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A predominance of alewives (Alosa pseudoharengus), a species having high thiaminase activity, in Lake Ontario lake trout (Salvelinus namaycush) diets, has been related to thiamine deficiency in lake trout eggs during 1994–2004. The late 1990s invasion by round goby (Neogobius melanostomus), that appear to have thiaminase activity of low biological activity, represented a potential to reduce the dietary importance of alewife and, as a result, increase lake trout thiamine levels if they became sufficiently important in lake trout diets. To evaluate whether lake trout thiamine levels increased as alewives were displaced by round gobies in lake trout diets, we collected 199 lake trout ranging from 305 to 893 mm in 2005–2006 and measured their muscle thiamine levels and diet composition. Diet composition (percent by weight) was estimated from MixSIR based on stable isotopes (δ15N and δ13C) measured from lake trout and their prey. Overall, alewife and goby dominated lake trout diet (78%), with round goby dominating the diet (55–57%) of smaller individuals (<600 mm), and alewife dominating the diet (59–73%) of larger, reproductively active individuals. Lake trout muscle thiamine declined with increases in lake trout length and the proportion of alewife eaten (p < 0.01). The proportion of lake trout below 500 pmol/g thiamine also declined; this threshold is associated with a loss of equilibrium in adults. Despite the increasing albeit size-related consumption of round goby, it remains inadequate as muscle thiamine levels in mature lake trout (i.e., >600 mm) during 2005–2006 appear unchanged from levels observed in 1996. [ABSTRACT FROM AUTHOR]

In the Great Lakes, an Alewife Alosa pseudoharengus diet has been reported to cause thiamine deficiency in salmonines as a result of high thiaminase activity. The ontogeny of thiamine deficiency and its relationship to Alewife consumption have not been determined in Chinook Salmon Oncorhynchus tshawytscha within this system. Using stable isotope mixing models along with muscle thiamine, we assessed ontogenetic changes in the diet and corresponding muscle thiamine status of Lake Ontario Chinook Salmon ranging in TL from 100 to 1,000 mm. Thiamine levels were highest in young of the year collected in a tributary of Lake Ontario but declined once Chinook Salmon entered Lake Ontario. In Lake Ontario, the diets of juvenile (200–400 mm; 97–99%) and adult (>400 mm; 97–100%) Chinook Salmon consisted almost entirely of Alewives as estimated using mixing models. This Alewife diet was associated with an ontogenetic decline in muscle thiamine among Chinook Salmon. The asymptotic decline in thiamine concentration with increasing size plateaued at 720–758 pmol/g of muscle. The proportion of individuals below a thiamine threshold of 500 pmol/g (associated with a loss of equilibrium) increased with TL up to 799 mm and then declined between 800 and 1,000 mm. At these muscle concentrations, no outward signs of thiamine deficiency were observed. Calculation of total mass accumulation of body stores of thiamine (muscle concentration times body weight) showed an unexpected and significant increase with size. Although it appears that dietary Alewives affected thiamine status, there were undetermined factors, such as incomplete destruction of thiamine by thiaminase, gut synthesis of thiamine, gill absorption of water thiamine, and/or other factors, that contributed to the overall thiamine status of these Chinook Salmon. [ABSTRACT FROM AUTHOR]

Abstract Lake Ontario supports a diversity of native and non-native salmonids which are managed largely through stocking practices. Ecological changes (e.g., invasive species) altering the food web structure accompanied with shifts in prey abundance, necessitate understanding the trophic niches of Lake Ontario salmonids to aid in management. The objectives of this study were to quantify salmonid (5 species) trophic niches and dietary proportions using stable isotope ratios (δ13C and δ15N) of a large sample set (adult fish (>300 mm; n = 672) and key offshore prey (5 species, n = 2037)) collected across Lake Ontario in 2013. Estimates of prey based on stable isotope ratios were similar to stomach contents. Based on stable isotope ratios, non-native prey dominated salmonid diet; in particular alewife (Alosa pseudoharengus) constituted the majority (0.31 to 0.93) of all salmonid diets, and round goby (Neogobius melanostomus) contributed 0.26 and 0.19 of brown trout (Salmo trutta) and lake trout (Salvelinus namaycush) diets, respectively. Trophic niche overlap was high between all salmonids, except lake trout. The largest trophic niche overlap occurred between Chinook (Oncorhynchus tshawytscha), coho (Oncorhynchus kisutch), and Atlantic salmon (Salmo salar), and their reliance on alewife infers a strong pelagic foraging strategy. Lake, brown and rainbow (Oncorhynchus mykiss) trout had larger and/or more distinct trophic niches indicative of a more variable diet across individuals and utilizing different foraging strategies and/or habitats. Overall, Lake Ontario salmonids maintained a high reliance on alewife, and their potential for plasticity in diet provides important information to management regarding population sustainability. [ABSTRACT FROM AUTHOR]

