Survival Of Trout Research Articles

Biomonitoring in the Boulder River Watershed, Montana, USA: Metal Concentrations in Biofilm and Macroinvertebrates, and Relations with Macroinvertebrate Assemblage

Portions of the Boulder River watershed contain elevated concentrations of arsenic, cadmium, copper, lead, and zinc in water, sediment, and biota. We measured concentrations of As, Cd, Cu, Pb, and Zn in biofilm and macroinvertebrates, and assessed macroinvertebrate assemblage and aquatic habitat with the objective of monitoring planned remediation efforts. Concentrations of metals were generally higher in downstream sites compared with upstream or reference sites, and two sites contained metal concentrations in macroinvertebrates greater than values reported to reduce health and survival of resident trout. Macroinvertebrate assemblage was correlated with metal concentrations in biofilm and macroinvertebrates. However, macroinvertebrate metrics were significantly correlated with a greater number of biofilm metals (8) than metals in invertebrates (4). Lead concentrations in biofilm appeared to have the most significant impact on macroinvertebrate assemblage. Metal concentrations in macroinvertebrates were directly proportional to concentrations in biofilm, indicating biofilm as a potential surrogate for monitoring metal impacts in aquatic systems.

Survival of reared Atlantic salmon and sea trout in relation to marine conditions of smolt year in the Baltic Sea

The marine survival of hatchery-reared Atlantic salmon ( Salmo salar) and sea trout ( Salmo trutta) was examined in relation to marine conditions during post-smolt migration and in relation to stock traits. In 1970–2001, Carlin-tagged smolts were released in the Iijoki and Oulujoki rivers, the northern Baltic Sea. When both species were analysed together, the abundance of the three prey fish, herring ( Clupea harengus), smelt ( Osmerus eperlanus) and vendace ( Coregonus albula) correlated positively with the survival of salmonids. In addition, the increase in smolt size appeared to improve the survival rate. Sea surface temperature (SST) may have affected indirectly through the abundance of prey fish during the post-smolt migration of salmon and sea trout. The smelt and vendace showed a statistical effect on survival only when the temperature effects were not included in the models. In sea trout, an increasing smolt length was not significantly correlated with the survival in good herring recruitment years, but in poor years survival increased very rapidly with increasing smolt size. The recapture rates of the salmonids tended to decrease between the years 1970 and 2001. During the same time period, the June SST slightly decreased. The positive correlation between the annual summer SST and recapture rate of salmon may partly explain the decreasing trend in recapture rates. An increase in smolt size did not compensate for the decline in the recapture rate of either species.

Zooplankton Size Selection Relative to Gill Raker Spacing in Rainbow Trout

AbstractRainbow trout Oncorhynchus mykiss are one of the most widely stocked salmonids worldwide, often based on the assumption that they will effectively utilize abundant invertebrate food resources. We evaluated the potential for feeding morphology to affect prey selection by rainbow trout using a combination of laboratory feeding experiments and field observations in Flaming Gorge Reservoir, Utah–Wyoming. For rainbow trout collected from the reservoir, inter–gill raker spacing averaged 1.09 mm and there was low variation among fish overall (SD = 0.28). Ninety‐seven percent of all zooplankton observed in the diets of rainbow trout collected in the reservoir were larger than the interraker spacing, while only 29% of the zooplankton found in the environment were larger than the interraker spacing. Over the size range of rainbow trout evaluated here (200–475 mm), interraker spacing increased moderately with increasing fish length; however, the size of zooplankton found in the diet did not increase with increasing fish length. In laboratory experiments, rainbow trout consumed the largest zooplankton available; the mean size of zooplankton observed in the diets was significantly larger than the mean size of zooplankton available. Electivity indices for both laboratory and field observations indicated strong selection for larger‐sized zooplankton. The size threshold at which electivity switched from selection against smaller‐sized zooplankton to selection for larger‐sized zooplankton closely corresponded to the mean interraker spacing for both groups (∼1–1.2 mm). The combination of results observed here indicates that rainbow trout morphology limits the retention of different‐sized zooplankton prey and reinforces the importance of understanding how effectively rainbow trout can utilize the type and sizes of different prey available in a given system. These considerations may improve our ability to predict the potential for growth and survival of rainbow trout within and among different systems.

