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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
Dean R. Jerry
), Trenna Stewart, Ian W. Purvis, Laurie R. Piper
CSIRO Animal Production Locked Bag 1 Armidale, New South Wales, 2350 AustraliaReceived 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
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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
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identify yabby Cherax destructor juveniles. Both tags proved useful in identifying juveniles
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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. q2001 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 matterq2001 Elsevier Science B.V. All rights reserved. Ž .
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
Ž breeding 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
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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
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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
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without having to sacrifice the animal Weingartner, 1982 . Two new internal tags that
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show promise for tagging crustaceans are visual implant elastomer VIE and soft visible
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implant alphanumeric VIalpha tags Northwest Marine Technology . VIE and VIalpha Ž
tags 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
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crustacean species has been limited to shrimp PenaeusÕannamei Godin et al., 1996
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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
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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
2.2. JuÕenile crayfish
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A total of 135 C. destructor juveniles average weight 0.9"0.8 g, range 0.1–4.6 g
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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
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and VIalpha tag groups 11% and 13%, respectively than in the control group 5% .
Table 1
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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
Table 2
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Visualisation of VIE and readability of VIalpha tags, each 2 weeks for 10 weeks in juvenile yabbies C.
. destructor
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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
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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,
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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
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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
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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
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et al. 1996 found a retention rate of 99.9% in juvenile and 100% in adult P.Õannamei
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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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