Lake trout, Salvelinus namaycush, spawning in the Great Lakes occurs primarily on cobble substrate at relatively shallow water depths that can experience strong water currents. Strong currents may limit embryonic survival by damaging or displacing eggs, but may also reduce the accumulation of fine material and limit foraging by potential egg predators. To better understand the importance of currents, we evaluated the role of currents in spawning habitat selection, egg density and survival, and egg predator density at a spawning reef in Lake Champlain (USA). Most spawning occurred one week after the largest storm event associated with the strongest currents and greatest upwelling. Highest spawning activity was associated with a relatively shallow part of the reef that had the highest current velocity and greatest potential for egg displacement. Within the interstices, the survival of naturally deposited eggs was unrelated to the concurrent loss of artificial eggs. We propose that the reproductive strategy of spawning on shallow areas of a reef that have the highest current velocity and high potential for egg loss represents a type of bet hedging to optimize survival of those embryos that remain within interstices. This strategy may have evolved in response to environmental stochasticity that resulted in higher egg survival. [ABSTRACT FROM AUTHOR]

The Lake Ontario–upper St. Lawrence River (LOUSL) population of American EelsAnguilla rostrata(hereafter, “eels”) was once one of the most important groups of the species but is now in a state of serious decline. Given that thiamine deficiency has been observed in almost all of the top predators in Lake Ontario, we assessed the potential that a diet-induced thiamine deficiency associated with consumption of AlewivesAlosa pseudoharenguscould be involved. Muscle thiamine was measured in eels from throughout the LOUSL corridor and was compared with putative threshold effect levels established from the literature. Mirex concentrations were used to separate Lake Ontario-resident eels from non-Lake Ontario-resident eels. Stable isotope analyses of eel muscle samples and potential prey, including Alewives, were combined with mixing model software to infer the diets consumed by Lake Ontario eels. Although residence in Lake Ontario was associated with a significant decline in muscle thiamine concentration, estimated Alewife consumption by eels was unexpectedly low. Instead, mixing model results indicated that crayfish and Round GobyNeogobius melanostomuswere the major prey. Both taxa are known to contain thiaminase and have the potential to cause thiamine deficiency, but there are no reports of thiamine deficiency associated with Round Goby consumption, thus implicating crayfish. There was no recovery in thiamine levels prior to the initiation of oceanic migration. As a result, thiamine levels of Lake Ontario-resident eels prior to migration were only slightly above putative threshold effect levels for pathological and behavioral effects in Japanese EelsAnguilla japonica, but this would require confirmation with American Eels. Since thiamine levels are expected to decline further during migration, additional effects on eel behavior, reproduction, and survival seem probable. Because of panmixia, such effects—when combined with the relatively high reproductive potential of Lake Ontario-resident eels—may have consequences for the entire species. Received August 24, 2012; accepted May 28, 2013 [ABSTRACT FROM AUTHOR]