Spatial and Seasonal Dynamics of Brook Trout Populations Inhabiting a Central Appalachian Watershed

AbstractWe quantified the watershed‐scale spatial population dynamics of brook trout Salvelinus fontinalis in the Second Fork, a third‐order tributary of Shavers Fork in eastern West Virginia. We used visual surveys, electrofishing, and mark–recapture techniques to quantify brook trout spawning intensity, population density, size structure, and demographic rates (apparent survival and immigration) throughout the watershed. Our analyses produced the following results. Spawning by brook trout was concentrated in streams with small basin areas (i.e., segments draining less than 3 km2), relatively high alkalinity (>10 mg CaCO3/L), and high amounts of instream cover. The spatial distribution of juvenile and small‐adult brook trout within the watershed was relatively stable and was significantly correlated with spawning intensity. However, no such relationship was observed for large adults, which exhibited highly variable distribution patterns related to seasonally important habitat features, including instream cover, stream depth and width, and riparian canopy cover. Brook trout survival and immigration rates varied seasonally, spatially, and among size‐classes. Differential survival and immigration tended to concentrate juveniles and small adults in small, alkaline streams, whereas dispersal tended to redistribute large adults at the watershed scale. Our results suggest that spatial and temporal variations in spawning, survival, and movement interact to determine the distribution, abundance, and size structure of brook trout populations at a watershed scale. These results underscore the importance of small tributaries for the persistence of brook trout in this watershed and the need to consider watershed‐scale processes when designing management plans for Appalachian brook trout populations.

Timing of predation by rainbow trout controls Daphnia demography and the trophic status of a Minnesota lake

Summary1. Stocking of lakes with rainbow trout is a common practice that presents a potential conflict for lake managers who must balance the interests of anglers with those concerned that zooplanktivory by trout may trigger a trophic cascade and result in decreased water clarity.2. This study examined how the timing of trout stocking (autumn versus spring) in a Minnesota (U.S.A.) lake affected (i) the population dynamics of their zooplankton food supply (Daphnia pulicaria), (ii) phytoplankton biomass and water clarity and (iii) trout survival. Sizes of both Daphnia and trout populations were estimated acoustically with high‐frequency (192 kHz) sonar.3. Daphnia were nearly eliminated from the lake during winters after trout were stocked in autumn. In both of these years (1996 and 1997), the Daphnia population was small in the spring, and grew during the summer and into the autumn as the trout population diminished.4. The lake was then stocked in spring for 2 years (1998 and 1999). This fisheries manipulation alleviated predation over the winter, but increased predation on D. pulicaria during the spring, summer and autumn. However, the high mortality caused by the spring‐stocked trout was offset by even higher rates of reproduction by the relatively large populations of fecund Daphnia that survived the winter in 1998 and 1999.5. Grazing by these dense populations of Daphnia produced clear‐water phases during May and June that were inhibited in autumn stocking years. In addition, the large Daphnia populations present during the spring and early summer of 1998 and 1999 provided abundant forage for trout.6. This fisheries manipulation achieved seemingly mutually exclusive management objectives: a robust planktivorous sport fishery, and clear water for other forms of recreation.

Erratum: Effect of Temperature on Growth and Survival of Bull Trout, with Application of an Improved Method for Determining Thermal Tolerance in Fishes

Erratum: Effect of Temperature on Growth and Survival of Bull Trout, with Application of an Improved Method for Determining Thermal Tolerance in Fishes

Habitat-specific biomass, survival, and growth of rainbow trout (Oncorhynchus mykiss) during summer in a small coastal stream

We observed significant habitat-scale variation in the density, survival, and growth of 811 passive integrated transponder tagged rainbow trout (Oncorhynchus mykiss) enclosed for 63–68 days at natural density in 59 individual habitats (pools and riffles) in a small coastal California stream in summer 2001. The initial habitat-scale densities of trout were positively related to both depth and cover, although by the end of the experiment, the influence of cover on density was less apparent. Survival varied substantially, but with no clear relationship to any of the physical factors that we measured. Mean growth was density dependent, positively influenced by habitat depth, and also increased downstream within the 2-km study reach. The overall change in trout biomass over the experiment was also negatively related to fish density and positively influenced by habitat depth. Individual growth within habitats appeared to be unrelated to body size. The positive influences of water depth and distance downstream on trout growth in this experiment suggest that management actions that increase dry season discharge and limit aggradation will benefit salmonids in small streams.

