The Israeli Journal of Aquaculture - Bamidgeh 54(2), 2002, 79-88

THE PROTEIN SPARING EFFECTS OF HIGH LIPID LEVELS
IN DIETS FOR RAINBOW TROUT
(ONCORHYNCHUS MYKISS, W.1792) WITH SPECIAL
REFERENCE TO REDUCTION OF TOTAL NITROGEN EXCRETION


Murat Yigit*
Laboratory of Nutrition, Department of Aquaculture, Faculty of Fisheries, Ondokuz Mayis University, Sinop 57000, Turkey


Öztekin Yardim
Department of Fisheries, The Vocational School of Susehri, Cumhuriyet University, Susehri -Sivas 58000, Turkey


Shunsuke Koshio
Laboratory of Aquatic Animal Nutrition, Faculty of Fisheries, Kagoshima University, Shimoarata 4-50-20, Kagoshima 890-0056, Japan

(Received 5.12.01, Accepted 1.5.02)

Key words: lipids, nitrogen excretion, protein sparing, rainbow trout

Abstract

This research sought to develop low-protein, high-energy (less-polluting) diets for rainbow trout to properly utilize protein and reduce total nitrogen excretion. Duplicate groups of rainbow trout were fed one of four experimental diets with a protein to energy (P:E) ratio of 25, 24, 22 or 19 mg/kJ and a lipid content of 12, 13, 17 or 26%, respectively. The diets were given to fish with a mean initial weight of 181 g for 70 days. At the conclusion of the trial, mean weights ranged from 353.17 g (94% weight gain) to 394.75 g (118% weight gain) with 100% survival in all treatments. Weight gain, feed efficiency and protein retention increased as the dietary lipid content increased and as the P:E ratio decreased. Fish fed the 22 mg protein/kJ energy diet (17% lipid, 44% protein, 20.34 kJ/g gross energy) performed best. This indicates that the protein content in practical trout feeds can be reduced from the currently used 47% to around 44% without reducing the growth rate and feed efficiency, if high quality protein is used and the gross energy is increased by lipid to about 20.34 kJ/g diet. The low-protein, high-energy diets reduced the total nitrogen excretion from the rainbow trout by 27%.

*Corresponding author. Fax: 90-368-2876255, e-mail: muratyigit@ttnet.net.tr
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