Increased duration of tag retention in difficult-to-tag ictalurid catfish

Objective Tagging methods used to deploy biologging devices must balance retention, fish welfare, and data reliability, yet limited comparative work has evaluated attachment techniques for Channel Catfish Ictalurus punctatus. We aimed to compare conventional internal tag placement as unsecured tags within the peritoneal cavity to external attachment via anchor tags, which have higher retainment rates but have not been previously used for biologger attachment. Methods We assessed dummy tag retention performance in juvenile–adult (market-sized) Channel Catfish across five attachment methods: two internal implantation approaches (midline and lateral incisions) and three external methods (T-bar tags with tape, T-bar tags with zip-tie fixation, and dart tags). Fish were surgically tagged, allowed to recover, and monitored for 160 d for wound healing, survival, and tag expulsion. Results Wound healing was high for all treatments, suggesting that tag loss was not associated with poor healing at incision sites. Internal tags had similarly high retention rates between the two groups, with mean durations of 142 d for midline incisions and 139 d for lateral incisions. Fish had 75% and 89% retention by 140 d and 38% and 55% retention by 160 d for midline and lateral incision groups, respectively. External tags exhibited markedly lower retention rates, with mean durations of 41–82 d for T-bar attachments and only 10 d for dart tags. Fish with dart tags had 0% retention by day 16, while fish that received the T-bar with tape had 11% retention and those receiving the T-bar with zip-tie attachment had 50% retention at 105 d. Postexperiment necropsies revealed predictable internal tag expulsion pathways, including hepatic adhesion and transintestinal movement, which suggested that the tags would have been eventually expelled. Conclusions These results demonstrate that unfixed internal implantation can provide better retention and healing outcomes compared with external attachment methods. Our work extends previous findings that difficult-to-tag catfish can have higher retention for 140 d with placement through a lateral incision.