Scott B. Brown

Development of Thiamine Deficiencies and Early Mortality Syndrome in Lake Trout by Feeding Experimental and Feral Fish Diets Containing Thiaminase

Abstract We conducted a laboratory investigation on the consequences of feeding predatory salmonids either experimental diets low in thiamine or diets containing alewife Alosa pseudoharengus. In experiment 1, adult lake trout Salvelinus namaycush were fed experimental diets containing bacterial thiaminase. In experiment 2, adult lake trout were fed natural prey species, alewives, and bloaters Coregonus hoyi. The diets consisted of four combinations of alewives and bloaters from Lake Michigan (100% alewives, 65% alewives–35% bloaters, 35% alewives–65% bloaters, and 100% bloaters), alewives from Cayuga Lake, a casein bacterial thiaminase, and a commercial trout diet. We assessed the effects of each diet on egg thiamine concentration and incidence of an embryonic early mortality syndrome (EMS). In experiment 1, incidence of EMS ranged from 0% to 100%. Significant relationships were found between the incidence of EMS and thiamine. In experiment 2, adult lake trout fed 100% alewives from either Lake Michigan o...

Thiamine and Thiaminase Status in Forage Fish of Salmonines from Lake Michigan

Abstract Dietary sources of thiamine (vitamin B1) and thiamine-degrading enzymes (thiaminases) are thought to be primary factors in the development of thiamine deficiency among Great Lakes salmonines. We surveyed major forage fish species in Lake Michigan for their content of thiamine, thiamine vitamers, and thiaminase activity. Concentrations of total thiamine were similar (P ≤ 0.05) among most forage fishes (alewife Alosa pseudoharengus, bloater Coregonus hoyi, spottail shiner Notropis hudsonius, deepwater sculpin Myoxocephalus thompsonii, yellow perch Perca flavescens, ninespine stickleback Pungitius pungitius, and round goby Neogobius melanostomus) and slightly lower in rainbow smelt Osmerus mordax. Concentrations of total thiamine were all above the dietary requirements of coldwater fishes, suggesting the thiamine content of forage fish is not the critical factor in the development of thiamine deficiency in Lake Michigan salmonines. Thiamine pyrophosphate was the predominant form of thiamine in most ...

Implications of Thiamine Deficiency in Great Lakes Salmonines

Abstract Our recent experimental work and ecoepizootiological assessments provide mechanistic data supporting a plausible hypothesis for an association between a prey base comprised of a large biomass of nonnative alewives Alosa pseudoharengus and the recruitment difficulties currently experienced by Great Lakes salmonines. We hypothesize that the thiamine deficiency induced by alewives, a species harboring high thiaminase activity, represents an ongoing cause of fry and adult mortality in salmonines. Overall ramifications of the thiamine deficiency on recruitment have not been firmly established but may represent a substantial bottleneck for natural recruitment in feral salmonine populations in the Great Lakes.

Toxicokinetics of three polychlorinated biphenyl technical mixtures in rainbow trout (Oncorhynchus mykiss).

Accumulation and depuration parameters of polychlorinated biphenyls (PCBs) in fish have been reported only for a few congeners. As well, there is little information on the ability of fish to biotransform PCBs. To address these issues, juvenile rainbow trout (Oncorhynchus mykiss) were exposed to dietary concentrations of three Aroclor mixtures (1248, 1254, 1260) in food for 30 d followed by an additional 160 d of nonspiked food at 8 degrees C. Accumulation, depuration, and potential biotransformation of 92 PCB congeners were assessed. Half-lives (t1/2) of PCB congeners ranged from 79 to 182 d, assimilation efficiencies ranged from 40 to 50% and biomagnification factors (BMF) ranged from 2.9 to 6.9. No evidence of significant biotransformation of any PCB congeners was found. All 92 congeners fell on the same t1/2 to Kow relationship as 16 preselected PCB congeners previously shown to persist in fish and no hydroxylated PCB metabolites (OH-PCBs) were detected in the plasma after 30 d of exposure. These findings suggest that OH-PCBs observed in feral fish may be accumulated from sources other than internal metabolism of the parent congeners, at least for juvenile fish at cool temperatures. Because t1/2s in this experiment were slower than t1/2s reported in other work, water temperature also may be an important factor in determining the t1/2s of all PCB congeners in fish.

