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At least 163 records · Page 9Linked to original sources
USGS2005

Ichthyophonus in Puget Sound rockfish from the San Juan Islands archipelago and Puget Sound, Washington, USA

In vitro explant cultures identified Ichthyophonus in 10.9% of 302 Puget Sound rockfish Sebastes emphaeus sampled from five sites in the San Juan Islands archipelago and Puget Sound, Washington, in 2003. None of the infected fish exhibited visible lesions and only a single fish was histologically positive. Significantly more females were infected (12.4%) than males (6.8%), and while infected males were only detected at two of the five sites, infected females were identified at all sites, with no significant differences in infection prevalence. Genomic sequences of Ichthyophonus isolates obtained from Puget Sound rockfish, Pacific herring Clupea pallasii, and Yukon River Chinook salmon Oncorhynchus tshawytscha were identical in both the A and B regions of the small subunit 18S ribosomal DNA but were different from Ichthyophonus sequences previously isolated from four different species of rockfish from the northeastern Pacific Ocean. Ichthyophonus in Puget Sound rockfish may not have been previously detected because the infection is subclinical in this species and earlier investigators did not utilize in vitro techniques for diagnosis of ichthyophoniasis. However, since clinical ichthyophoniasis has recently been identified in several other species of northeast Pacific rockfishes, it is hypothesized that this either is an emerging disease resulting from changing marine conditions or the result of introduction by infected southern species that appear during periodic El Nin??o events. ?? Copyright by the American Fisheries Society 2005.

Washiginton↗
USGS2005

Using fish biomarkers to monitor improvements in environmental quality

The percentage of splenic tissue occupied by macrophage aggregates and hepatosomatic index (HSI) were evaluated in rock bass Ambloplites rupestris from Burlington Harbor, Vermont. In 1992, fish collected from the inner Burlington Harbor area had a significantly greater percentage of splenic tissue occupied by macrophage aggregates and greater HSI than did fish from reference sites. These biomarkers often are correlated with exposure to various contaminants (e.g., polychlorinated biphenyls, polycyclic aromatic hydrocarbons, and some heavy metals, which were found in Burlington Harbor sediments during surveys in 1990 and 1991). Contaminants are believed to have entered Burlington Harbor through the city's main sewage treatment plant, which discharged effluent into the harbor for many years. In 1994, the city completed a significant upgrade of this treatment plant, which included an extension of the effluent pipe beyond the inner harbor area. In 1999, rock bass were again collected from Burlington Harbor as an index of whether there was any improvement in environmental quality. Our data showed a significantly lower percentage of splenic tissue occupied by macrophage aggregates and significantly lower HSI among nine age-4 rock bass in 1999 than among six age-4 rock bass in 1992. The significant changes in these biomarkers suggest decreased exposure to contaminants. Our study reinforces the value of macrophage aggregates and HSI as biomarkers of environmental contamination, and the correlation with remedial action shows their potential utility in documenting improvements in environmental conditions. ?? Copyright by the American Fisheries Society 2005.

Journal of Aquatic Animal Health↗
USGS2005

Thiamine status in adult salmonines in the Great Lakes

In 1996 and again in 1999, hatchery personnel noted that some Lake Michigan coho salmon Oncorhynchus kisutch from fall spawning runs on the Platte River weir exhibited abnormal wiggling behavior that was similar to the behavior exhibited by thiamine-deficient Atlantic salmon Salmo salar , from the Baltic Sea. Samples of eggs or gonads, muscle, and liver from salmon and lake trout Salvelinus namaycush exhibiting abnormal behaviors were collected to determine the extent to which the behaviors were related to a thiamine deficiency. We compared these values with those found in normally behaving fish that produced offspring with high embryonic survival. In all adult fish exhibiting abnormal behavior, tissue residues of thiamine were among the lowest observed in the Great Lakes. Where embryonic survival was assessed, abnormal adult behavior was also associated with very high levels of offspring mortality due to early mortality syndrome. While the overall ecological significance remains to be determined, it appears that adult fish also exhibit neurological dysfunction and mortality associated with thiamine deficiency.

