Transintestinal Expulsion of Surgically Implanted Tags by African CatfishHeterobranchus longifilisof Variable Size and Age

Transintestinal expulsion of surgical implants by fish is an exceptional phenomenon, except in the case of channel catfish Ictalurus punctatus. In order to test whether this mechanism was shared by other siluriform species, passive integrated transponder tags and epoxy dummy transmitters (0.5–2.0% of fish body weight) were surgically implanted into the peritoneal cavity of age-0, age-1, and age-2 African catfish Heterobranchus longifilis, which are known as vundu or sampa, (20 fish in each group). Transmitters were placed posterior to midventral incisions, which were closed with braided silk or polyamide stitches. Four tags were expelled through the incision within 4 d, and six others were expelled through the intestine from day 8 to day 12. Necropsies of sampled fish retaining their tag until day 14 indicated six additional situations that were indications of potential expulsion through the intestine (N = 5) or body wall (N = 1). No other tag was expelled later than day 14, and final necropsies on day 91 revealed no indication of later expulsion. As in channel catfish, transintestinal expulsion by vundu involved the formation of a capsule, its adhesion to the intestine, the rupture of the wall of the pyloric intestine, the passage of the tag into the lumen of the intestine, and its expulsion by peristalsis. Transintestinal expulsion was observed in vundu of all ages. Its occurrence was independent (P > 0.50) from fish sex, but significantly (P < 0.05) lower with polyamide monofilaments than with braided silk. This was not the case for silk-sutured age-2 mature males or prespawning females, in which the tag capsule adhered to the abdominal fat (males) or ovaries, and was consistently retained until 91 d. These findings suggest that the mechanism of transintestinal expulsion described for channel catfish may be shared by vundu. The possible impact on telemetry studies may be mitigated through appropriate procedures.