Oxidative stress in Lake Sturgeon (Acipenser fulvescens) orally exposed to 2,3,7,8-tetrachlorodibenzofuran

Juvenile lake sturgeon were orally dosed with gelatin containing nominal concentrations of 0, 0.16 or 1.6 ng [3H]-2,3,7,8-tetrachlorodibenzofuran (TCDF) kg−1 fish weight. Liver, kidney and blood were collected 10 and 27 days after exposure. Phase I mixed-function oxidase (MFO) and Phase II (glucuronyltransferase) enzyme activities were determined in liver. Concentrations of non-enzymatic (tocopherol, retinoids) and enzymatic (superoxide dismutase, catalase, glutathione peroxidase) antioxidant parameters were also quantified in liver and kidney. TCDF concentrations were elevated in liver and kidney of both dose groups at 10 and 27 days. Lower tissue concentrations of TCDF at 27 days, compared with 10 day exposures, as well as the presence of polar metabolites in bile, may indicate rapid metabolism and clearance of the contaminant. MFO enzyme activity, measured as ethoxyresorufin-O-deethylase (EROD), was induced in liver with activity at the two sample periods reflecting the TCDF concentrations. Greater concentrations of hepatic lipid peroxides in both dose groups, indicate that oxidative stress was produced by contaminant exposure and/or induced metabolism enzyme activity.

Thiamine Status in Adult Salmonines in the Great Lakes

Abstract 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,...

A protocol for estimation of cortisol plasma clearance in acid-exposed rainbow trout (Salmo gairdneri)

The cortisol metabolic clearance rate (MCR) and degradation rate (DR) were determined in acid (H2SO4)-stressed and control rainbow trout (260 g) cannulated via the dorsal aorta. Recovery from catheterization, as judged by plasma cortisol, glucose, protein, and packed cell volume (PCV), was complete by 6 days. However, serial blood sampling increased plasma cortisol. Furthermore, although no major or consistent diel change in plasma cortisol occurred in terminally sampled free-swimming control trout, fluctuations were observed in serially bled catheterized trout. These findings preclude cortisol MCR estimation by any serial sampling method. Although plasma cortisol was temporarily elevated by constant infusion (70 microliter hr-1) of saline:ethanol vehicle, a satisfactory protocol was established for determining cortisol MCR by infusion of labeled cortisol to constant plasma specific activity. The MCR for control trout in water, pH 7.7, for 7 days was 30.3 +/- 4.2 ml hr-1 100 g-1, which did not differ from that of trout in water, pH 5.0. However, the cortisol DR was greater at pH 5.0 (2.13 +/- 0.46 micrograms hr-1 100 g-1) than at pH 7.7 (0.56 +/- 0.12) due primarily to increased plasma cortisol at pH 5.0.

Accumulation of chemostimulatory amino acids by a sedimentable fraction isolated from olfactory rosettes of rainbow trout (Salmo gairdneri)

The accumulation of amino acids by a sedimentable fraction from olfactory rosettes of rainbow trout (Salmo gairdneri) was examined to determine the correspondence with established criteria for receptors. Physical parameters such as saturability, reversibility, affinity and quantity of sites were reasonably consistent with receptor criteria. The kinetics of association were slow and not in accord with values expected of sensory receptors. Accumulation correlated with electrophysiological effectiveness for most amino acids. The correlation was tissue specific, not being evident in brain or gill. Denervation experiments showed that high-affinity accumulation depended upon the presence of neuronal elements in the olfactory mucosa. Inhibition studies with amino acids and analogues generally indicated good correspondence with previous electrophysiological findings. Experiments with transport inhibitors, lack of Na+, counter-transport and increasing osmotic strength showed some involvement of amino acid transport. Inconsistencies between the various aspects of amino acid accumulation by the sedimentable fraction and electrophysiological response preclude unequivocal classification of the accumulation as representing olfactory receptors.

Egg Thiamine Status of Lake Ontario Salmonines 1995–2004 with Emphasis on Lake Trout

ABSTRACT 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 of fish 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.

The effects of aluminum and acid on the gill morphology in rainbow trout, Salmo gairdneii

SynopsisThe objective was to determine the effects of acid and aluminum in acidified hard and soft water on the histology and morphometry of rainbow trout gills, and to determine relevant toxicity indicators within the gill tissue. Acid and aluminum promoted measurable primary epithelial hyperplasia which proved to be a reliable biological indicator of acid and aluminum contamination and possibly of some predictive value. Low levels of aluminum and acid resulted in hypertrophied chloride cells, suggesting a role in adapting to the contaminants. High concentrations of aluminum (>10 μmolI-1) caused chloride cell necrosis and consequently a decline in cell numbers over time. Aluminum precipitates accumulating within the chloride cell cytoplasm probably lead to impaired function prior to cell degeneration. The morphological alterations resulted in a decrease in water space between secondary lamellae (up to 40% within 14 d) which may reduce the efficiency of gas exchange. Twice the aluminum was required in hard water to elicit a similar soft water tissue response. Pathological changes were more severe with aluminum at pH 5.2 than at pH 4.7; results of aluminum speciation suggest that both labile and non-labile fractions are responsible for the induction of gill lesions. Low levels of aluminum may protect fish from the effects of high hydrogen ion concentration.