Journal of Aquatic Animal Health↗
USGS2005

Intraovum infection caused by Flavobacterium psychrophilum among eggs from captive Atlantic salmon broodfish

This study indicated that the bacterium Flavobacterium psychrophilum induced an infection within eggs of Atlantic salmon Salmo salar that were held at federal New England restoration facilities. The pathogen, which originated from the Connecticut, Penobscot, Machias, East Machias, Dennys, Narraguagus, and Sheepscot rivers, was obtained from these eggs at concentrations that ranged from 5.0 ?? 102 to 2.5 ?? 108 colony-forming units per gram of egg, despite successive treatments with povidone iodine (I2). Treatments consisted of 50 mg/L of water for 30 min, then 100 mg/L for 10 min, followed at the eyed egg stage by 100 mg/L for 60 min. Collectively, 63% of the egg lots (77 of 122) obtained from paired matings of these captive broodfish were infected; 39% of these lots contained 10 or fewer infected eggs (60 eggs sampled per lot), and less than 10% of the lots contained more than 20 positive eggs. Consequently, standard iodophor disinfection procedures were ineffective. Eggs were positive from each of the river-specific captive brood populations during both of the spawning cycles that were studied. I concluded that F. psychrophilum established an intraovum infection that was prevalent among captive brood lots from different New England watersheds.

Journal of Aquatic Animal Health↗
USGS2006

An examination of environmental factors associated with Myxobolus cerebralis infection of wild trout in Pennsylvania

Salmonid whirling disease, caused by the myxosporean parasite Myxobolus cerebralis , was first observed in the United States in 1956 in central Pennsylvania. The parasite was subsequently discovered at several culture facilities throughout the state, and widespread distribution of this parasite via the stocking of subclinically infected brook trout Salvelinus fontinalis , rainbow trout Oncorhynchus mykiss , and brown trout Salmo trutta has been assumed. Although no monitoring of wild populations occurred until the late 1970s, it is a common belief that epizootics of whirling disease, now realized in the Intermountain West, are unlikely to have occurred in Pennsylvania. We conducted a review of historical information and a synoptic survey aimed at identifying factors that may prevent whirling disease outbreak in this region, reasoning that such information might be useful in identifying management strategies for populations affected by this parasite. Here we present data on parasite prevalence, fish populations, stream attributes, and the genetics of Tubifex tubifex (the obligate oligochaete host for the parasite) to evaluate various hypotheses proposed for low whirling disease impact in the region. We did not find clear associations between factors such as stream gradient, the genetics of T. tubifex populations, or the composition of resident trout populations and the pattern of M. cerebralis occurrence in Pennsylvania. We suggest that this pattern may be best explained by the association between T. tubifex host populations and point sources of organic enrichment. The potential restriction of T. tubifex populations to locations near sources of organic enrichment may be a factor in explaining why whirling disease has not been observed to cause population declines among wild trout in this region and should be further investigated.

Journal of Aquatic Animal Health↗
USGS2006

Myxobolus cerebralis in native cutthroat trout of the Yellowstone Lake ecosystem

The exotic parasite Myxobolus cerebralis was first detected in native adult Yellowstone cutthroat trout Oncorhynchus clarkii bouvierii from Yellowstone Lake in 1998, seriously threatening the ecological integrity of this pristine, naturally functioning ecosystem. We immediately began to assess the prevalence and spatial extent of M. cerebralis infection in Yellowstone cutthroat trout within Yellowstone Lake and to determine the infection risk of age-0 Yellowstone cutthroat trout, the relative abundance and actinospore production of lubificid worms, and the basic environmental characteristics of tributaries. During 1999-2001, juvenile and adult Yellowstone cutthroat trout were infected throughout Yellowstone Lake; the highest prevalence (15.3-16.4%) occurred in the northern and central regions. Exposure studies in 13 streams indicated that Pelican and Clear creeks and the Yellowstone River were positive for M. cerebralis; the highest prevalence (100%) and severity was found in Pelican Creek during mid-July. Sexually mature individuals of the oligochaete Tubifex tubifex were most abundant in early summer, were genetically homogenous, and were members of a lineage known to produce moderate to high levels of M. cerebralis triactinomyxons. Only 20 of the 3,037 sampled tubificids produced actinospores after 7 d in culture, and none of the actinospores were M. cerebralis. However, one non-actinospore-producing T. tubifex from Pelican Creek tested positive for M. cerebralis by polymerase chain reaction. Stream temperatures at Pelican Creek, a fourth-order, low-gradient stream, were over 20??C during the first exposure period, suggesting that T. tubifex were capable of producing triactinomyxons at elevated temperatures in the wild. Although the infection of otherwise healthy adult Yellowstone cutthroat trout within Yellowstone Lake suggests some resistance, our sentinel cage exposures indicated that this subspecies may be more susceptible to whirling disease than previous laboratory challenges have indicated, and M. cerebralis may be contributing to a significant recent decline in this population. ?? Copyright by the American Fisheries Society 2006.

