Growth Of Brook Trout Research Articles

Seasonal movement, growth and survival of brook trout in sympatry with brown trout in Midwestern US streams

AbstractSeasonal patterns in growth, survival and movement of brook trout Salvelinus fontinalis were monitored in two southeastern Minnesota streams divided into study reaches based on brown trout Salmo trutta abundance. We estimated survival and movement while testing for effects of stream reach and time using a multistrata Cormack–Jolly–Seber model in Program MARK. Multistrata models were analysed for three age groups (age‐0, age‐1 and age‐2+) to estimate apparent survival, capture probability and movement. Survival varied by time period, but not brown trout abundance and was lower during flood events. Age‐0 brook trout emigrated from reaches with low brown trout abundance, whereas adult brook trout emigrated from downstream brown trout‐dominated reaches. Growth was highest in spring and summer and did not differ across streams or reaches for the youngest age classes. For age‐2+ brook trout, however, growth was lower in reaches where brown trout were abundant. Interspecific interactions can be age or size dependent; our results show evidence for adult interactions, but not for age‐0. Our results suggest that brook trout can be limited by both environmental and brown trout interactions that can vary by season and life stage.

The Interactions of Climate and Biotic Factors on Life History Characteristics and Vital Rates of Yellowstone Cutthroat Trout in Spread Creek, WY

Habitat degradation and introduction of non-native salmonids have caused substantial declines in abundance and distribution of Yellowstone cutthroat trout. Additionally, global climate change is expected to exacerbate current threats through changes to thermal regimes, hydrology, stream productivity, and distributions of non-native species. Understanding how factors such as climate and local stressors (e.g., non-native species) interact to affect Yellowstone cutthroat trout is critical for developing management strategies to enhance future persistence. However, research investigating relationships among these factors and life history characteristics and vital rates of Yellowstone cutthroat trout is lacking. To address this need, we examined the influences of temperature, streamflow, food availability, and presence of brook trout on life history characteristics of Yellowstone cutthroat trout in Spread Creek, Wyoming. We used passive integrated transponder (PIT) tags and a combination of stationary and mobile PIT tag antennae within a capture-recapture framework to monitor growth, movement, and survival of Yellowstone cutthroat trout and brook trout throughout the Spread Creek drainage. Considerable differences existed in frequencies of movements between species and among tributaries. Significant differences existed among growth rates of trout in three tributary streams. Preliminary results suggest the observed differences were driven by the complex interactions of streamflows, fish densities, and prey abundances, rather than stream temperatures. We discuss our results in the context of maintaining diversity of life-history patterns within watersheds as a means to increase metapopulation resiliency. Our findings provide critical information needed to refine climate risk assessments and to better direct limited resources to ensure the long term persistence of the subspecies.

The effects of some fodder additives on the growth and consumption indices of brook trout (Salvelinus fontinalis M.).

The aim of this study was to follow the effects o f Bio-Mos, NuPro and SelPlex on the production indices of brook trout. The experime nt had been carried out during August 2008 - April 2009 (250 days) at the trout farm ICAS Gilau, situated in Cluj County. Four batches were implied: a Control batch and three experimental bat ches (Bio-Mos 0.2 %, NuPro 2 % and SelPlex 0.03%) each of them consisting of 250 brook trout j uveniles. The experiment took place in four concrete tanks, which offered the same rearing cond itions (the same water quality, rearing density, feeding hours, food quantity). The experimental bat ches received 0.2% Bio-Mos, 0.03% SelPlex and 2% NuPro, and at the end fish reached an average weight of 238.55 g/specimen and a survival rate of 82.8% for Bio-Mos batch, 212.2 g/specimen and a survival rate of 94.4% for SelPlex batch and 225.25 g/specimen and a survival rate of 80% for the NuPro batch comparatively to the Control batch where an average weight of 204.65 g/specimen and a survival rate of 77.28% had been registered.

