Comparative analysis of Nannochloropsis oculata, Dunaliella salina, and Tetraselmis gracilis as feed sources for rotifer, Brachionus plicatilis: Effects on population dynamics, biochemical composition, and fatty acid profile

The rotifer, Brachionus plicatilis, is a crucial live feed organism in marine fish hatcheries, necessitating optimised culture conditions through appropriate feed selection. This study evaluated the effects of three microalgae species (Nannochloropsis oculata, Dunaliella salina, and Tetraselmis gracilis) compared to Baker's yeast (control) on the growth, reproduction, biochemical composition, and fatty acid profile of B. plicatilis. Rotifers were cultured in triplicate 5 L beakers over 8 days (rotifer initial density: 20 ± 0 individuals mL^-1; microalgae feed concentration: 5×10⁶ cells mL^-1). Results revealed significant differences (p<0.05) in growth performance among treatments, with T. gracilis-fed rotifers achieving the highest population density (325 ± 48 individuals mL^-1) by day 8, followed by N. oculata and D. salina. Yeast-fed rotifers showed significantly lower (p<0.05) instantaneous growth rates and egg ratios throughout the study period. Biochemical and fatty acid analysis showed that T. gracilis-fed rotifers contained the highest protein and alpha-linolenic acid (ALA) levels (4.43 ± 0.52%), while N. oculata-fed rotifers demonstrated the highest lipid content and eicosapentaenoic acid (EPA) levels (8.37 ± 0.31%), significantly exceeding other treatments. Baker's yeast-fed rotifers showed significantly higher (p<0.05) carbohydrate content but lower omega-3 fatty acid levels compared to microalgal treatments. The investigation confirms the effectiveness of all three microalgal species in rotifer culture, with N. oculata and T. gracilis offering distinct nutritional advantages for marine fish larvae, while D. salina proves valuable as a supplementary feed. These findings provide hatchery operators with flexible options for optimising rotifer production protocols based on fish species and specific larviculture requirements.