Lake Trout Eggs Research Articles

Use of Egg Traps to Investigate Lake Trout Spawning in the Great Lakes

Disk-shaped traps were used to examine egg deposition by lake trout (Salvelinus namaycush) at 29 sites in the Great Lakes. The main objectives were to; first, evaluate the disk trap as a device for sampling lake trout eggs in the Great Lakes, and second, summarize what has been learned about lake trout spawning through the use of disk traps. Of the 5,085 traps set, 60% were classified as functional when retrieved. Evidence of lake trout egg deposition was documented in each of the lakes studied at 14 of 29 sites. A total of 1,147 eggs were trapped. The percentage of traps functioning and catch per effort were compared among sites based on depth, timing of egg deposition, distance from shore, size of reef, and type of reef (artificial or natural). Most eggs were caught on small, shallow, protected reefs that were close to shore. Use of disk traps on large, shallow, unprotected offshore reefs or along unprotected shorelines was generally unsuccessful due to the effects of heavy wind and wave action. Making multiple lifts at short intervals, and retrieval before and re-deployment after storms are recommended for use in exposed areas. On large reefs, preliminary surveys to identify preferred lake trout spawning habitat may be required to deploy disk traps most effectively. Egg deposition by hatchery-reared fish was widespread throughout the Great Lakes, and the use of artificial structures by these fish was extensive.

Comparison of Lake Trout-Egg Survival at Inshore and Offshore and Shallow-Water and Deepwater Sites in Lake Superior

We incubated lake trout (Salvelinus namaycush) eggs over winter at shallow (10 m) and deep locations (20 m) on Gull Island Shoal, Lake Superior; at a shallow-water (10 m) site off the mainland (Bark Point); and in flowing Great Lakes water at two laboratories. Survival to hatch was significantly higher in the laboratories and averaged 80.9%. In Lake Superior, egg survival among incubators at all sites was significantly higher (P < 0.0001) for incubators that remained buried in spawning substrates (15.1–21.0%) than for incubators that were partially or completely exposed to water currents (1.0–12.6%). Egg survival for incubators that remained buried at the shallow-water sites was significantly higher at Bark Point (44.6%) than at Gull Island Shoal (21.0%). Egg survival among incubators that remained buried at the deep (14.4%) and shallow-water sites (21.0%) on Gull Island Shoal was not significantly different. Because incubators that were completely buried or partially exposed only appeared to differ in their degree of exposure, we concluded that survival of eggs in the lake was reduced by mechanical stress associated with water turbulence. Lower egg survival at Gull Island Shoal, a known lake trout-spawning site, was not expected and appeared to have been caused by a strong gale that occurred when these eggs were in late epiboly, a sensitive embryological stage. We present a hypothesis suggesting that lake trout recruitment in the Great Lakes is limited by availability of spawning habitat.

A Critical Review of the Effects of Contaminants on Early Life Stage (ELS) Mortality of Lake Trout in The Great Lakes

A review was done to assess whether epizootics of early life stage (ELS) mortality in Great Lakes lake trout (Salvelinus namaycush) that occurred during the late 1970s to the present, could have been related to the concentrations of major contaminants such as PCBs, DDT, PCDDs, and PCDFs measured in their eggs. Results of laboratory studies were used to establish mode of action, toxic effects, and minimum concentrations required to induce these effects by these chemicals. It appears unlikely that the more common causes of mortality, including reduced hatching, blue sac disease, and swim-up syndrome mortality in lake trout eggs were solely related to the contaminants measured in eggs and larvae. Laboratory studies suggest the concentrations required to induce increased hatching mortality and blue sac disease are much higher than levels measured in feral fish eggs. Swim-up syndrome has never been correlated with chemical exposure. Several alternate explanations relating to egg rearing conditions, nutrition, poor egg quality, and altered physiology are discussed. These factors may have interacted with the sublethal concentrations of contaminants to cause some of the observed mortality.

