Effects of passive integrated transponder (PIT) implantation on Pacific lamprey ammocoetes

Little is known of the larval biology of Pacific lamprey (Entosphenus tridentatus), a species of conservation concern. With miniaturization of passive integrated transponder (PIT) tags, researchers now have the potential to individually mark larval lamprey. However, recent studies with sea lamprey (Petromyzon marinus) ammocoetes indicated that mortality was unacceptably high after surgical implantation of these tags. We examined survival, tag retention, growth, and swimming performance of Pacific lamprey ammocoetes tagged with uniquely coded 8.4-mm PIT tags and controls marked with visible implant elastomer (VIE). Ammocoetes as small as 71 mm in length were PIT-tagged. Of the 99 PIT-tagged individuals, four died (4%) and two lost their tags (2%) within 2 months of tagging. In this period, controls had 5% mortality and 15% VIE mark loss. Incisions were completely healed within 3 months of tagging, and mean specific growth rate during this period did not significantly differ between treatment groups. Ammocoetes bearing a PIT tag did not exhibit significant reductions in swimming performance relative to controls. We attribute the success of this tagging effort to changes in tag implantation technique, including use of a lateral incision and no sutures. The ability to individually mark wild larval lamprey will allow research on individual growth rates, environmental effects on growth and metamorphosis, timing and rates of movement, and, ultimately, stage-specific survival.