Assessing metabolic rate and post-tagging recovery in juvenile fish

Juvenile fish play a crucial role in the health of aquatic ecosystems, serving both as the foundation for future adult populations and as a valuable food source. Studying the juvenile life stage of fish using acoustic telemetry is inherently challenging due to their small size and associated difficulties in tracking and data collection. Recent advances in telemetry, including the miniaturization of tags, have enabled researchers to investigate previously understudied size classes of fish. Tagging fish can introduce sublethal effects that alter their physiology and behaviour, ultimately biasing the collected data; this effect is exacerbated in smaller-bodied fish, which are generally more sensitive to tagging procedures. Our study tested whether tagging juvenile brook trout (Salvelinus fontinalis) of two size classes (10-12 and 13-16 cm fork length, n = 80) with a LOTEK JSATS PinTag (0.22 g, mean tag burden 1.11% of body mass, range 0.54-2.00%) impacted their oxygen consumption rates ( ${\dot{M}}_{O_2}$ ) over the 2 days following tagging. Handling and tagging caused no mortalities, although we observed a nearly significant effect (p = 0.06) of the experimental group (control, anaesthesia, surgery, tagged) on standard metabolic rate (SMR). This was driven by a 7% decrease in the SMR of the tagged animals, which were significantly different from the control group when compared directly (p = 0.02). This marginal effect in standard metabolic rate, combined with the absence of significant effects on maximum metabolic rate, aerobic scope and post-exercise recovery, suggests that the JSATS PinTag does not impair the aerobic metabolic capacity of fish of this size. Our findings indicate that neither the surgery procedure nor the presence of the tag limit the brook trout's capacity for burst movement, which is highly relevant for predator-evasion responses after release in the wild. In addition, we evaluated wound recovery and suture retention over a 3-week period using either braided or monofilament suture material. While braided sutures caused more immediate irritation and were more prone to fungal growth, their quicker expulsion may reduce long-term discomfort compared to monofilament sutures. Determining the optimal suture type may ultimately depend on study duration and objectives, and longer-term monitoring could clarify which material best supports overall healing.