Adult Lake Whitefish Research Articles

Recolonization of lake whitefish river spawning ecotypes and estimates of riverine larval production in Green Bay, Lake Michigan

Lake whitefish (Coregonus clupeaformis) within the waters of Green Bay, Lake Michigan have recently shown a substantial increase in abundance. Furthermore, after over 100 years of extirpation, adult lake whitefish are found spawning within major Wisconsin tributaries to Green Bay. Many knowledge gaps still exist with respect to the chronology of adult river migrations, including the physical characteristics of upstream habitats selected for reproduction and the extent of larval production by these riverine ecotypes. Here, we use hydroacoustic imaging along with egg and larval surveys to evaluate this novel riverine spawning in 2017 and 2018. Highest abundance of adults was observed in the month of November as temperatures declined below 8 °C. Spawning areas consisted of cobble substrates, and site-specific fish densities were primarily correlated with river flows between 0.3 and 1.0 m/s, with specific values varying by tributary and year. Locations of egg deposition mirrored areas of high observed fish densities. Larval production was documented on each tributary using active trawl ichthyoplankton sampling, and larvae were observed outmigrating to open water environments. We estimated tributaries produced 452,000 larvae in 2017 and 721,000 larvae in 2018. To our knowledge, this represents the first documentation of successful lake whitefish larval production from Green Bay tributaries and suggests tributary spawning populations contribute to the greater abundance of lake whitefish observed in recent years.

Arsenic Bioconcentration in Freshwater Fish Species in a Pristine Lake in Yellowknife, NT

Yellowknife hosts one of the largest gold mining industries in Canada, including the renowned Giant Mine actively operating from 1948 to 2004, The mining operation in Giant Mine released enormous amounts of arsenic trioxide dust to the environment from the burning of arsenopyrite ores necessary to extract gold. Studies have revealed up to 100-fold increases in the concentration of arsenic in the surface water of lakes located within a 5-km radius of the mine. We summarized different factors from previous studies that contribute to the high arsenic levels found in lakes in Yellowknife: distance from the Giant Mine, prevailing wind direction to the Northwest, and the size of the lake. In this study, Small Lake was chosen as a pristine lake; a medium-sized lake located 27-km East of the mine and away from the city centre. Small Lake has the background concentration of arsenic of 1.4 µg/L in its surface water, unaffected by the historical activities from the Giant Mine. This background level of arsenic is expected from the slow natural weathering process of the bedrock geology. We collected two most common freshwater fish species in lakes in Yellowknife: adult Lake Whitefish (Coregonus clupeaformis) (n=8) and adult Northern Pike (Esox lucius) (n=8). Total arsenic concentration in the tissues was measured using ICP-MS method following FDA standard. Results show arsenic concentrations of 0.567 ± 0.216 mg/kg dry weight in the muscle tissue of Lake Whitefish and 0.458 ± 0.115 mg/kg dry weight in the muscle of Northern Pike. Although the Northern Pike species in this study is in a higher trophic position than the Lake Whitefish species, no significant difference in the arsenic concentration is observed in the muscle tissues (p > 0.05). The results of this study serve as reference data for fish arsenic monitoring programs and risk assessment projects in Yellowknife.

Mercury Accumulation, and the Mercury-PCB-Sex Interaction, in Lake Whitefish (Coregonus clupeaformis)

We determined whole-fish Hg concentrations of 26 female and 34 male adult lake whitefish (Coregonus clupeaformis) from northern Lake Huron captured during November 2010. Subsampling from these 60 fish, Hg concentration was also determined in both somatic tissue and ovaries (n = 5), while methylmercury (MeHg) concentration was determined in whole fish (n = 18). Bioenergetics modeling was used to assess the growth dilution effect on the difference in Hg concentrations between the sexes. Mean whole-fish Hg concentration in females (59.9 ng/g) was not significantly different from mean whole-fish Hg concentration in males (54.4 ng/g). MeHg accounted for 91% of the mercury found in the lake whitefish. Bioenergetics modeling results indicated that the growth dilution effect did not contribute to the difference in Hg concentrations between the sexes. We estimated that females increased in Hg concentration by 17.9%, on average, immediately after spawning due to release of eggs. Using polychlorinated biphenyl (PCB) data for the same 60 lake whitefish from a previous study, we detected a significant interaction between sex and contaminant type (Hg or PCBs), which was attributable to males being significantly higher in PCB concentration than females. Males may be eliminating Hg at a faster rate than females.

