Performance assessment of bi-directional knotless tissue-closure devices in juvenile Chinook salmon surgically implanted with acoustic transmitters

Acoustic transmitters used in telemetry studies to assess fish migration and survival are often surgically implanted into the coelomic cavity of the fish. While intra-coelomic implantation is a well-established method, the surgical process and/or implanted device may affect the health, behavior and survival of the fish under investigation, thus affecting study results. Tag effect research has focused on minimizing the aforementioned effects and continues to look for novel solutions. The first use of bi-directional knotless (barbed) suture material in fish occurred in 2009 to close incisions in juvenile Chinook salmon (Oncorhynchus tshawytscha). The suture barbs eliminate the need for knots, thereby reducing surgical time and concomitantly anesthetic and handling time for the fish. The bi-directional knotless suture had higher transmitter retention compared to the monofilament material, which was in a simple interrupted pattern. However, the incisions closed with bi-directional knotless sutures had an increased occurrence of ulceration and erythema. The objective of this study was to refine the suturing patterns of the bi-directional knotless suture used in 2009 by altering the needle size and retest suture performance in juvenile Chinook salmon. We examined the effects from the bi-directional knotless suture using three different suture patterns and two needle lengths: 6-Point (12-mm needle length), Wide “N” (12-mm needle length), Wide “N” Knot 12 (12-mm needle length), and Wide “N” Knot 18 (18-mm needle length). Using a performance rank index of observed metrics (mortality, transmitter expulsion, suture functionality, incision openness, ulceration and erythema), the Wide “N” Knot 12 suture pattern had an overall better performance than the other needle types and suture patterns. All needle types and suture patterns resulted in poor suture functionality by Day 14. The 6-Point, Wide “N” and Wide “N” Knot 18 treatments had no functional sutures by the end of the study; while the Wide “N” Knot 12 treatment had 33% functional sutures. Though bi-directional knotless sutures are novel to fish research, the two needle sizes and barbed suture material were successfully used in juvenile Chinook salmon implanted with acoustic transmitters and passive integrated transponders. In this study and in a study conducted in 2009, the bi-directional knotless sutures increased healing rates, while keeping transmitter expulsion low compared to other approaches, yet resulted in greater secondary tissue damage. The bi-directional suture rigidity possibly contributed to the inefficient anchoring of the barbs, and thus the low suture retention and increased tissue tearing. The bi-directional knotless sutures would likely perform better when used on fish with larger scales, and/or thicker skin or abdominal walls. Because the time for incision closure and concomitantly anesthetic exposure and handling time, and overall material waste was greatly reduced using the bi-directional knotless sutures compared to monofilament using the simple interrupted suture pattern, if a more flexible barbed suture material should come available, it warrants further examination in juvenile salmonids.