Both wild and hatchery Atlantic SalmonSalmo salarcan contribute to restoration but can exhibit differences in spawning habitat selection (e.g., water depth, current speed) and egg nutritional quality (e.g., thiamine), which affect reproductive success. Hence, there is a need to be able to differentiate the spawning contribution of the two groups in the wild. As diets of wild and hatchery-reared spawners are markedly dissimilar and diet is known to influence stable isotope signature, egg stable isotope signatures offer the potential to discriminate redds of each. Using stable isotope analysis of carbon and nitrogen (δ13C and δ15N) of naturally spawned Atlantic Salmon eggs, we were able to discriminate the redds of putative wild (i.e., previously stocked life stage feeding in Lake Ontario; EWSR) from putative hatchery-reared Atlantic Salmon (EHSR). Eggs of EWSR were significantly more enriched in nitrogen (δ15N: 15.0 ± 0.5‰ [mean ± SE]) but more depleted in carbon (δ13C: −26.6 ± 0.3‰) than eggs of EHSR (δ15N = 9.8 ± 0.6‰; δ13C = −17.5 ± 0.0‰). Eggs of EHSR were indistinguishable from eggs of known hatchery Atlantic Salmon for both δ13C and δ15N. Using stable isotopes to discriminate redd type, few differences were found between the spawning habitat of putative wild and hatchery spawners. Similarly using the same criteria, thiamine levels in eggs of EWSR (8,474 ± 840 pmol/g) were not significantly different from eggs of known wild Atlantic Salmon (3,691 ± 782 pmol/g) or of eggs of EHSR (14,865 ± 1,050 pmol/g), whose thiamine levels were indistinguishable from eggs of known hatchery Atlantic Salmon (14,200 ± 1,167 pmol/g). Egg thiamine levels for all groups were above established mortality thresholds. Our results indicate that both hatchery and wild Atlantic Salmon can make reproductive contributions, which can be differentiated and quantified using stable isotope signatures. Received August 24, 2012; accepted May 15, 2013 [ABSTRACT FROM PUBLISHER]

Abstract: The invasive Ponto-Caspian mysid Hemimysis anomala (hereafter Hemimysis) was first observed in south-eastern Lake Ontario in May 2006. In Lake Ontario, Hemimysis is most abundant at nearshore habitats characterised by cobble–rubble substrate, which it shares with the round goby Neogobius melanostomus (hereafter goby). To better understand the interaction if any between gobies and Hemimysis, gobies were collected throughout the summer and fall periods at three shallow (<3m) nearshore locations representing eastern, central, and western Lake Ontario where Hemimysis are relatively abundant. Goby stomach contents were examined for evidence of Hemimysis and other prey. In addition, gobies were collected at two locations in southwestern Lake Ontario in shallow- (3m) and deep- (11m) water nearshore habitat where stomach contents were also used to characterise diet. Despite higher Hemimysis abundance nearshore, Hemimysis were not consumed by any gobies collected from shallow nearshore locations, and only found in three of 23 gobies collected at the deep site. Goby abundance and consumption of Hemimysis by gobies at the deep site were unrelated to Hemimysis abundance in traps. At all locations, gobies fed on soft-bodied invertebrates and dreissenids although dreissenids were the dominant prey among large (>74mm) gobies. We suspect that the ability of Hemimysis to avoid predation by gobies is the result of a combination of anti-predator behaviours such as an evasive startle response, reduced activity and depth dependent segregation in interstitial spaces during the day, and a feeding mode used by gobies that is poorly suited for an evasive species like Hemimysis. [Copyright &y& Elsevier]

Abstract: In 2006 the bloody-red mysid (Hemimysis anomala), a new invasive species to the Great Lakes, was discovered in the Muskegon channel which flows into Lake Michigan. As predicted at the time of introduction, it quickly expanded its range in Lake Michigan and has recently been documented in Grand Traverse Bay near Elk Rapids, Michigan. Its effects on Great Lakes ecosystems, however, remain unclear owing to a lack of information on its abundance. Using a gear intended to sample lake trout and lake whitefish eggs from cobble substrate during spawning, we found variable densities of Hemimysis at three near shore reefs at Elk Rapids, Lake Michigan over a two year period. The highest densities of Hemimysis were found at the reef with the highest quality fish (i.e., lake trout and lake whitefish) spawning habitat based on the proportion of rounded cobble and rubble substrates, and the amount of interstitial space. Abundance of Hemimysis on all reefs was highly seasonally dependent, ranging from 0 to 31.4 per m². The highest numbers were seen during the fall when water temperatures were between 6 and 12°C. Based on the association of Hemimysis with cobble substrates and the abundance of this type of habitat in northeastern Lake Michigan, we predict substantial expansion of Hemimysis in this area of the lake. Additional evaluation of Hemimysis on fish spawning habitat is needed to determine potential interactions with other Great Lakes biota, particularly larval fish with which they may compete. [Copyright &y& Elsevier]

