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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]

Lake trout stocks in the Great Lakes basin show variability in the relationship between a thiamine-dependent early mortality syndrome (EMS) and egg thiamine (B1) concentration but the reasons are unclear. EMS has been linked to a diet of alewives and their high thiaminase activity. We examined the relationship among four alewife-dependent B1-deficient lake trout stocks, and determined B1 utilization rates for three of these stocks, and a non-alewife-dependent B1-replete stock. Although the EMS-B1 relationship was similar between an inland lake stock and Lake Ontario, there was almost no EMS in lake trout from two Finger Lakes: Cayuga (CL) and Seneca (SL) Lakes. B1 utilization rate for the SL stock was lower than for all other stocks. Similarity in the EMS-B1 relationship (CL, SL) and reduced thiamine utilization in the SL stock suggests that Finger Lakes lake trout are better able to cope with the low egg thiamine concentration resulting from an alewife diet. Reduced thiamine utilization during the embryonic stage, possibly as a result of adaptive genetic variation, may result in a greater contribution by Seneca Lake strain lake trout to wild lake trout populations in the Great Lakes. [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]

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]