Assessment of Lake Trout Spawning Habitat and Egg Deposition and Survival in Lake Ontario

Identification of the amount of lake trout spawning habitat and its actual use by lake trout in Lake Ontario is important for re-establishment of this species. From a combination of hydrographic field data, bathymetry measurements, and video observations, 20 reputed spawning sites, 14 of which were considered to be historically important, were evaluated for possible use by lake trout. Based on preliminary evaluations 13 of the 20 sites were rejected for further study because of inappropriate substrate or excessive infilling of interstitial spaces. Additional, more intense evaluations were made of seven sites, five that were of historical importance and two that were man-made. These seven sites had areas of suitable spawning habitat of from 6 to 4,000 m2, minimal water depths of from 2.2 to 10.8 m, mean cobble diameters of 9.8–20.0 cm, and slopes of 20–45°. Lake trout egg densities, estimated from recoveries in egg nets deployed in 1992, ranged from a mean of 6 to 6,200 eggs m−2 and the highest densities were found at man-made sites. The actual egg deposition on the seven sites studied intensely amounted to only 0.0003 to 0.6% of the potential deposition if all the lake trout that survived from stocking within a 30 km radius of each site spawned there.Egg survival to the eyed stage ranged from 21 to 82% and was inversely related to wind fetch. Spawning was earlier in western than in eastern Lake Ontario and was related to the rates of fall cooling. Duration of the spawning period ranged from 1 to 39 days but the low estimates were from collections of only a few eggs. A swim-up mortality syndrome observed in eggs reared in a laboratory was high, ranging from 31.0 to 74.5%. The potential for lake trout restoration in Lake Ontario appears to be limited by a scarcity of good spawning sites, low egg deposition on spawning sites recognized by researchers, and excessive swim-up mortality.

Introduction of Lake Trout (Salvelinus namaycush) to Inland Lakes of Ontario, Canada: Factors Contributing to Successful Colonization

We evaluated the success of 183 introductions of lake trout (Salvelinus namaycush) in small inland lakes in Ontario, Canada. Our purpose was to identify variables associated with successful versus failed natural recruitment after introductions of hatchery-reared lake trout. Origin of donor stocks, angling regulations, geophysical and water quality characteristics, and fish species presence-absence of the recipient lakes were evaluated as possible factors contributing to colonization success. Origin of donor stock had some minor influence on the success of introduced lake trout in these lakes, but other factors, including angling, were also important. Closure of lakes to fishing was strongly associated with some successful introductions. MANOVA revealed differences in the geophysical and water quality variables, and fish community structures among the native, successful, and failed lakes. The lake groups were further distinguished by canonical variate analysis using either geophysical and water quality variables and/or presence-absence of fish species. Lakes were correctly classified to one of the three lake groups with 63-83% accuracy using a cross-validated, chance corrected, discriminant analysis. Lakes in which new lake trout populations failed to become established were smaller and shallower, had higher total dissolved solids, larger littoral areas, smaller hypolimnions, and richer fish communities, including more lake trout egg and juvenile predators, than lakes that were successfully colonized. Intensity of pre-dation by indigenous species was a possible cause of failure of introduced lake trout to establish self-sustaining populations. Similar fish communities in native and failed lakes suggested that invasion and colonization by lake trout was possibly determined by the order of arrival of colonizing species. This suggested that the present day Great Lakes fish communities, which have experienced a recent net gain in species, might be resistant to reestablishment of self-sustaining lake trout stocks.

Do Toxic Substances Pose a Threat to Rehabilitation of Lake Trout in the Great Lakes? A Review of the Literature

Toxic substances have been suspected of being one of the causes of Great Lakes lake trout reproductive failure. Because toxic substances are present in the Great Lakes basin, managers should be aware of the role of contaminants in preventing lake trout rehabilitation. This paper summarizes studies which have sought to establish a relation between toxic substances and lake trout mortality or morbidity, and offers recommendations for future research and management. The review suggests that exposure to toxic substances has the possibility of affecting the species’ rehabilitation. A variety of toxic substances, specifically organochlorine compounds, concentrated in lake trout eggs, fry, and the environment, have affected the hatching success of lake trout in the laboratory, but the strength of the relation between toxic substances and lake trout mortality and morbidity in the field remains unclear. In order to clarify this relation, more information is needed on lake trout physiology, biochemistry, behavior, and genetics. An interdisciplinary workshop should be convened to evaluate existing evidence by epidemiological methods, to set priorities for further research, and to develop management strategies.

