Abstract In the last few years there has been an increasing interest in using traditional animal breeding techniques to improve important traits such as growth rate in freshwater crayfish. However, a major impediment to such programs is an inability to reliably identify individuals or family groups for long periods because of the non-retention of external tags through ecdysis. Visual implant Ž . Ž . elastomer VIE and visual alphanumeric VIalpha internal tags have proven useful in identifying finfish and amphibians. We evaluated the suitability of these two internal tags as a method to Ž . identify yabby Cherax destructor juveniles. Both tags proved useful in identifying juveniles Ž between 0.1 and 4.6 g, with the VIE having the higher retention rate of the two tags up to 92%, . as opposed to 79% for the VIalpha tag . Mortality, as a direct consequence of tagging juveniles with the VIE and VIalpha tags was 13% and 11%, respectively. The ability to reliably identify C. destructor juveniles will increase the efficiency of selective breeding programs for this species by allowing individuals and family groups to be pooled in growth experiments, thereby decreasing the impact of confounding environmental effects. q 2001 Elsevier Science B.V. All rights reserved.  Jerry et al.r Aquaculture 193 2001 149-154  15

Dean R Jerry

Ian W Purvis

Laurie R Piper

Trenna Stewart

CiteSeerX

Ž .Aquaculture 193 2001 149–154
www.elsevier.nlrlocateraqua-online
Evaluation of visual implant elastomer and
alphanumeric internal tags as a method to identify
juveniles of the freshwater crayfish,
Cherax destructor
Dean R. Jerry ), Trenna Stewart, Ian W. Purvis, Laurie R. Piper
CSIRO Animal Production Locked Bag 1 Armidale, New South Wales, 2350 Australia
Received 19 April 2000; received in revised form 6 July 2000; accepted 11 July 2000
Abstract
In the last few years there has been an increasing interest in using traditional animal breeding
techniques to improve important traits such as growth rate in freshwater crayfish. However, a
major impediment to such programs is an inability to reliably identify individuals or family groups
for long periods because of the non-retention of external tags through ecdysis. Visual implant
Ž . Ž .elastomer VIE and visual alphanumeric VIalpha internal tags have proven useful in identifying
finfish and amphibians. We evaluated the suitability of these two internal tags as a method to
Ž .identify yabby Cherax destructor juveniles. Both tags proved useful in identifying juveniles
Žbetween 0.1 and 4.6 g, with the VIE having the higher retention rate of the two tags up to 92%,
.as opposed to 79% for the VIalpha tag . Mortality, as a direct consequence of tagging juveniles
with the VIE and VIalpha tags was 13% and 11%, respectively. The ability to reliably identify C.
destructor juveniles will increase the efficiency of selective breeding programs for this species by
allowing individuals and family groups to be pooled in growth experiments, thereby decreasing
the impact of confounding environmental effects. q 2001 Elsevier Science B.V. All rights
reserved.
Keywords: Tagging; Visual implant elastomer; Alphanumeric; Selective breeding; Freshwater crayfish
) Corresponding author. Tel.: q61-67-761322; fax: q61-67-761333.
Ž .E-mail address: djerry@chiswick.anprod.csiro.au D.R. Jerry .
0044-8486r01r$ - see front matter q2001 Elsevier Science B.V. All rights reserved.
Ž .PII: S0044-8486 00 00477-4
( )D.R. Jerry et al.rAquaculture 193 2001 149–154150
1. Introduction
Unlike terrestrial animal industries, culture of most freshwater crayfish species is
based on the use of broodstock taken directly from wild populations. Until compara-
tively recently, there have been few attempts to domesticate crayfish species and to
increase their productivity and profitability through genetic improvement. However,
within the past few years there has been a surge in the application of traditional animal
Žbreeding techniques to improve the growth rates of various crayfish species Lester,
.1983; Lutz and Wolters, 1989, 1999; Jones et al., 2000 .
A major impediment to selective breeding programs involving crayfish is that
identification of individuals or families is difficult because of non-retention of tags
Ž .through ecdysis Caceci et al., 1999 . As a consequence of the need to preserve the
identity of individuals andror families, selective breeding programs usually require
large numbers of aquaria and tank facilities. The use of large numbers of tanks,
however, increases the potential for growth differences among families to be confounded
with environmental variation among tanks. The capacity to reliably mark juvenile
crayfish would allow individuals from different families to be grown in the same tank,
