Evaluation of implantation procedures for PIT-Tagging juvenile Nile tilapia

We evaluated three alternative procedures for tagging juvenile Nile tilapia Oreochromis niloticus (1.9-13.7 g) with passive integrated transponder (PI T) tags: injection with hypodermic syringe injectors (N = 40) and abdominal surgery with or without suturing (N = 55 and 40, respectively). The surviv al of Nile tilapia tagged with injectors was low (10-50% at 10 d) and propo rtional to fish size because of the difficulty of controlling the penetrati on of the syringe into the intraperitoneal cavity following the piercing of the body wall. Surgically implanted fish had much higher survival rates (7 8-100% at 10 d). Suturing reduced the risks of tag expulsion and protrusion of the viscera through the open incision within the first 3 d following su rgery (10% risk in the nonsutured fish). Over the first 3 d after tagging, tagged fish showed depressed growth rates (to a greater extent in smaller f ish and proportionally greater in sutured fish) but showed normal growth la ter on. These results demonstrate that surgery is suitable for PIT-tagging small juvenile Nile tilapia, which offers opportunities for studies of indi vidual performance.