Arsenic and mercury in lake whitefish and burbot near the abandoned Giant Mine on Great Slave Lake

Contaminant levels in fish are of public concern in northern Canada where they are an important food source. In this study, we investigated the concentration of total arsenic, four arsenic species (arsenite (AsIII), arsenate (AsV), dimethylarsinate (DMA), and monomethylarsonate (MMA)), and total mercury (Hg) in the muscle and liver of lake whitefish (Coregonus clupeaformis) and burbot (Lota lota) collected at two sites near the abandoned Giant Mine site (Baker Pond and Yellowknife Bay) and two reference sites more than 25 km away (Chitty Lake and southern Great Slave Lake). Total arsenic concentrations were typically higher in fish tissues collected near the mine site, and higher in burbot than lake whitefish. We found lower concentrations of arsenic in the muscle tissue of adult lake whitefish than juveniles. All four arsenic species were only detected in the liver tissues of adult lake whitefish collected from Baker Pond on the mine site, and juvenile lake whitefish from the adjacent Yellowknife Bay. Mercury levels were highest in fish from Chitty Lake, and higher for burbot than lake whitefish, similar with other research reporting elevated mercury in small northern lakes relative to larger waterbodies. However, mercury levels in fish were not elevated beyond consumption guidelines. Elevated arsenic concentrations in the fish tissues collected near the mine site suggest that the area continues to be a source of arsenic to the aquatic food web; therefore, continued monitoring is warranted, particularly with a large portion of the local population harvesting wild food sources.

Increased Piscivory by Lake Whitefish in Lake Huron

AbstractWe evaluated the diet of Lake Whitefish Coregonus clupeaformis in Lake Huron during 2002–2011 to determine the importance of Round Goby Neogobius melanostomus and other fish as prey items. Lake Whitefish that had reached approximately 400 mm in length incorporated fish into their diets. The overall percentage of adult Lake Whitefish in Lake Huron that had eaten fish increased from 10% in 2002–2006 to 20% in 2007–2011, with a corresponding decrease in the frequency of Lake Whitefish that ate Dreissena spp. from 52% to 33%. During 2002–2006, Round Goby (wet mass, 38%), sculpins (Cottidae) (34%), and Ninespine Stickleback Pungitius pungitius (18%) were the primary fish eaten, whereas Round Goby accounted for 92% of the fish eaten in 2007–2011. Overall, Round Goby were found in the fewest Lake Whitefish stomachs in the north region of Lake Huron (6%) and in the most in the central (23%) and south (19%) regions of the lake. In the central region, Round Goby were eaten during all seasons that were sampled (spring through fall). In the south region, Round Goby were eaten only in the winter and spring but not in the summer when Dreissena spp. and spiny water flea Bythotrephes longimanus dominated the diet. Based on the 2007–2011 diet composition, an individual Lake Whitefish would need to have increased their consumption relative to that in 1983–1994 by 6% in the north region, 12% in the central region, and 41% in the southern region in order to achieve the same growth that was observed before dreissenid mussels arrived. However, Lake Whitefish weight adjusted for length only increased by 2% between 2002–2006 and 2007–2011 in the central region, decreased by 4% in the northern region, and remained constant in the southern region. This suggests that a shift toward more frequent piscivory does not necessarily improve the condition of a generalist feeder like Lake Whitefish.Received June 14, 2013; accepted August 28, 2013