The Effect of B-Vitamins on a Swim-up Syndrome in Lake Ontario Lake Trout

Collect ions of lake trout spawners and eggs were made in Lake Ontario to assess the ameliorative effects of several B-vitamins (thiamine, riboflavin, folic acid, nicotinic acid, pyridoxine hydrochloride) on mortality associated with swim-up syndrome. Vitamins were administered either by water immersion (1 gm/L to eggs from one female) or intraperitoneal injection (30 ppm to eggs from five females) into the yolk sac. Thiamine, but none of the other B-vitamins, was effective both in reversal and prevention of the clinical signs and mortality associated with the syndrome.

Progress Toward Lake Trout Restoration in Lake Michigan

Progress toward lake trout restoration in Lake Michigan is described through 1993. Extinction of the native lake trout fishery by sea lamprey predation, augmented by exploitation and habitat destruction, resulted in an extensive stocking program of hatchery-reared lake trout that began in 1965. Sea lamprey abundance was effectively controlled using selective chemical toxicants. The initial stocking produced a measurable wild year class of lake trout by 1976 in Grand Traverse Bay, but failed to continue probably due to excessive exploitation. The overall lack of successful reproduction lakewide by the late 1970s led to the development and implementation in 1985 of a focused inter-agency lakewide restoration plan by a technical committee created through the Lake Committee structure of the Great Lakes Fishery Commission. Strategies implemented in 1985 by the plan included setting a 40% total mortality goal lakewide, creating two large refuges designed to encompass historically the most productive spawning habitat and protect trout stocked over their home range, evaluating several lake trout strains, and setting stocking priorities throughout the lake. Target levels for stocking in the 1985 Plan have never been reached, and are much less than the estimated lakewide recruitment of yearlings by the native lake trout stocks. Since 1985, over 90% of the available lake trout have been stocked over the best spawning habitat, and colonization of the historically productive offshore reefs has occurred. Concentrations of spawning lake trout large enough for successful reproduction, based on observations of successful hatchery and wild stocks, have developed at specific reefs. Continued lack of recruitment at these specific sites suggests that something other than stotk abundance has limited success. Poor survival of lake trout eggs, assumed to be related to contaminant burden, occurred in the late 1970s and early 1980s, but survival has since increased to equal survival in the hatchery. A recent increase in lamprey wounding rates in northern Lake Michigan appears to be related to the uncontrolled build-up of lampreys in the St. Marys River a tributary of Lake Huron. If left uncontrolled, further progress toward restoration in the Northern Refuge may be limited.

Survival and Development of Lake Trout Eggs and Fry in Eastern Lake Ontario —in situ Incubation, Yorkshire Bar, 1989–1993

Restricted production of lake trout fry in eastern Lake Ontario limits recruitment and the establishment of a self-sustaining population. To examine the survival and development of eggs and fry, incubation studies were conducted from 1989 to 1993 in situ on Yorkshire Bar and in the laboratory with untreated surface water from Lake on the Mountain. Eggs were collected at spawning time (16 October–9 November, median 24 October) from Lakes Ontario and Manitou, fertilized, and held individually for an average of 162 days in 290 50-cell Plexiglas incubation chambers. On Yorkshire Bar, significantly more eggs died (P < 0.001, 1.65× mean absolute difference (Δx¯) = 14%), and regardless of egg source, there were fewer hatched fry than in the laboratory (P < 0.001, 0.63×, Δx¯ = 29%); 75% of the fry that hatched died early in the incubation period, and 42% of these completely decomposed and disappeared by the end of the incubation period, leaving empty incubation cells. Significantly fewer live fry were produced on Yorkshire Bar than in the laboratory (11.2% versus 69.2%, Δx¯ = 58%). Abundance of live fry was inversely related to cumulative thermal units (CTU). Increased exposure on the bar from 370 to 690 CTU decreased survival from 25% to 0. In eastern Lake Ontario, spawning has been observed at a mean water temperature of 11.5°C (29 October) but ranged between 12.7°C (19 October) and 8.8°C (14 November); fry survival on 1 May from these dates and temperatures would be 10%, 0%, and 21%, respectively. If the mean temperature at spawning were 2°C lower (9.5°C, 9 days later), production of fry on 1 May would be almost double (19% vs.10%). Spawning at lower temperatures would increase fry production on shoals like Yorkshire Bar. Temperature inversely affects fry survival, especially if the spawning substrate is degraded by organic sedimentation, which causes increased biological oxygen demand and reduces oxygen concentrations.

