NOTE Bumguardner et a\ : Long-term tag retention in juvenile Saaenops ocellatus 



391 



muscle) with coded wire micro- 

 tags. Loss of coded wire tags was 

 initially high (32.7% after 24 

 hours), but the rate of tag loss 

 declined substantially 23 days 

 post-tagging. 



Tag retention by the same 

 group of fish initially tagged by 

 Bumguardner et al. (1990) was 

 monitored 115-464 days post- 

 tagging to determine if addition- 

 al tag loss occurred. Tag detec- 

 tion rates using two methods 

 of tag detection— a Northwest 

 Marine Technology Field Sam- 

 pling Device, and examination of 

 X-ray negatives— were also de- 

 termined and contrasted with 

 tag detection rates reported for 

 the two methods by Bumguard- 

 ner et al. (1990). Our primary ob- 

 jective was to determine if tag 

 retention rates declined between 

 114 and 464 days post-tagging, 

 and to what extent tag loss and 

 nondetection affected estimates 

 of tag retention rates. While Bumguardner et al. (1990) 

 considered mortality a component of tag loss and 

 reported differential mortality between tagged and un- 

 tagged fish, we limited the scope of this project to 

 investigation of tag loss and nondetection rates. We 

 did not consider mortality a component of tag loss 

 because the facilities to maintain a group of control fish 

 were not available. 



Materials and methods 



Coded-wire microtag retention for red drum was moni- 

 tored from tagging to 464 days post-tagging. About 

 2100 red drum fingerlings (x 52mmTL) were tagged 

 with coded wire microtags on 13 July 1987. Tags (1.07 

 X 0.25 mm) were inserted horizontally in the cheek mus- 

 cle using a Northwest Marine Technology (NMT) Model 

 MK2A tagging unit (Northwest Mar. Technol., Shaw 

 I., WA) equipped with a plastic side mold to orient fish 

 for consistent tag placement. An NMT Quality Control 

 Device was used to magnetize tags and separate tagged 

 from untagged fish. 



Tagged fish were held in a 3.0 x 0.6 x 0.6m tank for 

 24 hours, stocked in three 0.1 -ha ponds at 500 fish/ 

 pond for 23 days, then transferred to three 0.2-ha 

 ponds for 91 days (Table 1). Surviving fish harvested 

 from each 0.1 -ha pond were restocked as a group in 

 separate 0.2-ha ponds. Fish were fed a commercially- 



Table 1 



Coded wire microtag retention for red drum Sciaerwps ocellatus through 464 days post- 

 tagging, determined with the NMT Field Sampling Device. 



'Fish selected randomly from the total number of fish tagged. 



"Number of fish surviving at the end of the interval. 



"Reported as weighted average for three ponds with standard error. 



''First 52 fish encountered while monitoring tag retention were overwintered in indoor 



tanks. 

 " Cumulative percent tag retention for days 1 15-285 used to calculate percent tag retention 



for 286-464 day interval. 

 ' Cumulative percent tag retention fordaysll5-464 used to calculate percent tag retention 



for 286-464 day interval. 



prepared trout feed daily while in ponds. Tag reten- 

 tion was determined at 24 hours (prestocking), 23 days 

 (harvest from 0.1-ha ponds), and 114 days (harvest 

 from 0.2-ha ponds) post-tagging with an NMT Field 

 Sampling Device (FSD) (Bumguardner et al. 1990). 

 Fish were harvested from 0.2-ha ponds 114 days post- 

 tagging, and 52 fish (x 220mmTL) confirmed by the 

 FSD as retaining tags were placed in a 4200 L circular 

 fiberglass tank on 11 October 1987 for overwintering. 

 As available tank space was limited, overwintering was 

 restricted to 52 fish confirmed as retaining tags. Ex- 

 perience has shown indoor overwintering is required 

 to insure survival of red drum in hatcheries during 

 episodic freezing conditions on the Texas coast. Fish 

 were fed 300 g chopped fish and shrimp daily. Fish were 

 treated with a 0.25 mg/L Cu* * bath on four occasions 

 for a protozoan parasite infestation tentatively iden- 

 tified as Amyloodinium sp. Fish were immersed in a 

 20 mg/L oxytetracycline HCl bath, and about lOmL of 

 injectable oxytetracycline solution (50 mg oxytetra- 

 cycline HCl/mL solution) was placed in chopped shrimp 

 and fish offered as feed to combat a bacterial infection. 

 Surviving fish {n 33) were removed from the tank on 

 22 April 1988 (285 days after tagging), measured and 

 checked for tag presence with the FSD. 



The 33 surviving fish (x 352mmTL) were placed in 

 a 0.4-ha pond, with the exception of one fish that had 

 lost the caudal fin, presumably as the result of a bac- 

 terial infection. These fish were fed a a 35% protein 