Abstract: To more fully understand the secondary effects of thiamine deficiency on embryo development of lake trout Salvelinus namaycush, we used an immersion protocol to administer graded doses of the thiamine antagonist oxythiamine (OXY) (e.g., 0, 12.5, 25, 50, 100, 200, and 400mg/L). OXY was administered to eggs of six families at water hardening (fertilization) with the intent that early mortality syndrome (EMS), an acute thiamine deficiency mortality, would only occur at the highest OXY concentration. We assessed the effect of OXY and family on the occurrence of EMS and other embryonic mortality, and alevin growth dynamics up until 2weeks post emergence. EMS reached only 4% at the highest OXY concentration (400mg/L) where there was a significant decline in alevin length and yolkless alevin dry weight but not the dry weight of alevins whose yolk-sac was still attached. The dry weight of the yolk-sac as a percentage of total alevin dry weight was lower than controls at low concentrations of OXY (12.5, 25mg/L), but higher than controls at the highest concentration of OXY (400mg/L). OXY appeared to exert its effect on growth through reduced yolk-sac utilization although the mechanism(s) involved is unknown. Reduced growth and yolk-sac utilization of alevins resulting from thiamine deficiency may contribute to mortality through decreased ability of affected alevins to secure food and avoid predation. We conclude that even for very low EMS, alevin growth effects resulting from thiamine deficiency may pose a significant impediment to lake trout reproduction. [Copyright &y& Elsevier]

Abstract: Recent declines in growth and condition of several Great Lakes lake whitefish populations have raised concerns over potential impacts on juvenile physiological condition and ultimately recruitment. To test whether the condition of spawning adults influences juvenile condition via energy allocation dynamics, we partitioned the variation in age 0 juvenile physiological condition (i.e., growth in length and weight, whole-body moisture content, energy density, and protein content) among adult male and female (i.e., body condition, muscle moisture content, energy density, and protein content) and egg (i.e., wet and dry weight, moisture content, energy density, energy content per egg, and protein content) effects using redundancy analysis. Overall, a model that included sampling site, female condition, and egg quality explained 39% of the variation in juvenile physiological condition. After partitioning out the effects of females and eggs, site explained the most variation (23%). When other factors were accounted for, neither females (1.4%) nor eggs (2.7%) explained much variation in juvenile physiological condition. Of the variables studied, female muscle energy density, muscle moisture content, and egg moisture content were most closely associated with juvenile physiological condition. Our results suggest that parental effects, such as size, age, body condition, or body composition, may not be as important as extrinsic site-related effects or density-dependent effects in determining juvenile physiological condition. [Copyright &y& Elsevier]

Abstract: 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 1000m3 ±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. [Copyright &y& Elsevier]

Thiaminase activity of alewife (Alosa pseudoharengus) is variable across Lake Michigan, yet factors that contribute to the variability in alewife thiaminase activity are unknown. The fatty acid content of Lake Michigan alewife has not been previously reported. Analysis of 53 Lake Michigan alewives found a positive correlation between thiaminase activity and the following fatty acid: C22:1n9, sum of omega-6 fatty acids (Sw6), and sum of the polyunsaturated fatty acids. Thiaminase activity was negatively correlated with C15:0, C16:0, C17:0, C18:0, C20:0, C22:0, C24:0, C18:1n9t, C20:3n3, C22:2, and the sum of all saturated fatty acids (SAFA). Multi-variant regression analysis resulted in three variables (C18:1n9t, Sw6, SAFA) that explained 71% (R²=0.71, P<0.0001) of the variation in thiaminase activity. Because the fatty acid content of an organism is related is food source, diet may be an important factor modulating alewife thiaminase activity. These data suggest there is an association between fatty acids and thiaminase activity in Lake Michigan alewife. [ABSTRACT FROM AUTHOR]

