Movement behavior of juvenile salmonids in boulder-dominated channels: effects of boulder dispersion, flow, and species

We examined the effects of kin-biased territorial defense behavior on the distribution of foraging attempts and percent weight changes (fitness benefits) in juvenile Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss) in an artificial stream channel. The individual percent weight changes and frequency of aggressive interactions and foraging attempts were quantified in kin (full sibling) and non-kin groups of salmon and trout We observed kin groups of both species to obtain significantly greater mean and less variable percent weight gains that non-kin groups. In addition, faster-growing (dominant) individuals of both species within kin groups exhibited significantly fewer aggressive interactions than did faster-growing nonkin individuals, while we observed no difference between kin and non-kin slower-growing (subordinate) individuals. Slowergrowing kin individuals of both species obtained significantly more foraging opportunities than slower-growing non-kin individuals while there was no difference between faster-growing kin and non-kin individuals. These data suggest that reduced aggression by faster-growing individuals towards slower-growing kin enables slower-growing kin to obtain more foraging opportunities, resulting in higher and less variable percent weight changes. These data also suggest that as a result of kin-biased territorial defense and foraging behavior, juvenile Atlantic salmon and rainbow trout may be able to maximize inclusive fitness potential by defending territories near related conspecifics.

Magurran, Irving and Henderson (1997) have reported that a population of European minnows, Phoxinus phoxinus, did not show an obvious behavioural fright reaction when they were presented with conspecific skin extract in a wild situation. Fish from the same population show a strong response when tested in aquaria. From these data the authors conclude that the fright reaction may be contingent on such factors as assessed risk and hunger. From this reasonable hypothesis they progress to the assertion that the Schreckstoff of ostariophysan fishes should not be considered an alarm pheromone. Much of their paper is devoted to arguments supporting their hypothesis that Schreckstoff cannot operate as an alarm pheromone. I argue that it is appropriate and adaptive to respond to alarm signals in a contingent manner, and attempt to answer the various arguments regarding the validity of terming Schreckstoff an alarm pheromone.

The purpose of this study was to determine if juvenile Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss) can discriminate kin from non-kin, since other salmonid species (coho salmon (Oncorhynchus kisutch) and Arctic charr (Salvelinus alpinus)) have been shown to possess this ability. When tested in water conditioned by conspecifics (kin and non-kin) and heterospecifics in a two-choice tank, both rainbow trout and Atlantic salmon demonstrated a significant preference for kin over non-kin and heterospecifics, indicating that these species possess kin-discrimination abilities. This ability appears to be widespread among salmonid fishes.

Comparative trophic ecology of nearshore juvenile salmonids in Lake Ontario

Using semi-natural stream channels, we estimated the effects of competition and predation exerted by juvenile and adult exotic rainbow trout (Oncorhynchus mykiss) on the diel activity pattern of juvenile native Atlantic salmon (Salmo salar), a secondary consumer. We also evaluated the direct and indirect effects of competition, predation and abiotic factors (water depth and velocity) on the growth rate of salmon, the biomass of invertebrate grazers (primary consumers) and the biomass of periphytic algae (primary producers; chlorophyll a). The presence of chemical cues emanating from adult predatory trout reduced the daily activity of juvenile Atlantic salmon. In contrast, competition imposed by juvenile rainbow trout forced Atlantic salmon to be more active during the day, even if adult rainbow trout were also present. We found no effect of either competition or of predatory cues on the growth rate of Atlantic salmon, and no evidence of indirect effects on either the biomass of invertebrates or the biomass of chlorophyll a. In contrast, we demonstrated that this food chain (fish--invertebrate grazers--periphytic algae) was under the control of a critical abiotic factor, the water velocity, and of bottom-up processes. We concluded that the exotic species directly increases the risk of predation of the native Atlantic salmon, but behavioral compensation probably limits the effects on growth rate. The competition and predation imposed by the invaders had no indirect effects on lower trophic levels. Top-down effects may have been mitigated by the dominant influence of water velocity controlling all components of the food chain and by elevated levels of primary production.

In Atlantic salmon, as in most salmonids, males can mature early in the life cycle, as small freshwater fish, termed parr, and/or undergo a sea migration before maturing as full-size adults. The alternative life histories are contingent on environmental and social circumstances, such as growth rate, territory quality or any other factor that affects the individual's state. In order to model the choice of life history in this group of commercially valuable species, it is necessary to understand not only the relative contribution of the different male types to subsequent generations, but also to know the factors that affect reproductive success in each type. In this paper we present the results of a study designed to investigate the factors that affect the reproductive success of mature parr. We used highly polymorphic minisatellite DNA markers to analyse paternity in a series of mating experiments where the number and body size of parr were manipulated. The fraction of eggs fertilized by mature parr ranged from 26 to 40 per cent, with individual parr fertilizing up to 26 per cent of the eggs. A strong positive correlation was found between parr size and reproductive success. The relative success of parr decreased with increasing parr number. Data from this and other studies on variation in the timing and degree of parr reproductive success are discussed in relation to the evolution of male mating strategies and life history in salmonids.