Context‐specific influence of water temperature on brook trout growth rates in the field

Summary1. Modelling the effects of climate change on freshwater fishes requires robust field‐based estimates accounting for interactions among multiple factors.2. We used data from an 8‐year individual‐based study of a wild brook trout (Salvelinus fontinalis) population to test the influence of water temperature on season‐specific growth in the context of variation in other environmental (i.e. season, stream flow) or biotic factors (local brook trout biomass density and fish age and size) in West Brook, a third‐order stream in western Massachusetts, U.S.A.3. Changes in ambient temperature influenced individual growth rates. In general, higher temperatures were associated with higher growth rates in winter and spring and lower growth rates in summer and autumn. However, the effect of temperature on growth was strongly context‐dependent, differing in both magnitude and direction as a function of season, stream flow and fish biomass density.4. We found that stream flow and temperature had strong and complex interactive effects on trout growth. At the coldest temperatures (in winter), high stream flows were associated with reduced trout growth rates. During spring and autumn and in typical summers (when water temperatures were close to growth optima), higher flows were associated with increased growth rates. In addition, the effect of flow at a given temperature (the flow‐temperature interaction) differed among seasons.5. Trout density negatively affected growth rate and had strong interactions with temperature in two of four seasons (i.e. spring and summer) with greater negative effects at high temperatures.6. Our study provided robust, integrative field‐based estimates of the effects of temperature on growth rates for a species which serves as a model organism for cold‐water adapted ectotherms facing the consequences of environmental change. Results of the study strongly suggest that failure to derive season‐specific estimates, or to explicitly consider interactions with flow regime and fish density, will seriously compromise our ability to predict the effects of climate change on stream fish growth rates. Further, the concordance we found between empirical observations and likely energetic mechanisms suggests that our general results should be relevant at broader spatial and temporal scales.

Influence of Variable Interannual Summer Water Temperatures on Brook Trout Growth, Consumption, Reproduction, and Mortality in an Unstratified Adirondack Lake

AbstractStressful water temperatures negatively affect physiological processes in fishes, yet evidence for how elevated temperatures influence population‐level characteristics is rare. An 8‐year field study of brook trout Salvelinus fontinalis in an unstratified Adirondack lake revealed that an aggregate measure of chronically stressful summer water temperatures strongly influenced brook trout population‐level characteristics. We quantified chronic thermal stress using the cumulative degree‐days over which bottom temperatures exceeded a range of thresholds (18–22°C) and found that the strongest relationships were with cumulative degree‐days over 20°C (DD>20). Across years with similar brook trout densities, warmer summer water temperatures resulted in decreased brook trout growth, but growth was not reduced in a year with high water temperatures and low density. Maximum stomach fullness was negatively related to water temperature. Reproductive activity was negatively correlated with stressful summer thermal conditions and was less dependent on female brook trout density. Periods of chronically stressful summer water temperatures resulted in the apparent mortality of age‐2 and older fish during a moderately stressful summer (156 DD>20) and apparent mortality of age‐1 and older fish during the most stressful summer (210 DD>20). In contrast, extensive mortality was not evident in any year‐classes when DD>20 was less than 115. Anthropogenic impacts on the thermal conditions of aquatic ecosystems occur at small (hydrology) and large (climate change) spatial extents, and in situ studies at the margin of an organism's thermal range can provide important insights into changes that will occur if temperatures increase.

Comparisons of growth and condition of fluvial and resident brook trout within partially migratory populations

Abstract In partially migratory salmonid populations, growth and condition of migratory fish may be different than that of residents. To ascertain if a similar phenomenon exists in fluvial brook trout, Salvelinus fontinalis (Mitchell), populations, the growth and condition of fluvial and resident brook trout was measured in four Appalachian stream networks. Sites were sampled during summer, cohorts separated via scale analysis and differences in length and condition were investigated. Age‐1 and ‐2 fluvial fish were significantly longer (P < 0.001) than residents of the same cohort. Additionally, age‐2 fluvial fish had significantly greater condition (P < 0.005) than resident fish of the same cohort. This suggests that the use of spatially segregated resources can result in growth and condition advantages. However, potentially greater rates of mortality as suggested by low abundance in main stem sites may limit the fitness advantages of this energetically profitable, but ultimately risky, behaviour.

The Effects of Varied Densities on the Growth and Emigration of Adult Cutthroat Trout and Brook Trout in Fenced Stream Enclosures

ABSTRACT. We evaluated the effects of various density treatments on adult fish growth and emigration rates between Bonneville cutthroat trout Oncorhynchus clarki utah and brook trout Salvelinus fontinalis in stream enclosures in Beaver Creek, Idaho, We used 3 density treatments (low, ambient, and high fish densities) to evaluate density-related effects and to ensure a response. Intraspecific ambient-density tests using cutthroat trout only were also performed. Results indicated an absence of cage effects in the stream enclosures and no differences in fish growth between ambient-density stream-enclosure fish and free-range fish. Brook trout outgrew and moved less than cutthroat trout in the stream enclosures, especially as density increased, In all 3 density treatments, brook trout gained more weight than cutthroat trout, with brook trout gaining weight in each density treatment and cutthroat trout losing weight at the highest density. At high densities, cutthroat trout attempted to emigrate more frequentl...