Wyoming↗
USGS2006

Virulence comparisons of infectious hematopoietic necrosis virus U and M genogroups in sockeye salmon and rainbow trout

Infectious hematopoietic necrosis virus (IHNV) is an aquatic rhabdovirus that infects salmonids in the Pacific Northwest of the United States, Europe, and Asia. Isolates of IHNV have been phylogenetically classified into three major viral genogroups, designated U, M, and L. To characterize virulence of IHNV in the context of these three viral genogroups, seven strains of IHNV (three U genogroup strains, three M strains, and one L strain) were compared for their pathogenicity in juvenile sockeye salmon Oncorhynchus nerka, kokanee (lacustrine sockeye salmon), and rainbow trout O. mykiss. Fish were waterborne-exposed to the different viral strains, and virulence was assessed by comparing mortality curves and final cumulative percent mortality (CPM) in both species of fish at 10??C and 15??C. In sockeye salmon and kokanee, the U genogroup virus types were extremely virulent, causing average CPMs of 69-100%, while the M genogroup virus types caused very little or no mortality (CPM = 0-4%). The endangered Redfish Lake sockeye salmon stock exhibited extreme differences in susceptibility to the U and M genogroups. Conversely, in two stocks of rainbow trout, the M genogroup virus types were more virulent, inducing average CPMs of 25-85%, while the U genogroup viruses caused lower mortality (CPM = 5-41%). In both fish species, the single L genogroup strain caused low to intermediate mortality (CPM = 13-53%). Viral glycoprotein sequence comparisons of the seven challenge strains revealed three amino acid sites (247, 256, and 270) that consistently differed between the U and M genogroups, possibly contributing to pathogenicity differences. ?? Copyright by the American Fisheries Society 2006.

Journal of Aquatic Animal Health↗
USGS2006

An isolate of Piscirickettsia salmonis from white seabass is fully virulent for coho salmon

The virulence of the WSB-98 isolate of Piscirickettsia salmonis from white seabass Atractoscion nobilis was compared with that of the American Type Culture Collection type strain LF-89, which was originally isolated from coho salmon Oncorhynchus kisutch in Chile. In controlled laboratory challenges of juvenile coho salmon, the isolate from white seabass exhibited virulence that was equal to or greater than that of LF-89. The cumulative percent mortality (CPM) was similar between groups of coho salmon receiving an intraperitoneal injection of WSB-98 at 104.5 tissue culture infectious dose with 50% endpoint (TCID50)/fish (CPM = 98%) or an injection of LF-89 at 104.8 TCID50/fish (CPM = 95%). The mean day to death of 9.3 d for WSB-98 and 18.6 d for LF-89, however, differed significantly (P < 0.0001) between the two isolates. The virulence of an isolate of P. salmonis from white seabass for a salmonid species is consistent with the hypothesis that nonsalmonids can serve as natural marine hosts for the bacterium and potential sources for infection of salmonids. ?? Copyright by the American Fisheries Society 2006.