Is metabolic rate a reliable predictor of growth and survival of brown trout (Salmo trutta) in the wild?

In salmonids, there seems to be a positive correlation between standard metabolic rate and growth rate under artificial rearing conditions. Several recent studies have suggested that phenotypic correlations between physiological or behavioural traits and developmental or life history responses might be common when assayed in low-complexity habitats but rare in those with a high degree of spatiotemporal complexity. This study provides the first test of the connection between metabolic and growth rates of juvenile brown trout (Salmo trutta) in natural streams. In two out of four streams, there was no relationship between metabolic rates and subsequent growth, whereas in the two others, growth and metabolic rates were negatively correlated. Furthermore, survival rates were either unaffected or negatively correlated with metabolic rates. These results reveal complex relationships between metabolic rate, growth, and environmental variability and suggest that (i) in the wild, negative selection on high metabolic rates may result from both juvenile mortality and reduced growth rates, (ii) the conclusions derived from laboratory experiments are not directly applicable to natural populations, and (iii) the correlations between metabolic rate and growth can prove useful after selection of the appropriate spatial and temporal scales.

The effect of 4-nonylphenol on semen quality, viability of gametes, fertilization success, and embryo and larvae survival in rainbow trout ( Oncorhynchus mykiss)

The present study investigated in vivo and in vitro effects of environmental relevant concentrations of 4-nonylphenol (100–750 ng l −1) on the reproduction of rainbow trout ( Oncorhynchus mykiss). To determine the effect of 4-nonylphenol on semen quality rainbow trout were exposed to three concentrations of 4-nonylphenol in a flow-through system during the spawning period (60 days). At an estimated 4-nonylphenol concentration of 750 ng l −1 semen production was completely inhibited, at 280 and 130 ng l −1 the semen production was significantly reduced in comparison to the control. Sperm density, sperm motility and sperm fertility were not affected. Also the development of embryos and larvae at the end of yolk sac stage was affected by 4-nonylphenol. At estimated 4-nonylphenol exposure levels of 280 and 750 ng l −1 the percentage of eyed stage embryos was slightly but significantly lower (2–4%) than at 130 ng l −1 4-nonylphenol and in the control. At 4-nonylphenol concentrations of 750 ng l −1 only 23.8 ± 1.2% of the larvae survived to the end of the yolk sac stage, at 280 ng l −1 53.7 ± 8.2%, at 130 ng l −1 73.8 ± 1.5%, and in the control 70.9 ± 1.8%. Sperm motility was not affected by 4-nonylphenol as sperm motility rate, swimming velocity, swimming pattern and motility duration were similar in water and in water containing of 100, 250, or 750 ng l −1 4-nonylphenol. Incubation of eggs in physiological saline solution containing of 100, 250, or 750 ng l −1 4-nonylphenol did not change their fertilizability in comparison to the control. Therefore, 4-nonylphenol did not affect the egg viability. Also the fertilization process (sperm egg contact) was not influenced by 4-nonylphenol as the fertilization rate (percentage of hatched larvae) was similar to the control when eggs were fertilized in water containing of 100, 250, or 750 ng l −1 4-nonylphenol.

Activity-guided fractionation of phytochemicals of maca meal, their antioxidant activities and effects on growth, feed utilization, and survival in rainbow trout ( Oncorhynchus mykiss) juveniles

A feeding trial was conducted to examine the supplemental effects of maca ( Lepidium meyenii, Walper) meal and its components extracted by four different solvents on growth performance, feed utilization, and survival in rainbow trout fry. Eight casein-based semipurified diets were formulated to be isonitrogenous and isocaloric to contain the maca meal, its four extracts, mixture of the four extracts, and maca meal after extraction. The eight diets were each supplemented with 15% wheat flour (control diet, diet 1), 15% maca meal (diet 2), 12.5% maca meal after the extraction (diet 3), a mixture of four maca meal extracts (diet 4), a hexane extract (diet 5), a dichloromethane extract (diet 6), an ethyl acetate extract (diet 7), and a methanol extract (diet 8). In vitro 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical inhibition indices were observed to increase in a dose-dependent manner as the concentration of methanolic extracts of maca meal increased. For the antioxidant activities of the four extracts, only the methanolic extract showed a higher inhibition rate against DPPH radical compared to other extracts by hexane, ethyl acetate, and dichloromethane. After a 14-week feeding trial, fish fed diet 2 exhibited the highest ( P<0.05) growth among all the dietary treatments. Fish fed diets 2, 3, and 8 had significantly higher growth than the fish fed the control and the other diets. Feed intake was significantly higher in fish fed diets 2, 3, and 8 than fish fed the control diet and diet 5. Feed conversion ratio (FCR) and protein efficiency ratio (PER) were also significantly improved in the fish fed diets 2 and 3 than in fish fed the diets 1 (control), 5, 6, and 7. Survival was significantly higher in fish fed diet 2 than the control diet, diet 5, and diet 6. The results indicate that certain compounds in maca meal have growth enhancing effects in rainbow trout juveniles. The compounds of interest have high polarity and can be extracted by methanol. This compound has an antioxidant capacity that might increase resistance against stress and/or diseases.