In Chilean Patagonia relatively pristine aquatic environments are being modified by the introduction of exotic salmonids, initially through their deliberate release for sport fishing since the early twentieth century, and more recently via the accidental escape from fish farms. There is therefore a need to reliably distinguish between naturally reproducing and fugitive salmonids associated with the Chilean salmonid farming industry, the second largest in the world. We tested the ability of stable isotope analysis (SIA) and analysis of scale growth profiles to discriminate between farmed and free-living salmonids sampled around the Island of Chiloe. Juvenile Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss) from aquaculture facilities were significantly more enriched in δ15N and lipid-corrected δ13C than river-caught individuals. Scale growth slopes during the first year in freshwater were significantly higher in farmed than in wild-caught rainbow trout, indicating faster somatic growth under hatchery conditions. Stable isotopes analysis classified 94% of juvenile Atlantic salmon and rainbow trout to their correct farm or free-living groups. Our results, therefore, can help to elucidate the origin and spread of exotic invasive salmonids in Chile, and address one of the biggest threats to native freshwater fishes in Patagonia and other temperate zones of the Southern Hemisphere.

This study describes the development of procedures for the assessment of anaerobic capacity and swim performance in juvenile Atlantic salmon (Salmo salar), rainbow trout (Oncorhynchus mykiss), and brook trout (Salvelinus fontinalis). Three exercise tests, with exhaustion as an end point, were evaluated: a fixed-duration, high-intensity exercise; a fixed-velocity exercise; and an incremental-velocity exercise. Muscle (or whole body) lactate, phosphocreatine (PCr), and ATP were used to calculate, in ATP equivalents, the anaerobic energy expenditure (AEE, in µM ·g-1or µmoles) and to document the recovery from exhaustion. AEE was maximal in the first of these tests and submaximal in the second. Recovery was characterized by rapid restoration of PCr, slower recovery of ATP and lactate, and even slower recovery of glycogen. Mathematical expressions were developed to express the rates of recovery and thereby permit intra- and inter-species comparisons. Body size was the most important determinant of performance. Anaerobic capacity (AEE in the fixed duration test), sprint duration at fixed velocity, and maximum swimming speed scaled as length L4to L5, L4to L5, and L1.3, respectively. Each of these tests are effective measures for evaluating intra- and inter-specific differences in anaerobic capacity and swimming performance providing correction is made for the large scaling coefficients.

Competition with non‐native species may impede the restoration of native species, but differences in competitive abilities among intraspecific native populations may make some populations more suitable for reintroduction than others. Here, juvenile Atlantic salmon (Salmo salar) from two allopatric populations (LaHave and Sebago) being used for reintroduction into Lake Ontario were placed into two natural stream sites differing in the presence of ecologically similar rainbow trout (Oncorhynchus mykiss). We assessed the effects of competition in the natural streams on fitness‐related traits and habitat use of the Atlantic salmon. We then compared these effects to those observed in artificial streams from a previous study. Atlantic salmon in natural streams had reduced fitness‐related traits that were associated with suboptimal microhabitats in the presence of rainbow trout, but utilised optimal microhabitats in their absence. In the presence of rainbow trout, the two Atlantic salmon populations exhibited comparable recapture proportions to each other, but the individuals from the Sebago population had better performance (body size and condition) than those from the LaHave population. Responses of both Atlantic salmon populations to competition with rainbow trout were generally similar in both direction and magnitude when compared to results from the artificial stream study. The combined results suggest that native species restoration efforts should be focused on candidate populations that are ecologically suitable to reintroduction environments, as well as on suitable habitats that do not contain exotic competitors. Moreover, this study highlights the value of controlled experiments in artificial environments for predicting fitness‐related performance in natural environments.

Many organisms rely on chemosensory cues to mediate predation risks. Recent studies have demonstrated impaired chemosensory detection ability under weak acidification. Because rainfall may lead to episodic acidification of surface water, we assessed the effects of acid rain on chemosensory alarm functions. Under natural conditions, we quantified alarm behaviour of juvenile Atlantic salmon (Salmo salar) exposed to conspecific chemical alarm cues before and following rainfall. Before rainfall, salmon were capable of an alarm response in the study streams. After rainfall, salmon from Devil’s Brook did not respond to the alarm cues whereas the detection of salmon from Catamaran Brook (a comparable stream having higher acid neutralising capacity) was maintained. To relate these findings to predator–prey encounters, we performed a second experiment where we staged encounters between prey (rainbow trout, Oncorhynchus mykiss) and predator (largemouth bass, Micropterus salmoides) exposed to acidified and unacidified rainbow trout chemical alarm cues. Trout exposed to acidified alarm cues survived for a significantly shorter amount of time than trout exposed to unacidified alarm cues, whereas no difference in overall predator behaviour was observed. Our results suggest that episodic acidification in small nursery streams may disrupt the chemical information mediated by the chemical alarm cues that can translate into higher survival costs for prey.

