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

EFFECTS OF LOW-PHOSPHORUS DIETS ON BODY FAT CONTENT, FATTY ACID
COMPOSITION, AND LIPOLYTIC GENE EXPRESSION IN RAINBOW TROUT
Shozo H. Sugiura
School of Environmental Sciences
University of Shiga Prefecture
Hikone, Japan
sugiura@ses.usp.ac.jp
Fish feeds low in phosphorus (P) have been used widely in environmentally
friendly aquaculture. Such dietary regimens sometimes, though subconsciously,
induce marginal P deficiency in fish. P-deficient fish are known to
increase body fat deposition. However, the mechanism has not been well
researched. The present study examined the effect and mechanism of fat
deposition with low-P feeds. The ultimate aim of study was to increase
commercial and nutritional values of aquaculture fishes.
One hundred rainbow trout (mean BW 21.1g) were randomly stocked
into four 50L aquaria. Four test diets, differing in P content (low-P: LP
or high-P: HP) and fat source (fish oil or lard), were made as dry pellets
(Table 1), and hand-fed to fish twice daily to satiation for 2 months. At
the end of experiment, samples were taken (5 fish /tank) after 24h of
fasting for analyses. Fillet fatty acids were analyzed by GC, and hepatic
gene expressions were determined by realtime RT-PCR.
Bone P% of fish were 3.8, 8.9, 5.1, 9.0, respectively for LP/fish oil,
HP/fish oil, LP/lard, HP/lard diets. Fish fed LP diets reduced not only
bone P% (p