Survival of brown trout during spring flood in DOC-rich streams in northern Sweden: the effect of present acid deposition and modelled pre-industrial water quality

Mortality and physiological responses in brown trout ( Salmo trutta) were studied during spring snow melt in six streams in northern Sweden that differed in concentrations of dissolved organic carbon (DOC) and pH declines. Data from these streams were used to create an empirical model for predicting fish responses (mortality and physiological disturbances) in DOC-rich streams using readily accessible water chemistry parameters. The results suggest that fish in these systems can tolerate higher acidity and inorganic aluminium levels than fish in low DOC streams. But even with the relatively low contemporary deposition load, anthropogenic deposition can cause fish mortality in the most acid-sensitive surface waters in northern Sweden during spring flood. However, the results suggests that it is only in streams with high levels of organically complexed aluminium in combination with a natural pH decline to below 5.0 during the spring where current sulphur deposition can cause irreversible damage to brown trout in the region. This study support earlier studies suggesting that DOC has an ameliorating effect on physiological disturbances in humic waters but the study also shows that surviving fish recover physiologically when the water quality returns to less toxic conditions following a toxic high flow period. The physiological response under natural, pre-industrial conditions was also estimated.

Effects of phase-feeding dietary phosphorus on survival, growth, and processing characteristics of rainbow trout Oncorhynchus mykiss

A factorial experiment involving eight diets and three feeding periods was conducted to determine the minimal level of dietary phosphorus required to maintain survival, growth, and processing characteristics of post-juvenile rainbow trout. Trout were reared to an average size of 200, 300, or 400 g using a commercial feed (1.20% P), then allotted by triplicate groups of nine fish to one of seven experimental diets containing logarithmic increments of dietary phosphorus (0.15%%, 0.21%, 0.30%, 0.42%, 0.60%, 0.85%, and 1.20% P) or a commercial trout feed (1.20% P). At an average weight of 550 g, fish were transported to a commercial processing plant, mechanically filleted, and evaluated for quality. Fish survival and weight gain increased quadratically with increased dietary phosphorus for fish started on treatment at 200 and 300 g, but were similar among all fish started at 400 g. Phosphorus retention decreased with increasing dietary phosphorus level, from approximately 88% in groups fed diets containing 0.21% phosphorus to between 23% and 32% in groups fed diets containing 0.85% phosphorus. Calculated phosphorus losses increased as dietary phosphorus levels increased, from a low of approximately 0.4 g phosphorus kg −1 fish weight gain to between 9.5 and 13 g phosphorus kg −1 fish weight gain at the highest dietary phosphorus level. Dietary phosphorus did not affect carcass moisture, protein, lipid, or ash, but carcass phosphorus increased with increased dietary phosphorus among fish started on treatment at 200 and 300 g. There were no differences among any treatment group in carcass dressing or finishing percentage, or visual or textural appeal. The results indicate that available phosphorus levels can be reduced in rainbow trout diets to 0.60% at 200 g, to 0.30% at 300 g, or to 0.15% at 400 g live weight without loss in production or product quality in fish harvested at 550 g. Using these phase-feeding strategies would reduce the amount of phosphorus fed to the fish over the production cycle by 25%, and the amount lost to the environment by 12.5% for fish starting at 300 or 400 g.

