Abstract

Fish implanted with acoustic transmitters are assumed to behave and grow after stocking similar to untagged fish. In this study, three groups (tagged, sham, and control) of rainbow trout Oncorhynchus mykiss [mean (SD) initial length = 277 (24) mm] range were maintained together in three raceways for 90 days, with each raceway containing 10 tagged, 10 sham, and 10 control fish. The fish in the tagged group were anesthetized and had an inert transmitter inserted via a ventral incision. Fish in the sham group were anesthetized and had an incision without transmitter implantation, while the control group was anesthetized only. In each raceway, trout with the inert transmitters were significantly lighter and shorter than fish from the other two groups at the end of the experiment. However, the reduction in weight, length, and specific growth rate occurred primarily during the first 38 days post-tagging, with tagged fish growing at similar rates to the other two groups for the final 52 days of the experiment. Mortality data indicated a survival threshold of 280 mm length in the tagged fish, with 100% survival of the Rainbow Trout greater than 280 mm and only 59.1% survival of trout less than 280 mm. Based on the results of this study, rainbow trout implanted with 9 x 24 mm, 3.6 g acoustic transmitters should be held prior to release for a minimum of 38 days to ensure similar growth rates as untagged conspecifics, and only trout with an initial length greater than 280 mm should be used to maximize survival.