Journal of Aquatic Animal Health↗
USGS2007

Mycobacterial infections in striped bass from Delaware Bay

Eighty striped bass Morone saxatilis were obtained from Delaware Bay using commercial gill nets set adjacent to Woodland Beach (n = 70) and Bowers Beach (n = 10) in December 2003. Fish were examined for gross lesions. Total lengths (TLs) and eviscerated weights were determined to calculate condition factors (K). Portions of spleens were aseptically harvested for bacterial culture, and portions of spleens, kidneys (anterior and posterior), livers, and gonads were obtained for histological examination. The size distribution of the striped bass was relatively homogeneous; the mean TL was about 600 mm for all samples. Mean K exceeded 0.95 in all samples and was not significantly different (P > 0.05) among samples. Significant differences in mycobacterial infection prevalence (P ??? 0.05) were observed among samples; samples obtained at Woodland Beach (WB) on December 10 (53.8%, n = 13) and December 17 (7.1%, n = 42) exhibited the most striking differences in prevalence. Mycobacterial infection intensity ranged from 1 ?? 102 to 1 ?? 107 colony-forming units per gram of spleen. Acanthocephalan infection prevalence and intensity, non-acid-fast bacterial infection prevalence, and fish sex ratio were also significantly different among the samples (P ??? 0.05). Similar to the mycobacterial infections, differences in sex ratio, acanthocephalan infection, and non-acid-fast bacterial infection were observed between the WB samples taken on December 10 and 17. However, no significant associations (P > 0.05) were observed between sex ratio or these infections and mycobacterial infection. The differences in bacterial and parasite infection prevalence and intensity and fish sex ratio in some samples indicate that these fish had a different history and that the epizootiology of mycobacterial infection in striped bass from Delaware Bay may be relatively complex. ?? Copyright by the American Fisheries Society 2007.

Journal of Aquatic Animal Health↗
USGS2007

Thiamine and fatty acid content of walleye tissue from three southern U.S. reservoirs

We determined the thiamine concentration in egg, muscle, and liver tissues of walleyes Sander vitreus and the fatty acid content of walleye eggs from three southern U.S. reservoirs. In two Tennessee reservoirs (Dale Hollow and Center Hill), in which there were alewives Alosa pseudoharengus in the forage base, natural recruitment of walleyes was not occurring; by contrast in Lake James Reservoir, North Carolina, where there were no alewives, the walleye population was sustained via natural recruitment. Female walleye tissues were collected and assayed for thiamine (vitamin B1) and fatty acid content. Thiamine pyrophosphate was found to be the predominant form of thiamine in walleye eggs. In 2000, mean total egg thiamine concentrations were similar among Center Hill, Dale Hollow, and Lake James reservoirs (2.13, 3.14, and 2.77 nmol thiamine/g, respectively). Egg thiamine concentration increased as maternal muscle (r 2 = 0.73) and liver (r2 = 0.68) thiamine concentration increased. Walleye egg thiamine does not appear to be connected to poor natural reproduction in Tennessee walleyes. Threadfin shad Dorosoma petenense, which are found in all three reservoirs, had higher thiaminase activity than alewives. Six fatty acids differed among the walleye eggs for the three reservoirs. Two were physiologically important fatty acids, arachidonic acid (20:4[n-6]) and docosahexaenoic acid (22:6[n-3]), which are important eicosanoid precursors involved in the regulation of biological functions, such as immune response and reproduction. ?? Copyright by the American Fisheries Society 2007.

Journal of Aquatic Animal Health↗
USGS2007

Genetic diversity of infectious hematopoietic necrosis virus from Feather River and Lake Oroville, California, and virulence of selected isolates for Chinook salmon and rainbow trout

Infectious hematopoietic necrosis virus (IHNV) is a significant pathogen of young salmonid fishes worldwide but particularly within the historical range of the Pacific Northwest and California. In the Sacramento and San Joaquin River drainages of California, IHNV outbreaks in juvenile Chinook salmon Oncorhynchus tshawytscha have been observed regularly at large production hatcheries, including Coleman National Fish Hatchery (established in 1941) and Feather River State Fish Hatchery (FRH; established in 1967), since facility operations began. Recent severe epidemics at the FRH in 1998 and 2000-2002 prompted investigations into the characteristics and potential sources of virus at this facility. Both phylogenetic analyses of a variable portion of the glycoprotein gene and serologic comparisons based on neutralization with three polyclonal rabbit sera were used to characterize 82 IHNV isolates from the Feather River watershed between 1969 and 2004. All isolates examined were in the L genogroup and belonged to one of three serologic groups typical of IHNV from California. The IHNV isolates from the Feather River area demonstrated a maximum nucleotide sequence divergence of 4.0%, and new isolates appeared to emerge from previous isolates rather than by the introduction of more diverse subgroups from exogenous sources. The earliest isolates examined from the watershed formed the subgroup LI, which disappeared coincidently with a temporal shift to new genetic and serologic types of the larger subgroup LII. Experimental challenges demonstrated no significant differences in the virulence for juvenile Chinook salmon and rainbow trout O. mykiss from selected isolates representing the principal types of IHNV found historically and from recent epidemics at FRH. While most isolates were equally virulent for both host species, one isolate was found to be more virulent for Chinook salmon than for rainbow trout. ?? Copyright by the American Fisheries Society 2007.