Hatching, Dispersal, and Bathymetric Distribution of Age-0 Wild Lake Trout at the Gull Island Shoal Complex, Lake Superior

We studied age-0 lake trout (Salvelinus namaycush) associated with spawning and nursery areas of the Gull Island Shoal complex in western Lake Superior. Post-emergent age-0 lake trout were captured on rocky spawning substrate with a 3-m beam trawl and at the nursery area with a bottom trawl from June to September 1990 and June to August 1991. Catch data suggested that age-0 lake trout move distances of 7–11 km to the nursery area over a 3-month period. Water currents, measured at Gull Island Shoal, may be a part of the transport mechanism. Examination of daily-growth increments on the sagittae and back-calculation from the date of capture revealed that most fish hatched between 6 June and 19 July in 1990 and between 30 April and 30 May in 1991. The duration of the hatch was 100 days in 1990 and 120 days in 1991, and the estimated incubation period is about 7 months for lake trout eggs at this site. Similar hatch-date distributions of age-0 captured on different sampling dates suggested that natural mortality was low.

Occurrence of a Swim-up Syndrome in Lake Ontario Lake Trout in Relation to Contaminants and Cultural Practices

Collections of lake trout eggs were made from Lake Ontario adults to evaluate the occurrence of a swim-up mortality syndrome and determine its relationship to cultural practices and egg contaminant burdens (PCBs, pesticides, dioxins, furans, polynuclear aromatic hydrocarbons, and trace metals). The syndrome, characterized by hyperexcitability, anorexia, loss of equilibrium, and eventual death, was observed in fry hatched from eggs of 21 of 24 (87.5%) females. Mortality due to the syndrome averaged 33.5% but was not correlated with fertilization rate, hatching rate, or any of six specific mortality types monitored in eggs and fry. Occurrence of the syndrome was not related to rearing temperature (i.e., 4°C vs. 8°C) or feeding (i.e., fed vs. unfed). No significant correlations existed between any of the contaminants measured and either swim-up syndrome mortality or the six mortality types monitored.

Predator-Prey Relations and Competition for Food Between Age-0 Lake Trout and Slimy Sculpins in the Apostle Island Region of Lake Superior

Slimy sculpins (Cottus cognatus) are an important component of the fish community on reefs and adjacent nursery areas of the Great Lakes and overlap spatially with age-0 lake trout (Salvelinus namaycush). Important interactions between these fishes are possible during the lake trout's first year of life, which could include predation on each other's eggs and larvae, and competition for food resources. We investigated the diets of age-0 lake trout and slimy sculpins on a lake trout spawning reef (Gull Island Shoal) and adjacent nursery area (near Michigan Island) in the Apostle Island region of western Lake Superior during June through September from 1988 through 1991. Organisms in stomachs of 511 lake trout and 562 sculpins were identified and counted. Of the 11 major food types found in age-0 lake trout stomachs from both areas, Mysis was the dominant food item (mean volume in stomachs=68%) and occurred in about 3/4 of the fish analyzed. Copepods, cladocerans, chironomid pupae, fish, and Bythotrephes were also common in the diet (frequency of occurrence > 4%). Diets of lake trout were more diverse on the reef than on the nursery area where Mysis dominated the diet. Slimy sculpins were only found in lake trout greater than 50 mm. Mysis was an important food item of slimy sculpins over the reef but not over the nursery area, where Diporeia was by far the most important taxon. A variety ofben-thic invertebrates (Asellus, chironomids, benthic copepods, and snails) comprised the bulk of the sculpin diet over the reef. Sculpins also ate lake trout eggs in November. Based on cluster analysis, diets were most similar over the reef where both consumed Mysis, calanoid copepods and chironomid pupae. Diets diverged over the nursery areas where sculpins were strictly benthic feeders and lake trout maintained their planktonic diet. In Lake Superior, where lake trout recruitment through natural reproduction has become well established, the coexistence of the two species appears amicable. However, in other Great Lakes with higher sculpin to lake trout ratios on a reef, the coexistence of the two species may be a bottleneck for age-0 lake trout survival beginning with egg deposition and ending when age-0 lake trout move off the reef and the two species no longer compete for a common food resource.

