Impact of a telemetry-transmitter implant on daily behavioral rhythms and physiological stress indicators in gilthead seabream (Sparus aurata).

The effect of intracoelomic tagging of an acoustic telemetry transmitter (1.65% ratio of tag mass in the air to fish mass in the air) on behavioral (food intake and locomotor activity) and physiological (blood glucose and plasma cortisol) parameters of gilthead seabream was investigated. To this end, fish (289 ± 53 g, mean ± SD) were divided into 3 experimental groups: control (C), transmitter (T, inserted surgically) and sham group (S, subjected to surgery but without transmitter insertion). Blood was extracted during surgery and 9 days later. Throughout the trial, fish were fed by means of self-feeders and locomotor activity was measured by means of an infrared photocell. Two days after the first manipulation, a significant decrease in food intake could be observed in all the experimental groups. The fact that food intake was not affected after the second manipulation seems to indicate that a learning process took place for handling. The rhythmicity of feeding and locomotor activity was not affected by handling in any experimental group. However, group T showed increased plasma cortisol levels 9 days after surgery. In conclusion, while most behavioral parameters were not affected by handling, the plasma cortisol levels of seabream 9 days after insertion of the transmitter indicated a physiological impact that should be taken into account in long-term radiotracking studies, since such an operation could have negative effects on wild individuals after the end of the tracking experiments.