Antonyms for the phrase "showed gain" could include "suffered loss," "experienced decline," or "failed to improve." These terms suggest a negative outcome or a setback, rather than progress or success. Other opposing phrases might include "fell short," "regressed," "went backwards," or "lost ground." Essentially, any term that implies a failure to advance, grow, or succeed could serve as an antonym for "showed gain." It's important to consider the context in which these terms are used, as some may have different connotations depending on the situation.