The Relation Between Reproductive Capacity of a Lake Trout Population and the Apparent Availability of Spawning Habitat in Megisan Lake, Ontario

To compare the number of lake trout eggs deposited at spawning areas to the reproductive potential of a lake trout, Salvelinus namaycush, population, I estimated the area potentially available for spawning, the area used for spawning, the egg deposition rate, and the egg production potential of the lake trout population in Megisan Lake, Ontario. Megisan Lake, a 616 ha glaciated lake with a self-sustaining population of lake trout contained about 3,300 m2 of habitat apparently suitable for spawning. Lake trout deposited eggs in only about 840 m2 of this habitat. Egg densities estimated with buried egg-collection trays and an air-lift sampler were not significantly different (P < 0.05). Mean egg deposition estimated in 1989 from collections made at several spawning sites was 299 (sd = 42) eggs *m−2. There was no significant relationship between the density of lake trout eggs and water depth over the range, 0.2 to 1.2 m, in which eggs were found. The estimated total egg deposition (approximately 250,000 eggs) from our spawning survey was less than the mean egg production potential (718,300) of the estimated number of female lake trout but within the range for the female population. I was unable to use measures of substrate size, water depth or depth of interstices to differentiate potential and used spawning habitat.

Limitations to Lake Trout (Salvelinus namaycush) Rehabilitation in the Great Lakes Imposed by Biotic Interactions Occurring at Early Life Stages

We examine evidence that biotic factors, particularly predation, may be limiting early survival of wild lake trout (Salvelinus namaycush) juveniles in many areas of the Great Lakes. The Great Lakes contain numerous potential predators of lake trout eggs and fry, some of which are recent invaders, and most of which were probably absent when lake trout most recently re-invaded the Great Lakes after the last ice age. Simple quantitative models of predation suggest that plausible assumptions about prey densities, predator feeding rates, and duration of exposure of predator to prey can lead to very high estimates of predation mortality, in some instances approaching 100%. Indirect evidence from inter-Great Lake comparisons and inland lake examples also suggest that biotic factors may impede successful lake trout colonization. Our synthesis of the evidence leads to recommendations for research to better define field feeding rates of lake trout egg and fry predators and comparative studies of densities of potential egg and fry predators on lake trout spawning reefs. Management options should be designed to provide useful information as well as achieve short-term goals. From a management standpoint we recommend that: newly constructed lake trout reefs should be placed well away from concentrations of potential predators; offshore spawning reefs should be stocked; salmonine stocking, nutrient abatement, and commercial harvest of alewives should all be considered as options to enhance survival of young lake trout; hatchery lake trout should not be stocked at sites where wild lake trout are showing signs of recovery; and exotic species expansions or introductions must be curtailed to maintain or improve on our recent successes in lake trout rehabilitation.

Survival of Lake Trout Eggs on Reputed Spawning Grounds in Lakes Huron and Superior: in situ Incubation, 1987–1988

Lake trout reproduce widely in Lake Superior but little in Lake Huron. We examined whether survival of lake trout eggs and fry in either lake was reduced by physical disturbances and swim-up mortality. Eggs were collected from feral lake trout in Lake Superior and placed in 108 plastic incubators. A total of 48 incubators was set at Partridge Island Reef in southern Lake Superior, 48 were set at Port Austin Reef in southern Lake Huron, and 12 were held as controls inflowing well water at a laboratory. Survival-to-hatching of these eggs at Partridge Island Reef (18%) was significantly different from that at Port Austin Reef (43%) and significantly different in the laboratory (88%) from that at either reef (P < 0.05). During egg-fry incubation from 28 October 1987 to 5 May 1988, 11–18 cm of sediment accumulated in sediment traps placed on the reefs but < 1 cm of sediment was present on each reef in May 1988. Analysis showed that 44% of the eggs at Port Austin Reef and 28% of those at Partridge Island Reef were buried and killed by sediments. During the first week after deployment, mean wave energy was 90% higher at Partridge Island Reef and significantly different from that at Port Austin Reef. Wave energy may be a habitat condition that makes Partridge Island Reef less suitable than Port Austin Reef for incubation of lake trout eggs. Fry from eggs incubated at all three sites experienced no swim-up mortality. We conclude that in 1987–88 habitat conditions required for survival of lake trout eggs were more suitable at Port Austin Reef than at Partridge Island Reef.

