Common carp (Cyprinus carpio) are notoriously difficult to monitor in water temperatures above 20◦C using telemetry owing to transmitter expulsion. To reduce transmitter loss, radio transmitters were anchored to the pelvic girdle and a polymer coating was applied to acoustic transmitters to reduce tissue irritation in two tank trials. Ten dummy transmitters were surgically implanted in each of four groups of adult koi carp, a highly coloured strain of C. carpio. Water temperatures ranged between 7 and 24◦C. After 365 days, the control and test groups of each trial had similar expulsion rates (P≥0.30; two-tailed Fisher’s exact probability test). Expulsion rates for uncoated acoustic transmitters were 60% (n=6), coated acoustic transmitters 50% (n=5), unanchored radio transmitters 60% (n=6) and anchored radio transmitters 90% (n=9). Expulsions occurred 15–362 days after implantation as a result of ulcers at or near the surgical wound. Bacterial infection of the wound appears to be the primary mechanism for transmitter expulsion.