Journal of Aquatic Animal Health↗
USGS2008

Effectiveness and retention of thiamine and its analogs administered to steelhead and landlocked Atlantic salmon

We investigated the feasibility of enhancing the reproduction of steelhead Oncorhynchus mykiss and landlocked Atlantic salmon Salmo salar in lakes where the consumption of alewives Alosa pseudoharengus and other forage fishes containing thiaminase can cause them to become thiamine deficient and thereby reduce the survival of their fry. We evaluated feeding fingerling steelhead excess thiamine hydrochloride (THCl) for 1 or 2 weeks or equimolar amounts of thiamine mononitrate, thiamine-tetrahydrofurfuryl-disulfide, benfotiamine, or dibenzoyl thiamine (DBT). We found minimal internal reserves of thiamine after 6 months. We also compared the ability of injections of thiamine and its analogs to prevent mortality in thiamine-deficient steelhead and Atlantic salmon sac fry and found all forms to be effective, although benfotiamine was the least effective on an equimolar basis. Further, we injected yearling steelhead and found that DBT was tolerated at approximately 11,200 nmol/g of body weight, about 10 times more than thiamine in any other form. When yearling steelhead were injected with near-maximal doses of thiamine hydrochloride and several analogs and then fed a thiamine-deficient diet, DBT was retained for approximately 2 years - in contrast to other forms, which were retained for less than about 6 months. Therefore, these results suggest that neither feeding nor injecting young hatchery salmonids with DBT is likely to enhance their reproduction for more than 2 years after stocking. However, injecting DBT in nearly mature fish (either cultured fish from hatcheries or wild fish captured in lakes) may provide them with enough thiamine to successfully spawn within 2 years even though they consume mainly thiaminase-containing forage fishes. ?? Copyright by the American Fisheries Society 2008.

Journal of Aquatic Animal Health↗
USGS2008

Evaluating the effect of stressors on thiaminase activity in alewife

No consistent explanation has been found for the variability in the thiaminase activity of alewives Alosa pseudoharengus despite the role of alewife thiaminase in large-scale salmonine mortality in the Laurentian Great Lakes. We conducted experiments to evaluate the effect of two stressors, reduced salt content in the water and food limitation, on alewife thiaminase activity. Alewives were subjected to treatments in replicated tanks in which conductivity was lowered (<100 ??S/cm) for 8 d and feeding was limited for 39 d. Circulating white blood cells, plasma cortisol, plasma glucose, and whole-body thiaminase were measured in individual alewives to assess their response to these experimental treatments. Alewives from the controls had significantly larger numbers of circulating white blood cells than those in the salt-reduced and food-limited treatments (24,000 and 19,000 cells/??L and 11,000 and 9,000 cells/??L for alewives from the two control and salt-reduced treatment tanks, respectively, and 34,000 and 30,000 cells/??L and 21,000 and 16,000 cells/??L for alewives from the two control and food-limited treatment tanks). No significant differences in alewife thiaminase activity were found between treatment fish and their controls. The mean thiaminase activity in the alewives studied increased from 6,900 to 16,000 pmol??g -1??min-1 from the time of their collection in Cayuga Lake to the start of laboratory experiments 1.5-2.5 years later; the latter value was more than twice that of previously reported levels of thiaminase activity from alewives collected in the wild. These data suggest that the variability in alewife thiaminase is not related to stress from salt reduction or food limitation, but laboratory holding conditions significantly increased thiaminase through a mechanism not evaluated by our experimental treatments. ?? Copyright by the American Fisheries Society 2008.