Alewives (Alosa pseudoharengus), the major prey fish for Lake Ontario, contain thiaminase. They are associated with development of a thiamine deficiency in salmonines which greatly increases the potential for developing an early mortality syndrome (EMS). To assess the possible effects of thiamine deficiency on salmonine reproduction we measured egg thiamine concentrations for five species of Lake Ontario salmonines. From this we estimated the proportion of families susceptible to EMS based on whether they were below the ED20, the egg thiamine concentration associated with 20% mortality due to EMS. The ED20s were 1.52, 2.63, and 2.99 nmol/g egg for Chinook salmon (Oncorhynchus tshawytscha), lake trout (Salvelinus namaycush), and coho salmon (Oncorhynchus kisutch), respectively. Based on the proportion offish having egg thiamine concentrations falling below the ED20, the risk of developing EMS in Lake Ontario was highest for lake trout, followed by coho (O. kisutch), and Chinook salmon, with the least risk for rainbow trout (O. mykiss). For lake trout from western Lake Ontario, mean egg thiamine concentration showed significant annual variability during 1994 to 2003, when the proportion of lake trout at risk of developing EMS based on ED20 ranged between 77 and 100%. Variation in the annual mean egg thiamine concentration for western Lake Ontario lake trout was positively related (p < 0.001, r² = 0.94) with indices of annual adult alewife biomass. While suggesting the possible involvement of density-dependent changes in alewives, the changes are small relative to egg thiamine concentrations when alewife are not part of the diet and are of insufficient magnitude to allow for natural reproduction by lake trout. [ABSTRACT FROM AUTHOR]

Using laboratory experiments, we assessed the effect of temperature and predator density on consumption of trout eggs by crayfish. We quantified the effect of four temperature ranges (2-3, 4-5, 7-8, and 10-12°C) on consumption of lake trout (Salvelinus namaycush) and rainbow trout (Oncorhynchus mykiss) eggs by a native (Orconectes propinquus) and an exotic (Orconectes rusticus) crayfish found in the Great Lakes. Mean individual consumption ranged from 0.1 to 1.5 lake trout eggs per day and from 1.0 to 5.5 rainbow trout eggs per day, respectively. Temperature influenced consumption for O. rusticus feeding on rainbow trout eggs but not O. propinquus. The effect of conspecific predator competition on rainbow trout egg consumption was evaluated using three densities of crayfish (1, 5, 10 per tank). For O. rusticus, mean individual consumption rate was higher at the lowest crayfish density (1 crayfish/tank) than at medium (5 crayfish/tank) or high (10 crayfish/tank) densities. A similar conspecific effect was not evident in O. propinquus and total consumption per unit area increased with crayfish density. The effect of competition among crayfish species on consumption of rainbow trout eggs was examined by comparing feeding rates at high crayfish abundance levels in single and mixed species treatments. Mixed species interactions did not significantly alter crayfish feeding rates. Results from these experiments provide empirical data to aid in modeling how temperature and predator density affect lake trout egg predation rates in the field. [ABSTRACT FROM AUTHOR]

Invasion of the round goby Neogobius melanostomus in the Great Lakes has prompted investigation into qualitative and quantitative sampling strategies. Design of an optimal sampling strategy to monitor expanding round goby populations should consider the accuracy, precision, and associated costs of gears and their deployment strategies. The goal of this study was to compare three common, low-cost, readily available gear types used to sample round goby (gill nets, minnow traps, and trotlines) in terms of catch rates, size selectivity, and bycatch. During fall assessments, baited minnow traps were the most effective at collecting round goby, followed by trotlines and monofilament gill nets. Minnow traps were more selective of small round goby, while trotlines and gill nets were more selective of larger individuals. Bycatch associated with minnow traps and trotlines was lower than that associated with gill nets. Seasonal variation in gear effectiveness was apparent: during spring, gill nets caught 216 round goby and minnow traps caught none, while during the fall only 11 round goby were captured in gill nets and 868 were captured in minnow traps. During summer assessments, diel movements were evident, as gill nets set during periods of low or no light captured more round goby than those set during the day. The cost-benefit analysis indicated that passive gears had lower scores (i.e., were more cost-effective) than active gears. The financial cost of the three gears indicated that the cost per round goby varied among gears and seasons. Our results demonstrated that baited minnow traps set overnight were the most efficient, easily deployed, cost-effective gear and exhibited less variable catch rates during late summer and fall than either gill nets or trotlines. [ABSTRACT FROM AUTHOR]

