Successful high replacement of fishmeal in rainbow trout feed by consortia of aerobic heterotrophic bacteria results in equal growth, health, and muscle composition

The expanding aquaculture industry faces challenges due to limited fishmeal production, some of which is unsustainably sourced. Developing alternative protein sources for aquafeed is crucial to enhance the sector’s long-term sustainability. Microbial protein, and more particularly single-cell protein as dried microbial biomass, shows promise due to its relatively low environmental footprint. Open consortia of aerobic heterotrophic bacteria (AHB) enable an innovative and cost-efficient manner to upgrade resources from feed-grade wastewater, promoting a more circular and sustainable system. High-Rate Conventional Activated Sludge (HiCAS) and High-Rate Contact Stabilization (HiCS) are suitable compact AHB production processes. However, to the authors knowledge, no studies have explored AHB produced in HiCAS or HiCS systems as a fishmeal replacement. This pioneering research aimed to assess the impact of substituting fishmeal with HiCAS and HiCS biomass on the growth performance, health, and muscle quality of juvenile rainbow trout. The 7-week feeding trial utilized AHB biomass grown on brewery wastewater, with isonitrogenous, isolipidic, and isocaloric diets. Fishmeal substitution levels were 25%, 50%, and 75% for both HiCAS and HiCS AHB biomass. Results indicated that AHB diets performed similarly to the control (p> 0.05) in weight gain, specific growth rate, and feed conversion ratio. Fitness parameters, including standard metabolic rate, hepatosomatic index, viscerosomatic index, condition factor, and muscle quality, showed comparable observations between AHB diets and control. Overall, these findings suggest that both HiCAS and HiCS biomass can replace up to 75% of fishmeal protein content with similar effects on fish growth, health, and fillet quality. This research underscores the potential of AHB biomass as a sustainable alternative protein source for aquafeed.