Voluntary Ingestion of Soft Plastic Fishing Lures Affects Brook Trout Growth in the Laboratory

AbstractThirty‐eight brook trout Salvelinus fontinalis were fed a commercial trout diet mixed with a free‐choice assortment of soft plastic lures (SPLs) over a 90‐d period. Fish growth was recorded and compared with that of a control group. The brook trout readily ate the SPLs from the water's surface as well as from the tank bottom. At the conclusion of the study, SPLs were recovered from the stomachs of 63% of the test fish. Several fish stomachs contained multiple lures. Twelve percent of the fish voluntarily ingested more than 10% of their body mass in SPLs. These fish lost a significant amount of weight during the study, had a significant decrease in body condition factor, and began displaying anorexic behaviors. For these reasons, anglers should be discouraged from discarding used SPLs in trout waters.

Life history and large-scale habitat use of brown trout (Salmotrutta) and brook trout (Salvelinus fontinalis) — implications for species replacement patterns

Simple models of temperature-mediated interference competition have generally failed to explain salmonid species replacement patterns along altitudinal gradients, a fact that emphasizes the need to link individual features and their relation to habitat characteristics to population-level dynamics. We compared life history parameters in stream-resident populations of brook trout (Salvelinus fontinalis) and brown trout (Salmo trutta) in eight boreal streams. By use of electrofishing data from 1000 sites, we analyzed and related differences in life history traits to habitat- and interaction-related patterns of growth and densities of brook and brown trout, respectively. Brown trout were competitively dominant throughout the size span of sampled sympatric sites and lowered growth rates in sympatry were mainly caused by environmental factors, revealing a link between brook trout invasions and habitat-related limitations on brown trout performance. Still, the frequency of allopatric brook trout sites increased in the smallest watersheds, indicating that localities with a high degree of brook trout dominance rarely sustain brown trout over time. Brook trout populations had higher turnover rates and proportions of mature females than brown trout populations. Our results suggest growth potential and its effect on population fecundity as a critical factor limiting competitive ability and distribution of brown trout in Swedish brook trout dominated headwaters.

Population response to habitat fragmentation in a stream-dwelling brook trout population.

Fragmentation can strongly influence population persistence and expression of life-history strategies in spatially-structured populations. In this study, we directly estimated size-specific dispersal, growth, and survival of stream-dwelling brook trout in a stream network with connected and naturally-isolated tributaries. We used multiple-generation, individual-based data to develop and parameterize a size-class and location-based population projection model, allowing us to test effects of fragmentation on population dynamics at local (i.e., subpopulation) and system-wide (i.e., metapopulation) scales, and to identify demographic rates which influence the persistence of isolated and fragmented populations. In the naturally-isolated tributary, persistence was associated with higher early juvenile survival (∼45% greater), shorter generation time (one-half) and strong selection against large body size compared to the open system, resulting in a stage-distribution skewed towards younger, smaller fish. Simulating barriers to upstream migration into two currently-connected tributary populations caused rapid (2–6 generations) local extinction. These local extinctions in turn increased the likelihood of system-wide extinction, as tributaries could no longer function as population sources. Extinction could be prevented in the open system if sufficient immigrants from downstream areas were available, but the influx of individuals necessary to counteract fragmentation effects was high (7–46% of the total population annually). In the absence of sufficient immigration, a demographic change (higher early survival characteristic of the isolated tributary) was also sufficient to rescue the population from fragmentation, suggesting that the observed differences in size distributions between the naturally-isolated and open system may reflect an evolutionary response to isolation. Combined with strong genetic divergence between the isolated tributary and open system, these results suggest that local adaptation can ‘rescue’ isolated populations, particularly in one-dimensional stream networks where both natural and anthropogenically-mediated isolation is common. However, whether rescue will occur before extinction depends critically on the race between adaptation and reduced survival in response to fragmentation.

