The nutritional value of spirulina in aquafeeds has been studied extensively as a fishmeal replacer or as a functional feed additive to increase growth and health performance of fish in the last decade. Despite increased interest in spirulina research in aquaculture, its increased production cost still limits its use in commercial rations. Zarrouk’s medium is the standard substrate used for growing spirulina. Although this medium offers optimal biomass production, it incurs higher costs due to the expensive components needed for concocting the medium. In this regard, development of cost‐effective alternative culture medium or techniques is necessary for the industrial‐scale production of these microalgae. This paper reviews research on different alternative media for spirulina cultivation and its nutritive value as an aquafeed. Numerous alterations in the composition of Zarrouk’s medium with cheaper chemical ingredients have been explored as a potential substitute for cost‐effective microalgae cultivation. Industrial and processing wastes and by‐products with appropriate nutrient profiles for growing spirulina are also being considered as alternative culture media. The use of rice bran or other cheaper agricultural by‐products, as a cost‐effective growth medium for commercial‐scale spirulina production has yet to be explored extensively in agriculture‐based countries, especially in rice‐producing Asian countries.

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The rapid global growth in fish farming and limited supply of fish meal (FM) has consequently reduced FM inclusion levels in compound feeds leading to a higher reliance on alternative protein sources. Sasya is a single cell protein (SCP) product that has a similar amino acid profile as FM. The aim of this study was to evaluate the effects of replacing FM with SCP on in vivo digestibility, growth, feed efficiency, whole‐body proximate/amino acid composition and gene expression levels of various hepatic enzymes in rainbow trout (Oncorhynchus mykiss). Three isonitrogenous (470 g/kg crude protein) and isolipidic (18 g/kg crude lipid) diets were formulated as follows: Diet 1: control (30% FM); Diet 2:24% FM + 6% SCP and Diet 3:18% FM + 12% SCP. Each diet was hand‐fed to triplicate tanks containing 30 rainbow trout fingerlings (4.99 ± 0.20 g) for 9 weeks. Apparent digestibility coefficients of SCP for dry matter, crude protein, lipid and energy were 60, 80, 93 and 74% respectively. Growth performance (final weight: 69–71 g), feed conversion ratios (0.91–0.94) as well as whole‐body protein and amino acid composition were unaffected by diets. However, Diet 3 significantly increased whole‐body crude fat and energy. Fish fed the SCP‐based diets had significantly higher expression for carnitine palmitoyltransferase‐1b (CPT1b), fatty acid delta 6 desaturase (FADS6) and fatty acid elongase 5 compared to the control. Overall, the quality of the SCP was similar as FM. Therefore, this product could enlarge the portfolio of alternative protein sources that can be used in fish diets and thus open a new market opportunity for use of a new feed resource in the feed industry.