Evaluation of six methods for external attachment of electronic tags to fish: assessment of tag retention, growth and fish welfare.

External attachment of electronic tags has been increasingly used in fish studies. Many researchers have used ad hoc attachment methods and provided little or no validation for the assumption that tagging itself does not bias animal behaviour or survival. The authors compared six previously published methods for externally attaching acoustic transmitters to fish in a tank holding experiment with black sea bass Centropristis striata (L.). They tracked tag retention, fish growth and external trauma (as a measure of fish welfare) for 60 days. For each of these metrics, the results showed a wide range of responses among tagging treatments. A simple attachment method using a spaghetti tag passed through the dorsal musculature of the fish and tied to the end cap of the transmitter emerged as the preferred option based on high retention, no impact on growth and relatively low detriment to fish welfare. Future field studies using external electronic tagging should consider tag-related effects that could compromise results when selecting a method for tag attachment.