thereby eliminating tank effects and improving the efficiency of selective breeding
Ž .programs Godin et al., 1996 .
Ideally a tag suitable for marking crayfish must not interfere with the growth of the
animal, should be retained throughout moulting processes, should be applicable during
the early developmental stages and should provide reliable recognition of individuals
Ž .without having to sacrifice the animal Weingartner, 1982 . Two new internal tags that
Ž .show promise for tagging crustaceans are visual implant elastomer VIE and soft visible
Ž . Ž .implant alphanumeric VIalpha tags Northwest Marine Technology . VIE and VIalpha
Žtags have been successfully used to identify fishes and amphibians e.g. Anholt et al.,
.1998; Willis and Babcock, 1998 . However, their application as a method for identifying
Ž . Ž .crustacean species has been limited to shrimp Penaeus Õannamei Godin et al., 1996
Ž . Ž .and lobster Homarus gammarus Uglem et al., 1996; Linnane and Mercer, 1998 . In
this trial we examined the suitability of both VIE and VIalpha tags as a method for
Ž .identifying freshwater yabby Cherax destructor juveniles by observing tag retention
and survival over a 10-week period.
2. Methods
2.1. Internal tags
The VIE tag is a two-part chemical compound which, when mixed, cures into a
pliable, biocompatible solid. The elastomer is injected into transparent or translucent
tissue as a dot or line, where it is visible in ambient sunlight and becomes enhanced
when exposed to UV light. The elastomer is available in four fluorescent colours and in
this study red was the only colour that was evaluated. VIalpha tags are alphanumerically
numbered biocompatible tags, which are implanted beneath transparent tissue and are
designed to identify individual animals. The tags are approximately 2.5=1.25=0.25
mm3 and like the VIE tags become highly visible to the naked eye when illuminated
with UV light.
( )D.R. Jerry et al.rAquaculture 193 2001 149–154 151
2.2. JuÕenile crayfish
Ž .A total of 135 C. destructor juveniles average weight 0.9"0.8 g, range 0.1–4.6 g
Ž .were anaesthetised at 108C using diethyl ether 20 mgrl . When docile they were
weighed, tagged and stocked individually in 2-l plastic containers enclosed within an
aquaria recirculation system. Forty-five animals were each tagged with either the VIE or
VIalpha tags, or not tagged to act as a control group to examine post-tagging mortality
levels. The VIE was injected into the third sclerite of the abdomen, the left coxa of the
last pair of walking legs and the left-hand uropod using a 0.5 ml insulin syringe.
Approximately 0.1 ml of the VIE material was injected to produce a highly visible tag.
The VIalpha tags were inserted under the third sclerite and pushed up to the second
sclerite of the abdomen of the crayfish using the commercial applicator supplied by the
manufacturer. Except for insertion of tags, control animals were handled in a similar
fashion to those animals tagged. All animals were also marked with a dot of paint to
assist in the identification of yabbies that had moulted. Animals were checked for moults
twice daily. When moults were found they were removed from the container and the
paint dot re-applied.
2.3. Time frame
Tag retention and tag readability were checked at fortnightly intervals. To check the
readability of the VIalpha tag, animals were randomly chosen from aquaria and their tag
read first under ambient light and then under UV light. The VIE tags were checked
using UV light only. Loss or movement of the tag, tag rejection and any signs of
reaction to the tag were recorded.
3. Results
This experiment ran over 10 weeks. Each yabby moulted on average three times over
this period, with some of the smaller tagged yabbies moulting up to five times. Mortality
within the first 2 weeks following the tagging procedure was slightly higher in the VIE
Ž . Ž .and VIalpha tag groups 11% and 13%, respectively than in the control group 5% .
Table 1
Ž .Retention rates of VIE and VIalpha tags, each 2 weeks for 10 weeks in juvenile yabbies C. destructor . Note:
VIalpha tags were only injected into the third sclerite of the abdomen
Ž .Retention % each VIE VIalpha
2-week interval Coxa Uropod Abdomen
1–2 95 84 97 90
3–4 95 84 97 86
5–6 94 82 97 80
7–8 94 82 97 79
9–10 94 82 92 79
( )D.R. Jerry et al.rAquaculture 193 2001 149–154152
Table 2
ŽVisualisation of VIE and readability of VIalpha tags, each 2 weeks for 10 weeks in juvenile yabbies C.
.destructor
Ž .Readability % each VIE VIalpha
2-week interval Coxa Uropod Abdomen Without UV light With UV light
1–2 100 100 100 80 100
3–4 100 100 100 94 97
5–6 100 100 100 92 96
7–8 100 100 100 96 96
9–10 100 100 100 96 96
