Interspecific association of brown trout (Salmo trutta) with non-native brook trout (Salvelinus fontinalis) at the fry stage

The introduction of non-native brook trout (Salvelinus fontinalis) in Europe has led to displacement and decreasing populations of native brown trout (Salmo trutta). Some studies have found that brown trout shift to a diet niche similar to brook trout when the two species live in sympatry, which conflicts with the competitive exclusion principle. A change in feeding niche may be a sign of early interspecific association and social learning, leading to behavioral changes. As a first step to address this possibility, it is essential to assess the interspecific association between the species during the early ontogenetic life stages. In this study, we therefore assess whether juvenile brown trout associate with non-native juvenile brook trout to the same extent as with conspecifics by setting up two experiments: (i) a binomial choice test allowing visual and chemical cues to estimate the species specificity of group preference, and (ii) an association test without physical barriers to estimate the degree of association of a focal brown trout with a group of either conspecifics or heterospecifics. In experiment (1), we found that focal juvenile brown trout preferred to associate with the stimuli groups and did not discriminate either against conspecific or heterospecific groups. Furthermore, more active individuals showed stronger preference for the stimuli group than less active ones, regardless of species. In experiment (2), we found that brook trout groups had a tighter group structure than brown trout groups, and that focal brown trout showed stronger association with brook trout than with brown trout. These results indicate that brown trout may associate with brook trout at an early life stage, which would allow for interspecific social learning to occur. Future studies should look closer into causes and consequences of interspecific association and social learning, including potential effects on the phenotype selection in brown trout populations

Spatial distribution of introduced brook trout Salvelinus fontinalis (Salmonidae) within alpine lakes: evidences from a fish eradication campaign

Brook trout Salvelinus fontinalis have been used worldwide to stock fishless alpine lakes, negatively affecting native biota. Understanding its spatial ecology in invaded ecosystems can provide information to interpret and contrast its ecological impact. We opportunistically used capture points of brook trout gillnetted during an eradication campaign to assess the distribution patterns of four unexploited populations inhabiting high-altitude lakes. The main eradication method implies the use of many gillnets with several mesh sizes, which are selective for different fish sizes. For each lake we drew six capture maps associated with as many different mesh sizes, and we tested whether the distance from the coastline (which in alpine lakes is a reliable proxy of the most important spatial gradients, e.g. depth, temperature, prey availability, lighting conditions) influences the proportion of captured fish belonging to different size classes and the number of fish captured by the nets with different mesh sizes. To interpret the results, we also provide a cartographic description of the lakes’ bathymetry and littoral microhabitats. We found (1) a negative relationship between brook trout distribution and the distance from the coastline in all of the size classes, lakes and mesh sizes; (2) that large brook trout can thrive in the lakes’ center, while small ones are limited to the littoral areas; and (3) that the distance from the coastline alone cannot explain all the differences in the catch densities in different parts of the lakes. As in their native range, introduced brook trout populations also have littoral habits. Microhabitats, prey availability and distance from the spawning ground are other likely factors determining the distribution patterns of brook trout populations introduced in alpine lakes. The obtained results also provide useful information on how to plan new eradication campaigns

An investigation on the effects of juvenile rainbow trout (Oncorhynchus mykiss) and brook trout (Salvelinus fontinalis) monoculture and duo-culture farming in freshwater and seawater on growth performance

The objective of this study was to compare growth performance and feed conversion ratios of rainbow trout (Oncorhynchus mykiss) and brook trout (Salvelinus fontinalis) juveniles in monoculture and duo-culture in freshwater and seawater under aquarium conditions. The fish were about 2-months old hatchery-reared brook and rainbow trout with initial weights of 0.934±0.033 (n=360) and 1.014±0.019 (n=360) g, respectively. The juveniles were kept in 10 L aquaria. Each aquarium contained 40 fish: 40 fish from each species for monoculture, 20+20 (rainbow trout+brook trout) fish from each species for duo-culture. The fish were in 3 groups with three replicates in freshwater and seawater and 18 aquaria were used. At the end of the 45 day study; mean live weights of brook trout were 2.735±0.153 g, rainbow trout 2.925±0.262 g in monoculture and brook trout 2.354±0.186 g, rainbow trout 3.882±0.494 g in duo-culture in seawater, brook trout 3.088±0.085, rainbow trout 3.364±0.093 g in monoculture and brook trout 2.164±0.169, rainbow trout 3.948±0.124 g in duo-culture in fresh water. While there were similarities between brook trout and rainbow trout in monoculture groups in sea water and fresh water, some differences were realized in duo-culture (p<0.001)

Specific niche characteristics facilitate the invasion of an alien fish invader in boreal streams

We studied the ecological niche relations of native stream fish and an alien invader, brook trout (Salvelinus fontinalis), to examine if brook trout had located an underused environmental niche in our boreal study system. In both study years (1994 versus 2004), we found brook trout to have the most marginal niche position of all the fish species examined. The most important environmental variable affecting the distribution of brook trout was pH, with acid headwater sites being dominated by this species. Brown trout, in contrast, had relatively nonmarginal niche, occurring in average conditions across the sampled sites. Other fish species had niche positions between the two salmonids. Our results show that fish invasions may be strongly facilitated by the presence of suboptimally occupied environmental niche space in the recipient river system

