Ž . Aquaculture 180 1999 129–145 www.elsevier.nlrlocateraqua-online Effects of heat treatment and substitution level on palatability and nutritional value of soy defatted flour in feeds for Coho Salmon, Oncorhynchus kisutch Ronney E. Arndt a,1 , Ronald W. Hardy b,2 , Shozo H. Sugiura b,3 , Faye M. Dong a, ) a UniÕersity of Washington, School of Fisheries, 3707 Brooklyn AÕe., N.E., Seattle, WA 98105-6715, USA b Hagerman Fish Culture Experiment Station, 3059F National Fish Hatchery Road, Hagerman, ID 83332, USA Accepted 12 April 1999 Abstract An in vivo digestibility trial and a feeding trial were conducted to determine the extent to which heat treatment, nutritional quality, and palatability of hexane-extracted, defatted soy flour Ž . Ž SF influenced growth of fingerling coho salmon. Heat treatment of SF autoclave, 1.7 atm, . Ž . 1218C lowered trypsin units inhibited TUI from 181 to 1.8 after 20 min and lowered protein solubility from 98% to 70%. Longer heating periods further reduced SF protein solubility, but did Ž . not substantially reduce TUI. The apparent digestibility coefficient ADC of protein from heated Ž . Ž . SF 90.8 was significantly higher than the ADC of unheated SF 74.3 , but significantly lower Ž . than the ADC of the wheat gluten basal diet 98.2 . In the feeding trial, fish weight gain was Ž . reduced in a step-wise fashion at each level 15, 20, or 25% of unheated SF inclusion in the diet. Fish fed diets containing heat-treated SF gained more weight at each SF inclusion level compared to their corresponding unheated treatment groups, but inclusion of heat-treated SF greater than 15% substitution of herring meal protein resulted in reduced weight gain compared to fish fed the Ž . control diet. Krill supplementation 5%, combination of dried and frozen increased weight gain in ) Corresponding author. Tel.: q1-206-543-0603; fax: q1-206-543-1417; E-mail: fdong@fish.washington.edu 1 Current address. Utah Division of Wildlife Resources, Fisheries Experiment Station, 1465 West 200 North, Logan, UT 84321. 2 Tel.: q1-208-837-9096; fax: q1-208-837-6047. 3 Tel.: q1-208-837-9096; fax: q1-208-837-6047. 0044-8486r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. Ž . PII: S0044-8486 99 00186-6