Characterizing Seasonal Habitat Use and Diel Vertical Activity of Lake Whitefish in Clear Lake, Maine, as Determined with Acoustic Telemetry

AbstractSeasonal and daily vertical activity of lake whitefishCoregonus clupeaformiswas studied in Clear Lake, Maine (253 ha), using acoustic telemetry from November 2004 to June 2009. Twenty adult lake whitefish were tagged with acoustic tags that had either a depth sensor or both depth and temperature sensors to assess vertical habitat use at a seasonal and daily resolution. Vertical habitat selection varied seasonally and was strongly influenced by temperature. Between December and April, when the lake was covered with ice, surface temperature was below 2°C and tagged individuals occupied deep areas of the lake (∼15 m). After ice‐out, fish ascended into shallow waters (∼5 m), responding to increased water temperature and possibly to greater foraging opportunity. When surface water temperatures exceeded 20°C, fish descended below the developing thermocline (∼9 m), where they remained until surface temperatures fell below 20°C; fish then ascended into shallower depths, presumably for feeding and spawning. Through the winter, fish remained in thermal habitats that were warmer than the surface temperatures; in the summer, they selected depths with thermal habitats below 15°C. Though the amplitude varied greatly across seasons, lake whitefish displayed a strong diurnal pattern of activity as measured by vertical velocities. Fish were twofold more active during spring, summer, and fall than during winter. Lake whitefish exhibited diel vertical migrations, rising in the water column during nighttime and occupying deeper waters during the day. This pattern was more pronounced in the spring and fall and far less prominent during winter and summer. The strong linkage between temperature and habitat use may limit the current range of lake whitefish and may be directly impacted by climatic change.

Lake Whitefish in Lake Champlain after Commercial Fishery Closure and Ecosystem Changes

AbstractLake whitefish Coregonus clupeaformis were commercially fished in Lake Champlain until the 1913 fishery closure in U.S. waters. The only study of lake whitefish in the lake had been done in the 1930s. Our goals were to compare current biological parameters with historical information and to determine distribution and spatial differences in larval densities, with an emphasis on locating current spawning grounds, to gain insight on the current population in Lake Champlain. Adult lake whitefish (N = 545) were collected from 2006 to 2010 by using gill nets and trawls focused in the Main Lake. Larvae were collected extensively lakewide and intensively at Wilcox Cove and Rockwell Bay with an ichthyoplankton net. Population attributes (size, age, and sex composition; and growth, condition, and mortality) were typical of unexploited populations, as there was a wide range of length‐classes (126–638 mm total length) and age‐classes (1–26 years). Lake whitefish from the Main Lake had a high condition factor, and growth parameters were comparable with those of fish collected in the 1930s. Lake Champlain lake whitefish had greater asymptotic lengths than generally documented for the species. Larvae were found at sites throughout the Main Lake, and larval densities were among the highest recorded for the species (maximum = 2,558 larvae/1,000 m3); however, no lake whitefish were collected on the two historically documented spawning grounds. Lake whitefish in the Main Lake demonstrate characteristics of an unexploited population; however, evidence of spawning is absent or rare in portions of their historic range where habitat has been altered.Received February 22, 2011; accepted August 24, 2011

Spatial and temporal distributions of lake whitefish spawning stocks in Northern lakes Michigan and Huron, 2003–2008

