Altered Growth Rates, Carcass Fatty Acid Concentrations, and Tissue Histology in First-Feeding Steelhead Fed a Fish-Meal- and Fish-Oil-Free Diet

A 12-week feeding trial was conducted to evaluate a fish-meal-free, fish-oil-free diet for use with first-feeding steelhead Oncorhynchus mykiss. The marine-based control diet (marine diet) contained sardine (Sardinopsspp.) meal and pollock (Pollachius virens) liver oil as the primary sources of protein and lipid, respectively. The experimental diet (terrestrial diet) contained only terrestrial sources of protein (poultry by-product meal, blood meal, canola, corn gluten, and wheat gluten) and lipid (canola oil and flaxseed oil). Each diet was administered to five replicate groups of first-feeding fry. At the conclusion of the feeding trial, fish that were fed the marine diet exhibited significantly higher weight gain and feed efficiency than fish that were given the terrestrial diet. Survival was not significantly affected by dietary treatment. However, fish that received the terrestrial diet exhibited significantly lower hemoglobin concentration and percent packed cell volume. Histological examination indicated that in comparison with control fish, steelhead that were fed the terrestrial diet exhibited a lesser degree of vacuolation in hepatocytes, mild hypertrophy and hyperplasia of the nephron tubular epithelium, and intracellular vacuolation in epithelium of the pyloric caeca. Carcass crude protein concentration was significantly higher in fish that were fed the marine diet than in fish that were fed the terrestrial diet. After 2 weeks of feeding, steelhead that received the marine diet exhibited significantly higher carcass concentrations of 14:0, 16:0, 16:1, 20:1, 20:5(n-3), 22:5(n-3), and 22:6(n-3) fatty acids but significantly lower carcass concentrations of 18:1, 18:2(n-6), 18:3(n-6), 18:3(n-3), and 20:4(n-6) relative to fish that were given the terrestrial diet. These differences in carcass fatty acid concentrations persisted throughout the feeding trial. Results of this study indicate that the current terrestrial-based diet is not a satisfactory replacement for the standard marine-based diet used with first-feeding steelhead. Received January 21, 2010; accepted January 22, 2011