HOW FINE SEDIMENT IN RIVERBEDS IMPAIRS GROWTH AND SURVIVAL OF JUVENILE SALMONIDS

Although excessive loading of fine sediments into rivers is well known to degrade salmonid spawning habitat, its effects on rearing juveniles have been unclear. We experimentally manipulated fine bed sediment in a northern California river and examined responses of juvenile salmonids and the food webs supporting them. Increasing concentrations of deposited fine sediment decreased growth and survival of juvenile steelhead trout. These declines were associated with a shift in invertebrates toward burrowing taxa unavailable as prey and with increased steelhead activity and injury at higher levels of fine sediment. The linear relationship between deposited fine sediment and juvenile steelhead growth suggests that there is no threshold below which exacerbation of fine‐sediment delivery and storage in gravel bedded rivers will be harmless, but also that any reduction could produce immediate benefits for salmonid restoration.

POPULATION ECOLOGY OF AN INVASION: EFFECTS OF BROOK TROUT ON NATIVE CUTTHROAT TROUT

Invasion by nonnative brook trout (Salvelinus fontinalis) often results in replacement of cutthroat trout (Oncorhynchus clarki) in the inland western United States, but the underlying mechanisms are not well understood. We conducted a four‐year removal experiment to test for population‐level mechanisms (i.e., changes in recruitment, survival, emigration, and immigration) promoting invasion success of brook trout and causing decline of native Colorado River cutthroat trout (O. c. pleuriticus). We chose 700–1200 m segments of four small mountain streams where brook trout had recently invaded cutthroat trout populations, two each at mid elevation (2500–2700 m) and high elevation (3150–3250 m), and annually removed brook trout from two streams (treatments), but not the other two (controls). We used depletion electrofishing, two‐way fish weirs, and mark–recapture methods to estimate abundance, movement, and survival of trout. At mid elevation, age‐0 and age‐1 cutthroat trout survived at 13 times and two times higher rates on average, respectively, where brook trout were removed. At high‐elevation sites, recruitment of cutthroat trout failed despite brook trout removals, apparently because of cold water temperatures. In contrast, age‐2 and older cutthroat trout survived at similar rates, whether brook trout were removed or not and regardless of elevation. Summer movement by cutthroat trout was unaffected by removal of brook trout. We conclude that brook trout depress cutthroat trout populations at mid elevation through age‐specific biotic interactions that reduce juvenile cutthroat trout survival, whereas populations restricted to high‐elevation sites by invasion continue to decline because an abiotic factor (low temperature) causes recruitment failure. In comparison, brook trout survived at the same or higher rates than same‐aged cutthroat trout. High immigration by brook trout recolonized depleted segments, and may help sustain invasions in sink habitats where environmental conditions limit recruitment. In streams similar to those we studied, eradication of brook trout is likely necessary to eliminate the threat to native cutthroat trout, but selective removal regimes that capture a high percentage of the brook trout population for least three consecutive years, repeated periodically, may permit cutthroat trout populations to persist with brook trout. To identify underlying mechanisms responsible for successful invasion by mobile, age‐structured vertebrates such as stream fishes, experiments conducted at realistic spatial and temporal scales and including multiple age classes will be required.

Summer Habitat Use by Rainbow Trout and Brown Trout in Jocassee Reservoir

AbstractTemperature, dissolved oxygen, and depth preferences of Jocassee Reservoir rainbow trout Oncorhynchus mykiss and brown trout Salmo trutta implanted with temperature‐sensing radio transmitters were determined during July, August, and September 1994–1998. Specific knowledge of these preferences was needed to verify habitat criteria designed to assist in the management of water quality in this reservoir for trout survival in late summer and early fall. Rainbow trout exhibited temperature, dissolved oxygen, and depth preferences in the ranges 8.3–13.4°C, 2.9–8.7 mg/L, and 30.0–52.0 m, respectively, while brown trout exhibited preferences in the ranges 7.5–21.9°C, 4.2–10.0 mg/L, and 14.0–54.0 m, respectively. Even though rainbow trout selected cooler water temperatures and greater depths than brown trout, both species generally exhibited preferences for water 20°C or cooler and containing 5.0 mg/L or more of dissolved oxygen. Maintenance of these criteria in Jocassee Reservoir should ensure adequate habitat for the summer and early fall survival of rainbow and brown trout.

