NOTE Wallin et a I.: Retention of coded wire and internal anchor tags in juvenile Centropomus undecimalis 
875 
Retention of interna! anchor tags with 
external streamers 
We evaluated retention of internal anchor tags with 
external streamers (disk and T-style) in 110-180 mm 
SL common snook. Tags with disk anchors (Model 
FM-89SL, Floy Mfg., Seattle, WA) consisted of a plas- 
tic 5 x 15 mm imprinted elliptical disk and 50-mm 
imprinted streamer. T-anchor tags (IEX tags, 
Hallprint Ltd., Holden Hill, Australia) consisted of 
an 18-mm T-shaped anchor and a 42-mm imprinted 
streamer. Equal numbers of fish were randomly as- 
signed to one of three treatments: 1 ) fish tagged with 
disk anchor tags, 2) fish tagged with T-anchor tags, 
and 3) untagged fish that were handled in the same 
manner as tagged fish. 
All fish were anesthetized ( 100 ppm MS-222) and 
measured just prior to treatment. To apply disk an- 
chor tags, we used a scalpel to make an approxi- 
mately 6-mm vertical incision into the body wall and 
then inserted the disk into the incision. To apply the 
T-anchor tags, we used a sharpened tag-applicator 
needle to make an approximately 2-mm diameter 
puncture and then inserted the T-anchor into the 
opening. Incisions were made on the left ventral side 
of the fish, anterior to the vent and posterior to the 
pectoral fin. Anchors were dipped in betadyne prior 
to insertion to minimize infection. Fish in the tag 
treatments were distinguished by fin clips: disk an- 
chor-tagged fish received a left pectoral fin clip and 
T-anchor- tagged fish received a right pectoral fin clip. 
Fish in the untagged treatment were anesthetized, 
measured, and handled in the same manner as 
tagged fish but did not receive an incision or finclip. 
All fish were transferred immediately after treatment 
to a 13,300-L tank containing approximately 9,000 L 
of water. The tank was aerated and had sand, 
diatomateous earth, and biological filters. Water tem- 
peratures averaged 27°C (range: 24-29°C); salinity 
averaged 26 ppt (range: 11-30 ppt); dissolved oxy- 
gen averaged 6.5 ppm (range: 4. 9-8. 4 ppm), and pH 
averaged 7.8 (range: 7. 7-7. 9 ppm). Fish were fed live 
baitfish daily. 
Fish were checked for tag retention at 14 and 30 
days after tagging. At each tag check, fish were anes- 
thetized ( 100 ppm MS-222), checked for tag and fin- 
clip presence, measured, and weighed. The entire 
experiment was repeated twice; numbers of fish per 
treatment varied between trials from 61 to 78 fish 
per treatment (Table 1 ). During the first trial, necrop- 
sies were performed on three to ten fish from each 
treatment after 14 days to evaluate a bacterial in- 
fection. Six of ten T-anchor- tagged fish examined had 
anchors that were inserted into the swim bladder, 
whereas all disk-anchor-tagged fish examined (n=3) 
had anchors that were correctly placed in the perito- 
neal cavity. Because of the potential for misapplica- 
tion with the T-anchor tag, during the second trial 
we applied T-anchor tags by making a 3-mm scalpel 
incision rather than by making a puncture with a 
tag applicator needle. At the end of the second trial, 
ten randomly selected fish from each tag treatment 
were dissected and examined for tag implant loca- 
tions and tissue healing. 
Analyses 
Estimates of the rates of tag retention and survival 
were arcsine-transformed prior to analysis (Sokal 
and Rohlf, 1981). Fish size at the time of tagging dif- 
fered significantly among trials in both the CWT 
experiments ( ANOVA, df=5, P=517.6, P<0.01 ) and in 
the internal-anchor-tag experiments (ANOVA, df=l, 
F= 6.7, P<0.01). Therefore, mean size at tagging was 
used as a covariate in analysis of covariance (Sokal 
and Rohlf, 1981; SAS, 1989) to compare rates of tag 
retention, survival, and growth among time periods 
and treatment groups. Post hoc comparisons were 
conducted with the method of least-square means 
(SAS Institute, Inc., 1989). 
Results 
Overall, retention rates of coded wire tags averaged 
99.8%, 95.6%, and 93.7% at 3, 30, and 60 days after 
tagging, respectively (Table 1). At 3 days, tag reten- 
tion rates for all sizes of snook ranged from 98.6 to 
100% (Fig. 1). Fish size at the time of tagging sig- 
nificantly affected tag retention rates (F=12.5, 
P<0.01); larger fish had higher retention rates, par- 
ticularly during the 30- to 60-d period after tagging 
(Fig. 1). Tag retention of common snook >70 mm SL 
at the time of tagging was >95% at 30 and 60 days 
after tagging, whereas tag retention in snook <65 
mm SL was 92.0% and 85.4% at 30-60 days after 
tagging, respectively (Table 1; Fig. 1). Tag retention 
rates decreased between 3 and 30 days after tagging 
(LSMEANS, P=0.02) but did not change significantly 
between 30 and 60 days (LSMEANS, P=0.89; Fig. 2). 
Survival rates of CWT fish were not significantly 
different from those of the untagged or control fish 
(df=2, F= 0.5, P=0.61). Survival rates of fish in all 
treatments averaged 99.6%, 91.9%, and 84.7% at 3, 
30, and 60 days after tagging, respectively (Table 1). 
Poor survival of fish in the third trial (63%, Table 1) 
is attributed to parasitic infection. Growth rates of 
CWT fish were also not significantly different from 
those of untagged or control fish (df=2, F- 0.87, 
P=0.42). 
