A comparison of implantation methods for large PIT tags or injectable acoustic transmitters in juvenile Chinook salmon

The miniaturization of acoustic transmitters may allow greater flexibility in terms of the size and species of fish available to tag. New downsized injectable acoustic tags similar in shape to passive integrated transponder tags can be rapidly injected rather than surgically implanted through a sutured incision. Before wide-scale field use of these injectable transmitters, standard protocols to ensure the most effective and least damaging methods of implantation must be developed. Three implantation methods were tested in various sizes of juvenile Chinook salmon (Oncorhynchus tschawytscha). Methods included a needle bevel-down injection, a needle bevel-up injection with a 90° rotation, and tag implantation through an unsutured incision. Tagged fish were compared to untagged control groups. Weight and wound area were measured at tagging and every week for 3 weeks; holding tanks were checked daily for mortalities and tag losses. No significant differences among treatments were found in tag loss, or survival, but wound area was significantly reduced among fish tagged via an incision and growth was slightly reduced in bevel down fish. Although there were no significant differences, the bevel-up injection trended toward having the worst results in terms of tag loss and wound area and had high mortality. Implantation through an incision resulted in the lowest tag loss but the highest mortality. Fish from the bevel-down treatment group had the least mortality and smaller wound areas than the bevel-up treatment group but also showed reduced growth. Cumulatively, the data suggest that the unsutured incision and bevel-down injection methods were the most effective; the drawbacks of both methods are described in detail.