1. Introduction
It is important that fish be individually identified because performance varies Ž
substantially among individuals of different or the same size e.g., Jobling et al. 1989; .
Alanara and Brannas 1993; McCarthy et al. 1994 . This should ideally be done from the
¨ ¨ ¨ ¨
youngest possible age and extend over long periods of time. Passive integrated transpon- Ž
. ders PITs; Prentice et al. 1984, 1990a are among the best candidates for tagging small
Ž .
fish. These are low weight F 100 mg tags, with unlimited functional life and billions of individual codes, and can thus be applied to large samples of fish. The use of data
entry stations allows the automatic detection of PIT tagged fish passage or presence at Ž
. Ž
close range within 20 cm of detecting antennas Prentice et al. 1990b,c; Brannas and
¨ ¨
. Alanara 1993; Brannas et al. 1994; Armstrong et al. 1996 .
¨ ¨ ¨ ¨
Ž PIT tags have been applied mainly to large fish in husbandry management e.g.,
. Jenkins and Smith, 1990 . The tag is inserted into the dorsal musculature of broodfish,
represents a tiny proportion of their body weight, and has no marked effect on their physiology. Few studies have documented the feasibility of implanting PIT tags into the
Ž body cavity of small juveniles, and most of these concerned salmonids Prentice et al.,
. 1990a; Brannas and Alanara, 1993; Peterson et al., 1994 . Behavioural and physiological
¨ ¨ ¨ ¨
reactions to identical tagging procedures may differ substantially between species Ž
. Winter, 1983; Summerfelt and Smith, 1990; Baras et al., in press , and feasibility
studies on tag acceptance are strongly encouraged when no detailed data are available on the species of interest, both for ethical considerations and validation of results. This
Ž .
becomes crucial when using high tag ratios tag weightrfish weight , close to or above Ž
the mean adjustment capacity of the swimbladder in teleost fish ca. 1.75, Alexander, .
Ž 1966 , as most tagging biases were reported in these circumstances Greenstreet and
. Morgan, 1989; Summerfelt and Smith, 1990; Baras et al., in press . More recent studies
with carefully tailored procedures suggest that higher tag ratios can be used without Ž
causing substantial biases in the long run Claireaux and Lefranc
¸
ois, 1998; Martinelli et .
al., 1998; Baras et al., 1999 . This paper is a component of research programmes on the biology of cultured
juveniles of the Eurasian perch Perca fluÕiatilis, which rely on monitoring the activity of PIT tagged individuals through the use of automatic data entry stations. To evaluate
the adequacy of the tagging technique and to determine the minimum size at which perch can be tagged successfully, the intensity and duration of the perturbation caused
by the tagging procedure and tag presence were measured based on tag retention, survival, growth, healing progress and physiology of juvenile perch of different body
Ž .
weights 1.67–10.62 g, 55–96 mm fork length . As the detection of PIT tags is
governed by the laws of inductive coupling, the orientations of implanted tags and their stability over time were also examined to test whether all tagged fish would have the
same chances of being detected by automatic stations.
2. Material and methods
Kategori