The diatom genus, Halamphora subturgida, was exposed to various nitrate salt concentrations (882 µM, 441 μM and 1,764 μM) for a period of 18 days. The Chlorophyll content of diatom biomass (14.95 ± 0.04 µg/ml) reflected better growth, subjected to 1,764 µM NO−3 for a period of 12 days as compared to control (882 µM NO−3) and nitrogen depleted (441 µM NO−3) conditions. Fucoxanthin estimation showed a similar trend as chlorophyll content and reached its peak at nitrogen-repleted (1,764 µM NO−3) condition (25.70 ± 0.03 µg/ml). The total carotenoid (26.92 ± 0.05 µg/ml) and protein content (87.49 ± 0.06 mg/g) were found to be maximal after 12 days of incubation in nitrate sated medium. Thus, the diatom exposed to 12 days' nitrate sated medium (1,764 µM NO−3) was selected as fish feed ingredients to gold fish (Carassius auratus). Total Algal Feed (TAF) was prepared from mixed algal biomass of Halamphora subturgida, Spirulina and Leptolyngbia. The commercial feed (CF) was replaced by varying proportions of algal mix to formulate three different types of Value Added Feed (VAF-25%, 50%, 75% VAF). The feed type formulated as 75% VAF was found to be most effective in terms of skin pigmentation, growth and antioxidant activities of experimental fish showing almost 1.44- to 4- fold increase, compared with the control fish. Body weight gain and specific growth rate also changed significantly in experimental fish. © 2020 John Wiley & Sons Ltd