Swimming efficiency and growth of anchor‐tagged red drum (Sciaenops ocellatus) juveniles were compared with untagged controls. The O₂ consumption of fish swimming at different speeds was measured in a Blazka‐type respirometer. Daily growth rates of tagged and untagged red drum were compared over 42 d of feeding fixed rations of live mosquitofish (Gambusia affinis) to siblings held individually in 380 L tanks. At swimming speeds of ≤1.0 body lengths per second (bl s^‐1), no differences in O₂ consumption were found. However, at speeds of 1.5–2.5 bl s^‐1, tagged red drum O₂ consumption was significantly greater (by 36–39%) than that of untagged fish (ANOVA, P<0.05), indicating a substantially impaired swimming efficiency. Daily growth rates of tagged and untagged fish also differed significantly (P < 0.02). Tagged fish grew at a mean rate of 0.95 mm d^‐1 and 1.45 g d^‐1, while untagged fish (controls) grew at 1.14 mm d^‐1 and 1.62 g d^‐1. Results suggest that internal anchor tags, which weighed less than 1% offish body weight, represented a hydrodynamic drag burden that reduced swimming performance and growth. These effects may decrease growth and/or survival in the wild and thus bias estimates of biological parameters in stock assessment and enhancement studies.