Buoyancy Compensation by Atlantic Salmon (Salmo salar) Smolts Tagged Internally with Dummy Telemetry Transmitters

Abstract

Negative buoyancy was induced in Atlantic salmon (Salmo salar) smolts by insertion of dummy telemetry tags (4.0 g in water) into the stomach. Buoyancy adjustment by means of swimbladder volume change was determined in tagged and untagged (control) smolts either allowed or denied access to the water surface. Regression of percent recovery of initial buoyancy on recovery time showed that tagged fish with access to the surface gradually increased their buoyancy over a 6-h test period. Only 1 of 28 fish held 0.5–2.0 h recovered its initial buoyancy, while 7 of 26 held 2.5–4.0 h recovered, and 7 of 24 held 4.5–6.0 h recovered. Tagged fish without access to the surface never regained buoyancy and became slightly heavier with time. Two tagged fish without access to air were unable to compensate for negative buoyancy after 24 h, but exhibited total or partial recovery when examined 6 h after being allowed access. Control fish did not alter buoyancy with handling or over time.