Journal of Aquatic Animal Health↗
USGS2008

Genetic analysis of paramyxovirus isolates from pacific salmon reveals two independently co-circulating lineages

Viruses with the morphological and biochemical characteristics of the family Paramyxoviridae (paramyxoviruses) have been isolated from adult salmon returning to rivers along the Pacific coast of North America since 1982. These Pacific salmon paramyxoviruses (PSPV), which have mainly been isolated from Chinook salmon Oncorhynchus tshawytscha, grow slowly in established fish cell lines and have not been associated with disease. Genetic analysis of a 505-base-pair region of the polymerase gene from 47 PsPV isolates produced 17 nucleotide sequence types that could be grouped into two major sublineages, designated A and B. The two independently co-circulating sublineages differed by 12.1-13.9% at the nucleotide level but by only 1.2% at the amino acid level. Isolates of PSPV from adult Pacific salmon returning to rivers from Alaska to California over a 25-year period showed little evidence of geographic or temporal grouping. Phylogenetic analyses revealed that these paramyxoviruses of Pacific salmon were most closely related to the Atlantic salmon paramyxovirus (ASPV) from Norway, having a maximum nucleotide diversity of 26.1 % and an amino acid diversity of 19.0%. When compared with homologous sequences of other paramyxoviruses, PSPV and ASPV were sufficiently distinct to suggest that they are not clearly members of any of the established genera in the family Paramyxoviridae. in the course of this study, a polymerase chain reaction assay was developed that can be used for confirmatory identification of PSPV. ?? Copyright by the American Fisheries Society 2008.

Journal of Aquatic Animal Health↗
USGS2009

Variations of thiaminase I activity pH dependencies among typical Great Lakes forage fish and Paenibacillus thiaminolyticus.

The source of thiaminase in the Great Lakes food web remains unknown. Biochemical characterization of the thiaminase I activities observed in forage fish was undertaken to provide insights into potential thiaminase sources and to optimize catalytic assay conditions. We measured the thiaminase I activities of crude extracts from five forage fish species and one strain of Paenibacillus thiaminolyticus over a range of pH values. The clupeids, alewife Alosa pseudoharengus and gizzard shad Dorosoma cepedianum, had very similar thiaminase I pH dependencies, with optimal activity ranges (> or = 90% of maximum activity) between pH 4.6 and 5.5. Rainbow smelt Osmerus mordax and spottail shiner Notropis hudsonius had optimal activity ranges between pH 5.5-6.6. The thiaminase I activity pH dependence profile of P. thiaminolyticus had an optimal activity range between pH 5.4 and 6.3, which was similar to the optimal range for rainbow smelt and spottail shiners. Incubation of P. thiaminolyticus extracts with extracts from bloater Coregonus hoyi (normally, bloaters have little or no detectable thiaminase I activity) did not significantly alter the pH dependence profile of P. thiaminolyticus-derived thiaminase I, such that it continued to resemble that of the rainbow smelt and spottail shiner, with an apparent optimal activity range between pH 5.7 and 6.6. These data are consistent with the hypothesis of a bacterial source for thiaminase I in the nonclupeid species of forage fish; however, the data also suggest different sources of thiaminase I enzymes in the clupeid species.

Journal of Aquatic Animal Health↗
USGS2009

Quantitative polymerase chain reaction (PCR) assays for a bacterial thiaminase I gene and the thiaminase-producing bacterium Paenibacillus thiaminolyticus.

The thiaminase I enzyme produced by the gram-positive bacterium Paenibacillus thiaminolyticus isolated from the viscera of Lake Michigan alewives Alosa pseudoharengus is currently the only defined source of the thiaminase activity linked to thiamine (vitamin B1) deficiency in early mortality syndrome (EMS) in the larvae of Great Lakes salmonines. Diets of alewife or isolated strains of P. thiaminolyticus mixed in a semipurified diet and fed to lake trout Salvelinus namaycush have been shown to produce EMS in fry. We utilized quantitative polymerase chain reaction (Q-PCR) to aid in studies of the sources of P. thiaminolyticus and thiaminase I. Quantitative PCR assays were established to detect the thiaminase I gene of P. thiaminolyticus, the 16S rRNA gene from most species of bacteria, and the 16S rRNA gene specifically from P. thiaminolyticus and a few closely related taxa. The Q-PCR assays are linear over at least six orders of magnitude and can detect the thiaminase I gene of P. thiaminolyticus from as few as 1,000 P. thiaminolyticus cells/g of sample or the Paenibacillus 16S rRNA gene from as few as 100 P. thiaminolyticus cells/g of sample. The initial results from alewife viscera samples with high thiaminase activity yielded unexpectedly low densities of P. thiaminolyticus cells; Paenibacillus thiaminolyticus was detectable in 2 of 6 alewife viscera tested at densities on the order of 100 cells/g out of 100,000,000 total bacterial cells/g. The low numbers of P. thiaminolyticus detected suggest that alewives contain additional non-P. thiaminolyticus sources of thiaminase activity.

