Effects of fish meal- and fish oil-free diets on growth responses and fatty acid composition of juvenile coho salmon (Oncorhynchus kisutch)

Commercial diets fed to coho salmon (Oncorhynchus kisutch) contain high levels of fish meal and fish oil. Given concerns about future supplies and prices of these commodities, more nutritional research aimed at identifying alternative dietary ingredients for Pacific salmon is needed. Thus, utilizing a factorial design, terrestrial proteins and lipids were evaluated in practical diets fed to coho salmon. The two basal diets, containing mostly marine proteins or containing only terrestrial proteins, were extruded and top-coated with either marine fish oil or a 63:37 mixture of canola and flaxseed oils. Each of the four dietary treatments was fed to quadruplicate groups of juvenile coho salmon initially weighing 7.5 g/fish. At the end of the 15-wk feeding trial, weight gain (WG), feed efficiency (FE) and survival were significantly higher in fish fed diets containing marine protein compared with fish fed diets containing terrestrial proteins. Similarly, WG and FE were significantly higher in fish fed diets containing fish oil compared with fish fed diets containing plant oils. Survival was not significantly affected by dietary lipid source. Hemoglobin, hematocrit and total protein concentrations in whole blood were significantly higher in fish fed the marine protein diets compared with fish fed the terrestrial protein diets. Hematological responses were not significantly affected by dietary lipid source. Tissue (liver, muscle and carcass) lipids in fish fed the diets with added fish oil contained significantly higher proportions of 20:5n-3 and 22:6n-3 and significantly lower 18:1n-9, 18:2n-6 and 18:3n-3 percentages compared with fish fed the diets with added plant oils. Tissue fatty acid profiles also were significantly affected by dietary protein source, as liver, muscle and whole body lipids of fish fed the terrestrial protein diets contained significantly higher percentages of 18:2n-6 and total n-6 PUFA and a significantly lower total n-3:n-6 fatty acid ratio compared with fish fed the marine protein diets. Results of this study indicate complete replacement of dietary fish meal or fish oil individually have similar inhibitory growth effects in coho salmon, but have different effects on survival, hematological responses and tissue fatty acid percentages in this species.

► Fish meal or fish oil replacement have similar growth effects in coho salmon.
► A diet free of both ingredients resulted in further growth reductions in coho salmon.
► Tissue fatty acid profiles were not identical to dietary fatty acid profiles.