Effects of Water Temperature on Interspecific Competition between Juvenile Bull Trout and Brook Trout in an Artificial Stream

AbstractThe distribution and abundance of bull trout Salvelinus confluentus is influenced by a number of factors, including the presence of nonnative brook trout S. fontinalis, and populations are in decline across the native range. Where sympatric, bull trout are more likely to persist in higher‐elevation, cooler streams. To test the hypothesis that competition between juveniles of these species is independent of water temperature, behavioral observations were made of each species in artificial streams. Two temperature (8°C and 15°C) and three density (4.1, 8.2, and 4.1 fish of each species/m2) treatments were used. The results support the contention that bull trout are competitively disadvantaged in warmer water. In warm water, bull trout significantly increased intraspecific agonism. Temperature and density did not influence intraspecific brook trout behavior; however, brook trout tended to increase interspecific agonism in warm water. In mixed‐species treatments, brook trout agonism was positively associated with foraging rate at both temperatures, but the trend was weak for bull trout in the warmwater treatment and was reversed in the coldwater treatment. Although fish growth was variable and primarily negative, within temperature treatments the per capita bull trout weight loss consistently increased they were competing with brook trout and was greatest overall at 15°C. Intraspecific competition had the largest effect on brook trout growth in warm water; intraspecific and interspecific effects on brook trout growth were comparable at 8°C. If these condition‐specific behavioral responses occur in natural streams, juvenile bull trout may be disadvantaged when competing with brook trout in warmer waters.

Predicting local biological characteristics in streams: a comparison of landscape classifications

Summary1. Landscape classifications group tracts of land based on similar physico‐chemical attributes that may affect the biological characteristics of streams at local scales. We tested the ability of five landscape models to account for variation in algal and macroinvertebrate biomass, brook trout (Salvelinus fontinalis) growth and macroinvertebrate community composition from 132 riffles in 15 catchments in the Big Horn Mountains, Wyoming.2. A model created by the U.S. Forest Service (FS) combined catchment and ecoregion approaches to classify the landscape. Our model used digital elevations to create a landscape classification for streams (DEM). The last three models were based on: (1) standard ecoregions (Ecoregion), (2) the type of underlying bedrock (Geology) and (3) the geographical distance between sites (Site Proximity model).3. Overall, the Ecoregion and Geology models performed better than the two catchment models (FS and DEM) in predicting local biological characteristics. The Geology model was best at predicting differences in algal and macroinvertebrate biomass, the Site Proximity and Ecoregion models were best at predicting patterns of similarity in macroinvertebrate community composition, and the Site Proximity, Ecoregion, Geology, and FS models, in order from best to worst, accounted for significant variation in brook trout growth. The Site Proximity model performed well because of the effects of spatial autocorrelation. The DEM was consistently one of the worst models at predicting local biological characteristics because it failed to include important attributes (e.g. dominant geology). Calcareous geology was positively associated with greater macroinvertebrate biomass and faster brook trout growth, but it was inversely related to algal biomass.4. None of the models accounted for a large amount of variation in local biological characteristics. Single‐scale, landscape classifications may never accurately predict variation in local biological characteristics because: (1) landscapes show a high degree of spatial heterogeneity, (2) local effects are stronger than landscape attributes and (3) there are too many intervening levels between landscape and local scales in the nested hierarchy of streams. However, landscape classifications did account for significant variation in biological characteristics. Thus, they would be a valuable management tool as part of a multi‐scale, hierarchical technique for classifying stream ecosystems.

Growth, Movement, and Catch of Brook, Rainbow, and Brown Trout after Stocking into a Large, Marginally Suitable Adirondack River

AbstractPoststocking growth, movement, and catch were compared among hatchery brook trout Salvelinus fontinalis, rainbow trout Oncorhynchus mykiss, and brown trout Salmo trutta in a fifth‐order river. Associations of species, size, and stocking date with angler catch were also examined. The river is episodically acidified, and during summer it approaches lethal maximum temperatures for trout. Catchable‐sized brook and rainbow trout (168–458 mm total length) were stocked in the late spring of 1996 and 1997. Brown trout were stocked only in 1997. Fish were marked with visible implant tags and were recovered through October of each year. All three species had negative daily growth rates in weight over the summer and early fall. Rainbow trout stocked in 1997 tended to move downstream after stocking, whereas the other groups showed no strong movement trend. Recovery rates significantly differed between brook and brown trouts stocked in early June and those fish stocked in late May. Large (>300‐mm) rainbow trout were caught at higher rates than small (<260‐mm) fish were. Anglers were estimated to have caught 72% of the stocked brook trout, 51% of the rainbow trout, and 18% of the brown trout. High summer water temperatures (>20°C) did not affect angler catch rates because cool refuges within the river concentrated and made the stocked fish—especially brook trout—vulnerable to angling. By stocking more than one species, we were able to create diversified angling opportunities and sustain a fishery in this thermally marginal river over the entire summer season.

