The rapid expansion of aquaculture, combined with increasing demand for sustainable protein sources and growing concerns regarding food waste, has intensified the need for innovative feed ingredients with low environmental impacts. This thesis investigated the potential of converting stale bread into a novel aquafeed ingredient through solid-state fermentation (SSF) using edible filamentous fungi.

The SSF process was optimized to enhance fungal growth and improve the nutritional quality of stale bread. The produced mycelium-bread (MB) was characterized and assessed as an aquafeed ingredient using a two-stage in vitro digestion model simulating the gastrointestinal conditions of rainbow trout (Oncorhynchus mykiss) and Nile tilapia (Oreochromis niloticus). Subsequently, a 75-day feeding trial compared rainbow trout diets containing 10% and 20% MB with a conventional diet. Finally, the economic feasibility and environmental sustainability of MB production and utilization in aquafeeds were evaluated.

Fermentation substantially improved nutritional quality, increasing crude protein content from 12% to 34% of dry matter while enriching the substrate with endogenous enzymes, antioxidant compounds, and negligible aflatoxin levels. Furthermore, in vitro digestion demonstrated that mycelia of Aspergillus oryzae and Neurospora intermedia exhibited higher protein digestibility (86 and 73 mg amino acids per 100 mg protein, respectively) than conventional ingredients in the simulated rainbow trout model. The high levels of free amino acids and endogenous enzyme activity in the MB are considered the primary factors contributing to its functionality as an active ingredient. Following feed extrusion, diets containing MB retain higher phenolic compounds and measurable endogenous enzyme activities.

The feeding trial showed that MB improved growth performance and feed utilization, reducing the feed conversion ratio from 1.42 in the conventional diet to 1.19 and 1.17 in the MB10 and MB20 diets, respectively, without adversely affecting fish health, welfare, or oxidative status. The LCA revealed reductions in global warming potential of 23% and 31% for MB10 and MB20, respectively, compared with the conventional diet. Although the TEA indicated that MB production increased capital investment requirements by approximately 41% and feed production costs by 27-29%, these disadvantages were partly offset by improved feed efficiency and lower environmental impacts. 

Overall, mycelium-bread combined favorable nutritional properties, high nutrient bioaccessibility, positive effects on pellet quality, improved fish performance, and reduced environmental impacts, highlighting its potential as a sustainable ingredient for future aquaculture production.