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Amino acid nutrition and metabolism:
findings during a post-doctoral research stay in the United States
Utenlandsstipend/Overseas fellowship
Compared to mammalian or avian nutrition, the basic knowledge of amino acid
metabolism in fish is much less developed. During a one-year post-doctoral stay
at The Ohio State University, partly funded by the NRC, we focused on the
amino acid arginine which has many important roles in growth. New findings
were generated that in the long term may contribute towards formulation of
improved diets for farmed fish.
Background and objectives:
The post-doctoral research stay was hosted by The Ohio State University, and supervised
by Dr. Konrad Dabrowski. The principal objectives were to 1) test if the molecular form of
dietary arginine affects growth and metabolism in bony fishes, 2) study if the expression
of the urea cycle enzymes in fish early life stages affects arginine requirement, and
3) investigate if dietary antioxidants influence amino acid metabolism in fish.
A
rg
1.
0
0.
5
rg
A
A
Fr
ee
Fr
ee
rg
rg
p
A
Pe
p
Pe
1.
0
0.
5
+
tr
ol
on
C
C
on
tr
ol
-
Feed conversion ratio
(feed/gain)
Specific growth rate
Results:
Dipeptide arginine is utilized just as well as free arginine in the freshwater fish
species pacu
To determine amino acid requirements in fish, it is vital to supply the amino acids in an
optimal molecular form, that is able to generate the highest growth rate and survival. In
such studies, amino acids in the free form are usually added as supplements in a graded
fashion to the experimental diets. However, it was not known if dipeptides can be used
as supplements in such diets for adult fish. We studied how a dipeptide supplement,
containing arginine, compared to the growth performance of fish fed arginine in the free
form. The South American fish pacu
4
1
a
a
a
was studied, which is gaining
ab
bc
c
interest as an aquaculture species in
0.8
3
the region. The results showed that
arginine supplied in the dipeptide
0.6
form was able to sustain growth and
2
feed efficiency at a level comparable
0.4
to diets containing arginine in the
free form. In future studies, it would
1
0.2
be interesting to test how other fish
species, like salmon and trout,
0
0
perform when fed dipeptide
supplemented diets.
Treatment
Growth and feed conversion ratio of pacu fed supple-mental
arginine at two levels through principally protein (Control),
dipeptide (Pep Arg) or free form (Free Arg)
Arginine is an essential amino acid also in early life stages of rainbow trout,
despite their expression of urea cycle enzymes
In mammals, the urea cycle functions to detoxify ammonia formed during amino acid
catabolism. However, certain enzymes of the urea cycle together with other pathways,
also has a role in synthesizing net arginine for use in the organism. Thus, in many
mammals, arginine is not an essential amino acid. In fish however, arginine is an
essential amino acid in adults, but the requirements in early life stages have been very
little studied. In all fish species so far investigated, the urea cycle is active during early
life, but is seldom active in the adult fish. It was therefore of interest to study if rainbow
trout alevins were able to grow on diets very low in arginine, since they theoretically
should be able to generate net arginine. However, as in adult trout, our experiments
showed that the alevins grew insignificantly, and suffered high mortality, when fed diets
low in arginine. Thus, the urea cycle in early life stages of fish is likely expressed
primarily to combat toxic ammonia from amino acid catabolism. This study also
underlines the importance of developing experimental diets suitable for early life stages,
and in determining amino acid requirements in larvae and alevins.
µmol/L
The antioxidants lipoic acid and ascorbic acid, affect plasma amino acids
selectively in the freshwater fish species, pacu
Antioxidants are usual feed supplements for farmed fish. In general nutrition, new
compounds that have antioxidant properties are rapidly being discovered and considered
as feed supplements. However, how these antioxidants affect basic metabolic properties
in fish are often not focused on. In this study, we investigated the effects of the dietary
antioxidants lipoic acid and ascorbic acid (vitamin C) on the free amino acid levels in
plasma of the pacu. It was found that lipoic acid, a naturally occurring antioxidant, is able
to reduce the tissue loss of ascorbic acid in pacu fed ascorbic acid-devoid diets.
