Laboratory and field growth trials were conducted to determine the feasibility of using blue crab (Callinectes sapidus) or Atlantic herring (Clupea harenous) cannery waste as dietary protein substitutes in pelleted rainbow trout (Salmo gairdneri) feeds. In lab and field experiments, triplicate groups of trout were fed 3 nutritionally complete diets: (1) a commercial diet (38.8% protein); or 1 of 2 experimental diets containing either (2) blue crab scrap (35.9% protein) or (3) herring byproducts (33.9% protein). Complete replacement of conventional fish meal as a protein source in rainbow trout diets with blue crab or herring waste significantly impaired growth performance factors in both laboratory and field trials. Trout fed the experimental diets consumed less feed, grew more slowly and less efficiently and, in field growth trials, suffered higher mortalities than those fed the commercial diet. This study suggests that blue crab byproducts are poor total substitutes for fish meal as a source of raw protein in rainbow trout diets. However, they may prove suitable as low-cost dietary protein supplements in salmonid feeds, particularly if excess chitin and calcium is removed and the sulfur amino acid content is fortified. Herring cannery wastes may be acceptable as protein supplements if crude protein levels are regulated.