Passive integrated transponders in Gila elegans: Location, retention, stress, and mortality

Despite large-scale propagation and rearing efforts few of the critically endangered bonytail, Gila elegans, are recovered following release from hatcheries. This study tested the role of passive integrative transponder (PIT) tag loss and tagging associated stress and mortality in these low recoveries. Bonytail exhibited 98-100 percent tag retention regardless of insertion direction (ventral toward anterior and anterior toward ventral). Plasma cortisol levels were measured at 0, 0.5, 3, 6, 12, and 24 hours following PIT-tagging in fish held at three temperatures (12, 16, and 20°C) as an indicator of stress. Bonytail tagged at 16°C had significantly lower plasma cortisol levels than those of fish tagged at 12°C and 20°C. At all three temperatures cortisol levels returned to baseline with in 24 hours. Mortality associated with PIT-tagging was only observed at 20°C. These data suggest that PIT tag handling for bonytail should occur at 16°C