Lake Michigan Salmonid Stocking Costs in Wisconsin

The costs of stocking salmonids in the Wisconsin waters of Lake Michigan are estimated for 1985. Estimation procedures and costs per stocked and captured fish are presented. Fingerlings of a species were found in most cases to cost more per captured fish than yearlings. However chinook salmon fingerlings were least expensive at an average cost of only $0.35 per captured fish. Most expensive were brook yearlings and fingerlings at$12.67 and $10.14 respectively. While a full policy evaluation awaits additional research on species specific benefits, three tentative conclusions can be drawn for the Wisconsin fishery. First, the role of brook trout in the fishery should be reviewed. Second, despite difficulties with lake trout rehabilitation, the role of lake trout in the sport fishery is encouraging and may justify continued stocking. Finally, increased stocking of the popular chinook salmon may be justified if the recent problems of low capture-per-release rates can be solved.restocking costs, benefit-cost methodology, sport fisheries, salmonids, Lake Michigan, Environmental Economics and Policy, Resource /Energy Economics and Policy,

Growth, Condition, and Trophic Relations of Stocked Trout in Southern Appalachian Mountain Streams

Stream trout fisheries are among the most popular and valuable in the United States, but many are dependent on hatcheries to sustain fishing and harvest. Thus, understanding the ecology of hatchery‐reared trout stocked in natural environments is fundamental to management. We evaluated the growth, condition, and trophic relations of Brook Trout Salvelinus fontinalis, Brown Trout Salmo trutta, and Rainbow Trout Oncorhynchus mykiss that were stocked in southern Appalachian Mountain streams in western North Carolina. Stocked and wild (naturalized) trout were sampled over time (monthly; September 2012–June 2013) to compare condition and diet composition and to evaluate temporal dynamics of trophic position with stable isotope analysis. Relative weights (Wr) of stocked trout were inversely associated with their stream residence time but were consistently higher than those of wild trout. Weight loss of harvested stocked trout was similar among species and sizes, but fish stocked earlier lost more weight. Overall, 40% of 141 stomachs from stocked trout were empty compared to 15% of wild trout stomachs (N = 26). We identified a much higher rate of piscivory in wild trout (18 times that of stocked trout), and wild trout were 4.3 times more likely to consume gastropods relative to stocked trout. Hatchery‐reared trout were isotopically similar to co‐occurring wild fish for both δ13C and δ15N values but were less variable than wild trout. Differences in sulfur isotope ratios (δ34S) between wild and hatchery‐reared trout indicated that the diets of wild fish were enriched in δ34S relative to the diets of hatchery‐reared fish. Although hatcheryreared trout consumed prey items similar to those of wild fish, differences in consumption or behavior (e.g., reduced feeding) may have resulted in lower condition and negative growth. These findings provide critical insight on the trophic dynamics of stocked trout and may assist in developing and enhancing stream trout fisheries

Electrical phase angle as a new method to measure fish condition

In this study, phase angle (the ratio of resistance and reactance of tissue to applied electrical current) is presented as a possible new method to measure fish condition. Condition indices for fish have historically been based on simple weight-at-length relationships, or on costly and timeconsuming laboratory procedures that measure specific physiological parameters. Phase angle is introduced to combine the simplicity of a quick field-based measurement with the specificity of laboratory analysis by directly measuring extra- and intracellular water distribution within an organism, which is indicative of its condition. Phase angle, which can be measured in the field or laboratory in the time it takes to measure length and weight, was measured in six species of fish at different states (e.g., fed vs. fasted, and postmortem) and under different environmental treatments (wild vs. hatchery, winter vs. spring). Phase angle reflected different states of condition. Phase angles 15° indicated fish that were in better condition. Phase angle was slightly affected by temperatures (slope = – 0.19) in the 0–8°C range and did not change in fish placed on ice for <12 hours. Phase angle also decreased over time in postmortem fish because of cell membrane degradation and subsequent water movement from intra- to extracellular (interstitial) spaces. Phase angle also reflected condition of specific anatomical locations within the fish

Host Switching of Zoonotic Broad Fish Tapeworm (Dibothriocephalus latus) to Salmonids, Patagonia

Diphyllobothriosis is a reemerging zoonotic disease because of global trade and increased popularity of eating raw fish. We present molecular evidence of host switching of a human-infecting broad fish tapeworm, Dibothriocephalus latus, and use of salmonids as intermediate or paratenic hosts and thus a source of human infection in South AmericaFil: Kuchta, Roman. Academy of Sciences of the Czech Republic. Biology Centre. Institute of Parasitology; República ChecaFil: Radačovská, Alžbeta. Biology Centre of the Academy of Sciences of the Czech Republic; República ChecaFil: Bazsalovicsová, Eva. Slovak Academy of Sciences. Institute of Parasitology; EslovaquiaFil: Viozzi, Gustavo Pedro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Semenas, Liliana Graciela. Universidad Nacional del Comahue; ArgentinaFil: Arbetman, Marina Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Scholz, Tomáš. Biology Centre of the Academy of Sciences of the Czech Republic; República Chec

Distribution of freshwater fish in the south-western corner of Australia

This study investigates the distribution of freshwater fishes in the Busselton to Walpole Region. A total of 311 sites in 19 major catchments along the south-west coast from Capel to Walpole, were sampled using a variety of methods. New data was collated with that from previous studies to generate 15 species distribution maps. Habitat and life history notes and recommendations for conservation are made for each species. Changes in fish distribution are also commented upon. This study contributes to series of documents published for the purposes of water allocation planning in the Busselton to Walpole Region