Accumulation of polychlorinated biphenyl congeners from lake champlain sediments by Mysis relicta

AbstractPolychlorinated biphenyl (PCB) levels in lake trout (Salvelinus namaycush) from Lake Champlain often exceed the F.D.A. “tolerance level” of 2 μg/g (wet weight). Of added concern are recent studies that suggest a relationship between the dioxin‐like properties of non‐ortho‐substituted PCB congeners and impaired lake trout egg hatchability. Dietary accumulation of PCBs is thought to be an important exposure route for fish. The epibenthic freshwater shrimp Mysis relicta is an integral part of the benthic and pelagic food web in Lake Champlain and may act as a link between PCBs in sediments and lake trout. Previous investigations have shown that diurnal migrations of mysids enhance the movement and distribution of toxic contaminants, effectively coupling the benthic and pelagic zones. The objective of this research was to examine the role contaminated sediments play in the transfer of PCBs to mysids. Bioaccumulation was assessed by exposing mysids to such sediments in two ways: (a) with organisms screened from sediments; and (b) with organisms in direct contact with sediments. Accumulation of PCBs over the course of the 24‐day exposure period was examined on the following days: 0, 3, 6, 12, 21, and 24. Eighty‐nine individual PCB congeners were measured in tissue and sediment. Mysids in direct contact with sediments accumulated significantly higher levels of PCBs than did organisms screened from sediments. Mysids accumulated substantial levels of PCBs, suggesting they may play an important part in the transfer of PCBs from sediments into the Lake Champlain food web. It is clear from this research that sediments can play a critical role in the accumulation of PCBs by mysids.

Translocation of 2,3,7,8-Tetrachlorodibenzo-p-dioxin from Adult Female Lake Trout (Salvelinus namaycush) to Oocytes: Effects on Early Life Stage Development and Sac Fry Survival

There were no signs of overt toxicity in sexually mature female lake trout (Salvelinus namaycush) exposed to either a control or a 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-containing diet for 11 wk prior to spawning. At spawning the maternally derived egg TCDD concentrations were 42 ± 4 and 43 ± 6% of the maternal skeletal muscle TCDD concentration on a lipid and wet weight basis, respectively. Egg TCDD concentrations of 233–387 pg TCDD/g egg (wet weight) resulted in nonviable oocytes, while concentrations of 50–152 pg/g resulted in a dose-related increase in sac fry mortality associated with yolk sac edema, craniofacial alterations, and arrested development, resembling blue-sac disease. The dose–response relationship for sac fry mortality associated with blue-sac disease was essentially identical to that observed when fertilized lake trout eggs were exposed to either waterborne or injected TCDD. The no and lowest observable adverse effect levels for sac fry mortality were 23 and 50 pg/g (maternal egg exposure), 34 and 40 pg/g (waterborne egg exposure), and 44 and 55 pg/g (egg injection). LD50s, based on egg TCDD concentration, were 58 (36–90), 69 (64–75), and 80 (68–91) pg/g (95% fiducial limits) following egg exposure via maternal, waterborne, or injection routes, respectively.

Maternal Transfer of Organochlorine Compounds in Salmonines to Their Eggs

To investigate relationships between the concentrations of lipophilic organochlorine compounds in salmonine fish and their eggs and the role of lipids in maternal transfer of these compounds, muscle tissue and fertilized eggs from chinook salmon (Oncorhynchus tshawytscha) and lake trout (Salvelinus namaycush) were analyzed using gas chromatography. The concentrations of organochlorine compounds in the muscle tissue of the gravid fish were significantly correlated with the concentration of these compounds in the eggs (P &lt; 0.01). Egg lipid concentrations were species specific, poorly correlated with muscle tissue lipid concentration, and did not appear to influence organochlorine compound transfer to the eggs. Total concentrations of PCBs and p,p′-DDE concentrations in chinook salmon eggs and total concentrations of PCBs, p,p′-DDE, and dieldrin in lake trout eggs were significantly correlated with the concentrations of these compounds in the muscle tissue of the gravid fish. Consequently, spatial differences or temporal changes in the concentrations of lipophilic compounds in chinook salmon or lake trout may significantly influence the concentrations of these compounds in their eggs.

