Evaluation of external operculum loop tags to individually identify cage‐cultured Atlantic halibut Hippoglossus hippoglossus in commercial research trials

Abstract

The growth, survival and tag retention of double-tagged [external FT4 lock-on (FT4) and internal passive integrated transponder (PIT)-tagged] Atlantic halibut Hippoglossus hippoglossus were compared to internal PIT-tagged controls in a randomized trial. The objective was to assess the suitability of these tags for monitoring the performance of individual fish in longitudinal trials under commercial cage-culture conditions in the lower Bay of Fundy, New Brunswick, Canada. The FT4 tags were chosen due to their similarity to tags used by investigators to track H. hippoglossus in the wild. A subset of the population randomly received an external FT4 tag inserted through the operculum and were monitored over a 1105 day period. The specific growth rate of FT4-tagged fish was significantly reduced in the first sea summer with no significant difference observed for the remainder of the trial. The differential growth in the first sea summer created a relative size advantage, permitting controls to increase in size significantly faster than FT4 fish in all subsequent periods. The FT4 tags did not significantly influence survival under normal commercial cage-culture conditions. Results, however, suggest that the survival of FT4-tagged H. hippoglossus may be compromised during stressful handling events. Tag retention of FT4 tags was acceptable with 76% of tags remaining at the end of the 1105 day trial. FT4 tags proved to be an effective method to identify individual H. hippoglossus, with the caveat that they seriously bias productivity measures in commercial research trials.

Tag use to monitor fish behaviour in aquaculture: a review of benefits, problems and solutions

“…Examples of how these effects were reported in externally tagged fish include the following: Sykes et al . (2012), who reported cases of ripped opercula and chronic skin lesions around the tag attachment site in FT4 opercular loop tagged fish, and reduced growth rates in externally tagged fish compared to PIT tagged fish. Ferrer et al .…”

“…Common sublethal physical effects of following tag insertion include necrosis and inflammation (Lowartz et al 1999;Wagner et al 2000;Wagner & Cooke 2005). Despite Sykes et al (2012) detailing cases of ripped opercular and chronic skin lesions around the tag attachment site in FT4 opercular loop tagged fish, the focus of this study was to explicitly test tagging effects for this tag type. Researchers that are using tags to get answers on behavioural questions may not be as concerned with necrosis or inflammation at the tagging site if the fish's behaviour appears normal throughout the study.…”

“…skin/scale loss, necrosis, bacterial infection, fouling) was uncommon and brief when done so. Examples of how these effects were reported in externally tagged fish include the following: Sykes et al (2012), who reported cases of ripped opercula and chronic skin lesions around the tag attachment site in FT4 opercular loop tagged fish, and reduced growth rates in externally tagged fish compared to PIT tagged fish. Ferrer et al (2020) reported no signs of haemorrhaging or tissue damage in their externally tagged fish.…”

“…Infection of tagging-induced wounds may therefore be more likely to occur in a high-density environment and may lead to altered behaviour in the tagged fish, rendering it unrepresentative of the farmed population. In addition, common husbandry processes or environmental conditions on farms can induce stress that can suppress the immune system and cause altered behaviour or elevated mortality of tagged individuals if they are already under additional stress from tagging (Sykes et al 2012;Stehfest et al 2017). Aquaculture also forces spatially and seasonally restricted environments on fish, of which may include extreme experiences that normally would be avoided in the wild.…”

Ethical considerations in fish research

“…Biofouling in the field and laboratory can further alter the physical properties of external tags (Thorstad et al, 2001). Swimming with increased hydrodynamic drag and compensating for changes in buoyancy can increase a tagged fish's energy expenditure (Lefrançois et al, 2001;Lowe et al, 1998;Methling et al, 2011;Steinhausen et al, 2006) leading to reduced growth rates, delayed maturation (Manire & Gruber, 1991;McFarlane & Beamish, 1990;Sykes et al, 2012) reduced foraging ability and ability to escape predators (Adams et al, 1998;Feltham & MacLean, 1996;Ross & McCormick, 1981). As such, the inappropriate application of external tags to fishes can have direct consequences for individuals.…”