader emigrating from tributary streams into Deerfield Reservoir. We constructed a Von Bertalanffy growth model for wild Rainbow Trout in Deerfield Reservoir based on length frequency analysis and found that growth of fish up to age 4 was relatively slow in comparison to other populations, reaching only 210 mm by age 4. Using the growth parameters from the Von Bertalanffy growth model, we estimated survival of wild Rainbow Trout in the Deerfield Reservoir system to be as low as 3% during the first year of life. However, survival increased with each year of life, with relatively high survival (up to 66%) by age 4. In the absence of fin clips, identifying future trends in the wild Rainbow Trout population in Deerfield Reservoir requires the accurate classification of both wild and hatchery origins. Using stable isotope analysis we found that wild Rainbow Trout can be classified with greater than 75% accuracy using pectoral fin tissue, and greater than 85% accuracy using dorsal muscle tissue. We also used otolith microchemistry to identify the natal tributary stream origins of 9 wild Rainbow Trout collected in Deerfield Reservoir. Our results showed that 56% of wild Rainbow Trout in Deerfield Reservoir were classified to Castle Creek, while 44% were classified to South Fork Castle Creek. These results indicate that Castle Creek likely contributes a slightly greater number of wild Rainbow Trout recruits to the Deerfield Reservoir population than South Fork Castle Creek. Overall our results indicate a healthy, sustainable population of wild Rainbow Trout in Deerfield Reservoir. Our analysis of survival, abundance, and emigration data, as well as low risks of predation suggest that management of Deerfield Reservoir for wild Rainbow Trout in the absence of stocking or at reduced stocking rates is likely sustainable. Managing Deerfield Reservoir primarily for wild Rainbow Trout may be viable, however fisheries managers should consider the impact of reduced stockings on angler catch rates. In addition, a reduction or elimination of hatchery stockings would likely have positive impacts on the wild Rainbow Trout population and monitoring changes in the population dynamics of wild Rainbow Trout would be beneficial to the assessment of any stocking changes

Factors affecting growth and condition of stocked rainbow trout in eastern Washington lakes

Rainbow trout growth and condition were examined in 17 ecologically diverse lakes from which physical, limnological, and biological parameters were sampled. Parameters were correlated with rainbow trout growth and condition to identify factor(s) that predict rainbow trout growth and condition across eastern Washington lakes stocked annually with rainbow trout fry. We tested the hypothesis Ho: the environmental variables examined do not predict rainbow trout growth and condition. Data were natural log transformed for better fit, and were analyzed by season. Several models were identified using stepwise multiple regression analysis and general linear modeling which significantly predicted trout growth or condition using one or more of the biotic and abiotic independent variables. Trends in trout growth and condition correlated to biomass of odonates, amphipods, caddisflies, calanoid copepods and density of dipterans and hemipterans were generally positive regardless of season. Among autumn measures, single biological predictors including biomass of coenagrionid damselflies and Aglaodiaptomus copepods explained approximately 42% and 49% of the lake-to-lake variation in rainbow trout growth and condition, respectively. In addition, more than 84% of the variation in rainbow trout condition was explained by the variables maximum lake depth (Zmax), autumn caddisfly larvae biomass, and autumn dipteran density. Rainbow trout condition factor compared with spring measures was inversely proportional to Zmax and rainbow trout stocking density. Both variables explained 51% of the spring lake-to-lake variation in condition factor. Among combined measures (spring and autumn), odonate and calanoid copepod biomass, and odonate density and amphipod biomass were directly proportional to rainbow trout growth and condition,. respectively, with more than 54% of the lake-to-lake variation explained by the models. The best regression models explained as much as 95% of lake-to-lake variation in trout growth and condition. General linear models explained 58% to 99% of the variation in trout condition. General linear modeling identified several negative relationships with rainbow trout condition. Stocking density, presence of largemouth bass, green sunfish, brown trout, and tiger trout negatively affected rainbow trout condition. The collection of significant models suggests that rainbow trout stocked into eastern Washington lakes realize higher growth rates and better condition in the presence of abundant forage base and in the absence of competition or predation by resident fish species. Both single environmental variables and collections of environmental variables can significantly predict rainbow trout growth and condition. Thus, the environmental variables used in this study, or other variables, could be monitored and used by regional resource agencies in managing rainbow trout fisheries --Document