Fish telemetry is increasingly used to study fish behaviour in marine systems and it is crucial that the tagging does not affect fish behaviour and welfare negatively. Hence, the long-term effects of surgically implanted acoustic telemetry transmitters on survival, tag retention, healing and growth on Pomatomus saltatrix (known as tailor in Australia, elf in South Africa and bluefish in North America) were studied over 144 days. P. saltatrix are well suited for transmitter implants because no tagging-related short- or long-term mortality or transmitter expulsion was recorded. Small transmitters (9 × 28 mm, 3.3 g in water) did not affect the specific growth rate of tagged fish compared with an untagged control group. In contrast, the fish tagged with large transmitters (13 × 50 mm, 6.9 g in water) had a reduced specific growth rate. The small, but not the large transmitter, seemed suitable for tagging P. saltatrix of the body sizes represented in this study (215–621 g). The specific growth rate was negatively affected by increasing the transmitter-mass-in-water to body-mass ratio. It is recommended that this ratio should not exceed 1.4%.