February 15-18, 2009 Washington State Convention Center Seattle ...

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DIETARY CARBOHYDRATE LEVEL AFFECTS THE EXPRESSION OF GENES
REGULATING THE PRODUCTION OF REDUCTIVE POWER IN RAINBOW TROUT
Oncorhynchus mykiss, LIVER
Jurij Wacyk*, Madison Powell, Kenneth Rodnick, Gordon Murdoch, Barrie Robison, Rod Hill and Ronald Hardy
Hagerman Fish Culture Experimental Station (HFCES)
University of Idaho, Aquaculture Research Institute
3059F National Fish Hatchery Road
Hagerman, Idaho, 83332 USA
jwacyk@vandals.uidaho.edu.
The presence of carbohydrates (CHO) in plant ingredients and the fact that carnivorous fish like rainbow trout (RBT) are recognized
by their poor ability to use dietary carbohydrates represent a significant challenge for fish nutritionists. Considering that
high levels of dietary carbohydrates have been shown to be detrimental to fish performance, a study was designed to investigate
the effect of long-term dietary modifications (CHO levels) on the expression of genes related with the generation of reductive
power in trout liver. Seventy five RBT, average weight 28.3g, were distributed among 12 tanks (150 L), supplied with 6 L/min
(14.5ºC), spring water at the HFCES. Dietary treatments were formulated to be iso-nitrogenous (38% digestible protein) and
iso-lipidic (15% digestible lipid) with increasing levels of energy provided by gelatinized wheat starch. Fish were fed to apparent
satiation 3 times daily, 6 days a week for 12 weeks. Fish in each tank were bulk-weighed and counted at the beginning and
at the end of weeks 4 (T1), 8 (T2) and 12 (T3). At the same time periods, blood and liver samples were taken to monitor for
plasma glucose levels as well as gene expression changes. In our study we were successful in identifying significant differences
in plasma glucose and gene expression levels in the liver of rainbow trout. Increasing dietary starch level led to elevated levels
of plasma glucose. The response of this classic physiological parameter was expected and is characteristic of RBT fed diets
high in CHO. Comparing physiological and molecular data, it appears that the transcriptional machinery behind Glucose 6P
dehydrogenase expression, the regulatory entrance point to the pentose phosphate pathway, is able to adapt and closely follow
plasma glucose variations. The general up-regulation of Thioredoxin and Thioredoxin interacting protein by fish fed the wheat
starch containing diets may be indicative of an increased necessity for reductive power possibly linked with a modification of
the redox environment in the hepatocytes (REDOX stress).