Dissection on day 126 revealed no muscle necrosis, erythema, infection nor damage Ž
. to internal organs. Most tags had become embedded in the adipose tissue 21.7 , or
Ž .
encapsulated into a fibrous capsule inside the adipose tissue 60.3 . Capsules adhered Ž
. Ž
. to the parietal 7.4 or visceral peritoneum 4.8 , but never to the intestine. The
Ž .
remaining tags 5.8 were free in the body cavity of individuals with less adipose Ž
2
tissue than others. The host tissue response to the tag was independent of fish sex x ,
. Ž
2
. P s 0.7930 and was unaffected by the tag ratio x , P s 0.4851 .
4. Discussion
Surgery was adequate for PIT tagging juvenile perch, as the mortality of sutured tagged fish did not differ from that of controls, and was low compared to standards in
Ž .
perch culture Grignard et al., 1996b . Syringe injectors were less adequate than surgery techniques in an environment with fish pathogens, and this corroborated recent results in
Ž another warmwater Percomorph, the Nile tilapia Oreochromis niloticus Baras et al.,
. Ž
. 1999 . Prentice et al. 1990a reported that injectors did not compromise the survival of
salmonids, even in waters containing pathogens. Compared to salmonids, perch in this study were reared at higher temperatures, which are known to favour microbial
outbreak. Cultured perch are sensitive to numerous pathogens, and quite prone to
Ž .
develop pathologies in temperate or warm waters Grignard et al., 1996a,b . Open incisions increased the risk of microbial outbreak whereas sutured incisions did not.
Suturing permitted a more rapid repair of the epidermis, which is critical for maintaining Ž
. osmotic balance Anderson and Roberts, 1975 but the presence of the stitch compro-
mised the growth of perch. This is a further example to the potential detrimental effect Ž
of transcutaneous foreign bodies reported previously by several authors Roberts et al., 1973; Baras, 1992; Collins et al., 1994; Thoreau and Baras, 1997; Baras and Jeandrain,
. 1998 , and indicates that the stitch should be removed as soon as the fish has healed its
incision. Considering the risks of microbial outbreak, the use of antibiotic powders Ž
. terramycin, oxytetracycline, penicillin G, etc. that are injected into the caudal pedun-
cle, body cavity or applied as a mudpack over the incision, may be worth considering for PIT tagging perch.
On average, tagged perch healed their incision within 12–13 days at 22–238C. This is Ž
. slower than juveniles of tropical species 7–10 days; Baras et al., 1999, in press ,
Ž slightly faster than juveniles of cold-water species ca. 14 days; Moore et al., 1990;
. Prentice et al., 1990a and about twice as fast as adults of temperate species healing an
Ž incision of a similar relative length 4–6 weeks; Pedersen and Andersen, 1985; Baras,
. 1992; Knights and Lasee, 1996 . The dynamics of wound healing, which involves tissue
resorption then reconstitution, is a function of the main variables that influence fish Ž
growth, including species, life stage, metabolism and temperature Anderson and
. Roberts, 1975; Marty and Summerfelt, 1990; Baras et al., in press . Small perch, which
have higher growth potentialities than larger individuals, were expected to heal their incisions at a faster rate. However, the opposite was found, probably because the
standard incision length for PIT tagging was proportionally more severe to them than to
Ž .
larger individuals. Prentice et al. 1990a also noted that salmon could heal within 3
days incisions representing less than 0.5 of their body length, whereas longer incisions took longer to heal. Additionally, it can not be excluded that hierarchies established in
the groups of perch, restricted the access of the smallest fish to food, slowed down their growth and healing progress.
A clear difference between the growth of perch with tag ratios in the water above and Ž
. below 1.25 was observed. Ross and McCormick 1981 found that yellow perch
Perca flaÕescens tagged with ratios higher than 1.5 could no longer maintain their equilibrium or swim normally. However, we observed that small perch showed catch-up
growth over the following days, then growth rates similar to those of larger fish and controls, although their tag ratio was still higher than 1.25. This indicates that juvenile
perch can adapt very rapidly to tag ratios lower than this value, need longer time to adapt to higher ratios, but apparently can adapt completely to these within less than two
weeks. This interpretation agrees with the conclusions of Claireaux and Lefranc
¸
ois Ž
. Ž
. Ž
. 1998 , Martinelli et al., 1998 and Baras et al., 1999 that high tag ratios can be used
without causing substantial biases in the long run. The observation that the development of gonads and capacity of perch to store reserves of abdominal fat, were unaffected by
tagging or tag presence in all weight classes, also supports this statement. Implanted tags caused no internal damage, presumably because their midventral
location excluded most contacts with organs, and associated risks of erosion. The encapsulation of most tags by host tissue, and the resulting limited migration of tag
Ž inside the cavity may have contributed to reduce this risk too see Pedersen and
. Andersen, 1985; Lucas, 1989 . Tag encapsulation has often been associated with a
Ž .
higher risk of expulsion since Marty and Summerfelt 1986, 1990 have showed that tag capsules contain myofibroblasts, which contract and add to the gravity pressure by the
negatively buoyant tag over the fish tissue, resulting into the eventual expulsion of the tag. In this study, as in other studies with PIT-tags or epoxy dummies, which eventually
Ž became encapsulated Thoreau and Baras, 1997; Baras and Jeandrain, 1998; Baras et al.,
. 1999 , tag retention was 100. Considering that the gravity pressure by the tag rapidly
decreases in a fast growing juvenile, the risk of later expulsion through the body wall is Ž
deemed to be minimal. Similarly, there was little risk of transintestinal expulsion see .
Marty and Summerfelt, 1986; Baras and Westerloppe, 1999 , as no capsule adhered to the intestinal peritoneum of perch.
Tag readability by hand detectors was 100 throughout the study. However, we found that tags had different orientations and thus variable chances of being automati-
Ž .
cally detected by fixed antennas F 40 = 40 cm for TROVAN tags connected to data entry stations. This was also noted for tags inserted into the isthmus of Arctic char
Ž .
SalÕelinus alpinus Brannas and Alanara, 1993 . We observed some changes in the
¨ ¨ ¨ ¨
orientation of individual tags, which could also compromise the consistency of auto- matic detection over a long period. Considering that most tags that were, or became
disorientated were near midgut, care should be taken at the time of tagging to position the tag as close as possible to the abdominal body wall. However, this additional
accuracy can hardly be achieved without making a longer incision, which requires longer to heal. Assuming the combination of initial misplacement and change of
orientation over time, 95 of the perch tagged with the methodology above would suffer from reductions of coupling that would not exceed 13. Therefore, the confident
automatic detection of perch passage could be achieved by slightly reducing the size of Ž
. detecting antennas i.e., from 40 = 40 cm to 35 = 35 cm .
5. Conclusions
