Effects of baker’s yeast feeding level on short-term population growth and fatty acid composition of Brachionus plicatilis

Brachionus plicatilis is one of the most important live feeds used in marine larviculture, and its nutritional quality directly influences larval growth and survival. Although baker’s yeast (Saccharomyces cerevisiae) is widely used as a cost-effective feed for rotifer production, information regarding the effects of different yeast feeding rates on rotifer fatty acid composition remains limited. This study evaluated the effects of three yeast concentrations LF (0.40 g × 106 ind.-1 day-1), MF (0.55 g × 106 ind.-1 day-1), and HF (0.70 g × 106 ind.-1 day-1) on population dynamics, total lipid content, and fatty acid profiles of B. plicatilis. Rotifers were stocked at an initial density of 200 ind. mL-1 and cultured for 5 days. Population density, egg-carrying individuals, fecundity, and growth rate were monitored at 24-h intervals. At the end of the experiment, rotifers were harvested for total lipid and fatty acid analyses. The highest rotifer density (2294 ± 201 ind. mL-1) and number of egg-carrying individuals (639 ± 64 ind. mL-1) were obtained in the LF group. This group also exhibited the highest egg-carrying ratio (27.8 ± 1.1%) and population growth rate (0.48 ± 0.01 div. day-1). Total lipid content increased markedly from 3.59 ± 1.01% dry weight in the 24-h starved control group to 9.32–10.93% dry weight in yeast-fed rotifers, with the highest value recorded in the 0.40 g × 106 ind.-1 treatment. Yeast supplementation also increased total n-6 polyunsaturated fatty acids from 9.65 ± 1.18% in the control group to 12.48–13.01%, primarily through elevated linoleic acid (18:2n-6) levels. Arachidonic acid (20:4n-6) was detected in the MF and HF groups. In contrast, n-3 polyunsaturated fatty acids, including α-linolenic acid, EPA, DPA, and DHA, were absent in all yeast-fed groups, resulting in n-3/n-6 and EPA/ARA ratios of zero. The results demonstrate that S. cerevisiae effectively enhanced biomass production, reproductive performance, and lipid accumulation in B. plicatilis, with the LF feeding regime yielding the best overall performance among the feeding regimes tested. However, baker’s yeast alone is insufficient to provide the essential n-3 highly unsaturated fatty acids required for marine fish larvae. Therefore, although yeast can serve as an economical biomass-building feed, its application should be combined with marine lipid- or microalgae-based enrichment products to improve the nutritional quality of rotifers for marine larviculture.