Kappaphycus alvarezii is a renewable resource rich in dietary sources such as vitamins, proteins, carbohydrates and trace minerals. The solid waste of this marine macroalgae produced from bioethanol production was used to produce fish feed. This study aims to evaluate the efficacy of K. alvarezii fish feed in Barbonymus schwanenfeldii fish growth. The proximate analysis, micro and macronutrient and mycotoxin in the K. alvarezii fish feed were determined using a standard protocol. For the fish culture design, fish were randomly divided into two groups: group I – feed with commercial fish feed (control); group II – feed with K. alvarezii fish feed (experimental group). The initial body weight of the fish was recorded, and thereafter weekly for 12 weeks. Proximate analysis indicated that the dried K. alvarezii fish feed is high in nitrogen (46.30+0.1%) and low in moisture (6.40+0.1%), ash (4.50+0.1%) and fiber (4.75+0.1%) contents, while rich in macro and micronutrients. There was no mycotoxin found in the K. alvarezii fish feed. For the 12 weeks of the feeding of commercial and K. alvarezii fish feed, our results did not show any significant difference (P > 0.05) in the B. schwanenfeldii specific growth rate between the groups, 0.36+0.03% in the control group and 0.34+0.02% in the experimental group, respectively. Proximate analysis of the B. schwanenfeldii fish, indicated a moisture content of 19.20+0.1%, crude extract protein of 74.70+0.1% and crude lipid of 3.50+0.1% in the control group, which are significantly higher (P < 0.05) than in the experimental group [moisture content (15.60+0.1%), crude extract protein (70.00+0.1%) and crude lipid (2.60+0.1%)]. Although the proximate analysis in the control group is significantly higher than the experimental group, the use of K. alvarezii as fish feed supplement is still a good option as it utilizes the waste of K. alvarezii and can support towards the UN Sustainable Development Goal 12, Responsible Consumption and Production.