Equivalent Survival and Different Development Rates in Reciprocal Apache Trout × Rainbow Trout Hybrids

Abstract Hybrid individuals from naturally spawning populations of Apache Trout (Oncorhynchus gilae apache) and Rainbow Trout (Oncorhynchus mykiss) have been reported to hybridize successfully in only one direction. This is suggested by the absence of Rainbow Trout mitochondrial haplotypes in hybrid individuals. By artificially producing reciprocal crosses of Apache Trout and Rainbow Trout, the apparent unidirectional fertilization in naturally spawning hybrid populations was shown not to be the result of gametic incompatibility or early zygote death. Although survival rate differences between the reciprocal hybrid crosses were not significantly different, development rate differed significantly between the groups (P < 0.001). Using time to hatch as the indicator of development rate, Apache female by Rainbow male hybrids had a mean time to hatch seven days faster than Rainbow female by Apache male hybrids with both developing intermediate to the pure crosses. Although this could account for the perceived ...

Summary of Case Studies Investigating the Causes of Pulp and Paper Mill Effluent Regulatory Toxicity

Abstract In Canada, effluents from pulp and paper mills are regulated for toxicity. The regulation requires ≥50% survival of rainbow trout (Oncorhynchus mykiss) exposed to full-strength (i.e., 100%) effluent for 96 h in tests that must be conducted monthly. The regulation also calls for ≥50% survival of Daphnia magna exposed to 100% effluent for 48 h in weekly monitoring tests. Every year, about 10 to 25% of the mills exceed the regulatory limit at least once in tests with either rainbow trout or Daphnia magna. Between 1996 and 2003, we investigated 84 such cases from 32 mills. Of the 84 investigations, 49 involved only trout, 29 involved only Daphnia, and six involved both species. We identified the actual cause of toxicity in 70% of the cases and partially or tentatively identified the toxicant(s) in 17% more. In the cases involving only trout, the most frequent causes of toxicity were related to biotreatment performance (e.g., ammonia). In the cases involving only Daphnia, the most frequent cause of toxicity seemed to be related to polymeric formulations. For those cases involving both trout and Daphnia, the cause of toxicity was traced to more than one compound or to excess concentrations of a specific compound resulting from a spill or biotreatment-related problems.

Early ocean survival and marine movements of hatchery and wild steelhead trout (Oncorhynchus mykiss) determined by an acoustic array: Queen Charlotte Strait, British Columbia

Early ocean movements, residency, and survival of steelhead (Oncorhynchus mykiss) were examinedin Queen Charlotte Strait, a large (20 � 100 km 2 ) marine area separating Vancouver Islandfrom the mainland . The results provide the first detailed data on the ocean biology of hatchery and wild steelhead smolts. Initial ocean movements were not strongly directed, with most smolts swimming in the range of 0.2–0.5 body length (BL) s � 1 . The majority (78%) vacatedQueen Charlotte Strait within 1 week of release in freshwater. Relative marine survival of hatchery smolts surgically implanted1 month prior to release was id entical to that of wildsmolts implantedon the d ay of release; survival of hatchery smolts transported to the study site, implanted, and released all on the same day was significantly lower. The results suggest that the early marine survival of hatchery andwildsmolts may be fundamentally similar, but that the cumulative stress of transportation andsurgery may red uce post-surgery survival. Hatchery smolts movedat higher average swimming speeds than wild smolts, but the difference was not statistically significant. Early marine survival within the study region appears to be relatively high (X55%), contradicting assumptions that the early marine phase is the critical periodfor d etermining salmon recruitment. r 2004 Elsevier Ltd. All rights reserved.

Drought effect on stream morphology and brook trout (Salvelinus fontinalis) populations in forested headwater streams

We assessed the effect of a severe drought in 1999 upon stream morphology and brook trout (Salvelinus fontinalis) populations in seven headwater streams in the Greenbrier and Potomac River watersheds, West Virginia. During the drought, stream discharge was 96% lower than in years of normal precipitation. As a result, habitat availability and quality over all study streams was significantly lower. Riffle area was greatly reduced (−54%) relative to available pool area (−2%). Fine sediment levels ( 6.0 mg l −1 , respectively) for brook trout survival in all streams during the drought. Brook trout populations were significantly reduced (adult 60%, Youngof-the-year 67%), and individual fish had significantly lower body condition during the drought relative to the post-drought period. Reductions in brook trout density and population condition during, and in the-post drought period, were related to spatially-limited food resources and/or increased fine sediment levels, but not to degraded water quality. Fisheries managers should consider the effect of periodic drought on brook trout populations and consider short-term harvest restrictions to abet recovery after such stochastic events.

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.