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

INCREASING LEVELS OF DIETARY CARBOHYDRATES ARE ABLE TO
DIFFERENTIALLY MODIFY THE EXPRESSION LEVELS OF TRANSAMINASES 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
Despite the fact that carnivorous fish are recognized by their poor ability to utilize dietary carbohydrates (CHO), the impact of
this group of nutrients in fish metabolism is far from being small and simple. Depending on factors like the CHO form and level
of inclusion among many others, fish like rainbow trout (RBT) are able to use them and improve productive performance.
One of the assumed advantages of using CHO as source of metabolic energy is spare dietary protein. As in mammals, fish
amino-transferases are key metabolic enzymes that remove amine of amino acids to free the carbon skeletons for purposes
like supplying energy. To gain further understanding on the protein sparing effect of dietary CHO a study was carried out to
evaluate changes in expression levels of alanine amino transferase (ALAT), aspartate amino transferase (ASAT) and glutamate
dehydrogenase (GlDH) in RBT. Seventy five RBT, with an average weight 28.3g, were distributed in each of 12 tanks (150
L) supplied with 6 L/min (14.5ºC), spring water at the HFCES, University of Idaho. 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, 8 and 12. At the same time periods, liver samples
were taken to monitor for liver glycogen levels as well as gene expression changes. Fish fed diets 0% and 15% CHO presented
significantly higher protein retention efficiencies than the other two groups. Increasing CHO levels in the diet generated a
significant increase in liver glycogen which was strongly and negatively correlated with ALAT expression levels (-0.75). The
other two transaminases did not follow a pattern of expression similar to ALAT even when significantly affected by the diet.
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