These data set contain experimental data from a series of laboratory feeding experiments designed to investigate the predation effects of the invasive ctenophore Mnemiopsis leidyi on yolk-sac larvae of herring (Clupea harengus) in the Baltic Sea. This dataset includes detailed records of predator-prey interactions, specifically focusing on the clearance rates of M. leidyi based on variables such as larval age, predator size, and the presence of alternative prey. Key data features includes (1) predator size and clearance rates: data on the clearance rates of M. leidyi specimens of various sizes, showing the relationship between predator size and feeding efficiency on herring larvae, (2) larval age and predation: Information on how the age of herring larvae influences their susceptibility to predation by M. leidyi, and (3) prey selection experiments: results from experiments assessing the impact of the presence of alternative prey (Acartia tonsa) on the predation rates of herring larvae by M. leidyi. Environmental conditions under which the experiments were conducted, ensuring reproducibility and comparative analysis with field conditions. This dataset is crucial for understanding the potential ecological impact of M. leidyi on herring populations in the Baltic Sea, particularly in light of ongoing environmental changes and the species' invasive nature. The data support further research on jellyfish-ichthyoplankton interactions and contribute to broader ecological and fisheries management discussions.