Long-term effects of different-sized surgically implanted acoustic transmitters on the sciaenid Arygyrosomus japonicus: breaking the 2% tag-to-body mass rule

Biotelemetry is an increasingly popular and effective tool to study fish movements. Interpretation of the results relies on the assumption that fish behaviour and physiology is not affected by the presence of the tag. Although the long-term effects of tagging should be evaluated before field telemetry studies, this has rarely been quantified. As a precursor to a long-term telemetry study on Argyrosomus japonicus (Termminck and Schlegel 1843) in South Africa, the effects of surgical implantation of two different-sized tags were assessed in a 256-day experiment. We hypothesised that the larger 13-mm-diameter tags, which exceeded the general 2% tag-to-body mass rule, would have adverse effects on growth, survival and tag retention compared with the smaller 9-mm-diameter tags and an untagged control group. Because no adverse effects in growth were observed among the three groups, nor any long-term tag-related mortality, tag expulsion or internal damage, we suggest that the general 2% tag-to-body mass rule should be regarded only as a broad guide. Further, we conclude that juvenile A. japonicus individuals are well suited for surgical implantation of commercially available 9- and 13-mm-diameter tags and are good candidates for long-term telemetry studies.