Evaluation of six methods for external attachment of electronic tags to fish: assessment of tag retention, growth and fish welfare

Positional effects of passive integrated transponder tags on rejection, survival, and health biomarkers in pearlspot cichlid (Etroplus suratensis)

Passive integrated transponder (PIT) tagging is essential in fisheries research to monitor fish growth, health, and migration, and facilitate selective breeding and aquaculture advancement. The study was conducted for 30 days to assess the effect of the PIT tag (12 mm × 2.1 mm) on juvenile Etroplus suratensis. The tagging study consisted of five treatments, viz., dorsal horizontal (DH), dorsal vertical (DV), peritoneal cavity via injection (PCI), peritoneal cavity via incision and manual insertion (PCM), and untagged control (UT) in triplicate. Fifteen circular containers containing 60 L of UV-sterilized water were stocked with 15 juveniles each, with an average weight of 10.60 ± 0.06 g and a total length of 67.75 ± 1.07 mm. Fish were given commercial floating feed with 38% crude protein thrice daily (9 am, 1 pm, and 5 pm). In the present study, the DV-tagged juveniles had the highest survival (95.55 ± 2.22%) with a low tag rejection rate (4.44 ± 2.22%) and a higher weight gain (5.10 ± 0.76 g), followed by the DH-tagged, which showed survival of 91.11 ± 2.22% with a tag rejection of 31.11 ± 2.22% and a weight gain of 4.36 ± 0.23 g. The serum biochemical and haematological parameters were substantially higher in tagged fish than in untagged fish. Histological examination of tagged fish revealed observable changes in myocytes compared with untagged fish. Analysis of growth, survivability, tag rejection rate, and histological interpretations indicate that DV tagging is the best practice for E. suratensis juveniles. This study highlighted the importance of optimizing PIT tagging procedures for E. suratensis and demonstrated that the insertion position significantly influences tag retention, survival, and stress parameters. The results enhance the acceptability of PIT tagging in pearlspot for aquaculture and stock assessment studies.

Effects of handling and surgical implant on juvenile wild trout: Physiological and behavioral impact

Fish involved in telemetry studies are usually handled, anaesthetized, and subjected to internal tag implantation, all of which have the potential to disrupt the fish's physiology, migratory patterns, food-seeking behavior, growth, and survival. As fish tagging is a widespread standard method in aquaculture, it is crucial to gain a better understanding of the short- and long-term effects on various aspects of fish welfare. The experimental outcomes of each phase of the surgical process and how it affects the fish's ability to recover during the post-tagging period, particularly in small salmonids, are poorly understood. Thus, it is essential to measure the extent of these adverse effects to precisely extrapolate differences in surgical intervention for tagged fish compared to their unmanipulated counterparts. In our study, we explored the post-tagging impacts on wild-captured brown trout (Salmo trutta) (1+) juveniles. We examined the time effect on fish recovery after each phase of the surgical procedure, which included anaesthetized fish, followed by surgery with/without internal tagging, within the first 2 and 25 h post-surgery. Common blood parameters (glucose levels and haematocrit) and endpoints related to swimming behavior, including fish movement, direction, and social distancing aspects, were studied. The findings of the study indicated no significant changes in glucose and haematocrit levels over the observational period. Fish subjected to anesthesia and tagging procedures exhibited a significant decrease in swimming activity, recovering to baseline levels 1 h after anesthesia and 24 h after surgical (tagging) procedures in recirculating aquaculture systems. Tagged fish showed less social proximity than non-tagged fish in the first 2 h post-surgery. A significant effect size was observed between nonsurgical (anesthesia) and surgical (non-tagged/tagged) groups, highlighting a more pronounced impact associated with surgical tag interventions. Our data indicate that the magnitude of behavioral response was significantly influenced by tag weight (~1.4% body/tag weight ratio in water) among manipulated fish groups. Consequently, our study reveals that wild-captured S. trutta juveniles, tagged with commercially available low-weight acoustic tags (V6, 69 kHz), experienced negative effects on swimming performance. In surgical studies, acknowledging potential influences is crucial for accurately inferring fish physiological and behavioral status. Emphasizing fish recovery potential in both short- and long-term periods is essential for quantifying tagging effects. Future research should prioritize exploring alternative tagging technologies and refining methodologies, with a particular focus on assessing telemetry's impact on socioeconomically relevant small salmonids.

