The expansion of commercial aquaculture over the past several decades has been crucial in realizing its potential to provide affordable and nutritious, high-protein food for the world’s growing population. Ocean-derived small fish like anchovies and sardines for fishmeal (FM) and fish oil (FO) in aquafeeds, especially for salmonoids—the most significant users—has raised sustainability concerns. These concerns have driven the search for sustainable alternative ingredients for aquafeeds. Microalgae-derived protein and lipids have emerged as promising candidates to replace fishmeal and fish oil. We report our recent study aimed at developing a fish-free feed formulation for rainbow trout, which combines protein-rich, defatted biomass from Nannochloropsis oculata with either whole cells or oil derived from DHA-rich Schizochytrium sp.
We conducted an 89-day nutritional feeding experiment to determine the optimal level of FMFO replacement for growth and filet biochemical composition. We finally used the Cruz Aquafeed Sustainability Tool to dtect the diets’ environmental impacts, including biotic resource use (BRU), global warming potential (GWP), water use (WU), land use (LU), marine eutrophication potential (MEP), and freshwater eutrophication potential (FEP). Growth study results showed that trout fed a fish-free diet by combining N. oculata co-product and Schizochytrium sp whole cells did not significantly differ from fish fed the reference diet in feed conversion ratio, growth, specific growth rate, and survival rates. The environmental impact analysis showed that BRU was significantly lower in the fish-free diet compared to the reference diet. WU, LU, FEP, and MEP were lower in the reference diet compared to other experimental diets, while GWP was not significantly different from the fish-free diet (NSW).
Thus, using N. oculata co-product with Schizochytrium sp. whole cells in trout feed can replace FMFO while maintaining growth, flesh composition, and GWP comparable to the reference diet.