Transintestinal expulsion of surgically implanted tags by African catfish Heterobranchus longifilis of variable size and age

Transintestinal expulsion of surgical implants by fish is an exceptional ph enomenon, except in the case of channel catfish Ictalurus punctatus. In ord er to test whether this mechanism was shared by other siluriform species, p assive integrated transponder tags and epoxy dummy transmitters (0.5-2.0% o f fish body weight) were surgically implanted into the peritoneal cavity of age-0, age-1, and age-2 African catfish Heterobranchus longifilis, which a re known as vundu or sampa, (20 fish in each group). Transmitters were plac ed posterior to midventral incisions, which were closed with braided silk o r 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 Chat were indications of potential expulsion through the intestine (N = 5) or body wall (N = 1). No other tag was expelled late r than day 14, and final necropsies on day 91 revealed no indication of lat er expulsion. As in channel catfish, transintestinal expulsion by vundu inv olved the formation of a capsule, its adhesion to the intestine, the ruptur e of the wall of the pyloric intestine, the passage of the rag into the lum en of the intestine, and its expulsion by peristalsis. Transintestinal expu lsion 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 mo nofilaments 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 unt il 91 d. These findings suggest that the mechanism of transintestinal expul sion described for channel catfish may be shared by vundu. The possible imp act on telemetry studies may be mitigated through appropriate procedures.