Adult lake whitefish were tagged and released from the Big Bay de Noc (BBN) and Naubinway (NAB) stocks in northern Lake Michigan, and the Detour (DET) and Cheboygan (CHB) stocks in northern Lake Huron during 2003–2006 to describe their spatial and temporal distributions. The contemporary spatial distributions were compared with past distributions of the BBN and NAB stocks. Sixty-two percent of BBN tag recoveries occurred in Wisconsin waters during winter, spring and summer, but 83% of fall tag recoveries were made near the tagging site. Eighty-eight percent of the NAB tag recoveries were made in the management unit of tagging and 7% occurred into northern Lake Huron. Over 90% of the DET stock remained in the vicinity of the tagging sites regardless of the season, while 75% of the CHB tag recoveries were made in northwestern Lake Huron and 17% were made in Ontario. Based on regression tree analysis, there were strong stock, season, and year effects on movement distances, with weaker effects due to sex and length at tagging. Spatial distribution of the BBN stock changed from 1978–1982 to 2003–2008, but spatial distribution of the NAB stock did not. Substantial differences in movement and distribution existed among the four stocks, large seasonal differences in spatial distribution were found within some stocks, and lake whitefish exhibited strong spawning site fidelity. Present management unit boundaries are inappropriate for managing three of our four stocks, and agencies should consider developing single harvest limits for both northern Lake Huron and western Lake Michigan.

Measures of larval lake whitefish length and abundance as early predictors of year-class strength in Lake Michigan

Many lake whitefish stocks in Lake Michigan have experienced substantial declines in growth and condition since the 1990s. Reduced growth and condition could result in reduced quality or quantity of eggs produced by spawning females, which in turn could negatively impact recruitment. We evaluated the potential for reduced recruitment by measuring early life stage density and length, and we discuss the utility of these measures as early indicators of lake whitefish year-class strength. Overall, mean larval density (number per 1000 m 3 ± SE) in Lake Michigan was greater in 2006 (373.7 ± 28.3) than in 2005 (16.6 ± 24.8); whereas, mean length (mm ± SE) of larval lake whitefish was smaller in 2006 (12.87 ± 0.07) than in 2005 (14.38 ± 0.13). The ratio of zooplankton to fish density did not show an expected relationship with larval fish density or length. Rather, variation in larval density was best explained by a multiple-regression model that included larval length, spring wind intensity, and adult stock density as predictor variables. Our results suggest that the density of larval lake whitefish is not directly regulated by temperature or zooplankton density at the time of emergence, but that a potential for density-dependent regulation exists when larval emergence rates are high. We conclude that the observed declines in growth and condition of adult lake whitefish are not resulting in substantial reductions in recruitment.

Estimates of fishing and natural mortality rates for four Lake Whitefish stocks in Northern Lakes Huron and Michigan

We analyzed tag-recovery data to estimate instantaneous fishing ( F) and natural mortality ( M) rates of four lake whitefish stocks in lakes Michigan and Huron during 2004–2007. We tagged and released 22,452 adult lake whitefish of which 8.7% were subsequently recovered. Annual tag-reporting rates ranged from 17.8% to 56.2%. Tag retention was high for the first 5–6 months after tagging, but tag loss increased substantially thereafter. Nine tag-recovery models were evaluated with respect to whether F and/or M varied among stocks, lakes, or years. There was support for three models based on Akaike information criteria. The best model had yearly and stock-specific estimates of F of 0.03 to 0.79 and lake-specific estimates of M of 0.35 for Lake Michigan and 0.60 for Lake Huron. The second best model had yearly and stock-specific estimates of F of 0.04 to 0.71 and a constant estimate for M of 0.52. The third model had yearly and stock-specific estimates of F of 0.04 to 0.85 and stock-specific estimates of M of 0.32 to 0.67. Model-averaged estimates of F ranged from 0.04 to 0.78 and were substantially different than statistical catch-at-age estimates of F. Model-averaged estimates of M ranged from 0.40 to 0.59 and were greater than estimates obtained from prediction equations, possibly due to sea lamprey-induced mortality. We recommend that tag-recovery estimates of F and M be used as Bayesian priors in future lake whitefish stock assessments to help refine mortality estimates for the stocks.

Cloning and localization of three forms of gonadotropin-releasing hormone, including the novel whitefish form, in a salmonid, Coregonus clupeaformis.

