Effects of Predation Tags on Growth and Stress Response in Juvenile Rainbow Trout Oncorhynchus mykiss

Abstract

Acid-sensitive predation tags have recently been introduced to fisheries management. The objective of this study was to ascertain the impact of these tags on juvenile rainbow trout Oncorhynchus mykiss physiology and growth after implantation. Twenty approximately 13 g rainbow trout were placed into each of five tanks, with ten surgically implanted with dummy acid-sensitive predation tags and ten control fish not subjected to surgical procedures. Glucose, hematocrit, tag-retention, survival, and growth metrics were collected for 30 days post-surgery. Four tagged fish died while no control fish died. Tag retention was 76%, with tags lost in weeks 2, 3, and 4. Control fish were significantly longer and gained significantly more weight at the end of the experiment. Hematocrit levels for the tagged fish dropped significantly over the course of the trial and were 30% lower than those of the untagged control fish at the end of 30 days. Glucose levels were highly variable for both treatments. The results of this study indicate the negative impacts of predation tagging on the physiology of juvenile rainbow trout. Results from predation field trials should be interpreted with caution because the tagged fish are likely at a competitive disadvantage compared to their untagged conspecifics.