However, one-way ANOVA analyses demonstrated that differences in mortality due to
Ž .treatment were not significantly different Ps0.51 . This suggests that mortality levels
were probably the result of handling stress. Tag retention varied among the treatments,
Ž .with retention of the VIE higher than that of the VIalpha tag Table 1 . The major period
of tag loss occurred before or during the first moult, with tag retention generally
stabilising after the animal had moulted once. Placement of the VIE tag into the coxa
and abdomen of the yabby appeared to give the highest retention rates.
Visualisation of the red elastomer was very high in those animals where the tag was
Ž .retained with 100% visualisation of the VIE tag when viewed under UV light Table 2 .
However, in many instances the tag was observed to have fragmented into several
pieces, or to have moved slightly from the point of insertion. Readability of the VIalpha
Ž .tag was slightly less than that of the VIE tag, particularly under ambient light Table 2 .
The ease with which the VIalpha tag could be read was found to be highly dependent on
how deep the tag was inserted under the juvenile yabby’s exoskeleton. If it was inserted
too deep, or under the heavily chitinised sternite junction, numbers became hard to
distinguish, while those inserted in the middle of the sternite, or inserted shallow, could
easily be read. Often a yellowish scarring was noticed around the VIalpha tag insertion
point.
4. Discussion
This study has demonstrated that tagging juveniles of C. destructor with both VIE
and VIalpha tags has the potential to reliably identify individuals as small as 0.1 g. Both
tags had relatively good retention rates, especially that of the VIE tag when inserted into
the coxa and abdomen of the animal. These results for C. destructor are similar to other
studies that have examined the utility of the VIE tag in crustaceans. For example, Godin
Ž .et al. 1996 found a retention rate of 99.9% in juvenile and 100% in adult P. Õannamei
Ž .over a 10–14-week period. Similarly, Uglem et al. 1996 found 100% retention rates of
the VIE tag after three moults in H. gammarus. The findings in our paper, when viewed
in association with these other studies, suggest that the VIE tag is a reliable, non-intru-
sive, approach to identifying crustaceans. Likewise, the VIalpha tag may have merit for
use in situations where individual identification is required.
( )D.R. Jerry et al.rAquaculture 193 2001 149–154 153
Although the tags were only evaluated for 10 weeks, most losses of the tag occurred
during the first moult period after insertion. This suggests that if the tags are retained
through the first moult then they tend to remain in the animal during subsequent moults,
although some fragmentation and movement of the tag may occur. Indeed some
experimental animals held for 6 months after the conclusion of the experiment still
possessed their tag. To account for tagging losses through the first moult after insertion,
a strategy when tagging juveniles in a selective breeding program may be to tag them a
few weeks before stocking and then examine whether the tag has been retained through
the first moult. If not, then remarking the animal before stocking should give retention
rates close to 100%.
Readability andror visualisation of tags remained high throughout the duration of
this experiment. However, it should be noted that juveniles in this experiment were
grown in water within a recirculation system with little possibility of algal andror
sediment staining of the exoskeleton. Readability of tags and, in particular, that of the
VIalpha tag, may decrease in animals cultured in earthen ponds.
The ease of insertion, high retention rate and readability of both the internal
elastomer and alphanumeric tags will increase the efficiency of selective breeding
programs by allowing juvenile C. destructor from multiple families or strains to be
collectively reared in one pond. This ability to rear numerous families collectively in the
same environment will reduce the number of tank facilities required, as well as
eliminating possible differences in growth among families due to tank environmental
effects.
Acknowledgements
The authors would like to acknowledge John Smith for technical assistance.
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Evaluation of visual implant elastomer and alphanumeric internal tags as a method to identify juveniles of the freshwater crayfish, Cherax destructor

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Evaluation of visual implant elastomer and alphanumeric internal tags as a method to identify juveniles of the freshwater crayfish, Cherax destructor

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