Cells containing different GnRH peptides currently are thought to have distinct locations and functions in the brain. Lake whitefish is the first salmonid species to have three forms of GnRH peptide in contrast to later-evolving salmonids (salmon and trout) in which only two forms have been identified. Our objective was to isolate the cDNAs that code for these transcripts and to localize the transcripts for the three forms of GnRH in adult lake whitefish brain. Also, we provide phylogenetic analysis of these three whitefish genes based on their preprohormone sequence. From whitefish we isolated cDNAs encoding chicken (c)GnRH-II, salmon (s)GnRH, and the novel whitefish (wf)GnRH. The three cDNAs each encode only one GnRH and are placed in separate groups with phylogenetic analysis. A combination of in situ hybridization and immunocytochemistry with two antisera revealed neurons that expressed protein and/or mRNA for cGnRH-II in the midbrain and hindbrain; sGnRH in the olfactory nerve and bulb, ventral telencephalon, and preoptic area; and wfGnRH in the same latter two brain regions and the hypothalamus. Thus, in the anterior brain, cells containing sGnRH and wfGnRH were in the same brain areas but not at identical locations in the ventral telencephalon and preoptic area. Based on our results, we speculate that both sGnRH and wfGnRH have gonadotropin-releasing roles in the lake whitefish brain.

Toxicology of dietary nickel in lake whitefish ( Coregonus clupeaformis)

The sublethal toxicity associated with exposure of adult lake whitefish ( Coregonus clupeaformis) to diets containing 0, 10, 100, and 1000 μg Ni per g for 10, 31, and 104 days was assessed through the measurement of responses, through a range of levels of biological organization. The accumulation and distribution of Ni in these fish are described in the previous manuscript (Ptashynski and Klaverkamp, 2001. Aquat. Toxicol. in press). Hematological parameters, including concentrations of glucose and hemoglobin and hematocrit, were not different between control and treated fish. Organ and whole organism parameters, including LSI, growth, and condition factor, were also unaffected. Histopathological lesions in kidney and liver proved to be the most sensitive and reliable indicators of Ni exposure. In livers of treated fish, areas of focal necrosis and altered bile ducts were observed. Histological alterations were observed throughout the posterior kidneys, in glomeruli, tubules, collecting ducts, and hematopoietic tissue, in fish fed medium and high dose diets. In whitefish kidneys, the frequency (%) of altered distal tubules and fields of views with alterations increased with the dose and duration of exposure. Significant increases in metallothionein concentrations were observed in intestine of whitefish fed the high dose diet on day 10, but these increases were not sustained. Significant increases in lipid peroxide concentrations were also observed in plasma of whitefish fed the high dose diet on day 31, but were not observed on day 104. These biochemical responses to dietary Ni require further evaluation. To evaluate exposure of natural populations of fish to Ni, analysis of Ni in kidney and liver and assessment of renal and hepatic histopathology are recommended for use in field bio-monitoring programs.

Accumulation and distribution of dietary arsenic in lake whitefish ( Coregonus clupeaformis)

Adult lake whitefish ( Coregonus clupeaformis) were fed As contaminated diets at nominal concentrations of 0, 1, 10 and 100 μg As/g food (d.w.) for 10, 30 and 64 days. Liver, kidney, stomach, intestine, pyloric caeca, gallbladder, skin and scales were analyzed for As content. The pattern of As accumulation in fish tissues was influenced by reduced feed consumption beginning on day 45 by fish fed the 100 μg As/g food. Significant As accumulation occurred in all tissues examined from fish exposed to the 100 μg As/g food for 30 days, with the exception of gallbladder. After 30 days of exposure, the highest concentration of As was observed in pyloric caeca of fish fed the 100 μg As/g food. Significant accumulation of As occurred in livers and scales of fish fed concentrations of As as low as 10 μg/g for 30 and 64 days. Muscle, gonad, spleen, gills and bone of lake whitefish fed a control diet for 10 days and 100 μg As/g food for 10, 30 and 64 days were also analyzed for As content. As concentrations increased in gonads, spleen and gills of fish fed the 100 μg As/g food for 30 days. Increased concentrations of As were observed in bone of fish fed the high dose food after each duration of exposure. As concentrations did not increase in muscle of fish after 10, 30 or 64 days of exposure. The following manuscript (Pedlar et al., 2001) documents toxicological effects observed in these fish. Analyses of As in pyloric caeca, intestine, liver and scales are recommended to evaluate the bioavailability of As to freshwater fish in environmental monitoring programs.

