Radio-tagging flexible-bodied fish: temporary confinement enhances radio-tag retention

Animals that occupy holes or squeeze into interstitial spaces often have particularly flexible bodies and can be difficult to tag effectively. The present study evaluated three methods for radio-tagging the cryptic, eel-like fish Gadopsis bispinosus, a species that inhabits interstitial spaces among cobbles and boulders in streams. The three methods were an externally attached radio-tag with a whip antenna, an internally implanted coil radio-tag (internal coil) and an internally implanted radio-tag with an externally exited whip antenna (internal-external). Successful radio-tagging was determined in aquaria trials based on a combination of four indicators: (1) survival; (2) retention of the radio-tag; (3) healing of the surgical incision; and (4) rapid resumption of feeding. Externally attached radio-tags were shed and proved to be unsuitable (100%). Three of nine individuals with internal-external tagging completed the study with regular feeding, healed incisions and retained radio-tags. Conversely, five of nine individuals with internal coils were successful. This included two of three individuals held in either a simple environment for 3 days or for the duration of the trial and one of three individuals held in a complex environment. Temporary confinement following implantation with coil radio-tags offers a viable means of radio-tagging G. bispinosus. Temporary confinement following radio-tagging may also be useful for reducing radio-tag rejection and mortality for other fish species with similar body morphs and habitat use (e. g. eel species and sculpin).