Optimizing the carbon‐to‐nitrogen ratio in biofloc technology enhances growth performance, reproductive output, and nutritional quality of the brine shrimp A. parthenogenetica

Abstract This study evaluated the effects of dietary carbon‐to‐nitrogen (C/N) conditions, generated by combining Dunaliella salina with sugar beet raffinate, on the growth, survival, reproductive performance, biochemical composition, fatty‐acid profile, digestive enzyme activity, microbial community, and biomass production of Artemia parthenogenitica cultured in biofloc systems. Eight treatments were evaluated for 21 days. The control treatment consisted of 25% algae and 75% yeast and was designated as C/N 3.5. The experimental treatments were designated according to their composition and C/N ratio as follows: A2.5‐R0.625 (C/N 11), A2.5‐R1.25 (C/N 11), A5‐R0.625 (C/N 10.5), A5‐R1.25 (C/N 10.5), A10‐R0.625 (C/N 9.5), A10‐R1.25 (C/N 9.5), and the probiotic reference treatment, consisting of 25% algae and 75% Bacillus subtilis (C/N 3.5). The A10:R1.25, corresponding to C/N 9.5, resulted in the highest survival rate (88.8 ± 2.3%), total length (12.03 ± 0.41 mm), total offspring production (1600 ± 87 individuals), and wet biomass (2518 ± 98 g), compared with 75.3 ± 2.0%, 9.67 ± 0.32 mm, 1067 ± 54 individuals, and 1690 ± 75 g, respectively, in the control. The DS10‐R1.25 had the lowest numerical feed conversion ratio (FCR; 0.150), which was significantly lower than that of the control (0.224) but did not differ significantly from that of The DS10‐R0.625 (0.169), and the highest alkaline protease, amylase, and lipase activities. However, the control treatment showed higher body protein and total carotenoid contents, indicating that improved growth and reproductive output were not accompanied by uniform improvement in all biochemical characteristics. Raffinate‐containing treatments also modified the fatty‐acid composition of both Artemia and biofloc, although the magnitude and direction of these changes depended on the dietary combination. Overall, under the conditions tested, supplementation with 10% D. salina and 1.25% sugar beet raffinate at a C/N ratio of 9.5 improved several production‐related indicators while reducing the required proportion of microalgae. These findings support the potential use of sugar beet raffinate as an auxiliary carbon source in biofloc‐based Artemia culture; however, further studies are required to determine the reproducibility of these responses at larger production scales and under different environmental conditions.