Restoration of self-sustaining populations of lake trout is underway in all of the Great Lakes and Lake Champlain, but restoration has only been achieved in Lake Superior and in Parry Sound, Lake Huron. We evaluated progress toward restoration by comparing spawning habitat availability, spawner abundance, egg and fry density, and egg survival in Parry Sound in Lake Huron, in Lake Michigan, and in Lake Champlain in 2000-2003. Divers surveyed and assessed abundance of spawners at 5 to 15 sites in each lake. Spawning adults were sampled using standardized gill nets, eggs were sampled using egg bags, and fry were sampled using emergent fry traps and egg bags left on spawning reefs over-winter. Spawning habitat was abundant in each lake. Adult lake trout abundance was low in Lake Michigan and Parry Sound, and very high at one site in Lake Champlain. Egg deposition was lowest in Lake Michigan (0.4-154.5 eggs·m-2, median = 1.7), intermediate in Parry Sound (39-1,027 eggs·m-2, median = 278), and highest in Lake Champlain (0.001-9,623 eggs·m-2, median = 652). Fry collections in fry traps followed the same trend: no fry in Lake Michigan, 0.005-0.06 fry·trap-1 day-1 in Parry Sound, and 0.08-3.6 fry·trap-1 in Lake Champlain. Egg survival to hatch in overwinter egg bags was similar in Lake Michigan (7.6%) and Parry Sound (2.3-8.9%) in 2001-02, and varied in Lake Champlain (0.4-1.1% in 2001-02, and 1.8-18.2 in 2002-03). Lake trout restoration appears unlikely in northern Lake Michigan at current adult densities, and failure of restoration in Lake Champlain suggests that there are sources of high mortality that occur after fry emergence. [ABSTRACT FROM AUTHOR]

Rainbow trout Oncorhynchus mykiss in Cayuga Lake, New York, appear to be suffering from a thiamine deficiency because their progeny develop general weakness, loss of equilibrium, and increased mortality, which are prevented by treatment with thiamine. Thiamine status and its effect on adults are unknown. In 2000 and 2002, we captured, tagged, and released 64 and 189 prespawning rainbow trout, respectively, in Cayuga Inlet at a collection weir to evaluate their thiamine status and the effect of thiamine injection (150 nmol/g) on instream migration. Half of the rainbow trout in each year (32 in 2000 and 95 in 2002) were injected with thiamine and half were uninjected; all rainbow trout were released above the weir to continue their upstream migration, By means of electrofishing in 2000, we recaptured significantly more thiamine-injected (N = 7) than uninjected (N = 0) rainbow trout approximately 7.0-9.3 river kilometers upstream from the weir. In 2002, the concentration of thiamine in the muscle of rainbow trout collected above a 1.8-m cascade was significantly higher (mean ± SD = 5.47 ± 5.04 nmol/g; range = 1.0-13.8 nmol/g; N = 8) than that of rainbow trout collected either above a 1.0-m cascade (1.36 ± 0.71 nmol/g; range = 0.6-3.3 nmol/g; N = 16) or below the cascades (1.20 ± 0.46 nmol/g; range = 0.7-1.9 nmol/g: N = 5). The lowest concentration of thiamine observed in the muscle of rainbow trout collected upstream of the 1.8-m cascade was 1.0 nmol/g, suggesting that the threshold concentration required for rainbow trout to ascend the cascade was no more than that. Analyses of thiamine in the muscle of 26 untagged rainbow trout captured in Cayuga Inlet in 2002 showed that 16 fish (62%) had at least 1.0 nmol/g, which was apparently sufficient to support vigorous migration. [ABSTRACT FROM AUTHOR]

To understand the factors affecting natural recruitment of lake trout , we evaluated natural egg deposition, the rate of egg loss of seeded eggs, and the relationship of interstitial predators to egg mortality at a protected nearshore lake trout spawning area in Lake Michigan. Egg mortality and predator densities were evaluated with collection bags that were buried above the drop-off on spawning substrate at 1-, 3-, and 9-m depths. Habitat selection by spawning lake trout was probably related to the coverage by periphyton and zebra mussels given that abiotic characteristics of the spawning habitat such as slope (55- 65°), interstitial depth (30-50 cm), and substrate type did not differ across depths. The results of seeding eggs during spawning and recovering them throughout the incubation period (2-177 d) indicated that egg mortality was extremely high early in the spawning period: over 40% of seeded eggs were lost by 2 d and over 80% of the eggs were lost after only 2 weeks. The rate of egg loss declined significantly after the spawning period, possibly as a result of declining water temperature, which caused reduced predator activity, and ice cover, which reduced the impact of physical disturbance. The greatest proportions of seeded eggs were recovered at the shallowest depths (12.5 ± 1.2% [mean ± SE] at 1 m and 9.0 ± 1.5% at 3 m), where predator densities averaged 11.4 ± 1.8/m2; a significantly smaller proportion was recovered at 9 m (3.9 ± 1.2), where predator densities were highest (22.3 ± 2.0/m2). Because lake trout preferred the shallowest depth for spawning and predation was lowest at this depth, we conclude that this strategy improved the probability of egg survival. [ABSTRACT FROM AUTHOR]

Discusses a study which presented data on abundance and egg consumption by sculpins and crayfish in relation to egg abundance as determined in the previous studies. Result of conducting spatially and temporally extensive sampling; Factors that may contribute to the lack of natural recruitment of lake trout in Lake Ontario; Overview of sculpin egg consumption.

