Micro-acoustic Transmitter Implantation Impacts Juvenile Rainbow Trout Oncorhynchus mykiss Growth, Hematocrit and Splenosomatic Index

Micro-acoustic transmitters are becoming increasingly popular in fisheries management. This study examined the short-term effects of micro-transmitter surgical insertion on juvenile rainbow trout Oncorhynchus mykiss (mean (SE) initial weight=23.9 (1.8) g, length=124 (2) mm). One group of trout were anesthetized and surgically implanted with micro-acoustic transmitters (tag-to-body ratio=2.94 (0.07) %). A second control group only underwent anesthesia. Ten fish from each group were placed in one of five experimental tanks for eight weeks, with weight, length, hematocrit, hepatosomatic index, viscerosomatic index and splenosomatic index data collected weekly. Survival in the untagged control group was 100%, which was significantly greater than 91.8% in the tagged group. Tag retention was 71%. Total lengths and weights were significantly less for the first six weeks after surgery in tagged fish compared to the control fish. Hematocrit was significantly lower and splenosomatic index was significantly higher in the tagged trout for the first three weeks. Hepatosomatic index and viscerosomatic index were not significantly different between the groups throughout the study. This study provides additional documentation of the potential negative effects of micro-acoustic tag implantation on juvenile rainbow trout. A minimum three-week recovery period is recommended for juvenile fish tagged at a 2.9% tag-to-body ratio. Keywords Rainbow trout; Oncorhynchus mykiss; Microacoustic transmitter; Surgery