Journal of Aquatic Animal Health↗
USGS2009

Egg fatty acid composition from lake trout fed two Lake Michigan prey fish species.

We previously demonstrated that there were significant differences in the egg thiamine content in lake trout Salvelinus namaycush fed two Lake Michigan prey fish (alewife Alosa pseudoharengus and bloater Coregonus hoyi). Lake trout fed alewives produced eggs low in thiamine, but it was unknown whether the consumption of alewives affected other nutritionally important components. In this study we investigated the fatty acid composition of lake trout eggs when females were fed diets that resulted in different egg thiamine concentrations. For 2 years, adult lake trout were fed diets consisting of four combinations of captured alewives and bloaters (100% alewives; 65% alewives, 35% bloaters; 35% alewives, 65% bloaters; and 100% bloaters). The alewife fatty acid profile had higher concentrations of arachidonic acid and total omega-6 fatty acids than the bloater profile. The concentrations of four fatty acids (cis-13, 16-docosadienoic, eicosapentaenoic, docosapentaenoic, and docosahexaenoic acids) were higher in bloaters than in alewives. Although six fatty acid components were higher in lake trout eggs in 2001 than in 2000 and eight fatty acids were lower, diet had no effect on any fatty acid concentration measured in lake trout eggs in this study. Based on these results, it appears that egg fatty acid concentrations differ between years but that the egg fatty acid profile does not reflect the alewife-bloater mix in the diet of adults. The essential fatty acid content of lake trout eggs from females fed alewives and bloaters appears to be physiologically regulated and adequate to meet the requirements of developing embryos.

Journal of Aquatic Animal Health↗
USGS2009

Influence of thiamine deficiency on Lake Trout larval growth, foraging, and predator avoidance

Diet‐related thiamine deficiency increases the acute mortality, known as early mortality syndrome, of salmonines from some of the Great Lakes. The consequences of thiamine deficiency as measured at the egg stage for other important early life stage processes like growth, foraging efficiency, and predator avoidance that may also result in mortality, are unknown. Accordingly, we investigated the impacts of low thiamine on the specific growth rate (SGR) of first‐feeding fry, the ability of first‐feeding fry to capture Daphnia , fry emergence in the presence of a potential predator (round goby Apollina (formerly Neogobius ) melanostomus ), and predation by slimy sculpin Cottus cognatus . We used a combination of thiamine‐deficient and thiamine‐replete wild stocks of lake trout Salvelinus namaycush for this purpose. From these investigations we developed predictive relationships. Specific growth rate was related to egg thiamine concentration. From the exponential relationship, it was predicted that the threshold egg thiamine concentrations associated with 20% and 50% reductions in SGR are 8.1 and 5.1 nmol/g, respectively. The foraging rate on Daphnia was also related to egg thiamine concentration by an exponential relationship. It was predicted that the threshold concentrations associated with 20% and 50% reductions in this rate are 6.9 and 2.9 nmol/g, respectively. The presence of a round goby significantly reduced emergence success, but the level of goby predation was unrelated to egg thiamine concentration. Sculpin predation was related, although weakly, to the initial egg thiamine concentration. This research found that thiamine deficiency affected growth, foraging, and predator avoidance in lake trout fry. Growth effects resulting from thiamine deficiency may represent the most sensitive means of monitoring the impact of the secondary consequences of thiamine deficiency. Mortality associated with the combined effects of reduced growth and foraging has the potential to seriously impair lake trout recruitment.

Journal of Aquatic Animal Health↗