Examines the occurrence of a testicular anomaly in lake trout from the Great Lakes basin. How the anomaly was uni- and to a much lesser extent bilateral constriction along varying lengths of either testis.

Broodfish of Atlantic salmon Salmo salar were fed either thiamin-deficient diets fortified with 0.05% and 0.1% amprolium chloride (Amp, a thiamin antagonist) or thiamin-sufficient diets (0% Amp and ASD2-30, a U.S. Fish and Wildlife Service open-formula feed) for 6 months before spawning. We observed Cayuga syndrome (CS) only in the fry produced from broodfish fed the amprolium diets. The percent fry mortality due to CS was less than 1% in the 0.05% Amp group and was more than 3% in the 0.1% Amp group. Free thiamin was the predominant form of thiamin in the eggs of all broodfish; concentrations were two orders of magnitude greater than that of thiamin pyrophosphate (TPP) and thiamin monophosphate (TMP). Free thiamin was greatest in eggs of broodfish fed the thiamin-sufficient diets. Total thiamin and TMP in red blood cells (RBCs) of broodfish fed the thiamin-deficient diets were reduced to the initial levels by the end of the study. Levels of free thiamin in RBCs were similar in all treatment groups at spawning, as were levels of TPP. Amprolium feeding significantly reduced total thiamin levels in heart, liver, and muscle but not in kidney. Except for thiamin found in eggs, TPP was the predominant form of thiamin in all the other tissues, whereas free thiamin was the least predominant. The data support the hypothesis that thiamin deficiency may cause Cayuga syndrome in Atlantic salmon sac fry. The low incidence of the syndrome in this study may be due to the short duration of the feeding trial or to the low levels of amprolium added to the diets. [ABSTRACT FROM AUTHOR]

A maternally transmitted, noninfectious disease known as the Cayuga syndrome caused 100% mortality in larval offspring of wild-caught landlocked Atlantic salmon Salmo salar from several of New York's Finger Lakes. Survival of lake trout Salvelinus namaycush from Lakes Erie and Ontario was also impaired, but not until yolk absorption was nearly complete; moreover, mortality was greatly reduced relative to that of the salmon (range: 5-87%). Tissue concentrations of thiamine hydrochloride were severely reduced in these salmonid fish relative to unaffected control stocks. Afflicted Atlantic salmon treated with thiamine by yolk-sac injection or by bath immersion recovered completely from the Cayuga syndrome, as evidenced by the quantified reversal of abnormal swimming behaviors only 2 d after treatment and by the excellent survival (>95%) of the treated Atlantic salmon through 1.5 months of feeding. These data represent the first evidence of a vitamin deficiency causing the complete reproductive failure of an animal population in nature. These lethal vitamin deficiencies are presumably caused by a diet of alewives Alosa pseudoharengus, nonnative forage fishes of the herring family that exhibit high thiaminase activity. [ABSTRACT FROM AUTHOR]

Lake trout (Salvelinus namaycush) that received a physical shock between fertilization and hatching had higher mortality rates than unshocked lake trout embryos. Lowest survival occurred when embryos were shocked during the final stages of epiboly. Comparison of an inland lake stock and a Great Lakes stock indicated that the effect of shocking on embryo survival was stock specific. [ABSTRACT FROM PUBLISHER]

In 1994 and 1995, 180 lake trout (Salvelinus namaycush) eggs were collected from two spawning sites in southeastern Lake Erie. This provides the first evidence of spawning by lake trout in the lake since stocking began in 1975. Egg abundances (11 and 63 eggs/m2) were similar to the mean reported for natural spawning areas in Lake Ontario (52 eggs/m2). No spawning was evident at one site sampled in northeastern Lake Erie in 1995. [ABSTRACT FROM AUTHOR]