The effect of PIT tags on growth and physiology of age-0 cultured Eurasian perch Perca fluviatilis of variable size

Abstract For many biological reasons, it is often necessary to tag and monitor fish from a very early age. However, tagging can adversely affect fish, especially for high tag to body weight ratios. To determine the minimum size for passive integrated transponders (PIT) tagging in juvenile perch Perca fluviatilis , surgical implantation was evaluated in fish ranging from 1.67 to 10.62 g (55–96 mm FL). The survival, gonadal development, and capacity of tagged perch to store abdominal fat was affected neither by the tagging procedure, tag presence, nor tag to body weight ratio. Four months after tagging, no tag had caused internal damage or had been expelled, despite about 95% of them becoming encapsulated by host tissues. Negative effects from tagging were restricted to slower healing rates, and depressed growth of fish with high tag to body weight ratios during the first post-tagging days, which was compensated for by catch-up growth within less than 2 weeks. Surgical PIT tagging can be confidently applied to perch weighing less than 2 g, but the collection of biological data should be delayed by about 2 weeks after tagging. X-ray photographs revealed variable orientations of tags (95% CI: 26°) and slight (ca. 4°) changes of orientation over time. These discrepancies may affect the probability that the tag is detected by automatic data entry stations, and should be compensated for by using smaller antennas (≤87% of maximal antenna size).