Furthermore, both antioxidants affected the plasma free amino acid levels. Lipoic acid
dietary supplementation led to a decline
8000
a
in the concentration of non-essential free
a
amino acids, probably due to increased
ab
b
catabolism. Essential amino acids were
6000
x
x
not significantly affected. Ascorbic acid
xy
only influenced the sulfur amino acids, in
y
4000
particular taurine, which decreased
considerably when ascorbic acid was
2000
added to the diets. The study shows that
dietary supplementation of these
antioxidants will likely change the amino
0
acid metabolism of fish. These findings
+AA +LA +AA -LA -AA +LA -AA -LA
should be taken into account when
Total free amino acids (white bars) and non-essential free
changing antioxidant levels in diets, or
amino acids (grey bars) in pacu blood plasma when fed
when using feed ingredients that contain
one of four diets differing in antioxidant content (AA:
different amounts of endogenous
ascorbic acid, LA: lipoic acid).
antioxidants compared to fish meal.
Norsk sammendrag:
Aminosyreernæring og -metabolisme: resultater oppnådd gjennom et
post-doktor opphold i USA
Sammenlignet med pattedyr og fugl er vår basale forståelse av aminosyre-metabolisme
og -ernæring hos fisk mindre utviklet. Gjennom et post-doktoropphold ved The Ohio
State University, delvis finansiert av NFR, fokuserte vi på arginin, en aminosyre som har
mange viktige roller i vekstprosesser.
Det ble vist at arginin-supplement i form av dipeptider tilsatt fôr og gitt den SørAmerikanske fisken pacu, gir like bra vekst og fôrutnyttelse som arginin tilført i fri
aminosyre form.
I et annet forsøk fokuserte vi på endogen argininsyntese hos ørretyngel fordi disse
uttrykker enkelte ureasyklus-enzymer som teoretisk kan danne netto arginin, slik det
skjer hos de fleste pattedyr. I voksen ørret derimot, har de sentrale ureasyklusenzymene lav aktivitet og arginin er essensiell. Vi fant at på tross av den aktive urea
syklusen og tilstøtende enzymer, trenger ørretyngelen i likhet med den voksne fisken
arginin i fôret for å overleve og vokse. Dette kan bety at ureasyklusen hos tidlige
livsstadier hos fisk blir uttrykt primært for å håndtere giftig ammoniakk fra
aminosyrenedbrytningen.
I et tredje forsøk undersøkte vi hvordan antioksidanter i fôret influerer aminosyrenivået i
blodplasma hos pacu. Det er viktig å opparbeide kunnskap om hvordan slike
fôrtilsetninger virker inn på basale prosesser hos fisken. Tilsetning av antioksidanten
lipoat førte til reduksjon i flere aminosyrer i plasma, trolig på grunn av økt katabolisme,
mens tilsetning av askorbinsyre virket særlig inn på de svovelholdige aminosyrene.
Resultatene oppnådd gjennom dette oppholdet kan bidra til kunnskapen om
aminosyremetabolisme hos fisk, et felt som er viktig for videre forbedring av fôr til
oppdrettsfisk.
Lenker:
www.akvaforsk.no
http://www.blackwell-synergy.com/doi/abs/10.1111/j.13652095.2005.00373.x?prevSearch=allfield%3A%28terjesen%29
http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%2
34972%232006%23997459998%23621847%23FLA%23&_cdi=4972&_pubType=
J&view=c&_auth=y&_acct=C000050221&_version=1&_urlVersion=0&_userid=10
&md5=17ed4ccadf46489bb6551b69795148c9
http://jeb.biologists.org/cgi/content/abstract/208/15/2885?maxtoshow=&HITS=1
0&hits=10&RESULTFORMAT=&author1=terjesen&andorexacttitle=and&andorexact
titleabs=and&andorexactfulltext=and&searchid=1&FIRSTINDEX=0&sortspec=rele
vance&resourcetype=HWCIT
http://jn.nutrition.org/cgi/content/abstract/134/11/2930?maxtoshow=&HITS=10
&hits=10&RESULTFORMAT=&author1=terjesen&searchid=1&FIRSTINDEX=0&sort
spec=relevance&resourcetype=HWCIT
Samarbeidende institusjoner:
The Ohio State University, Columbus, U.S.A. (www.osu.edu),
Aquaculture Protein Center, CoE (www.apc-coe.no)
159934/S40
Ansvarlig: AKVAFORSK,
Institutt for Akvakulturforskning AS
Prosjektleder: Ståle J. Helland
Kontaktperson: Bendik Fyhn Terjesen, AKVAFORSK Sunndalsøra
Telefon: +47 71 69 53 32 E-mail: [email protected]
01.01.2004 01.04.2005