Influence of intraperitoneal implantation of 12 mm PIT on the welfare of juvenile brown trout (Salmo trutta)

The influence of the implantation of 12 mm passive integrated transponders (PIT) tags on juvenile brown trout (fork length approximately 19 cm) for 28 days after tagging was analyzed. The fish were divided into three groups: control, sham (injected with a syringe without PIT tag insertion), PIT tagged. Biological data were collected on days 0 (initial sample), 7, 14, and 28 of the experiment. Growth performance, feeding effectiveness, PIT retention, implantation wound healing, and hematological, biochemical blood plasma (stress indicators, nutritional status), and phagocytic activity indicators were analyzed. On day 28, the implantation wounds were fully healed, and PIT retention was 97.5%. The treatment did not influence growth performance, feeding effectiveness, survival, or the majority of hematological indexes. After day 7, significant changes were noted in plasma cortisol levels (PIT and sham groups), white blood cell counts (all groups), hemoglobin levels, and differential leukocyte counts (PIT group), and cidal ability after day 14 (PIT and sham groups). After day 28, the physiological indicators in the control, sham, and PIT groups did not differ significantly. These results should be taken into consideration when stocking natural streams with juvenile brown trout tagged with PITs, e.g., the period that tagged fish are held prior to stocking.