Abstract

Transmitters can be surgically implanted into the body cavity (internal) of fish, inserted into the stomach (gastric), or fixed to the surface of the body (external)¹. Internal implantation of transmitters is a technique well suited for long-term experiments, but care must be taken to reduce postoperative trauma. Gastric implantation is known to interfere with feeding; external tagging can significantly alter behavior or swimming ability. Although transmitters are often implanted into salmon and trout (Oncorhynchus and Salmo spp.), and numerous other freshwater fish species (catfish; Pylodictis, bass; Morone spp., bluegill; Lepomis, and crappie; Pomoxis), few marine fishes have been successfully implanted². Twenty-three adult (>40 cm TL) Nassau grouper were internally implanted with ultrasonic transmitters and released. No individuals expired from the surgical procedure. These cylindrical transmitters (16 mm diameter, 75 mm long, and 12 grams) are pressure-sensitive, powered by a lithium battery, and have a battery life of 60 days. MS-222 (tricaine methanesulfonate, an isomer of benzocaine) anesthesia was used as both a calming agent (1 gram MS-222/1 L seawater) and as a tranquilizer (125 mg MS-222/1 L seawater). After 4-6 minutes in the anesthesia bath, the fish were prepared for surgery. All procedures were conducted on a 15' boat. An approximate 1-3 cm para-median incision into the left lateral body wall was made midway between the pelvic fin origin and the cloaca with a scalpel. This incision was made in two steps: the first cut through the integument, and muscle, the second cut through the coelomic cavity into the parietal peritoneum. Acoustic transmitters were then inserted into the coelomic cavity of the grouper through the incision to a position anterior to the anus and behind (at least 9 cm) the pelvic fin to ease tension on the incision. The incision was closed with a single row of three interrupted sutures through the peritoneum and the dermis using a curved cutting needle (FS-1) swedged with 2-0 chromic gut (Ethicon8). Amikacin antibiotic (5mg/kg body weight) was injected into the dorsal musculature³. Fish were allowed to recover in a holding pen for 24-36 hours and fed before release. Normal feeding and swimming behavior observed upon release indicated that post-operative trauma was not extensive. Visual sighting of individuals (n=6) 3 weeks after surgery revealed healing wounds with slight swelling, and at 4-6 weeks (n=10) the incision was barely noticeable. Three individuals sighted a year after surgery had no visible external scar; the transmitter obviously still implanted (outline visible through the abdomen). A single individual recaptured a year later revealed a well-healed incision with an encapsulated transmitter. All but 3 animals were verified to be alive at 3 weeks post-operative by tracking data; two individuals perished, and one individual's transmitter malfunctioned and was never recorded. Hence, post-operative survivability at 3 weeks was 92%.

The above surgical procedure was utilized in an investigation of Nassau grouper home range. Nassau grouper are a listed Acandidate species@ (Endangered Species Act) and are protected from harvest in the U.S. Nassau grouper are coral reef associated top-level predators and are distributed throughout the islands of the western Atlantic, southern Florida, and along the coasts of central and northern South America. All fish in this study were tagged and released in the Exuma Cay Land and Sea Park (a no-fishing zone) located in the central Bahamas (24°34'N, 76°33'W). The home range study utilized a buoy tracking system which recorded (via transmitter) individual position per minute. The purpose of the home range study is to identify the aerial coverage of a home range and to investigate the affects of habitat productivity on home range size.

Table 1. Summary of ultrasonically tagged Nassau grouper 1997 and 1998 with post-operative field observations.

*Recaptured one year later with peritoneal transmitter encapsulated, released as fish #19 with new transmitter.
TL = total length in centimeters; kg = kilograms

References

1.  Peake S, RS McKinley, DA Scruton, R Moccia. 1997. Influence of transmitter attachment procedures on swimming performance of wild and hatchery-reared Atlantic Salmon smolts. Trans. Amer. Fish. Soc.126: 707-714.

2.  Stasko AB, DG Pincock. 1977. Review of underwater biotelemetry, with emphasis on ultrasonic techniques. J. Fish. Res. Board. Can.34: 1261-1285.

3.  Carpenter JW, Mashima TY, DJ Ruiper. 1996. Exotic animal formulary. Greystone Publications, Manhattan, Kansas, p. 15.