An egg injection method for assessing early life stage mortality of polychlorinated dibenzo- p-dioxins, dibenzofurans, and biphenyls in rainbow trout, ( Oncorhynchus mykiss)

To characterize the risk that polychlorinated dibenzo- p -dioxins (PCDDs), dibenzofurans (PCDFs), and biphenyls (PCBs) pose to salmonid early life stage survival, we developed a method to expose rainbow trout ( Oncorhynchus mykiss ) eggs to graded doses of PCDD, PCDF, and PCB congeners, using 2,3,7,8-tetrachlorodibenzo- p -dioxin (TCDD) as a prototype. Rainbow trout eggs were injected 24–50 h post-fertil ization with 0.2 μl of 50 mM phosphatidylcholine (PC) liposomes (control) or 0.2 μl of 5–7 graded doses of TCDD incorporated into 50 mM PC liposomes. Injection volume never exceeded 0.6% egg volume. Immediately following injection, the injection site was sealed with Super glue R , resulting in 92–97% of TCDD dose retained by the egg. Following both egg injection and waterborne egg exposure. TCDD toxicity in rainbow trout was manifested by half-hatching mortality but predominantly by sac fry mortality associated with hemorrhages, pericardial edema, and yolk sac edema. TCDD LD 50 s, following injection and waterborne exposure of rainbow trout eggs, were 421 (331–489) and 439 (346–519) pg TCDD/g egg (LD 50 , 95% fiducial limits), respectively. As in rainbow trout, TCDD toxicity in lake trout ( Salvelinus namaycush ) following the same two routes of exposure was manifested by half-hatching mortality but predominantly by sac fry mortality preceded by hemorrhages and yolk sac edema. LD 50 s, based on the dose of TCDD in lake trout eggs, were 47 (21–65) and 65 (60–71) pg/g following injection and waterborne exposure, respectively. The egg injection method is ideal for assessing the relationship between early life stage mortality in rainbow trout and graded egg doses of individual PCDD, PCDF, or PCB congeners.

Potencies of polychlorinated dibenzo- p-dioxin, dibenzofuran, and biphenyl congeners, relative to 2,3,7,8-tetrachlorodibenzo- p-dioxin, for producing early life stage mortality in rainbow trout ( Oncorhynchus mykiss)

The presence of polychlorinated dibenzo- p-dioxins (PCDDs), dibenzofurans (PCDFs), and biphenyls (PCBs) in feral lake trout eggs ( Salvelinus namaycush) may increase the risk of lake trout early life stage mortality in the Great Lakes. To assess the combined toxicity of PCDDs, PCDFs, and PCBs to lake trout early development, toxic potencies, relative to 2,3,7,8-tetrachlorodibenzo- p-dioxin (2,3,7,8-TCDD), were determined for individual PCDD, PCDF, and PCB congeners, based on rainbow trout ( Oncorhynchus mykiss) early life stage mortality. Newly fertilized rainbow trout eggs were injected with graded doses of 2,3,7,8-TCDD, or a PCDD, PCDF, or PCB congener. LD 50 values were determined based on the egg dose that caused mortality from hatching onset to swim-up. Toxic equivalency factors (TEFs) were calculated as 2,3,7,8-TCDD LD 50/congener LD 50. TEFs were for PCDDs: 2,3,7,8-TCDD = 1.0; 1,2,3,7,8-PeCDD = 0.730;and 1,2,3,4,7,8-HxCDD = 0.319; for PCDFs: 2,3,4,7,8-PeCDF = 0.359; 1,2,3,4,7,8-HxCDF = 0.280; 1,2,3,7,8-PeCDF = 0.034; and 2,3,7,8-TCDF = 0.028; and for PCBs: 3,3',4,4',5-PeCB = 0.005; 3,3',4,4'-TCB = 0.00016; 2,3,3',4,4'-PeCB and 2,3',4,4',5-PeCB < 0.00007. For PCDDs, fish-specific TEFs were 10- to 100-fold higher than TEFs determined in H4IIE rat hepatoma cells, but were similar to TEFs proposed for risk assessment. For PCDFs, fish specific TEFs were similar to TEFs determined in H4IIE cells and TEFs proposed for risk assessment. However, the most significant finding was that for the coplanar PCBs and mono- ortho-chlorinated analogues of the coplanar PCBs fish-specific TEFs were 1 14 to 1 80 less than both those determined in H4IIE cells and proposed for risk assessment. Using these fish-specific TEFs, the risk associated with exposure of early life stages of Sake trout to complex mixtures of PCDDs, PCDFs, and PCBs in the Great Lakes can be estimated.