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HAVBRUK - En næring i vekst Faktaark www.forskningsradet.no/havbruk 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.
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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.
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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)
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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