Effects of stream enclosures on drifting invertebrates and fish growth

AbstractStream ecologists often use enclosure experiments to investigate predator–prey interactions and competition within and among fish species. The design of enclosures, manipulation of species densities, and method of replication may influence experimental results. We designed an experiment with enclosure cages (1 m2, 6-mm mesh) to examine the relative influence of fish size, density, and prey availability on growth of brown trout (Salmo trutta), brook trout (Salvelinus fontinalis), and slimy sculpin (Cottus cognatus) within enclosures in Valley Creek, Minnesota. In addition, we examined water flow and invertebrate drift entering enclosures and in open riffles to investigate whether enclosures reduced the supply of invertebrate prey. Growth of small (age-0) brook and brown trout was not influenced by fish density, but growth of larger (age-1) trout generally decreased as density increased. Sculpin growth was not related to fish size or density, but increased with mean size of invertebrates in the drif...

Survival, Growth and Maturation of Triploid Brook Trout (Salvelinus Fontinalis) Induced by Heat Shock

ABSTRACTComparisons of survival, growth and sexual maturation of mixed-sex diploid and triploid brook trout (Salvelinus fontinalis) were performed during a 2-year growth trial. Survival was similar between ploidy groups, except for significantly lowers survival of triploids during the 24-hour period immediately after heat-shock treatment of the eggs, and in one instance of a dramatic temperature increase and dissolved oxygen decrease, which occurred during rearing at 7 months of age. No differences in morphometric traits or characteristics associated with sexual maturation were observed between triploid and diploid males. However, at maturation, triploid females were significantly different from diploid females in dressed weight (mean ±SE) (289.9 ± 11.1 vs. 222.1 ± 13.5); Clark coefficient (1.92 vs.1.01); gonad weight (0.15 ± 0.01 vs. 43.25 ± 6.17); gonado-somatic index (0.01 % vs. 18.6%); specific growth rate (1.52 ± 0.21% vs. 1.16 ± 0.11%). The commercial relevance and ecological advantage for use of triploid brook trout are discussed.

The effects of long-term estradiol-17β treatment on the growth and physiology of female triploid brook trout ( Salvelinus fontinalis)

Triploid female fish show impaired gonadal development, which results in the production of only a few oocytes relative to diploids. The rate of maturation of these few oocytes in much slower relative to those of diploids and is attributed to an insufficient estradiol-17β (E 2) stimulus. Female triploid brook trout, aged 2+, were fed E 2 for seven months (i.e., July 1998 to February 1999) in an attempt to increase plasma E 2 comparable to diploid levels and thereby accelerate rates of oocyte growth. Compared to triploids fed a normal diet (i.e., control-triploids), the administration of 30 mg E 2/ kg feed to triploids (i.e., E 2-treated-triploids) led to the development of secondary sex characteristics, a significant reduction in hematocrit and total blood hemoglobin level, a decrease in plasma testosterone and no weight gain. Plasma vitellogenin was significantly higher in E 2-treated-triploids than in control-triploids and diploids at every month except October 1999. Although greater than in the control-triploids, plasma E 2 for the E 2-treated-triploids did not attain the high levels shown by the diploids during the months of peak vitellogenesis (i.e., September and October). Following maturation and spawning of diploids, sacrificed E 2-treated and control-triploids showed no differences in ovarian development or liver size. The E 2 dose for the treated-triploids was increased to 80 mg E 2/ kg feed for approximately seven more weeks in a further attempt to increase plasma E 2, with no success. It is suggested that the low plasma E 2 of the treated-triploids was the result of a high metabolic clearance rate.

Response of a Brook Trout Population and Instream Habitat to a Catastrophic Flood and Debris Flow

