Progress 07/01/04 to 06/30/06
Outputs
The time-course of accumulation of dietary organic and inorganic selenium (Se; 1.5 mg Se kg-1 dry weight feed) was studied in muscle and hepatic tissues of hybrid striped bass (HSB; Morone saxatilis (male) x M. chrysops (female); 58 g wet wt; 162 mm FL) over a 6 week period. Animals, which had been fed a Se deficient diet for 2 months prior to study, were maintained in a recirculating life support system at 28 C. PIT tagged fish were randomly assigned to one of 24 120 L aquaria (n = 5 per tank) which were subsequently randomly assigned to one of four diets: a fishmeal-based diet (control), soybean-casein-based feeds either supplemented with organic (SelPlex) or inorganic (sodium selenite) Se or as a basal diet, purposefully deficient in Se. Fish were fed twice daily on a 4 percent body weight basis. Samples taken at trial start (week 0), mid-way (3 weeks) and termination (6 weeks) included weight and length data, condition factor (CF), hepatosomatic (HSI) and visceral
(VSI) indices, intraperitoneal fat (IPF) and muscle (MR) and feed conversion (FCR) ratios, serum protein (SP), hematocrit (PCV), and glutathione peroxidase (GPx) activity and muscle and heaptic Se concentrations. Survival was also monitored throughout the study. Muscle and hepatic Se levels increased in fishmeal and Se supplmeneted diets throughout the study. At trial end, greatest weight gain (P less than 0.05) was observed in fish fed the control, fishmeal-based diet. Comparison of tissue Se levels indicated that the liver accumulated this mineral at greater concentrations than the muscle with highest levels being observed in the organic Se fed fish (P less than 0.05). Se accumulation in control and inorganic Se fed fish was similar, while Se in the liver of fish fed the Se deficient diet was lowest among groups (P less than 0.05). Likewise, muscle Se accumulation was found to be greatest in organic Se containing diets (P less than 0.05), whereas the basal, Se deficient diet group,
returned lowest levels (P less than 0.05). Plasma GPx activity was similar in HSB fed the fishmeal and organic Se diets. The fishmeal fed group expressed higher (P less than 0.05) GPx levels than that recorded for either the inorganic or basal diets. At trial end, no differences were recorded between groups for PCV or HSI, VSI or IPF. SP levels and MR were higher (P less than 0.05) in fishmeal control fed fish. FCRs were lowest in fishmeal fed fish and highest for the Se deficient or basal diet. The results indicate that muscle tissue provides a more conspicuous guage of dietary Se dose-response than liver tissue.Studies that have evaluated Se availability of edible fish flesh have demonstrated that Se absorption is excellent, with absorption and retention efficiencies of 88 and 85%, repesectively, even following cooking and storage. A 100 g portion of HSB fillets from the present study, therefore, would contain between 33-109 micrograms Se, amounting to a dietary intake of 25-80
micrograms Se;a level that would satisfy present daily intake recommendations. Our data also indicate that production of Se-enhanced fillets would require a Se-containing finishing diet to be fed for 6 to 8 weeks.
Impacts
This study has illustrated that organic selenium (Se) can be utilized to increase fillet content of Se, thereby producing a value-added product as well as a functional food for the aquaculture industry. with the recent evidence of the beneficial role that Se plays in human health, more and more emphasis is being directed at Se intake in humans for optimal health and well-being. This trial also showed no negative effects of high dietary levels of Se on the health and welfare of fish fed these diets. Finally, as these feeding trials were conducted in recirculating life support systems with minimal water exchange, no accumulation of Se in the water column was noted, even with the feeding of several high Se containing diets over a period of 6 weeks. This is an extremely important finding from an environmental perspective.
Publications
- Cotter, P.A., Craig, S.R. and McLean, E. 2007. Hyperaccumulation of selenium in hybrid striped bass: A functional food for aquaculture? Aquaculture Nutrition. (Accepted).
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Progress 10/01/04 to 09/30/05
Outputs
Further work with selenium (Se) incorporation into aquafeeds for hybrid striped bass conducted utilizing smaller fish as well as investigating potential impacts on animal health and welfare through the determination of acute phase protein activities and hematological parameters. After a second, 10 week feeding trial, there were no significant impacts of dietary Se supplemetation on weight gain or feed efficiency. Dietary Se also did not significantly impact acute phase protein levels (ceruloplasmin or lyzozyme) or activity levels of glutathione peroxidase. Hematological parameters (packed cell volume and plasma protein) were significantly affected by supplemental Se. Packed cell volume ranged from 49.4 in fish fed diets containing 0.2 ppm inorganic Se to 56.9 in fish fed diets containing 0.4 ppm inorganic Se, while plasma protein levels ranged from 7.9, again in fish fed the diets containing 0.2 ppm inorganic Se to 9.5 in fish fed the diet containing 0.2 pm organic
Se.
Impacts
These studies indicate that Se can effectively be accumulated in tissues of hybrid striped bass (HSB), thereby adding to the health value of fish for the consumer. The form of Se (inorganic or organic) did not impact accumulation in the muscle or liver of HSB. Also, there were no significant impacts on weight gain or immune function as measured by levels of acute phase proteins in HSB fed high levels of dietary Se. Hematological parameters such as packed cell volume and plasma protein levels were significantly affected by level and type of dietary Se supplmentation. These results suggest that Se levels in the flesh of HSB can be increased through dietary supplementation of Se.
Publications
- No publications reported this period
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Progress 10/01/03 to 09/30/04
Outputs
The initial eight-week feeding trial has been completed in which a dose response curve was established for selenium accumulation in the flesh of hybrid striped bass. Tissue accumulation in the muscle was static until dietary levels of selenium reached 0.4 ppm, after which point, tissue accumulation significantly increased. Liver selenium levels followed similar trends as observed in the muscle. There was no significant impact of selenium incorporation on weight gain and feed efficiency, most likely due to the larger size of the fish utilized in the initial trial. Future trials will utilize smaller, faster growing fish to determine whether production efficiencies could be impacted by dietary selenium incorporation.
Impacts
Increasing selenium levels in the flesh of cultured fish will provide producers with a value added product, while potentially increasing the health and well being of the cultured animals. The increased attention being given to selenium and it's potential role in the prevention/treatment of cancers and other devastating diseases in human nutrition makes this work important, as well as timely.
Publications
- No publications reported this period
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