Little is known about the long-term consequences of surgically implanted telemetry devices on wild fish, as they are rarely recaptured. We used wild largemouth bass Micropterus salmoides as a model to evaluate the long-term impacts of telemetry devices on fish physiology and nutritional condition in a closed freshwater lake where recapture rates were reasonably high. Between 2003 and 2005, 68 fish were surgically implanted with acoustic telemetry devices. Between 2005 and 2008, 17 of the tagged fish were recaptured after carrying a transmitter for 335 to 1402 d. Incision sites were examined, and individuals were non-lethally sampled for blood and measured prior to release. Plasma samples were analysed, and physiological measures of stress (glucose, Na+, Cl–, K+), tissue damage (aspartate aminotransferase), and nutritional status (Ca++, Mg+, phosphorus, total protein, triglycerides, cholesterol) were compared between fish carrying transmitters and temporally- and size-matched controls. Of the 17 recaptured fish, 3 retained at least 1 of the absorbable monofilament sutures and showed localised signs of inflammation and infection despite an elapsed time of 362 d post surgery. Five individuals showed signs of pressure necrosis at the incision site despite the fact that the transmitters averaged only 1.89% (range: 0.84 to 3.59%) of the body mass. There was no difference in any physiological parameter measured between the 2 groups, or within the telemetered fish, in relation to days since tagging or condition of the incision site. In summary, transmitter implantation was not correlated with any long-term change in any of the physiological parameters investigated. However, there is opportunity for additional research to optimise surgical techniques, guidelines on transmitter mass to body mass ratios, and choice of suture material to enhance the healing and long-term welfare of tagged fish.
Study site. Warner Lake is a small (approximately 8.2 ha surface area) private research lake in eastern Ontario (44° 31’ N, 76° 22’ W). In November of 2003, the lake was equipped with a code division multiple access technology (CDMA)-based acoustic telemetry array (Cooke et al. 2005a, Hanson et al. 2007a,b). Warner Lake is a closed system, and has been used by researchers to study largemouth bass population dynamics since 1996 using passive integrated transponder (PIT) tags (Biomark) for long-term monitoring. Largemouth bass are the largest species, apex predator, and the only tagged species of fish in the lake.
Transmitter implantation. Between 2003 and 2005, 68 adult largemouth bass (all >28 cm total length) were implanted with acoustic telemetry devices (see Hanson et al. 2007b). The transmitters were embedded within a polyethylene sleeve, with a bio-compatible epoxy on one end, with no antenna. Fish were implanted with acoustic telemetry devices on 3 separate occasions: October 2003, October 2004, and October 2005 (see Hanson et al. 2007b for details). The size of the transmitters used varied among the different years depending upon the sensors aboard the device and other settings that influenced battery size (see Hanson et al. 2007b for details on all of the devices). We attempted to abide by the ‘2% rule’ (that the mass of the device should be no more than 2% of the body mass of the fish; Winter 1983, Brown et al. 1999), although on occasion we violated it slightly (largest deviation was 3.59% ratio of transmitter mass in air to fish mass in air). More importantly, prior to implanting an individual and again during surgery, we determined that there was adequate room within the abdominal cavity for the device such that there would not be any pressure on viscera or the body wall that could lead to problems with feeding or pressure necrosis. For all occasions, fish were implanted using standard surgical procedures (see Cooke et al. 2003). Briefly, fish were anaesthetised by placing individuals in an induction bath containing 60 mg l–1 clove oil emulsified in ethanol. After loss of equilibrium (5 min), total length measurements were taken, and fish were placed on a foam surgery table. During the surgery, the gills were continuously irrigated with recirculating water containing a maintenance dose (20 mg l–1) of clove oil in ethanol. A small incision (~1.5 cm) was made on the ventral side of the fish using a sterilised scalpel. An acoustic transmitter was then inserted into the intraperitoneal cavity, and the incision was closed using 3 independent absorbable monofilament PDS II sutures (size 3/0, FSL needle, Ethicon). Measures were taken to ensure a near-sterile environment, including the use of surgical gloves and disinfection of all surgical instruments using iodine. Additionally, all fish were individually identified with PIT tags. After surgery, the fish were placed in a recovery bath and were released upon regaining equilibrium (10 to 20 min). Experienced surgeons performed all implants (Cooke et al. 2003), no immediate (i.e. <1 h) mortality was observed, and all fish were released following the surgeries.