In June 1995, a massive flood and debris flow impacted fish and habitat along the lower 1.9 km of the Staunton River, a headwater stream located in Shenandoah National Park, Virginia. In the area affected by debris flow, the stream bed was scoured and new substrate materials were deposited, trees were removed from a 30-m-wide band in the riparian area, and all fish were eliminated. In the area that was unaffected by debris flow, habitat was moderately altered by the flood and fish populations persisted at decreased densities. Basinwide fish population and habitat surveys provided data to compare (1) the pre- and postevent population densities of brook trout Salvelinus fontinalis and instream habitat conditions and (2) postevent population density, brook trout growth, and instream habitat in the debris-flow-affected and unaffected areas. By June 1998, brook trout had recolonized the entire debris-flow-affected area, and population density exceeded preevent levels. Brook trout growth was significantly greater in the debris-flow-affected area than in the unaffected area through fall 1998, but it was not significantly greater in 1999. Population density appeared to have a negative influence on fish growth. A 1995 postevent habitat survey revealed increases in the number of pools and riffles and substrate size and decreases in pool and riffle surface area and depth. By 1999, the total number, surface area, and depth of pools and riffles had returned to near preevent levels and substrate size had decreased. Between 1995 and 1999, the amount of large woody debris increased in the debris-flow-unaffected area, where riparian trees had remained intact, and decreased in the affected area, where riparian trees had been eliminated. A number of factors, including a relatively intact watershed and nearby source populations, allowed the Staunton River to quickly respond to this dramatic natural event. Given the proper conditions for recovery, such events are less catastrophic than activities that lead to chronic stream degradation.

Response of fish communities to different levels of white sucker (Catostomus commersoni) biomanipulation in five temperate lakes

The goal of this study was to evaluate the response of white sucker (Catostomus commersoni), brook trout (Salvelinus fontinalis), and other fish species to the mass removal of white sucker in five Québec (Canada) lakes. White sucker removal ranged from 14.2 kg·ha–1 to 31.3 kg·ha–1 3 years after mass removal. In four of the study lakes, the proportion of 2+ to 4+ white sucker increased following mass removal. Mean catch and biomass per unit of effort of 1+ brook trout increased significantly in the lakes where white sucker removal was highest. All white sucker populations experienced growth increases after mass removal, and improved brook trout growth was observed in lakes where the most intensive mass removal occurred. These growth increases led to higher mean length at maturity in white sucker females and decreases in mean age at maturity in white sucker males and brook trout males and females. Mean adjusted fecundity significantly increased in white sucker and brook trout in lakes where mass removal was most intense. The present study suggests that white sucker and brook trout exhibit compensatory responses following a reduction of intra- and inter-specific competition and that these responses are related to the intensity of mass removal.

Using 137Cs to measure and compare bioenergetic budgets of juvenile Atlantic salmon (Salmo salar) and brook trout (Salvelinus fontinalis) in the field

Through the 137Cs mass balance method, annual consumption rates were estimated for juvenile Atlantic salmon (Salmo salar) parr and precocious males as well as for brook trout (Salvelinus fontinalis) at four sites in the Ste-Marguerite River system, Québec. With explicit age analysis, consumption rates and growth rates were derived on an individual fish and age-class basis. These represent the first consumption estimates for Atlantic salmon in the wild. Precocious males had consumption rates 1.5 times greater than nonmaturing parr, while Atlantic salmon parr consumption rates were 2.7 times greater than brook trout. There was a strong positive relationship between individual annual consumption and growth rates for Atlantic salmon and brook trout at all sites. Subsequently the concept of field maintenance ration was introduced as the intercept of consumption over growth. Maintenance rations for Atlantic salmon parr ranged from 0.010 to 0.016 g·g-1·day-1 between sites. Brook trout had maintenance rations approximately half those of Atlantic salmon at 0.0059 g·g-1·day-1. Precocious male growth efficiencies were half those of nonmaturing parr despite higher feeding and growth rates. Brook trout growth efficiencies were significantly greater than those of Atlantic salmon parr. The lower growth efficiencies observed for Atlantic salmon are likely due to increased metabolic costs associated with higher activity. On average, Atlantic salmon parr spent 2.4-fold more energy in activity than brook trout. Atlantic salmon precocious males spent 1.7 times more energy in activity than parr.

Comparative growth and food consumption of diploid and triploid brook trout ( Salvelinus fontinalis) monitored by radiography

The production of triploids is the only economically-feasible method available for producing sterile salmonids destined for human consumption. Triploids differ from diploids in cell size and number, consequently triploids may be less efficient than diploids when competing for, and processing, food. Comparisons of food intake and growth were made of 144 individually PIT-tagged brook trout ( Salvelinus fontinalis) held in separate and mixed ploidy groups, and fed a limited food supply from a single point in the tanks. The fish were weighed and fed a diet containing radio-opaque glass beads once every three weeks for a forty-two week period. After eating the labelled diet each fish was radiographed and food intake was determined by counting the number of glass beads on the X-ray plate. No difference in growth or food consumption was found between diploids and triploids whether cultured separately or in mixed ploidy groups.