We examined the effects of suture material (braided silk versus Monocryl) and relative ultrasonic transmitter size on healing, growth, mortality, and tag retention in rainbow trout Oncorhynchus mykiss. In experiment 1, 40 fish (205–281 mm total length [TL], 106–264 g) were implanted with Sonotronics IBT‐96–2 (23 × 7 mm; weight in air, 4.4 g; weight in water, 2.4 g) or IBT 96–2E (30 × 7 mm; weight in air, 4.9 g; weight in water, 2.4 g) ultrasonic telemetry tags. In experiment 2, 20 larger fish (342–405 mm TL; 520–844 g) were implanted with Sonotronics IBT‐96–5 ultrasonic tags (36 × 11 mm; weight in air, 9.1 g; weight in water, 4.1 g). The tag burdens for all implanted fish ranged from 1.1% to 3.4%, and fish in both studies were held at 10–15°C. At the conclusion of both experiments (65 d after surgery), no mortalities were observed in any of the 60 tagged fish, most incisions were completely healed, and all fish in both experiments grew in length, although tagged fish grew more slowly than control fish in experiment 1. In both experiments, fish sutured with silk expelled tags more frequently than those sutured with Monocryl. Expulsion was observed in 45–50% of the fish sutured with silk and 0–25% of the fish sutured with Monocryl. Tag expulsion was not observed until 25–35 d after surgery. Fish sutured with silk exhibited a more severe inflammatory response 3 weeks after surgery than those sutured with Monocryl. In experiment 1, the rate of expulsion was linked to the severity of inflammation. Although braided silk sutures were applied faster than Moncryl sutures in both experiments, knots tied with either material were equally reliable and fish sutured with Monocryl experienced less inflammation and lower rates of tag expulsion.