Very few studies have investigated the effect of genetic diversity on the behavioral and phenotypic traits linked to the competitive ability of individuals. In this study, we reared juvenile Atlantic salmon (Salmo salar) alone or with the competitive rainbow trout (Oncorhynchus mykiss) in order to: (1) to assess correlations between heterozygosity and traits related to individual competitive ability [i.e., heterozygosity–fitness correlations (HFCs)] in Atlantic salmon, and (2) to evaluate the effect of the competitive rainbow trout on any such HFCs. We also tested whether a few loci had a disproportionately large effect (i.e., the local effect hypothesis) or, on the contrary, if all loci contributed equally (i.e., the global effect hypothesis) in explaining the observed HFCs. We found significant HFCs for phenotypic traits related to the competitive ability of juvenile Atlantic salmon, i.e., the growth rate and the distance to the feeding source. Some HFCs were nonlinear, suggesting that individuals with intermediate levels of heterozygosity were favored. In addition, we found that the competition exerted by rainbow trout only weakly modified these HFCs as the relationships were highly consistent across treatments. We demonstrated that the local-effect hypothesis best explained both linear and nonlinear HFCs. Overall, our results illustrated the importance of genetic diversity in explaining the behavioral variability observed within populations. Moreover, we provide evidence that, even if a competitive species can have strong ecological effects, the relationships between genetic diversity and fitness-related traits in juvenile Atlantic salmon were not influenced by such effects.

Since the regulation of the river Laerdalselva in 1974 many juvenile Atlantic salmon Salmo salar and brown trout S. trutta have been stocked above the natural reach of anadromous fishes to compensate for possible loss in Atlantic salmon production. The parental material for the stocking was obtained from the lower parts of the river. In 1988 the numbers of fish stocked were drastically reduced. The density of Atlantic salmon (all year-classes) was 75–80% less in years of light stocking than in years of intensive stocking. For Atlantic salmon, a strongly significant (P < 0.001) correlation was found between the numbers of young-of-the-year parr (age-0 fish) stocked in the river and the corresponding density of age-0 fish. The reduction in Atlantic salmon density occurred even though the fish ladders allowed fish migration to the spawning grounds. However, few of the Atlantic salmon moving up through the fish ladders were females, so natural recruitment was severely limited.

Habitat use by juvenile salmonids in Lake Ontario tributaries-species, age, diel and seasonal effects

Replacing fishmeal with blends of alternative proteins on growth performance of rainbow trout (Oncorhynchus mykiss), and early or late stage juvenile Atlantic salmon (Salmo salar)

Two unambiguous discoveries involving rainbow trout require scientific name changes. First, the rainbow trout has been demonstrated to be the same species as the Kamchatka trout. Second, studies of osteology and biochemistry of trout and salmon show that rainbow and cutthroat trout, and their close relatives, the golden, Mexican golden, Gila, and Apache trouts, are more closely related to Pacific salmons (Oncorhynchus) than to brown trout and Atlantic salmon (Salmo). The different names required by these two discoveries will cause some confusion in communications in which the formal classification is used, so we present evidence to acquaint biologists and managers with the rationale for the changes. The species name of the rainbow trout becomes mykiss, an older Latinized indigenous name of the Kamchatka trout. The generic designation of rainbow and cutthroat trout poses a more subjective problem, involving four possibilities: Salmo, Oncorhynchus, Rhabdofario, and Parasalmo. The balance of evidence indicates to us that the generic name for Pacific trouts and salmons should be Oncorhynchus. We suggest recognition of two divergent sister lineages, (1) Atlantic trout and salmon, and (2) Pacific trouts and salmons, as the genera Salmo and Oncorhynchus, respectively. Alternative generic classifications considered include the following: (a) Enlarge Salmo to include all Atlantic and Pacific trouts and salmons. This would be well supported by morphological and biochemical characters, but would fail to emphasize the distinctions between the Pacific and Atlantic groups. (b) Use a separate generic name, Rhabdofario, for rainbow and cutthroat trout, and their inland relatives. This would be valid, but would fail to recognize the gradation between Pacific trouts and Pacific salmons. (c) Continue to assign Pacific trout to the genus Salmo, separate from Oncorhynchus. This would be stable, but at the expense of evolutionary information in the classification—rainbow and cutthroat trout are on the same branch of evolution as the Pacific salmon. To reflect these biological relationships in the classification of trouts and salmons will contribute to better understanding of their life histories and better predictions for their management.