Toxicological effects of dietary arsenic exposure in lake whitefish ( Coregonus clupeaformis)

Adult lake whitefish were fed As contaminated diets at nominal concentrations of 0, 1, 10, and 100 μg As/g food (dry weight) for 10, 30, and 64 days. Reduced feed consumption was observed in lake whitefish fed the 100 μg As/g food, beginning on day 45 of exposure. The accumulation and distribution of As in these fish are described in the previous manuscript [Pedlar, R.M., Klaverkamp, J.F., 2001. The accumulation and distribution of dietary arsenic in lake whitefish ( Coregonus clupeaformis). Aquat. Toxicol., in press]. At the molecular level of organization, metallothionein (MT) induction occurred in lake whitefish fed the 100 μg As/g food after 10 and 30 days, and in fish fed the 1 and 10 μg As/g diets for 64 days. Dietary As exposure did not have a significant effect on plasma lipid peroxide (LPO) concentrations. At the tissue and organ level, mean liver somatic index decreased significantly in lake whitefish fed the 100 μg As/g food for 64 days. Blood parameters (hematocrit, hemoglobin concentration, red blood cell count, mean cell volume, mean corpuscular hemoglobin, and mean corpuscular hemoglobin concentration) were not affected by exposure to As contaminated diets. Liver and gallbladder histopathologies were observed in lake whitefish fed all As contaminated diets after each duration of exposure. Histopathology observed in liver included nuclear, architectural and structural alterations, areas of inflammation, and focal necrosis. Sloughing of the epithelium, dilation of vascular elements, inflammation, edema, fibrosis, and increased width of the submucosa were some of the alterations observed in gallbladders of lake whitefish fed As contaminated diets. Both organs were sensitive to As exposure, as damage occurred with exposure to dietary concentrations of As as low as 1 μg/g. Whole organism parameters were unaltered by dietary As exposure. Based on the results of this study, histopathological alterations in liver and gallbladder, and hepatic MT induction may be useful indicators of As toxicity in environmental monitoring programs that also measure As concentrations in those tissues.

Accumulation, distribution and toxicology of dietary nickel in lake whitefish ( Coregonusclupeaformis) and lake trout ( Salvelinusnamaycush)

An 18-day experiment was conducted to investigate the uptake and sublethal toxicity of dietary Ni in adult lake whitefish (LWF, Coregonus clupeaformis) and lake trout (LT, Salvelinus namaycush) fed diets containing 0, 1000 and 10 000 μg Ni/g, prepared with and without brine shrimp. The results of this experiment were used to design an experiment of longer duration in which one of the fish species was selected and exposed to lower dietary Ni doses. In the present study feed refusal was observed in LT and LWF fed 10 000 μg Ni/g, after three and 4–5 feedings, respectively. LT fed Ni-contaminated diets exhibited different patterns of Ni accumulation than LWF. Increased Ni concentrations in all LWF tissues, except the intestine, were associated with increased doses of Ni. Copper and Zn concentrations in kidney and liver of LWF were altered. Metallothionein concentrations in kidneys of LT fed 1000 μg Ni/g and 10 000 μg Ni/g and LWF fed 10 000 μg Ni/g and in livers of LWF fed 10 000 μg Ni/g (diet without shrimp only) increased significantly. Increased lipid peroxide production in the plasma of LT fed 10 000 μg Ni/g was observed. Blood glucose and electrolytes were affected by Ni exposure. Histopathological alterations were observed in kidneys of LWF fed low and high dose diets, livers of whitefish fed high dose diets, and intestines of LWF fed high dose diets and LT fed low and high dose diets. LT fed high dose diets exhibited significant decreases in weight.