Evaluation of Post-Surgical Recovery in Olive Flounder (Paralichthys olivaceus) by Assessing Behavior, Heart Rate, and Wound Healing

This study examined the post-surgery recovery of olive flounder (Paralichthys olivaceus) following tag insertion by analyzing behavior, heart rate, and wound healing. The experiments used 30 individuals (length: 38.67 ± 2.12 cm; weight: 742.48 ± 116.41 g). Heart rate was measured using a DST milli-HRT (Star-Oddi) bio-logger. To assess the influence of water temperature on the recovery process after surgical tag insertion, behavioral analyses, heart rate, and wound healing were conducted in two experimental groups: Experiment 1 (22 °C, optimal water temperature); Experiment 2 (28 °C, high water temperature); and control group (22 °C, non-operated fish). The experiment was repeated twice over a 7-day period for each experimental group. Compared to the non-operated fish, the operated fish exhibited stable levels after the 3rd to 4th day in Experiment 1. Statistical analyses based on heart rate in Experiment 1 indicated that the appropriate post-surgery recovery time point was approximately 3 days, representing the point at which behavioral fluctuations stabilized. In the case of Experiment 2, abnormal behavioral patterns (e.g., tilted swimming) and changes in average swimming time and daily heart rate were found to stabilize after 4 days post-surgery.

A method for long-term retention of pop-up satellite archival tags (PSATs) on small migratory fishes

Achieving long-term retention of pop-up satellite archival tags (PSATs) has proven difficult for all fishes but is particularly challenging for small migrant species due to the relatively large size of tags. In this study, the authors tested the latest and smallest PSAT model on the market, the mark-report satellite tag (mrPAT), and developed a simple, cost-effective method of tag attachment on sheepshead Archosargus probatocephalus (Walbaum 1792), a small marine fish. During laboratory trials, the method of tag attachment used in this study outperformed the existing methods with two c. 40 cm fish retaining their tags for 3 months (the duration of the laboratory study). During field deployments, data were successfully obtained for 17 of the 25 tagged fish [37-50 cm fork length (FL)]. Of these, 14 tags (82%) remained on the fish until the pre-programmed release date resulting in tag retention times of up to 172 days (mean: 140 days). The investigation represents the first extensive study into the feasibility of PSATs for monitoring fishes in this size range. The authors demonstrate that their method of attachment and this latest PSAT model are feasible for c. 5-month deployments on fishes that are relatively small (c. 45 cm FL). These results with A. probatocephalus represent a potentially significant advance in PSAT methodology for fishes of this size. Future investigations are needed to determine if this method is transferrable to other species in the same size range.

European seabass show variable responses in their group swimming features after tag implantation

The usefulness of acoustic telemetry on the study of movements, interactions, and behaviors has been revealed by many field and laboratory studies. The process of attaching acoustic tags on fish can, however, impact their physiological, behavioral, and growth performance traits. The potential negative effects are still unknown for several species and behavioral attributes. Previous studies have attempted to shed light on the effects of tag implantation on fish, focusing mainly on fish growth and physiological parameters, and one or two behavioral properties mainly on the individual level. However, the effect of this procedure could also be expressed at the group level. This study investigated the short-term effects of dummy and active body-implanted acoustic tags on the group-level swimming performance of adult European seabass (Dicentrarchus labrax) using optical flow analysis. We studied four main swimming performance properties—group speed, alignment (polarization), cohesion, and exploratory behavior. To help in the interpretation of any detected differences, physiological stress-related parameters were also extracted. The results show that the tag implantation procedure has variable effects on the different swimming performance attributes of fish. Group cohesion, polarization, and the group’s exploratory tendency were significantly impacted initially, and the effect persisted but to a lesser extent two weeks after surgery. In contrast, group speed was not affected initially but showed a significant decrease in comparison with the control group two weeks post-surgery. In addition, the physiological parameters tested did not show any significant difference between the control and the treated group 14 days after the onset of the experiment. The findings suggest that the effect of tagging is non-trivial, leading to responses and response times that could affect behavioral studies carried out using acoustic telemetry.