The rapid growth of aquaculture and scarcity of conventional fish feed supplements has prompted the introduction of new sustainable supplementation sources. In this study, the potential of five strains of fungal biomass of Ascomycetes and Zygomycetes edible filamentous fungi, Aspergillus oryzae, Neurospora intermedia, Rizhopus oryzae, Monascus purpureus, and Fusarium venenatum, cultivated on vinasse, a by-product of the bioethanol industry, as alternative protein sources for fishmeal in the fish diet was evaluated. It was observed that 5% vinasse with an initial pH of 5–6.5 can support fungal biomass yields of 34.3 ± 2.4–118.5 ± 3.9 g DM/L for A. Oryzae, N. intermedia, and R. oryzae. High protein contents of about 44.7%, 57.6%, and 50.9% (w/w), and fat contents of 7.0%, 3.5%, and 5.5% (w/w) were obtained for A. oryzae, N. intermedia, and R. oryzae, respectively. The latter three fungi species contained noticeable amino acid contents, including promising profiles of amino acids that are highly compatible with those of fishmeal. These findings provide evidence that fungal biomasses, with their relatively high protein content, good amino acid profiles, and other essential nutrients, are a promising supplementation alternative that can be produced from low-value by-products and organic-rich waste streams like vinasse to meet the dietary protein requirements in fish feed.

Organic-rich waste and industrial by-product streams, generated in enormous amounts on a daily basis, contain substantial amounts of nutrients that are worthy of recovery. Biological conversion of organic-waste streams using filamentous fungi is a promising approach to convert nutrients into value-added bioproducts, such as fungal biomass. High-protein fungal biomass contains different kinds and levels of amino acids, fatty acids, immunostimulants, antioxidants, pigments, etc., which make it a potential choice for application in animal feed supplementation. Considering the challenges long faced by the aquaculture industry in fishmeal production due to the increasing prices and environmental concerns, the aquaculture industry is forced to provide alternative protein-rich sources to replace conventional fishmeal. In this review, the possibilities of utilization of filamentous fungi biomass cultivated on organic-rich waste streams, as an alternative nutrient source in fish feed, were thoroughly reviewed.

The rapid growth of aquaculture and the lack of fish meal demand new sustainable ingredients. Although fungal biomass is found to be a promising sustainable fish feed supplementation candidate, the characteristics of this protein-rich source are closely influenced by the quality of the applied growth medium. In this work, the nutritional properties of pure filamentous fungal biomass provided from the cultivation of Aspergillus oryzae, Neurospora intermedia and Rhzopus oryzae were evaluated to assess their potential as alternative novel protein sources in fish feed. In this regard, fungal biomass yields of up to 0.19 ± 0.005 (g dry biomass/g substrate glucose) were obtained during submerged cultivation of fungal strains. The pure fungal biomass acquired could contain significant amounts of protein up to 62.2 ± 1.2% (w/w). The obtained protein had a high quality with notable inclusion of essential amino acids such as lysine, arginine, methionine and threonine with comparable concentrations to those of fish meal. Fungal biomass is mainly considered as protein source, however, entitlement of 6.9 ± 0.5, 4.0 ± 0.7 and 17.2 ± 1.1% (w/w) of lipids and ratio of polyunsaturated fatty acids (PUFA) to saturated fatty acids (SFA) of 1.37:1, 1.74:1 and 1.47:1 in A. oryzae, N. intermedia and R. oryzae, respectively, signal health benefits for the fish. Considering the results, protein-rich pure fungal biomass with amino acid composition is greatly compatible with fish meal, and contains essential nutrients such as fatty acids and minerals. This pure biomass constitutes a promising sustainable alternative supplement to be introduced in fish feed industry.

As global aquaculture expands to meet the growing protein demand, the industry faces mounting pressure to reduce reliance on conventional protein sources. Identifying alternative protein sources that are environmentally sustainable, resource‐efficient and nutritionally viable is crucial for the future of aquafeed development. In this regard, filamentous fungi have emerged as a promising alternative protein source due to their favourable nutritional profile and sustainable production potential. Although filamentous fungi contain high protein content and can be efficiently cultivated on organic waste materials, they are not yet utilised in commercial aquafeeds. In this study, juvenile rainbow trout ( Oncorhynchus mykiss ) were fed an extruded commercial‐like reference (Ref) diet and four experimental diets where Ref was mixed with 30% biomass of Aspergillus oryzae (AO), Neurospora intermedia (NI), Rhizopus delemar (RD), or Rhizopus oligosporus (RO) grown on thin waste from ethanol production. The fungal diets exhibited nutritional profiles and growth performance comparable to the Ref diet, despite significantly higher feed conversion ratios (FCRs) observed in the AO, NI and RO groups. Dietary digestibility was generally lower in the fungal‐diet groups than in the Ref group, although the digestibility of some amino acids in the AO group did not differ significantly from Ref. Dietary inclusion of fungal biomass induced noticeable shifts in gut microbial composition compared to the Ref diet, with the RO diet resulting in a distinct beta diversity profile. Firmicutes phylum members, including Weissella , Lactobacillus and Bacillus , were significantly more abundant in fish fed the NI, RD and RO diets, respectively. Overall, the evaluated filamentous fungi produced species‐dependent nutritional and microbiota responses in rainbow trout, although further optimisation is required to improve their nutritional value at the tested inclusion level.