Accumulation and distribution of dietary uranium in lake whitefish ( Coregonus clupeaformis)

We investigated the accumulation and distribution of uranium (U) in adult lake whitefish ( Coregonus clupeaformis) fed a commercial diet containing 100, 1000 and 10 000 μg U/g for 10, 30, and 100 days. No food avoidance or refusal occurred. The major sites of U accumulation were in the mineralized tissues, bone and scales, and in intestine, liver, kidney, and, in the highest treatment, gonads. Significant accumulation in fish fed 100 μg U/g was observed only in scales. Duration-dependent accumulation was observed in bone, scales, liver, and kidney of fish fed 10 000 μg U/g and in scales of fish fed 1000 μg U/g. Dose-dependent accumulation was observed in scales of fish exposed for 100 days. U accumulation in gonads and gill peaked on day 30 when fish gonads were in the most advanced stage of maturation, of the sampling days evaluated. To evaluate the biological availability of U to fish inhabiting contaminated aquatic systems, analyses of U in scales, bone, intestine, kidney, and liver are recommended for biomonitoring programmes. The toxicology of U in these fish is described in the following manuscript (Cooley, H.M., Evans, R.E. Klaverkamp, J.F., 2000. Toxicology of dietary uranium in lake whitefish ( coregonus clupeaformis) Aquat. Toxicol., 48, 393–413).

Toxicology of dietary uranium in lake whitefish ( Coregonusclupeaformis)

Using responses ranging from whole animal to the molecular level, the toxicological significance of the accumulation and distribution of uranium (U) in adult lake whitefish fed a commercial diet contaminated with three concentrations of U, 100, 1000 and 10 000 μg U/g, for 10, 30, and 100 days, as described in the previous manuscript (Cooley, H.M., Klaverkamp, J.F., 2000. Accumulation and distribution of dietary uranium in Lake whitefish ( Coregonus clupeaformis), Aquat. Toxicol., 48, 375–392), was evaluated. Whole organism morphometrics were unaltered by U exposure. Haematological variables were either unchanged or only transiently affected. Liver and kidney metallothionein concentrations were largely unaltered. Concentrations of serum lipid peroxides were significantly elevated in all treatment groups on days 30 and 100, indicating that U may damage cellular and sub-cellular membranes. Dose- and duration-dependent histopathologies were present in liver and posterior kidney of treated lake whitefish. The most consistent and pronounced lesions in liver were focal hepatocyte necrosis and alterations of bile ductule epithelium. Dose- and duration-dependent renal lesions were most evident in proximal tubules. However, we observed a range of histopathologies in this organ, including tubular necrosis, inflammation, haemorrhaging, depletion of haematopoietic tissues, alterations of distal tubules and collecting ducts, tubule dilation, pigmented macrophage proliferation, and glomerular lesions. Pathologies were observed in lake whitefish at all concentrations of dietary U following prolonged exposure. When used in conjunction with U tissue residue analyses, histopathological lesions and indices of lipid peroxidation may prove useful indicators of U toxicity when assessing fish health in U biomonitoring programmes.

Phenotypic Variation in the Lake Whitefish, Coregonus clupeaformis, Induced by Introduction into a New Environment

Adult lake whitefish (Coregonus clupeaformis) from Clearwater Lake and second generation adults of offspring from Clearwater whitefish transplanted to Lyons Lake were compared with respect to morphometric and meristic characters and isozymes of L-glycerol-3-phosphate dehydrogenase (GPDH). Feeding habits and abundance of pelagic and benthic foods were compared in the two lakes.Gill raker number, lateral line scale count, and interorbital width remained constant between parental and offspring populations. Gill raker length was the main character found to differ between the populations. This was found to be related to the percentage and type of benthic food eaten. Abrasion of the gill rakers is offered as an explanation for the differences in gill raker length. Differences were found in various other meristic and morphological characters, as well as in electrophoretic phenotype frequencies of isozymes of GPDH.